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Friday, December 07, 2007
How to select an ISO 17025 consultant
Consultants are many
an ISO 17025 consultant must be an engineering graduate
well versed in Metrology
with a firm grounding in basic statistics in measurement
knowledgeable about concepts like measurement uncertainty, confidence intervals, etc
and have prior experience with ISO 17025 clients
He should have a good track record of completing his projects on time
he should have a team of consultants
an ISO 17025 consultant must be an engineering graduate
well versed in Metrology
with a firm grounding in basic statistics in measurement
knowledgeable about concepts like measurement uncertainty, confidence intervals, etc
and have prior experience with ISO 17025 clients
He should have a good track record of completing his projects on time
he should have a team of consultants
GUIDELINES FOR ESTIMATION of uncertainty of Measurement
We give here excerpts from the document published by NABL
free downlaod is available from http://www.nabl-india.org/
ISSUE NO : 02
AMENDMENT NO : 03
GOVT. OF INDIA
MINISTRY OF SCIENCE & TECHNOLOGY
Technology Bhavan, New Mehrauli Road,
New Delhi - 110016
PROFESSOR V.S. RAMARMURTHY
SECRETARY
FOREWARD
The expression of “Uncertainty in Measurements” is an integral component of the accreditation certificate being issued to the calibration laboratories. Globalization of trade and technology implies the need for interchangeability of components, which must be produced with a high degree of exactness in measurement system. This concept is equally true for all other fundamental units of measurement. The International Bureau of Weights and Measures (BIPM), in consultation with various international bodies, have arrived at a new ISO standard on Expression of Uncertainty in Measurements, in 1995.
I am glad to dedicate the document of NABL on Guidelines for Estimation and Expression of Uncertainty in Measurement to the cause of calibration laboratories in the country. I take this opportunity to congratulate the scientists who have made handsome contributions in bringing out this document based on the latest ISO standard.
New Delhi
2nd April, 2000
V. S. Ramamurthy,
Chairman, NABL
and Secretary, DST
1. Introduction
1.1 Purpose
The purpose of the document is to harmonize procedures for evaluating uncertainty in measurements and for stating the same in calibration certificates as are being followed by the NABL with the contemporary international approach. The document will apprise calibration laboratories of the current requirements for evaluating and reporting uncertainty and will assist accreditation bodies with a coherent assignment of test measurement capability to calibration laboratories accredited by them. The document will also provide broad guidelines to all those who are concerned with measurements about uncertainty in measurement, estimation and apportionment of uncertainty and interpretation of uncertainty. In fact, the purpose is to provide guidelines to users about contemporary requirements for global acceptance of various kinds of measurements. Attempts have been made to make the provisions of this document easy to understand and ready for implementation. The present document will replace NABL’s document 141 (1992).
1.2 Scope
Provisions of this document apply to measurements of all sorts as are carried out in calibration laboratories. For specialized measurements, these may have to be supplemented by more specific details and, in some cases, appropriately modified forms of the concerned formulae. Measurements which can be treated as outputs of several correlated inputs have been excluded from the scope of this document. The document covers the following topics:
- Uncertainty – concept, sources and measures
- Definitions of related terms and phrases
- Evaluation of standard uncertainty in input estimates
- Evaluation of standard uncertainty in output estimates
- Expanded uncertainty in measurement
- Statement of uncertainty in measurement
- Apportionment of standard uncertainty
- Step by step procedure for calculating the uncertainty in measurement
- Appendix – A: Use of relevant probability distribution
- Appendix – B: Coverage factor and effective degrees of freedom
- Appendix – C: Solved examples showing the application of the method outlined here to eight specific problems in different fields.
1.3 Normative References :
This document is based primarily on the Guide to the expression of uncertainty in measurement (1993) jointly prepared by BIPM, IEC, ISO and OIML for definition of various terms and phrases. One should refer to ISO 3534-I (1993) part – I probability and general statistical terms.
1. Guidelines for estimation and statement of overall uncertainty in measurement results, NABL – 141, Department of Science and Technology, New Delhi (India), (1992).
2. Guide to the expression of uncertainty in measurement, International Bureau of Weights and Measures (BIPM), International Organization for Standardization (ISO) et. al., Switzerland, 1995.
3. International vocabulary of basic and general terms in metrology, International Bureau of Weights and Measures (BIPM), International Organization for Standardization (ISO) et. al. ., Switzerland , 1993.
4. Expression of the uncertainty of measurement in calibration, European Cooperation for Accreditation of laboratories (EAL – R-2), 1997
5. Guidelines on the evaluation and expression of the measurement uncertainty, Singapore Institute of Standards and Industrial Research, Singapore 1995.
6. International standard ISO 3534 – I, statistics – vocabulary and symbols – Part I. Probability and general statistical terms, first edition, International Organization for Standardization (ISO) , Switzerland ,1993.
2. Uncertainty – Concept, Sources and Measures
2.1 Concept
2.1.1 Quality of measurements has assumed great significance in view of the fact that measurements (in a broad sense) provide the very basis of all control actions. Incidentally, the word measurement should be understood to mean both a process and the output of that process.
2.1.2 It is widely recognized that the true value of a measurand (or a duly specified quantity to be measured) is indeterminate, except when known in terms of theory. What we obtain from the concerned measurement process is at best an estimate of or approximation to the true value. Even when appropriate corrections for known or suspected components of error have been applied, there still remains an uncertainty, that is, a doubt about how well the result of measurement represents the true value of the quantity being measured.
2.1.3 A statement of results of measurement (as a process) is complete only if it contains both the values attributed to the measurand and the uncertainty in measurement associated with that value. Without such an indication, measured results can not be compared, either among themselves or with reference values given in a specification or standard.
2.1.4 The uncertainty of measurement is a parameter, associated with the result of a measurement, that characterizes the dispersion of the true values, which could reasonably be attributed to the measurand. The parameter may be, for example, the standard deviation (or a given multiple of it), or the half-width of an interval having a stated level of confidence.
4. Evaluation of standard uncertainty in Input estimates
4.1 General considerations
4.1.1 The uncertainty of measurement associated with the input estimates is evaluated according to either a “Type A” or a “Type B” method of evaluation. The Type A evaluation of standard uncertainty is the method of evaluating the uncertainty by the statistical analysis of a series of observations. In this case the standard uncertainty is the experimental standard deviation of the mean that follows from an averaging procedure or an appropriate regression analysis. The Type B evaluation of standard uncertainty is the method of evaluating the uncertainty by means other than the statistical analysis of a series of observations. In this case the evaluation of the standard uncertainty is based on some other scientific knowledge.
Examples:
Case – I : Digital multimeter (DMM)
Let us consider, an experiment in which a high accuracy reference standard e.g. a 6 ½ digit stable meter calibrator is used to calibrate a device of much lower accuracy like 4 ½ digit DMM . The readings of the test DMM may remain unchanged or undergo flicker ±1 count due to its digitizing process. In this case, the Type A evaluation of the uncertainty may be taken to be negligible, and the uncertainty on account of repeatable observations can be treated as Type B on the basis of the resolution error of the test DMM.
Case – II : Length Bar
While calibrating a length bar by comparison method, one has to include the component of uncertainty associated with the thermal expansion coefficient in the uncertainty budget. Usually, a for the test and standard is taken from handbook or as per manufacturers specification, in this case, although the estimation of uncertainty in temperature measurement is Type A but the estimation of uncertainty in a is Type B. However, in a special case where high precision is needed, in situ measurement of thermal expansion is carried out. In such a case, the evaluation of uncertainty in both temperature and a are of Type A.
4.2 Type A evaluation of standard uncertainty
4.2.1 Type A evaluation of standard uncertainty applies to situation when several independent observations have been made for any of the input quantities under the same conditions of measurement. If there is sufficient resolution in the measurement process, there will be an observable scatter or spread in the values obtained.
4.2.2 Let us denote by Q the repeatedly measured input quantity Xi. With n statistically independent observations (n > 1), the estimate of Q is `q, the arithmetic mean of the individual observed values qj (j = 1, 2,…….n).
(4.1)
The uncertainty of measurement associated with the estimate `q is evaluated according to one of the following methods
4.2.3 An estimate of the variance of the underlying probability distribution of q is the experimental variance s2 (q) of values qj given by,
(4.2)
The positive square root of s2 (q) is termed experimental standard deviation. The best estimate of the variance of the arithmetic mean `q is given by
(4.3)
4.3 Type B evaluation of standard uncertainty
4.3.1 The Type B evaluation of standard uncertainty is the evaluation of the uncertainty associated with an estimate xi of an input quantity Xi by means other than the statistical analysis of a series of observations. The standard uncertainty u(xi ) is evaluated by scientific judgment based on all available information on the possible variability of Xi.
Values belonging to this category may be derived from
- previous measurement data ;
- experience with or general knowledge of the behaviour and properties of relevant materials and instruments ;
- manufacturer’s specifications ;
- data provided in calibration and other certificates;
- uncertainties assigned to reference data taken from handbooks.
4.3.2 The proper use of the available information for a Type B evaluation of standard uncertainty of measurement calls for insight based on experience and general knowledge. It is a skill that can be learned with practice. A well-based Type B evaluation of standard uncertainty can be as reliable as a Type A evaluation of standard uncertainty, especially in a measurement situation where a Type A evaluation is based only on a comparatively small number of statistically independent observations. The following cases must be discerned:
(a) When only a single value is known for the quantity Xi, e.g. a single measured value, a resultant value of a previous measurement, a reference value from the literature, or a correction value, this value will be used for xi. The standard uncertainty u (xi) associated with xi is to be adopted where it is given. Otherwise it has to be calculated from unequivocal uncertainty data. If data of this kind are not available, the uncertainty has to be evaluated on the basis of experience taken as it may have been stated (often in terms of an interval corresponding to expanded uncertainty).
(b) When a probability distribution [see Appendix – A] can be assumed for the quantity Xi, based on theory or experience, then the appropriate expectation or expected value and the standard deviation (s) of this distribution have to be taken as the estimate xi and the associated standard uncertainty u (xi), respectively.
Examples:
In cases, where the uncertainty is quoted to be particular multiple of standard deviation (s), the multiple becomes the specific factor (see Appendix – A).
Case I:
A calibration certificate states that the mass of a given body of 10 kg is 10.000650 kg. The uncertainty at 2 s (at confidence level of 95 .45 %) is given by 300 mg. In such a case, the standard uncertainty is simply,
u(m) = 300 / 2 = 150 mg (4.12)
and estimated variance is
u2(m) = 0.0225 g2 (4.13)
Case II:
Suppose in the above example, the quoted uncertainty defines an interval having a 90% level of confidence. The standard uncertainty is then
u(m) = 300 / 1.64 = 182.9 mg (4.14)
Where we have taken 1.64 as the factor corresponding to the above level of confidence, assuming the normal distribution unless otherwise stated.
Case III:
A calibration certificate states that the resistance of a standard resistor, Rs of nominal value 10 W is 10.000742 W ± 129 mW at 23 0 C and that the quoted uncertainty of 129 mW defines an interval having a level of confidence of 99%. The standard uncertainty of the resistor may be taken as
u(Rs ) = 129 mW / 2.58 = 50 mW (4.15)
Therefore, in this case, specific factor is 2.58. The corresponding relative standard uncertainty
u(Rs )/ Rs = 5 ´ 10-6 (4.16)
The estimated variance is
u2 = (50 mW)2 = 2.5 ´ 10-9 W2 (4.17)
Case IV:
A calibration certificate states that the length of a standard slip gauge (SG) of nominal value 50 mm is 50.000002 mm. The uncertainty of this value is 72 nm, at confidence level of 99.7 % (corresponding to 3 times of standard deviation). The standard uncertainty of the standard slip gauge is then given by
u(SG) = 72 nm /3 = 24 nm (4.18)
(c) If only upper and lower limits and can be estimated for the value of the quantity Xi (e.g. manufacturer’s specifications of a measuring instrument, a temperature range, a rounding or truncation error resulting from automated data reduction), a probability distribution with constant probability density between these limits (rectangular probability distribution) has to be assumed for the possible variability of the input quantity Xi . According to case (b) above this leads to
(4.19)
for the estimated value and
(4.20)
for the square of the standard uncertainty . If the difference between the limiting values is denoted by , Eq. (4.20) yields
(4.21)
Examples:
The specifications of a dial type pressure gauge are as follows :
Range : 0 to 10 bar,
Scale : 1 division = 0.05 bar,
Resolution : ½ division = 0.025 bar
Accuracy : ± 0.25 % Full Scale Deflection
Assuming that with the above specifications, there is an equal probability of the true value lying anywhere between the upper and lower limits. Therefore, for rectangular distribution,
(4.22)
Here ,
(4.23)
and
(4.24)
(4.25)
Hence the standard uncertainty is given by ,
(4.26)
5. Evaluation of standard uncertainty in output estimate
5.1 For uncorrelated input quantities the square of the standard uncertainty associated with the output estimate y is given by,
(5.1)
The quantity ui(y) (i = 1, 2,…, n) is the contribution to the standard uncertainty associated with the output estimate y resulting from the standard uncertainty associated with the input estimate xi,
ui (y) = ci u(xi) (5.2)
where ci is defined as sensitivity coefficients associated with the input estimate xi i.e. the partial derivative of the model function f with respect to Xi , evaluated at the input estimates xi .
c i = (¶f /¶xi ) = (¶f /¶Xi ) at Xi = xi (5.3)
5.2 The sensitivity coefficient ci, describes the extent to which the output estimate y is influenced by variations of the input estimate xi. It can be evaluated from the function f by Eq. (5.3) or by using numerical methods, i.e. by calculating the change in the output estimate y due to a change in the input estimate xi of + u(xi) and -u(xi) and taking as the value of ci the resulting difference in y divided by 2u (xi) . Sometimes it may be more appropriate to find the change in the output estimate y from an experiment by repeating the measurement at e.g. xi ± u (xi).
5.3 If the model functions is a sum or difference of the input quantities Xi,
f (X1 ,X2 , ………XN) = (5.4)
the output estimate according to Eq. (2.2) is given by the corresponding sum or difference of the input estimate
(5.5)
whereas the sensitivity coefficients equal to pi and Eq. (5.1) converts to
(5.6)
5.4 If the model function f is a product or quotient of the input quantities XI
(5.7)
the output estimate again is the corresponding product or quotient of the input estimates
(5.8)
The sensitivity coefficients equal piy/xi in this case and an expression analogous to Eq. (5.6) is obtained from Eq. (5.1), if relative standard uncertainties w(y) = u(y)/y and w (xi) = u (xi) / xi are used,
(5.9)
6. Expanded uncertainty in measurement
6.1 Calibration laboratories shall state an expanded uncertainty in measurement (U), obtained by multiplying the standard uncertainty u(y) of the output estimate y by a coverage factor k,
U = ku (y) (6.1)
In cases where a normal (Gaussian) distribution can be attributed to the measurand and the standard uncertainty associated with the output estimate has sufficient reliability, the standard coverage factor k = 2 shall be used. The assigned expanded uncertainty corresponds to a coverage probability of approximately 95 %.
6.2 The assumption of a normal distribution cannot always be easily confirmed experimentally. However, in the cases where several (i.e. N ³ 3) uncertainty components derived from well–behaved probability distributions of independent quantities, e.g. normal distributions or rectangular distributions, contribute to the standard uncertainty associated with the output estimate by comparable amounts, the conditions of the central limit theorem are met and it can be assumed to a high degree of approximation that the distribution of the output quantity is normal.
6.3 The reliability of the standard uncertainty assigned to the output estimate is determined by its effective degrees of freedom (see Appendix B). However, the reliability criterion is always met if none of the uncertainty contributions is obtained from a Type A evaluation based on less than ten repeated observations.
6.4 If one of these conditions (normality or sufficient reliability) is not fulfilled, the standard coverage factor k = 2 can yield an expanded uncertainty corresponding to a coverage probability of less than 95 %. In these cases, in order to ensure that a value of the expanded uncertainty is quoted corresponding to the same coverage probability as in the normal case, other procedures have to be followed. The use of approximately the same coverage probability is essential whenever two results of measurement of the same quantity have to be compared, e.g. when evaluating the results of an interlaboratory comparison or assessing compliance with a specification.
6.5 Even if a normal distribution can be assumed, it may still occur that the standard uncertainty associated with the output estimate is of insufficient reliability. If, in this case, it is not expedient to increase the number n of repeated measurements or to use a Type B evaluation instead of the Type A evaluation of poor reliability, the method given in Appendix – B should be used.
6.6 For the remaining cases, i.e. all cases where the assumption of a normal distribution cannot be justified, information on the actual probability distribution of the output estimate must be used to obtain a value of the coverage factor k that corresponds to a coverage probability of approximately 95 %.
7. Statement of uncertainty in measurement
7.1 In calibration certificates the complete result of the measurement consisting of the estimate y of the measurand and the associated expanded uncertainty U shall be given in the form (y ±U). To this an explanatory note must be added which in the general case should have the following content: The reported expanded uncertainty in measurement is stated as the standard uncertainty in measurement multiplied by the coverage factor k = 2, which for a normal distribution corresponds to a coverage probability of approximately 95 %.
7.2 However, in cases where the procedure of Appendix A has been followed, the additional note should read as follows: The reported expanded uncertainty in measurement is stated as the standard uncertainty in measurement multiplied by the coverage factor k which for a t-distribution with neff effective degrees of freedom corresponds to a coverage probability of approximately 95 %. (See Appendix – B).
7.3 The numerical value of the uncertainty in measurement should be given to at most two significant figures. The numerical value of the measurement result should in the final statement normally be rounded to the least significant figure in the value of the expanded uncertainty assigned to the measurement result. For the process of rounding, the usual rules for rounding of numbers have to be used. However, if the rounding brings the numerical value of the uncertainty in measurement down by more than 5 %, the rounded up value should be used.
8. Apportionment of standard uncertainty
8.1 The uncertainty analysis for a measurement-sometimes called the Uncertainty Budget of the measurement-should include a list of all sources of uncertainty together with the associated standard uncertainties of measurement and the methods of evaluating them. For repeated measurements the number n of observations also has to be stated. For the sake of clarity, it is recommended to present the data relevant to this analysis in the form of a table. In this table all quantities should be referenced by a physical symbol Xi, or a short identifier. For each of them at least the estimate xi, the associated standard uncertainty in measurement u (xi), the sensitivity coefficient ci and the different uncertainty contributions ui(y) should be specified. The degrees of freedom have to be mentioned. The dimension of each of the quantities should also be stated with the numerical values in the table.
8.2 A formal example of such an arrangement is given as Table (8.1) applicable for the case of uncorrelated input quantities. The standard uncertainty associated with the measurement result u(y) given in the bottom right corner of the table is the root sum square of all the uncertainty contributions in the outer right column. Similarly, neff has to be evaluated as mentioned in Appendix –B.
9. Step-by-step procedure for calculating the uncertainty in measurement
The following is a guide to the use of this document in practice:
Step 1 Express in mathematical terms the dependence of the measured (output quantity) Y on the input quantities Xi according to Eq. (2.1). In the case of a direct comparison of two standards the equation may be very simple, e.g.
Y = X1 + X2 (9.1)
Step 2 Identify and apply all significant corrections to the input quantities.
Step 3 List all sources of uncertainty in the form of an uncertainty analysis in accordance with Section 8.
Step 4 Calculate the standard uncertainty for repeatedly measured quantities in accordance with sub-section 4.2.
Step 5 For single values, e.g. resultant values of previous measurements, correction values or values from the literature, adopt the standard uncertainty where it is given or can be calculated according to paragraph 4.3.2(a). Pay attention to the uncertainty representation used. If no data are available from which the standard uncertainty can be derived, state a value of u (xi) on the basis of scientific experience.
Step 6 For input quantities for which the probability distribution is known or can be assumed, calculate the expectation and the standard uncertainty u (xi) according to paragraph 4.3.2 (b). If only upper and lower limits are given or can be estimated, calculate the standard uncertainty u (xi) in accordance with paragraph 4.3.2(c).
Step 7 Calculate for each input quantity Xi the contribution ui (y) to the uncertainty associated with the output estimate resulting from the input estimate xi according to Eqs. (5.2) and (5.3) and sum their squares as described in Eq. (5.1) to obtain the square of the standard uncertainty u(y) of the measurand.
Step 8 Calculate the expanded uncertainty U by multiplying the standard uncertainty u(y) associated with output estimate by a coverage factor k chosen in accordance with Section 6.
Step 9 Report the result of the measurement comprising the estimate y of the measurand, the associated expanded uncertainty U and the coverage factor k in the calibration certificate in accordance with Section 7.
B.2 The procedure for calculating an appropriate coverage factor k :
Step 1 Obtain the standard uncertainty associated with the output estimate.
Step 2 Estimate the effective degree of freedom neff of the standard uncertainty u(y) associated with the output estimate y from the Welch-Satterthwaite formula.
Step 3 Obtain the coverage factor k from the table of values of student “t” distribution. If the value of neff is not an integer, it is truncated to the next lower integer and the corresponding coverage factor k is obtained from the table.
B.3 Welch-Satterthwaite formula is as follows:
(B.1)
where u i (y) (i = 1,2,3,……..N) defined in Eqs. (5.1) and (5.2) , are the contributions to the standard uncertainty associated with the output estimate y resulting from the standard uncertainty associated with the input estimate x i which are assumed to be mutually statistically independent , and the ni is the effective degrees of freedom of the standard uncertainty contributions u i (y).
Note :
The calculation of the degrees of the freedom n for Type A and Type B of the evaluation may be as follows:
Type A Evaluation
For the results of direct measurement (Type A evaluation), the degree of freedom is related to the number of observations (n) as,
n i = n - 1 (B.2)
Type B Evaluation
For this evaluation, when lower and upper limits are known
ni ® ¥ (B.3)
It is suggested that ni should always be given when Type A and Type B evaluations of uncertainty components are documented.
Where high precision measurements are undertaken, the accredited calibration laboratories shall be required to follow ISO Guide to the expression of uncertainty in Measurement (1995). Concerned laboratories should refer to Annexure – G (with special emphasis on table G-2 ) and Annexure –H for related examples.
However, assuming that ni ® ¥ is not necessarily unrealistic, since it is a common practice to chose a- and a+ in such a way that the probability of the quantity lying outside the interval a- to a+ is extremely small.
Further interpretation on the above is given on page 29 & 30
Interpretation on Effective Degrees of Freedom
“Whilst the reason for determining the number of degrees of freedom associated with an uncertainty component is to allow the correct selection of value of student’s t, it also gives an indication of how well a component may be relied upon. A high number of degrees of freedom is associated with a large number of measurements or a value with a low variance or a low dispersion associated with it. A low number of degrees of freedom corresponds to a large dispersion or poorer confidence in the value.
Every component of uncertainty can have an appropriate number of degrees of freedom,n, assigned to it. For the mean, `x, for example n = n - 1, where n is a number of repeated measurements. For other Type A assessments, the process is also quite straightforward. For example, most spreadsheets provide the standard deviation of the fit when data is fitted to a curve. This standard deviation may be used as the uncertainty in the fitted value due to the scatter of the measurand values. The question is how to assign components evaluated by Type B processes.
For some distributions, the limits may be determined so that we have complete confidence in their value. In such instances, the number of degrees of freedom is effectively infinite. The assigning of limits, which are worst case, leads to this instance, namely infinite degrees of freedom, and simplifies the calculation of effective degrees of freedom of the combined uncertainty.
If the limits themselves have some uncertainty, then a lesser number of degrees of freedom must be assigned. The ISO Guide to the expression of uncertainty in measurement (GUM) gives a formula that is applicable to all distributions. It is equation G.3 that is:
n » ½ [ Du(xi)/ u(xi) ]-2 ……… ………… 1
Where :
Du(xi)/ u(xi) is the relative uncertainty in the uncertainty
This is a number less than 1, but may for convenience be thought of as a percentage or a fraction. The smaller the number, the better defined is the magnitude of the uncertainty.
For example, if relative uncertainty is 10%, i.e.
Du(xi)/ u(xi) = 0.1
Then it can be shown that the number of degrees of freedom is 50. For a relative uncertainty of 25 % then n = 8 and for relative uncertainty of 50 %, n = is only 2.
Rather than become seduced by the elegance of mathematics, it is better to try to determine the limits more definitely, particularly if the uncertainty is a major one. It is of the interest to note that equation (1) tells us that when we have made 51 measurements and taken the mean, the relative uncertainty in the uncertainty of the mean is 10%. This shows that even when many measurements are taken, the reliability of the uncertainty is not necessarily any better than when a type B assessment is make. Indeed, it is usually better to rely on prior knowledge rather than using an uncertainty based on two or three measurements. It also shows why we restrict uncertainty to two digits. The value is usually not reliable enough to quote to better than 1 % resolution.
Once the uncertainty components have been combined, it remains to find the number of degrees of freedom in the combined uncertainty. The degrees of freedom for each component must also be combined to find the effective number of degrees of freedom to be associated with the combined uncertainty. This is calculated using the Welch-Satterthwaite equation, which is:
n
neff = [uc4 (y)/ å{ ui4 (y)/ ni}] …. 2
1
Where:
neff is the effective number of degrees of freedom for uc the combined uncertainty
ni is the number of degrees of freedom for u i , the ith uncertainty term
u i (y) is the product of c i u i
“The other terms have their usual meaning”.
Adopted from NATA document on “Assessment of uncertainties in Measurement”, 1999.
Table B.1: Student t-distribution for degrees of freedom n. The t-distribution for n defines an interval -t p (n) to + t p (n) that encompasses the fraction p of the distribution. For p = 68.27 %, 95.45 %, and 99.73 %, k is 1, 2, and 3, respectively.
Solved examples showing the applications of the method outlined here to eight specific problems in different fields
C.1 Micrometer calibration using “0” grade slip gauge at 25mm
Introduction
The instrument under calibration is a micrometer of 0 – 25 mm range with a slip gauge of 25 mm of nominal size.
The detailed specifications of the slip gauge are as follows:
Range = 25 mm,
Standard reference temperature (Tr e f) = 20 0 C,
Actual calibrating temperature (Tc) = 23 0 C,
Calibrated value = 25.00010 ± 0.00008 mm, and
Least count of thermometer used = 1 0 C.
Mathematical model
YGUT = XSTD + DX (C.1)
Where YGUT is the micrometer reading [Gauge under test (GUT), XSTD is the gauge block size and DX is the error or the difference between the micrometer reading and gauge block size.
Uncertainty equation
The combined standard uncertainty equation is given by,
(C.2)
Measured results
Type A evaluation
Five readings are taken and the deviation from the nominal value is as follows.
Mean Deviation:
(C.3)
Standard deviation :
(C.4)
Table C.1 : Data for calculation of mean and standard deviation
Observation
numbers
Deviation from nominal value (xj)
(mm)
`x
(mm)
(xj - `x)2 ´ 10-7
(mm)
1.
0.001
1.6
2.
0.000
3.6
3.
0.001
0.0006
1.6
4.
0.000
3.6
5.
0.001
1.6
Standard deviation of the mean:
(C.5)
Standard uncertainty:
(C.6)
Degrees of freedom (ni)
n = n – 1 = 5 –1 = 4 (C.7)
Type B evaluation
The uncertainty quoted in the gauge block calibration certificate is considered to be Type B uncertainty of normal distribution.
Standard uncertainty (u1) due to the temperature measurement ±1 0 C.
Standard thermal expansion coefficient of the gauge block is 11.5´10-6/ 0C
u 1 = 25 ´ 1´11.5 ´ 10-6 mm = 287.5 ´ 10-6 mm = 0.2875 mm (C.8 )
Standard uncertainty (u2) due to difference in temperature of micrometer and slip gauge
Assuming the temperature of the slip gauges and micrometer are the same but still it can have a difference ±1 0 C. Hence, again uncertainty component
u2 = 0.2875 mm (C.9)
Standard uncertainty (u3) due to difference in thermal expansion coefficient of the slip gauge and micrometer
It is assumed that the difference in thermal expansion coefficient of standard slip gauge and the micrometer screw is amounting to 20 %, hence the uncertainty component
[DT = Tc – Tref = 30 C],
u3 = 25 ´ 3 ´ 11.5 ´ 10-6 ´ (20 /100) mm = 0.1725 mm (C.10)
Standard uncertainty (u4) due to the flatness of micrometer faces’
(C.11)
Standard uncertainty (u5) due to the parallelness of micrometer faces’
(C.12)
Standard uncertainty (u6) due to the Standard used for calibration
The uncertainty in the value of the standard is taken from the calibration certificate say 0.08 mm. Assuming rectangular distribution, the standard uncertainty is
(C.13)
The sensitivity coefficients (ci) are 1 and degree of freedom is ni = ¥ [Type B components ] in all six cases .
Degrees of freedom (neff )
(C.14)
@ 89 @ ¥
Combined uncertainty
Combined uncertainty [uc (YGUT)] is ,
(C.15)
uc (YGUT ) = 0.531 mm (C.16)
National Accreditation Board for Testing and Calibration Laboratories
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New Delhi – 110 067
Tel.: 91-11 26529718 – 20, 26526864
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Website: http://www.nabl-india.org/
free downlaod is available from http://www.nabl-india.org/
ISSUE NO : 02
AMENDMENT NO : 03
GOVT. OF INDIA
MINISTRY OF SCIENCE & TECHNOLOGY
Technology Bhavan, New Mehrauli Road,
New Delhi - 110016
PROFESSOR V.S. RAMARMURTHY
SECRETARY
FOREWARD
The expression of “Uncertainty in Measurements” is an integral component of the accreditation certificate being issued to the calibration laboratories. Globalization of trade and technology implies the need for interchangeability of components, which must be produced with a high degree of exactness in measurement system. This concept is equally true for all other fundamental units of measurement. The International Bureau of Weights and Measures (BIPM), in consultation with various international bodies, have arrived at a new ISO standard on Expression of Uncertainty in Measurements, in 1995.
I am glad to dedicate the document of NABL on Guidelines for Estimation and Expression of Uncertainty in Measurement to the cause of calibration laboratories in the country. I take this opportunity to congratulate the scientists who have made handsome contributions in bringing out this document based on the latest ISO standard.
New Delhi
2nd April, 2000
V. S. Ramamurthy,
Chairman, NABL
and Secretary, DST
1. Introduction
1.1 Purpose
The purpose of the document is to harmonize procedures for evaluating uncertainty in measurements and for stating the same in calibration certificates as are being followed by the NABL with the contemporary international approach. The document will apprise calibration laboratories of the current requirements for evaluating and reporting uncertainty and will assist accreditation bodies with a coherent assignment of test measurement capability to calibration laboratories accredited by them. The document will also provide broad guidelines to all those who are concerned with measurements about uncertainty in measurement, estimation and apportionment of uncertainty and interpretation of uncertainty. In fact, the purpose is to provide guidelines to users about contemporary requirements for global acceptance of various kinds of measurements. Attempts have been made to make the provisions of this document easy to understand and ready for implementation. The present document will replace NABL’s document 141 (1992).
1.2 Scope
Provisions of this document apply to measurements of all sorts as are carried out in calibration laboratories. For specialized measurements, these may have to be supplemented by more specific details and, in some cases, appropriately modified forms of the concerned formulae. Measurements which can be treated as outputs of several correlated inputs have been excluded from the scope of this document. The document covers the following topics:
- Uncertainty – concept, sources and measures
- Definitions of related terms and phrases
- Evaluation of standard uncertainty in input estimates
- Evaluation of standard uncertainty in output estimates
- Expanded uncertainty in measurement
- Statement of uncertainty in measurement
- Apportionment of standard uncertainty
- Step by step procedure for calculating the uncertainty in measurement
- Appendix – A: Use of relevant probability distribution
- Appendix – B: Coverage factor and effective degrees of freedom
- Appendix – C: Solved examples showing the application of the method outlined here to eight specific problems in different fields.
1.3 Normative References :
This document is based primarily on the Guide to the expression of uncertainty in measurement (1993) jointly prepared by BIPM, IEC, ISO and OIML for definition of various terms and phrases. One should refer to ISO 3534-I (1993) part – I probability and general statistical terms.
1. Guidelines for estimation and statement of overall uncertainty in measurement results, NABL – 141, Department of Science and Technology, New Delhi (India), (1992).
2. Guide to the expression of uncertainty in measurement, International Bureau of Weights and Measures (BIPM), International Organization for Standardization (ISO) et. al., Switzerland, 1995.
3. International vocabulary of basic and general terms in metrology, International Bureau of Weights and Measures (BIPM), International Organization for Standardization (ISO) et. al. ., Switzerland , 1993.
4. Expression of the uncertainty of measurement in calibration, European Cooperation for Accreditation of laboratories (EAL – R-2), 1997
5. Guidelines on the evaluation and expression of the measurement uncertainty, Singapore Institute of Standards and Industrial Research, Singapore 1995.
6. International standard ISO 3534 – I, statistics – vocabulary and symbols – Part I. Probability and general statistical terms, first edition, International Organization for Standardization (ISO) , Switzerland ,1993.
2. Uncertainty – Concept, Sources and Measures
2.1 Concept
2.1.1 Quality of measurements has assumed great significance in view of the fact that measurements (in a broad sense) provide the very basis of all control actions. Incidentally, the word measurement should be understood to mean both a process and the output of that process.
2.1.2 It is widely recognized that the true value of a measurand (or a duly specified quantity to be measured) is indeterminate, except when known in terms of theory. What we obtain from the concerned measurement process is at best an estimate of or approximation to the true value. Even when appropriate corrections for known or suspected components of error have been applied, there still remains an uncertainty, that is, a doubt about how well the result of measurement represents the true value of the quantity being measured.
2.1.3 A statement of results of measurement (as a process) is complete only if it contains both the values attributed to the measurand and the uncertainty in measurement associated with that value. Without such an indication, measured results can not be compared, either among themselves or with reference values given in a specification or standard.
2.1.4 The uncertainty of measurement is a parameter, associated with the result of a measurement, that characterizes the dispersion of the true values, which could reasonably be attributed to the measurand. The parameter may be, for example, the standard deviation (or a given multiple of it), or the half-width of an interval having a stated level of confidence.
4. Evaluation of standard uncertainty in Input estimates
4.1 General considerations
4.1.1 The uncertainty of measurement associated with the input estimates is evaluated according to either a “Type A” or a “Type B” method of evaluation. The Type A evaluation of standard uncertainty is the method of evaluating the uncertainty by the statistical analysis of a series of observations. In this case the standard uncertainty is the experimental standard deviation of the mean that follows from an averaging procedure or an appropriate regression analysis. The Type B evaluation of standard uncertainty is the method of evaluating the uncertainty by means other than the statistical analysis of a series of observations. In this case the evaluation of the standard uncertainty is based on some other scientific knowledge.
Examples:
Case – I : Digital multimeter (DMM)
Let us consider, an experiment in which a high accuracy reference standard e.g. a 6 ½ digit stable meter calibrator is used to calibrate a device of much lower accuracy like 4 ½ digit DMM . The readings of the test DMM may remain unchanged or undergo flicker ±1 count due to its digitizing process. In this case, the Type A evaluation of the uncertainty may be taken to be negligible, and the uncertainty on account of repeatable observations can be treated as Type B on the basis of the resolution error of the test DMM.
Case – II : Length Bar
While calibrating a length bar by comparison method, one has to include the component of uncertainty associated with the thermal expansion coefficient in the uncertainty budget. Usually, a for the test and standard is taken from handbook or as per manufacturers specification, in this case, although the estimation of uncertainty in temperature measurement is Type A but the estimation of uncertainty in a is Type B. However, in a special case where high precision is needed, in situ measurement of thermal expansion is carried out. In such a case, the evaluation of uncertainty in both temperature and a are of Type A.
4.2 Type A evaluation of standard uncertainty
4.2.1 Type A evaluation of standard uncertainty applies to situation when several independent observations have been made for any of the input quantities under the same conditions of measurement. If there is sufficient resolution in the measurement process, there will be an observable scatter or spread in the values obtained.
4.2.2 Let us denote by Q the repeatedly measured input quantity Xi. With n statistically independent observations (n > 1), the estimate of Q is `q, the arithmetic mean of the individual observed values qj (j = 1, 2,…….n).
(4.1)
The uncertainty of measurement associated with the estimate `q is evaluated according to one of the following methods
4.2.3 An estimate of the variance of the underlying probability distribution of q is the experimental variance s2 (q) of values qj given by,
(4.2)
The positive square root of s2 (q) is termed experimental standard deviation. The best estimate of the variance of the arithmetic mean `q is given by
(4.3)
4.3 Type B evaluation of standard uncertainty
4.3.1 The Type B evaluation of standard uncertainty is the evaluation of the uncertainty associated with an estimate xi of an input quantity Xi by means other than the statistical analysis of a series of observations. The standard uncertainty u(xi ) is evaluated by scientific judgment based on all available information on the possible variability of Xi.
Values belonging to this category may be derived from
- previous measurement data ;
- experience with or general knowledge of the behaviour and properties of relevant materials and instruments ;
- manufacturer’s specifications ;
- data provided in calibration and other certificates;
- uncertainties assigned to reference data taken from handbooks.
4.3.2 The proper use of the available information for a Type B evaluation of standard uncertainty of measurement calls for insight based on experience and general knowledge. It is a skill that can be learned with practice. A well-based Type B evaluation of standard uncertainty can be as reliable as a Type A evaluation of standard uncertainty, especially in a measurement situation where a Type A evaluation is based only on a comparatively small number of statistically independent observations. The following cases must be discerned:
(a) When only a single value is known for the quantity Xi, e.g. a single measured value, a resultant value of a previous measurement, a reference value from the literature, or a correction value, this value will be used for xi. The standard uncertainty u (xi) associated with xi is to be adopted where it is given. Otherwise it has to be calculated from unequivocal uncertainty data. If data of this kind are not available, the uncertainty has to be evaluated on the basis of experience taken as it may have been stated (often in terms of an interval corresponding to expanded uncertainty).
(b) When a probability distribution [see Appendix – A] can be assumed for the quantity Xi, based on theory or experience, then the appropriate expectation or expected value and the standard deviation (s) of this distribution have to be taken as the estimate xi and the associated standard uncertainty u (xi), respectively.
Examples:
In cases, where the uncertainty is quoted to be particular multiple of standard deviation (s), the multiple becomes the specific factor (see Appendix – A).
Case I:
A calibration certificate states that the mass of a given body of 10 kg is 10.000650 kg. The uncertainty at 2 s (at confidence level of 95 .45 %) is given by 300 mg. In such a case, the standard uncertainty is simply,
u(m) = 300 / 2 = 150 mg (4.12)
and estimated variance is
u2(m) = 0.0225 g2 (4.13)
Case II:
Suppose in the above example, the quoted uncertainty defines an interval having a 90% level of confidence. The standard uncertainty is then
u(m) = 300 / 1.64 = 182.9 mg (4.14)
Where we have taken 1.64 as the factor corresponding to the above level of confidence, assuming the normal distribution unless otherwise stated.
Case III:
A calibration certificate states that the resistance of a standard resistor, Rs of nominal value 10 W is 10.000742 W ± 129 mW at 23 0 C and that the quoted uncertainty of 129 mW defines an interval having a level of confidence of 99%. The standard uncertainty of the resistor may be taken as
u(Rs ) = 129 mW / 2.58 = 50 mW (4.15)
Therefore, in this case, specific factor is 2.58. The corresponding relative standard uncertainty
u(Rs )/ Rs = 5 ´ 10-6 (4.16)
The estimated variance is
u2 = (50 mW)2 = 2.5 ´ 10-9 W2 (4.17)
Case IV:
A calibration certificate states that the length of a standard slip gauge (SG) of nominal value 50 mm is 50.000002 mm. The uncertainty of this value is 72 nm, at confidence level of 99.7 % (corresponding to 3 times of standard deviation). The standard uncertainty of the standard slip gauge is then given by
u(SG) = 72 nm /3 = 24 nm (4.18)
(c) If only upper and lower limits and can be estimated for the value of the quantity Xi (e.g. manufacturer’s specifications of a measuring instrument, a temperature range, a rounding or truncation error resulting from automated data reduction), a probability distribution with constant probability density between these limits (rectangular probability distribution) has to be assumed for the possible variability of the input quantity Xi . According to case (b) above this leads to
(4.19)
for the estimated value and
(4.20)
for the square of the standard uncertainty . If the difference between the limiting values is denoted by , Eq. (4.20) yields
(4.21)
Examples:
The specifications of a dial type pressure gauge are as follows :
Range : 0 to 10 bar,
Scale : 1 division = 0.05 bar,
Resolution : ½ division = 0.025 bar
Accuracy : ± 0.25 % Full Scale Deflection
Assuming that with the above specifications, there is an equal probability of the true value lying anywhere between the upper and lower limits. Therefore, for rectangular distribution,
(4.22)
Here ,
(4.23)
and
(4.24)
(4.25)
Hence the standard uncertainty is given by ,
(4.26)
5. Evaluation of standard uncertainty in output estimate
5.1 For uncorrelated input quantities the square of the standard uncertainty associated with the output estimate y is given by,
(5.1)
The quantity ui(y) (i = 1, 2,…, n) is the contribution to the standard uncertainty associated with the output estimate y resulting from the standard uncertainty associated with the input estimate xi,
ui (y) = ci u(xi) (5.2)
where ci is defined as sensitivity coefficients associated with the input estimate xi i.e. the partial derivative of the model function f with respect to Xi , evaluated at the input estimates xi .
c i = (¶f /¶xi ) = (¶f /¶Xi ) at Xi = xi (5.3)
5.2 The sensitivity coefficient ci, describes the extent to which the output estimate y is influenced by variations of the input estimate xi. It can be evaluated from the function f by Eq. (5.3) or by using numerical methods, i.e. by calculating the change in the output estimate y due to a change in the input estimate xi of + u(xi) and -u(xi) and taking as the value of ci the resulting difference in y divided by 2u (xi) . Sometimes it may be more appropriate to find the change in the output estimate y from an experiment by repeating the measurement at e.g. xi ± u (xi).
5.3 If the model functions is a sum or difference of the input quantities Xi,
f (X1 ,X2 , ………XN) = (5.4)
the output estimate according to Eq. (2.2) is given by the corresponding sum or difference of the input estimate
(5.5)
whereas the sensitivity coefficients equal to pi and Eq. (5.1) converts to
(5.6)
5.4 If the model function f is a product or quotient of the input quantities XI
(5.7)
the output estimate again is the corresponding product or quotient of the input estimates
(5.8)
The sensitivity coefficients equal piy/xi in this case and an expression analogous to Eq. (5.6) is obtained from Eq. (5.1), if relative standard uncertainties w(y) = u(y)/y and w (xi) = u (xi) / xi are used,
(5.9)
6. Expanded uncertainty in measurement
6.1 Calibration laboratories shall state an expanded uncertainty in measurement (U), obtained by multiplying the standard uncertainty u(y) of the output estimate y by a coverage factor k,
U = ku (y) (6.1)
In cases where a normal (Gaussian) distribution can be attributed to the measurand and the standard uncertainty associated with the output estimate has sufficient reliability, the standard coverage factor k = 2 shall be used. The assigned expanded uncertainty corresponds to a coverage probability of approximately 95 %.
6.2 The assumption of a normal distribution cannot always be easily confirmed experimentally. However, in the cases where several (i.e. N ³ 3) uncertainty components derived from well–behaved probability distributions of independent quantities, e.g. normal distributions or rectangular distributions, contribute to the standard uncertainty associated with the output estimate by comparable amounts, the conditions of the central limit theorem are met and it can be assumed to a high degree of approximation that the distribution of the output quantity is normal.
6.3 The reliability of the standard uncertainty assigned to the output estimate is determined by its effective degrees of freedom (see Appendix B). However, the reliability criterion is always met if none of the uncertainty contributions is obtained from a Type A evaluation based on less than ten repeated observations.
6.4 If one of these conditions (normality or sufficient reliability) is not fulfilled, the standard coverage factor k = 2 can yield an expanded uncertainty corresponding to a coverage probability of less than 95 %. In these cases, in order to ensure that a value of the expanded uncertainty is quoted corresponding to the same coverage probability as in the normal case, other procedures have to be followed. The use of approximately the same coverage probability is essential whenever two results of measurement of the same quantity have to be compared, e.g. when evaluating the results of an interlaboratory comparison or assessing compliance with a specification.
6.5 Even if a normal distribution can be assumed, it may still occur that the standard uncertainty associated with the output estimate is of insufficient reliability. If, in this case, it is not expedient to increase the number n of repeated measurements or to use a Type B evaluation instead of the Type A evaluation of poor reliability, the method given in Appendix – B should be used.
6.6 For the remaining cases, i.e. all cases where the assumption of a normal distribution cannot be justified, information on the actual probability distribution of the output estimate must be used to obtain a value of the coverage factor k that corresponds to a coverage probability of approximately 95 %.
7. Statement of uncertainty in measurement
7.1 In calibration certificates the complete result of the measurement consisting of the estimate y of the measurand and the associated expanded uncertainty U shall be given in the form (y ±U). To this an explanatory note must be added which in the general case should have the following content: The reported expanded uncertainty in measurement is stated as the standard uncertainty in measurement multiplied by the coverage factor k = 2, which for a normal distribution corresponds to a coverage probability of approximately 95 %.
7.2 However, in cases where the procedure of Appendix A has been followed, the additional note should read as follows: The reported expanded uncertainty in measurement is stated as the standard uncertainty in measurement multiplied by the coverage factor k which for a t-distribution with neff effective degrees of freedom corresponds to a coverage probability of approximately 95 %. (See Appendix – B).
7.3 The numerical value of the uncertainty in measurement should be given to at most two significant figures. The numerical value of the measurement result should in the final statement normally be rounded to the least significant figure in the value of the expanded uncertainty assigned to the measurement result. For the process of rounding, the usual rules for rounding of numbers have to be used. However, if the rounding brings the numerical value of the uncertainty in measurement down by more than 5 %, the rounded up value should be used.
8. Apportionment of standard uncertainty
8.1 The uncertainty analysis for a measurement-sometimes called the Uncertainty Budget of the measurement-should include a list of all sources of uncertainty together with the associated standard uncertainties of measurement and the methods of evaluating them. For repeated measurements the number n of observations also has to be stated. For the sake of clarity, it is recommended to present the data relevant to this analysis in the form of a table. In this table all quantities should be referenced by a physical symbol Xi, or a short identifier. For each of them at least the estimate xi, the associated standard uncertainty in measurement u (xi), the sensitivity coefficient ci and the different uncertainty contributions ui(y) should be specified. The degrees of freedom have to be mentioned. The dimension of each of the quantities should also be stated with the numerical values in the table.
8.2 A formal example of such an arrangement is given as Table (8.1) applicable for the case of uncorrelated input quantities. The standard uncertainty associated with the measurement result u(y) given in the bottom right corner of the table is the root sum square of all the uncertainty contributions in the outer right column. Similarly, neff has to be evaluated as mentioned in Appendix –B.
9. Step-by-step procedure for calculating the uncertainty in measurement
The following is a guide to the use of this document in practice:
Step 1 Express in mathematical terms the dependence of the measured (output quantity) Y on the input quantities Xi according to Eq. (2.1). In the case of a direct comparison of two standards the equation may be very simple, e.g.
Y = X1 + X2 (9.1)
Step 2 Identify and apply all significant corrections to the input quantities.
Step 3 List all sources of uncertainty in the form of an uncertainty analysis in accordance with Section 8.
Step 4 Calculate the standard uncertainty for repeatedly measured quantities in accordance with sub-section 4.2.
Step 5 For single values, e.g. resultant values of previous measurements, correction values or values from the literature, adopt the standard uncertainty where it is given or can be calculated according to paragraph 4.3.2(a). Pay attention to the uncertainty representation used. If no data are available from which the standard uncertainty can be derived, state a value of u (xi) on the basis of scientific experience.
Step 6 For input quantities for which the probability distribution is known or can be assumed, calculate the expectation and the standard uncertainty u (xi) according to paragraph 4.3.2 (b). If only upper and lower limits are given or can be estimated, calculate the standard uncertainty u (xi) in accordance with paragraph 4.3.2(c).
Step 7 Calculate for each input quantity Xi the contribution ui (y) to the uncertainty associated with the output estimate resulting from the input estimate xi according to Eqs. (5.2) and (5.3) and sum their squares as described in Eq. (5.1) to obtain the square of the standard uncertainty u(y) of the measurand.
Step 8 Calculate the expanded uncertainty U by multiplying the standard uncertainty u(y) associated with output estimate by a coverage factor k chosen in accordance with Section 6.
Step 9 Report the result of the measurement comprising the estimate y of the measurand, the associated expanded uncertainty U and the coverage factor k in the calibration certificate in accordance with Section 7.
B.2 The procedure for calculating an appropriate coverage factor k :
Step 1 Obtain the standard uncertainty associated with the output estimate.
Step 2 Estimate the effective degree of freedom neff of the standard uncertainty u(y) associated with the output estimate y from the Welch-Satterthwaite formula.
Step 3 Obtain the coverage factor k from the table of values of student “t” distribution. If the value of neff is not an integer, it is truncated to the next lower integer and the corresponding coverage factor k is obtained from the table.
B.3 Welch-Satterthwaite formula is as follows:
(B.1)
where u i (y) (i = 1,2,3,……..N) defined in Eqs. (5.1) and (5.2) , are the contributions to the standard uncertainty associated with the output estimate y resulting from the standard uncertainty associated with the input estimate x i which are assumed to be mutually statistically independent , and the ni is the effective degrees of freedom of the standard uncertainty contributions u i (y).
Note :
The calculation of the degrees of the freedom n for Type A and Type B of the evaluation may be as follows:
Type A Evaluation
For the results of direct measurement (Type A evaluation), the degree of freedom is related to the number of observations (n) as,
n i = n - 1 (B.2)
Type B Evaluation
For this evaluation, when lower and upper limits are known
ni ® ¥ (B.3)
It is suggested that ni should always be given when Type A and Type B evaluations of uncertainty components are documented.
Where high precision measurements are undertaken, the accredited calibration laboratories shall be required to follow ISO Guide to the expression of uncertainty in Measurement (1995). Concerned laboratories should refer to Annexure – G (with special emphasis on table G-2 ) and Annexure –H for related examples.
However, assuming that ni ® ¥ is not necessarily unrealistic, since it is a common practice to chose a- and a+ in such a way that the probability of the quantity lying outside the interval a- to a+ is extremely small.
Further interpretation on the above is given on page 29 & 30
Interpretation on Effective Degrees of Freedom
“Whilst the reason for determining the number of degrees of freedom associated with an uncertainty component is to allow the correct selection of value of student’s t, it also gives an indication of how well a component may be relied upon. A high number of degrees of freedom is associated with a large number of measurements or a value with a low variance or a low dispersion associated with it. A low number of degrees of freedom corresponds to a large dispersion or poorer confidence in the value.
Every component of uncertainty can have an appropriate number of degrees of freedom,n, assigned to it. For the mean, `x, for example n = n - 1, where n is a number of repeated measurements. For other Type A assessments, the process is also quite straightforward. For example, most spreadsheets provide the standard deviation of the fit when data is fitted to a curve. This standard deviation may be used as the uncertainty in the fitted value due to the scatter of the measurand values. The question is how to assign components evaluated by Type B processes.
For some distributions, the limits may be determined so that we have complete confidence in their value. In such instances, the number of degrees of freedom is effectively infinite. The assigning of limits, which are worst case, leads to this instance, namely infinite degrees of freedom, and simplifies the calculation of effective degrees of freedom of the combined uncertainty.
If the limits themselves have some uncertainty, then a lesser number of degrees of freedom must be assigned. The ISO Guide to the expression of uncertainty in measurement (GUM) gives a formula that is applicable to all distributions. It is equation G.3 that is:
n » ½ [ Du(xi)/ u(xi) ]-2 ……… ………… 1
Where :
Du(xi)/ u(xi) is the relative uncertainty in the uncertainty
This is a number less than 1, but may for convenience be thought of as a percentage or a fraction. The smaller the number, the better defined is the magnitude of the uncertainty.
For example, if relative uncertainty is 10%, i.e.
Du(xi)/ u(xi) = 0.1
Then it can be shown that the number of degrees of freedom is 50. For a relative uncertainty of 25 % then n = 8 and for relative uncertainty of 50 %, n = is only 2.
Rather than become seduced by the elegance of mathematics, it is better to try to determine the limits more definitely, particularly if the uncertainty is a major one. It is of the interest to note that equation (1) tells us that when we have made 51 measurements and taken the mean, the relative uncertainty in the uncertainty of the mean is 10%. This shows that even when many measurements are taken, the reliability of the uncertainty is not necessarily any better than when a type B assessment is make. Indeed, it is usually better to rely on prior knowledge rather than using an uncertainty based on two or three measurements. It also shows why we restrict uncertainty to two digits. The value is usually not reliable enough to quote to better than 1 % resolution.
Once the uncertainty components have been combined, it remains to find the number of degrees of freedom in the combined uncertainty. The degrees of freedom for each component must also be combined to find the effective number of degrees of freedom to be associated with the combined uncertainty. This is calculated using the Welch-Satterthwaite equation, which is:
n
neff = [uc4 (y)/ å{ ui4 (y)/ ni}] …. 2
1
Where:
neff is the effective number of degrees of freedom for uc the combined uncertainty
ni is the number of degrees of freedom for u i , the ith uncertainty term
u i (y) is the product of c i u i
“The other terms have their usual meaning”.
Adopted from NATA document on “Assessment of uncertainties in Measurement”, 1999.
Table B.1: Student t-distribution for degrees of freedom n. The t-distribution for n defines an interval -t p (n) to + t p (n) that encompasses the fraction p of the distribution. For p = 68.27 %, 95.45 %, and 99.73 %, k is 1, 2, and 3, respectively.
Solved examples showing the applications of the method outlined here to eight specific problems in different fields
C.1 Micrometer calibration using “0” grade slip gauge at 25mm
Introduction
The instrument under calibration is a micrometer of 0 – 25 mm range with a slip gauge of 25 mm of nominal size.
The detailed specifications of the slip gauge are as follows:
Range = 25 mm,
Standard reference temperature (Tr e f) = 20 0 C,
Actual calibrating temperature (Tc) = 23 0 C,
Calibrated value = 25.00010 ± 0.00008 mm, and
Least count of thermometer used = 1 0 C.
Mathematical model
YGUT = XSTD + DX (C.1)
Where YGUT is the micrometer reading [Gauge under test (GUT), XSTD is the gauge block size and DX is the error or the difference between the micrometer reading and gauge block size.
Uncertainty equation
The combined standard uncertainty equation is given by,
(C.2)
Measured results
Type A evaluation
Five readings are taken and the deviation from the nominal value is as follows.
Mean Deviation:
(C.3)
Standard deviation :
(C.4)
Table C.1 : Data for calculation of mean and standard deviation
Observation
numbers
Deviation from nominal value (xj)
(mm)
`x
(mm)
(xj - `x)2 ´ 10-7
(mm)
1.
0.001
1.6
2.
0.000
3.6
3.
0.001
0.0006
1.6
4.
0.000
3.6
5.
0.001
1.6
Standard deviation of the mean:
(C.5)
Standard uncertainty:
(C.6)
Degrees of freedom (ni)
n = n – 1 = 5 –1 = 4 (C.7)
Type B evaluation
The uncertainty quoted in the gauge block calibration certificate is considered to be Type B uncertainty of normal distribution.
Standard uncertainty (u1) due to the temperature measurement ±1 0 C.
Standard thermal expansion coefficient of the gauge block is 11.5´10-6/ 0C
u 1 = 25 ´ 1´11.5 ´ 10-6 mm = 287.5 ´ 10-6 mm = 0.2875 mm (C.8 )
Standard uncertainty (u2) due to difference in temperature of micrometer and slip gauge
Assuming the temperature of the slip gauges and micrometer are the same but still it can have a difference ±1 0 C. Hence, again uncertainty component
u2 = 0.2875 mm (C.9)
Standard uncertainty (u3) due to difference in thermal expansion coefficient of the slip gauge and micrometer
It is assumed that the difference in thermal expansion coefficient of standard slip gauge and the micrometer screw is amounting to 20 %, hence the uncertainty component
[DT = Tc – Tref = 30 C],
u3 = 25 ´ 3 ´ 11.5 ´ 10-6 ´ (20 /100) mm = 0.1725 mm (C.10)
Standard uncertainty (u4) due to the flatness of micrometer faces’
(C.11)
Standard uncertainty (u5) due to the parallelness of micrometer faces’
(C.12)
Standard uncertainty (u6) due to the Standard used for calibration
The uncertainty in the value of the standard is taken from the calibration certificate say 0.08 mm. Assuming rectangular distribution, the standard uncertainty is
(C.13)
The sensitivity coefficients (ci) are 1 and degree of freedom is ni = ¥ [Type B components ] in all six cases .
Degrees of freedom (neff )
(C.14)
@ 89 @ ¥
Combined uncertainty
Combined uncertainty [uc (YGUT)] is ,
(C.15)
uc (YGUT ) = 0.531 mm (C.16)
National Accreditation Board for Testing and Calibration Laboratories
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Measurement Uncertainty
Essentials of expressing measurement uncertainty Basic definitions Evaluating uncertainty components Combining uncertainty components Expanded uncertainty and coverage factor Examples of uncertainty statements
Background International and U.S. perspectives on measurement uncertainty
Bibliography Online publications and purchasing information
more
Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results
Barry N. Taylor and Chris E. Kuyatt
Brief summary
A method of evaluating and expressing uncertainty in measurement adapted from NIST Technical Note 1297.
TN 1297 also available as a PDF file
To view documents which are "pdf files," Adobe Acrobat Reader is required. This software may be downloaded without charge.
Contents (Cover page)
Preface to the 1994 Edition
Foreword
1. Introduction
2. Classification of Components of Uncertainty
3. Type A Evaluation of Standard Uncertainty
4. Type B Evaluation of Standard Uncertainty
5. Combined Standard Uncertainty
6. Expanded Uncertainty
7. Reporting Uncertainty
8. References
Appendices
A: Law of Propagation of Uncertainty
B: Coverage Factors
C: Statements of Uncertainty Associated with Measurement Results
D: Clarification and Additional Guidance
D.1 Terminology
D.2 Identification of uncertainty components
D.3 Equation (A-2)
D.4 Measurand defined by the measurement method; characterization of test methods; simple calibration
D.5 tp and the quantile t1-α
D.6 Uncertainty and units of the SI; proper use of the SI and quantity and unit symbols
D.7 References
more
Measurement uncertainty
From Wikipedia, the free encyclopedia
Jump to: navigation, search
It has been suggested that Uncertainty of measurement be merged into this article or section. (Discuss)
The measurement uncertainty narrows down the difference between the actually measured value of a physical quantity and the true value of the same physical quantity. The result of a physical measurement comprises two parts: an estimate of the true value of the measurand and the uncertainty of this estimate. This also applies to a physical property as measured by a test method.
The observed value of a measurement does not coincide with the true value of the measurand. The observed value may be considered as an estimate which may be greater or smaller than the true value. This measurement uncertainty is not a "mistake" in the common usage but is rather an inherent part of any measurement.
The experimenter requests the interval estimate measurement uncertainty
to "localize" the true value of the measurand. The true values of physical quantities are and remain unknown.
To illustrate the meaning of true values, let us consider the law of falling bodies:
This law only holds using the true (error free) values of the distance s, the gravitational acceleration g and the time t. Otherwise the mathematical formula would be inconsistent.
Physical laws need to be proven experimentally. As true values have to be localized by means of intervals, metrology judges the analysis and accounting of measurement errors of utmost importance.
Measurement uncertainties have to be estimated by means of declared procedures. These procedures, however, are intrinsically tied to the error model referred to. Currently, error models and consequently the procedures to assess measurement uncertainties are considered highly controversial. As a matter of fact, today the metrological community is deeply divided over the question as to how to proceed. For the time being, all that can be done is to put the diverginig positions side by side.
Contents[hide]
1 Background
2 The GUM
3 An Alternative Approach
4 See also
5 Literature - The GUM
6 Literature - An Alternative Approach
7 External links
//
more
Background International and U.S. perspectives on measurement uncertainty
Bibliography Online publications and purchasing information
more
Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results
Barry N. Taylor and Chris E. Kuyatt
Brief summary
A method of evaluating and expressing uncertainty in measurement adapted from NIST Technical Note 1297.
TN 1297 also available as a PDF file
To view documents which are "pdf files," Adobe Acrobat Reader is required. This software may be downloaded without charge.
Contents (Cover page)
Preface to the 1994 Edition
Foreword
1. Introduction
2. Classification of Components of Uncertainty
3. Type A Evaluation of Standard Uncertainty
4. Type B Evaluation of Standard Uncertainty
5. Combined Standard Uncertainty
6. Expanded Uncertainty
7. Reporting Uncertainty
8. References
Appendices
A: Law of Propagation of Uncertainty
B: Coverage Factors
C: Statements of Uncertainty Associated with Measurement Results
D: Clarification and Additional Guidance
D.1 Terminology
D.2 Identification of uncertainty components
D.3 Equation (A-2)
D.4 Measurand defined by the measurement method; characterization of test methods; simple calibration
D.5 tp and the quantile t1-α
D.6 Uncertainty and units of the SI; proper use of the SI and quantity and unit symbols
D.7 References
more
Measurement uncertainty
From Wikipedia, the free encyclopedia
Jump to: navigation, search
It has been suggested that Uncertainty of measurement be merged into this article or section. (Discuss)
The measurement uncertainty narrows down the difference between the actually measured value of a physical quantity and the true value of the same physical quantity. The result of a physical measurement comprises two parts: an estimate of the true value of the measurand and the uncertainty of this estimate. This also applies to a physical property as measured by a test method.
The observed value of a measurement does not coincide with the true value of the measurand. The observed value may be considered as an estimate which may be greater or smaller than the true value. This measurement uncertainty is not a "mistake" in the common usage but is rather an inherent part of any measurement.
The experimenter requests the interval estimate measurement uncertainty
to "localize" the true value of the measurand. The true values of physical quantities are and remain unknown.
To illustrate the meaning of true values, let us consider the law of falling bodies:
This law only holds using the true (error free) values of the distance s, the gravitational acceleration g and the time t. Otherwise the mathematical formula would be inconsistent.
Physical laws need to be proven experimentally. As true values have to be localized by means of intervals, metrology judges the analysis and accounting of measurement errors of utmost importance.
Measurement uncertainties have to be estimated by means of declared procedures. These procedures, however, are intrinsically tied to the error model referred to. Currently, error models and consequently the procedures to assess measurement uncertainties are considered highly controversial. As a matter of fact, today the metrological community is deeply divided over the question as to how to proceed. For the time being, all that can be done is to put the diverginig positions side by side.
Contents[hide]
1 Background
2 The GUM
3 An Alternative Approach
4 See also
5 Literature - The GUM
6 Literature - An Alternative Approach
7 External links
//
more
Aims & Objectives of NABL
Some of the Aims & Objectives of NABL are:
To promote, coordinate, guide, implement and maintain a accreditation system for laboratories suitable for the country in accordance with the relevant national and international standards and guides.
To ensure that all measurements either during calibration or testing by accredited laboratories are traceable to appropriate national / international standards maintained at National Physical Laboratory (NPL) and at Bhabha Atomic Research Centre (BARC) through an unbroken chain of comparisons.
To encourage Proficiency Tests / Inter-laboratory comparisons in order to ensure accuracy, reliability and reproducibility of test results.
To ensure that the accredited laboratories adhere to all the conditions of accreditation, by periodic surveillance.
To organize Awareness Programmes on all aspects of laboratory accreditation for the laboratories by various means including seminars, workshops and laboratory-industry-accreditation body meets etc.
To acquire travelling standards and artifacts for conducting studies on measurements by the accredited laboratories and thereby to help improve reliability and reproducibility of results.
To establish and maintain strong linkages with international and regional for a such as International Laboratory Accreditation Conference (hitherto referred to as ILAC), European Accreditation Cooperation for Laboratories (hitherto referred to as EAL), Asia Pacific Laboratory Accreditation Cooperation (hitherto referred to as APLAC) etc. and to take active participation in Plenary Sessions, Committee Meetings etc. in order to keep pace with the latest developments and for promoting Bi-lateral .
To undertake all the activities which shall promote undertaking Bi-lateral / Multilateral Recognition Agreements between NABL and laboratory accreditation bodies in other countries so that test results of NABL accredited laboratories become acceptable in all countries.
Scope of Accreditaion
Accreditation is a formal recognition of the technical competence of a laboratory based on third party assessment and following international guidelines. The assessment is carried out by trained Assessors taken from institutions all over India, with established credentials in testing and calibration activities. Currently, NABL Accreditation is limited to the following fields:
Testing Laboratories
To promote, coordinate, guide, implement and maintain a accreditation system for laboratories suitable for the country in accordance with the relevant national and international standards and guides.
To ensure that all measurements either during calibration or testing by accredited laboratories are traceable to appropriate national / international standards maintained at National Physical Laboratory (NPL) and at Bhabha Atomic Research Centre (BARC) through an unbroken chain of comparisons.
To encourage Proficiency Tests / Inter-laboratory comparisons in order to ensure accuracy, reliability and reproducibility of test results.
To ensure that the accredited laboratories adhere to all the conditions of accreditation, by periodic surveillance.
To organize Awareness Programmes on all aspects of laboratory accreditation for the laboratories by various means including seminars, workshops and laboratory-industry-accreditation body meets etc.
To acquire travelling standards and artifacts for conducting studies on measurements by the accredited laboratories and thereby to help improve reliability and reproducibility of results.
To establish and maintain strong linkages with international and regional for a such as International Laboratory Accreditation Conference (hitherto referred to as ILAC), European Accreditation Cooperation for Laboratories (hitherto referred to as EAL), Asia Pacific Laboratory Accreditation Cooperation (hitherto referred to as APLAC) etc. and to take active participation in Plenary Sessions, Committee Meetings etc. in order to keep pace with the latest developments and for promoting Bi-lateral .
To undertake all the activities which shall promote undertaking Bi-lateral / Multilateral Recognition Agreements between NABL and laboratory accreditation bodies in other countries so that test results of NABL accredited laboratories become acceptable in all countries.
Scope of Accreditaion
Accreditation is a formal recognition of the technical competence of a laboratory based on third party assessment and following international guidelines. The assessment is carried out by trained Assessors taken from institutions all over India, with established credentials in testing and calibration activities. Currently, NABL Accreditation is limited to the following fields:
Testing Laboratories
Salient features of ISO 17025 vs ISO 9001
ISO 17025 requires
Technical Management in addition to Quality Management
Policy and Procedures not only procedures
Quality Manager instead of Management representative
ISO 17025 allows
hand corrections to documents pending formal re-issue of new documents
off site calibration
mobile calibration site
sub-contracted calibrators
Technical Management in addition to Quality Management
Policy and Procedures not only procedures
Quality Manager instead of Management representative
ISO 17025 allows
hand corrections to documents pending formal re-issue of new documents
off site calibration
mobile calibration site
sub-contracted calibrators
Thursday, December 06, 2007
Accreditation procedure
Laboratory Accreditation, 7 October 2005
Accreditation
Laboratory accreditation is a procedure by which an authoritative body gives formal recognition of technical competence for specific test(s)/ measurement(s), based on third party assessment and following international standard.
Assures the client that the procedures are technically valid
Recognizes the technical competence of laboratory staff
Assures the client that the results are technically valid
Endorses the quality management system
Certification
Procedure by which a third-party (certification body) gives a written assurance that a product, process or service (of an organisation) conforms to specified requirements.
Specified requirements - ISO 9000 series;
Assures the client that the organisation has in place an effective quality or environmental management system
Does not confer technical credibility of the test result
Some Benefits of Laboratory Accreditation
Provides formal recognition to competent laboratories and ensures that they perform their work in accordance with international standard.
Minimizes the risk of unreliable results.
Minimizes the chances of retesting and hence reduces chances of additional financial burden and time delays.
Enhances Customer confidence and Satisfaction.
International acceptability of test results. Based on Mutual Recognition Arrangements (MRA).
This is relevant in case of insurance coverage, placement agencies, overseas health authorities, labour department etc.
About NABL
Government of India has authorized NABL as the sole accreditation body for Testing and Calibration laboratories.
NABL has established its accreditation system in accordance with ISO/IEC 17011, which is followed internationally.
NABL provides laboratory accreditation services to laboratories that are performing tests/ calibrations in accordance with ISO/ IEC 17025: 2005 (General requirements for the competence of Testing and Calibration Laboratories).
ISO 15189:2003 (Medical laboratories- Particular requirements for quality and competence).
Accreditation Procedure
Accreditation
Laboratory accreditation is a procedure by which an authoritative body gives formal recognition of technical competence for specific test(s)/ measurement(s), based on third party assessment and following international standard.
Assures the client that the procedures are technically valid
Recognizes the technical competence of laboratory staff
Assures the client that the results are technically valid
Endorses the quality management system
Certification
Procedure by which a third-party (certification body) gives a written assurance that a product, process or service (of an organisation) conforms to specified requirements.
Specified requirements - ISO 9000 series;
Assures the client that the organisation has in place an effective quality or environmental management system
Does not confer technical credibility of the test result
Some Benefits of Laboratory Accreditation
Provides formal recognition to competent laboratories and ensures that they perform their work in accordance with international standard.
Minimizes the risk of unreliable results.
Minimizes the chances of retesting and hence reduces chances of additional financial burden and time delays.
Enhances Customer confidence and Satisfaction.
International acceptability of test results. Based on Mutual Recognition Arrangements (MRA).
This is relevant in case of insurance coverage, placement agencies, overseas health authorities, labour department etc.
About NABL
Government of India has authorized NABL as the sole accreditation body for Testing and Calibration laboratories.
NABL has established its accreditation system in accordance with ISO/IEC 17011, which is followed internationally.
NABL provides laboratory accreditation services to laboratories that are performing tests/ calibrations in accordance with ISO/ IEC 17025: 2005 (General requirements for the competence of Testing and Calibration Laboratories).
ISO 15189:2003 (Medical laboratories- Particular requirements for quality and competence).
Accreditation Procedure
SEPTEMBER 2006 NEWS
International cGMP Training Offered by PTi International
Recent NABL Accreditations to Laboratories in India
Bookham Qualification Labs Achieve International Standard ISO/IEC 17025
Cebu CITE Calibration Laboratory Meets ISO Standards
GMP Webinars Now Available As Recordable Webinars
more
International cGMP Training Offered by PTi International
Recent NABL Accreditations to Laboratories in India
Bookham Qualification Labs Achieve International Standard ISO/IEC 17025
Cebu CITE Calibration Laboratory Meets ISO Standards
GMP Webinars Now Available As Recordable Webinars
more
Thursday, October 18, 2007
ISO/IEC 17025:2005
ISO/IEC 17025:2005 specifies the general requirements for the competence to carry out tests and/or calibrations, including sampling. It covers testing and calibration performed using standard methods, non-standard methods, and laboratory-developed methods.
It is applicable to all organizations performing tests and/or calibrations. These include, for example, first-, second- and third-party laboratories, and laboratories where testing and/or calibration forms part of inspection and product certification.
ISO/IEC 17025:2005 is applicable to all laboratories regardless of the number of personnel or the extent of the scope of testing and/or calibration activities. When a laboratory does not undertake one or more of the activities covered by ISO/IEC 17025:2005, such as sampling and the design/development of new methods, the requirements of those clauses do not apply.
ISO/IEC 17025:2005 is for use by laboratories in developing their management system for quality, administrative and technical operations. Laboratory customers, regulatory authorities and accreditation bodies may also use it in confirming or recognizing the competence of laboratories. ISO/IEC 17025:2005 is not intended to be used as the basis for certification of laboratories.
Compliance with regulatory and safety requirements on the operation of laboratories is not covered by ISO/IEC 17025:2005.
Revision information
Revises: ISO/IEC 17025:1999
Corrigenda, Amendments and other parts
ISO/IEC 17025:2005/Cor 1:2006
more
It is applicable to all organizations performing tests and/or calibrations. These include, for example, first-, second- and third-party laboratories, and laboratories where testing and/or calibration forms part of inspection and product certification.
ISO/IEC 17025:2005 is applicable to all laboratories regardless of the number of personnel or the extent of the scope of testing and/or calibration activities. When a laboratory does not undertake one or more of the activities covered by ISO/IEC 17025:2005, such as sampling and the design/development of new methods, the requirements of those clauses do not apply.
ISO/IEC 17025:2005 is for use by laboratories in developing their management system for quality, administrative and technical operations. Laboratory customers, regulatory authorities and accreditation bodies may also use it in confirming or recognizing the competence of laboratories. ISO/IEC 17025:2005 is not intended to be used as the basis for certification of laboratories.
Compliance with regulatory and safety requirements on the operation of laboratories is not covered by ISO/IEC 17025:2005.
Revision information
Revises: ISO/IEC 17025:1999
Corrigenda, Amendments and other parts
ISO/IEC 17025:2005/Cor 1:2006
more
ISO/IEC 17025 in Analytical Laboratories
Introduction and Regulatory Requirements
Scope
Content Overview
Management Requirements
Technical Requirements
Impact on Analytical Laboratories
Implementing ISO 17025
ISO 17025 Audit: Preparation - Conduct - Follow-up
Required Documentation
Comparison with GxP and Other FDA Regulations
References
Links
Questions and Answers
Expert Advice on Selected Topics
more
Scope
Content Overview
Management Requirements
Technical Requirements
Impact on Analytical Laboratories
Implementing ISO 17025
ISO 17025 Audit: Preparation - Conduct - Follow-up
Required Documentation
Comparison with GxP and Other FDA Regulations
References
Links
Questions and Answers
Expert Advice on Selected Topics
more
Monday, July 16, 2007
NABL, India
NABL has been established with the objective of providing Government, Industry Associations and Industry in general with a scheme of laboratory accreditation which involves third-party assessment of the technical competence of testing and calibration laboratories. NABL also provides laboratory accreditation to medical testing laboratories.
The laboratory accreditation services to testing and calibration laboratories are provided in accordance with ISO/ IEC 17025: 2005 ‘General Requirements for the Competence of Testing and Calibration Laboratories’ and ISO 15189: 2003 ‘Medical laboratories - Particular requirements for quality and competence’. The fields and groups under which the accreditation services are offered are listed in ‘Scope of NABL Accreditation’.
NABL offers laboratory accreditation services in a non-discriminatory manner. These services are accessible to all testing and calibration laboratories in India and other countries in the region that do not have accreditation bodies of their own, regardless of the size of the applicant laboratory or its membership of any association or group or number of laboratories already accredited by NABL.
NABL has established its accreditation system in accordance with ISO/ IEC 17011: 2004 ‘Conformity Assessment – General requirements for accreditation bodies accrediting conformity assessment bodies’. NABL accreditation system also takes note of the requirements of Mutual Recognition Arrangements (MRAs) of which NABL is a member.
go here
The laboratory accreditation services to testing and calibration laboratories are provided in accordance with ISO/ IEC 17025: 2005 ‘General Requirements for the Competence of Testing and Calibration Laboratories’ and ISO 15189: 2003 ‘Medical laboratories - Particular requirements for quality and competence’. The fields and groups under which the accreditation services are offered are listed in ‘Scope of NABL Accreditation’.
NABL offers laboratory accreditation services in a non-discriminatory manner. These services are accessible to all testing and calibration laboratories in India and other countries in the region that do not have accreditation bodies of their own, regardless of the size of the applicant laboratory or its membership of any association or group or number of laboratories already accredited by NABL.
NABL has established its accreditation system in accordance with ISO/ IEC 17011: 2004 ‘Conformity Assessment – General requirements for accreditation bodies accrediting conformity assessment bodies’. NABL accreditation system also takes note of the requirements of Mutual Recognition Arrangements (MRAs) of which NABL is a member.
go here
Saturday, June 23, 2007
ISO/IEC/EN 17025
ISO/IEC/EN 17025
(formerly ISO Guide 25 & EN45001)
General Requirements for the Competence of Calibration and Testing Laboratories
all the links you will find here
http://www.fasor.com/iso25/
(formerly ISO Guide 25 & EN45001)
General Requirements for the Competence of Calibration and Testing Laboratories
all the links you will find here
http://www.fasor.com/iso25/
Sunday, November 19, 2006
Monday, April 17, 2006
Indian clinical laboratories
Are Indian clinical laboratories prepared to accept the present accreditation system?
S Chakraborty
The concept of quality concept in clinical laboratories is undergoing rapid changes. Quality control programme participation is not ensuring the consistency of test results and reports delivered to the patient. Laboratories are now establishing quality system in the ‘laboratory report lifecycle’, which covers pre-analytical, analytical and post-analytical phase.
Accreditation speaks about formal recognition of technical competency of laboratory testing. Quality system of laboratory is developed based on the 4 Ms and A (Man, Machine, Materials, Method of testing & Accommodation condition). Accreditation system is now practiced in every countries. Quality system standard ISO/IEC 17025 is now mostly followed for developing quality system in a clinical laboratory and this will be revised to ISO/IEC 1589.
Depending on the countries, laboratory tests performed in the pre-clinical phase follow several GLP (good laboratory practice) standards. In the European Union, the GLP directives are based on OECD guideline and FDA controls the US GLP.
The Accreditation Body uses the word the technical competence for granting accreditation to lab but appropriate medical competence is also required while granting accreditation.
Many countries have prepared specific guideline proposal, few examples are given below:
Germany: Accreditation of medical/ medical diagnostic Laboratory, (Eurochem/D-22G-AML)
Netherlands: CCKL guide of practice.
UK: CPA manual for lab accreditation.
In India, NABL as accreditation authority, publishes a book "Specific Guidelines for Accreditation of Clinical Laboratories (112) and Nuclear Medicine Laboratories (112A)". The two books published by NABL "Specific Guidelines for Accreditation of Clinical Laboratories (112)" and "Nuclear Medicine Laboratories (112A)" cannot be considered as specified requirements for laboratories. Their appointed assessor decides the technical requirements.
Accreditation scheme is available in our country based on the compliance and implementation of ISO/ IEC 17025 standard. Laboratories are forced to develop four level quality systems. Four level documentation becomes a bulky system. This spoon-feeding documented system is designed with the help of the consultants to add an USP in their certificates.
In India, accreditation for clinical laboratories is started by NABL who are newborn players in the clinical field and they are experienced in industrial testing. They are not backed by any professional medical organisation. The body, whose active involvement is required, is Indian Council of Medical Research (ICMR), which can develop the accreditation system considering the geographical size and role in the society. Indian clinical laboratories are not yet prepared for accepting the accreditation system offered by NABL.
Clinical labs are now required to meet the following from the accreditation body:
All the requirements should be available as standard and should be self-explanatory.
Less documentation effort.
Implementation procedure should be simple checklist type.
Record requirement to be clearly defined.
Auditors should not tell anything beyond the standard.
All accreditation requirements shall be clearly explained by the expert of accreditation body. It should not be under the discretion of the appointed assessor.
Accreditation process will be transparent, so there will be no doubt about the requirement of accreditation.
Now we will review the accreditation system from the experience of the consultants working for it, accredited laboratory and feedback received from the members of professional bodies like Indian Association of Pathologists and Microbiologists (IAPM):
Effect of the accreditation process among the clinical labs:
1. Quality Manual:
Labs are not prepared to spend on improving quality of testing.
Assessors create trouble for changing manual as per his liking.
This documentation exercise is not required in the beginning of accreditation system.
A common policy manual should be prepared by the accreditation body.
2. Quality System Procedure:
In the absence of effective guidelines for sample handling or control of pre-analytical, analytical and post analytical error, labs face trouble.
Health regulatory authority or accreditation body has to prescribe the standards for maintaining sample handling and quality control procedure.
3. Standard Test Operating Procedure:
Confidence is developed among consultants, technicians and lab management.
Due to the absence of common standard practices, SOP standardisation depends on the auditor’s acceptance. Documentation becomes a burden for the lab.
Common standard test practices should be developed by regulatory authority or shall be prescribed by the accreditation Body.
4. Records
Labs are too burdened with records to satisfy the audit requirements.
Accreditation body should give records maintenance requirement guideline/checklist. Records maintenance requirement guideline / checklist should be given by accreditation body.
5. Quality control (Interlab/external)
Inter-laboratory test expenses are not worthy as non-compliance test results are not identified in case of different test results.
There are no health regulatory authorities for exercising quality control activities.
They receive different opinions and prescriptions from the auditors on quality control activities.
Labs feel the frequency of QC practices by using external control or participation in external program for biochemistry, hematology and clinical pathology, as prescribed, are not commercially viable. Accreditation procedure and its maintenance are expensive.
Regulatory authority or accreditation body should conduct external quality assurance or proficiency testing program. Guideline for small labs for PT or EQA should be fixed. Cost-effective EQA or PT program to be introduced.
Inter-laboratory comparison with accredited labs to be organised by accreditation body.
Guiding laboratories to taking corrective action should be looked after by the regulatory authority or accreditation body.
6. Internal audit
It is a time-consuming exercise.
Audit documentation creates a burden for the labs.
Simple checklist type audit is preferable and checklist should be supplied by accreditation body.
7. Overall cost/expenses for Audit:
A laboratory testing covering all common disciplines (Bio-chemistry, Clinical Pathology, Hematology, Histopathology and Microbiology) need auditors (covers pre-audit and final audit) for their Audit, but heavy amount is required for air fare, hotel expenses etc.
Number of assessors should be reduced and local assessors appointed.
4Ms & A requirement to be developed by accreditation body
MACHINE: Type is not specified by accreditation body
Calibration Requirement: Specified by accreditation body.
Remarks: Approval required from the regulatory authority about its performance and acceptability in producing test results.
METHOD: Sample handling and testing is not specified by accreditation body.
MATERIALS: Type of reagent and Consumables: Not specified by the accreditation body.
Remarks: Should be approved from regulatory authority, specification procedure for handling of reagent kit by the manufacturer and supplier to be developed.
ACCOMODATION: Not specified by accreditation body.
Remarks:
Specification to be developed, the specification prescribed by state health regulatory requires changes.
(The author is director- Institute of Applied Quality Management. He can be contacted at iaqm@vsnl.net)
Back to Top
http://www.expresshealthcaremgmt.com/labwatch/lab7.shtml
For Consultancy and training, contact www.tqmc.org
S Chakraborty
The concept of quality concept in clinical laboratories is undergoing rapid changes. Quality control programme participation is not ensuring the consistency of test results and reports delivered to the patient. Laboratories are now establishing quality system in the ‘laboratory report lifecycle’, which covers pre-analytical, analytical and post-analytical phase.
Accreditation speaks about formal recognition of technical competency of laboratory testing. Quality system of laboratory is developed based on the 4 Ms and A (Man, Machine, Materials, Method of testing & Accommodation condition). Accreditation system is now practiced in every countries. Quality system standard ISO/IEC 17025 is now mostly followed for developing quality system in a clinical laboratory and this will be revised to ISO/IEC 1589.
Depending on the countries, laboratory tests performed in the pre-clinical phase follow several GLP (good laboratory practice) standards. In the European Union, the GLP directives are based on OECD guideline and FDA controls the US GLP.
The Accreditation Body uses the word the technical competence for granting accreditation to lab but appropriate medical competence is also required while granting accreditation.
Many countries have prepared specific guideline proposal, few examples are given below:
Germany: Accreditation of medical/ medical diagnostic Laboratory, (Eurochem/D-22G-AML)
Netherlands: CCKL guide of practice.
UK: CPA manual for lab accreditation.
In India, NABL as accreditation authority, publishes a book "Specific Guidelines for Accreditation of Clinical Laboratories (112) and Nuclear Medicine Laboratories (112A)". The two books published by NABL "Specific Guidelines for Accreditation of Clinical Laboratories (112)" and "Nuclear Medicine Laboratories (112A)" cannot be considered as specified requirements for laboratories. Their appointed assessor decides the technical requirements.
Accreditation scheme is available in our country based on the compliance and implementation of ISO/ IEC 17025 standard. Laboratories are forced to develop four level quality systems. Four level documentation becomes a bulky system. This spoon-feeding documented system is designed with the help of the consultants to add an USP in their certificates.
In India, accreditation for clinical laboratories is started by NABL who are newborn players in the clinical field and they are experienced in industrial testing. They are not backed by any professional medical organisation. The body, whose active involvement is required, is Indian Council of Medical Research (ICMR), which can develop the accreditation system considering the geographical size and role in the society. Indian clinical laboratories are not yet prepared for accepting the accreditation system offered by NABL.
Clinical labs are now required to meet the following from the accreditation body:
All the requirements should be available as standard and should be self-explanatory.
Less documentation effort.
Implementation procedure should be simple checklist type.
Record requirement to be clearly defined.
Auditors should not tell anything beyond the standard.
All accreditation requirements shall be clearly explained by the expert of accreditation body. It should not be under the discretion of the appointed assessor.
Accreditation process will be transparent, so there will be no doubt about the requirement of accreditation.
Now we will review the accreditation system from the experience of the consultants working for it, accredited laboratory and feedback received from the members of professional bodies like Indian Association of Pathologists and Microbiologists (IAPM):
Effect of the accreditation process among the clinical labs:
1. Quality Manual:
Labs are not prepared to spend on improving quality of testing.
Assessors create trouble for changing manual as per his liking.
This documentation exercise is not required in the beginning of accreditation system.
A common policy manual should be prepared by the accreditation body.
2. Quality System Procedure:
In the absence of effective guidelines for sample handling or control of pre-analytical, analytical and post analytical error, labs face trouble.
Health regulatory authority or accreditation body has to prescribe the standards for maintaining sample handling and quality control procedure.
3. Standard Test Operating Procedure:
Confidence is developed among consultants, technicians and lab management.
Due to the absence of common standard practices, SOP standardisation depends on the auditor’s acceptance. Documentation becomes a burden for the lab.
Common standard test practices should be developed by regulatory authority or shall be prescribed by the accreditation Body.
4. Records
Labs are too burdened with records to satisfy the audit requirements.
Accreditation body should give records maintenance requirement guideline/checklist. Records maintenance requirement guideline / checklist should be given by accreditation body.
5. Quality control (Interlab/external)
Inter-laboratory test expenses are not worthy as non-compliance test results are not identified in case of different test results.
There are no health regulatory authorities for exercising quality control activities.
They receive different opinions and prescriptions from the auditors on quality control activities.
Labs feel the frequency of QC practices by using external control or participation in external program for biochemistry, hematology and clinical pathology, as prescribed, are not commercially viable. Accreditation procedure and its maintenance are expensive.
Regulatory authority or accreditation body should conduct external quality assurance or proficiency testing program. Guideline for small labs for PT or EQA should be fixed. Cost-effective EQA or PT program to be introduced.
Inter-laboratory comparison with accredited labs to be organised by accreditation body.
Guiding laboratories to taking corrective action should be looked after by the regulatory authority or accreditation body.
6. Internal audit
It is a time-consuming exercise.
Audit documentation creates a burden for the labs.
Simple checklist type audit is preferable and checklist should be supplied by accreditation body.
7. Overall cost/expenses for Audit:
A laboratory testing covering all common disciplines (Bio-chemistry, Clinical Pathology, Hematology, Histopathology and Microbiology) need auditors (covers pre-audit and final audit) for their Audit, but heavy amount is required for air fare, hotel expenses etc.
Number of assessors should be reduced and local assessors appointed.
4Ms & A requirement to be developed by accreditation body
MACHINE: Type is not specified by accreditation body
Calibration Requirement: Specified by accreditation body.
Remarks: Approval required from the regulatory authority about its performance and acceptability in producing test results.
METHOD: Sample handling and testing is not specified by accreditation body.
MATERIALS: Type of reagent and Consumables: Not specified by the accreditation body.
Remarks: Should be approved from regulatory authority, specification procedure for handling of reagent kit by the manufacturer and supplier to be developed.
ACCOMODATION: Not specified by accreditation body.
Remarks:
Specification to be developed, the specification prescribed by state health regulatory requires changes.
(The author is director- Institute of Applied Quality Management. He can be contacted at iaqm@vsnl.net)
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http://www.expresshealthcaremgmt.com/labwatch/lab7.shtml
For Consultancy and training, contact www.tqmc.org
Wednesday, February 15, 2006
ISO 15189
Particular requirements for medical labs
http://www.eaglegroupusa.com/ISO%2015189.htm
QA in clinical labs
http://www.expresshealthcaremgmt.com/20050815/diagnostics01.shtml
Guest Essay: ISO 15189 QSE 5.6: Assuring the Quality of ...
http://www.eaglegroupusa.com/ISO%2015189.htm
QA in clinical labs
http://www.expresshealthcaremgmt.com/20050815/diagnostics01.shtml
Guest Essay: ISO 15189 QSE 5.6: Assuring the Quality of ...
NABL
Guidelines for testing labs
http://www.nabl-india.org/nabl/asp/users/documentMgmt.asp?docType=both
What is the process for accreditation at NABL…?
Stage I
Prepare your laboratory's application for NABL accreditation, giving all desired information and enlisting the test(s) / calibration(s) along with range and accuracy for which the laboratory has the competence to perform. Laboratory can apply either for all or part of their testing / calibration facilities. Formats NABL 151 & NABL 152 are to be used by Testing Laboratories and Calibration Laboratories respectively for applying to NABL for accreditation.
Laboratory has to take special care in filling the scope of accreditation for which the laboratory wishes to apply. In case, the laboratory finds any clause (in part or full) not applicable to the laboratory, it shall furnish the reasons.
Laboratories are required to submit five sets of duly filled in application forms for each field of testing / calibration along with five sets of Quality Manual and Application Fees.
NABL Secretariat on receipt of application will issue acknowledgement to the laboratory. After scrutiny of application for it being complete in all respects, a unique Customer Registration Number will be allocated to laboratory for further processing of application.
NABL Secretariat shall then nominate a Lead Assessor for giving Adequacy Report on the Quality Manual / Application submitted by the laboratory. A copy of Adequacy Report by Lead Assessor will be provided to Laboratory for taking necessary corrective action, if any. The laboratory shall submit Corrective Action Report.
After satisfactory corrective action by the laboratory, a Pre-Assessment audit of the laboratory will be organised by NABL. Laboratories must ensure their preparedness by carrying out its internal audit before Pre-Assessment.
Stage II
NABL Secretariat shall organise the Pre-Assessment audit, which shall normally be carried by Lead Assessor at the laboratory sites.
The pre-assessment helps the laboratory to be better prepared for the Final Assessment. It also helps the Lead Assessor to assess the preparedness of the laboratory to undergo Final Assessment apart from Technical Assessor(s) and Total Assessment Man-days required vis-à-vis the scope of accreditation as per application submitted by the laboratory.
A copy of Pre-Assessment Report will be provided to Laboratory for taking necessary corrective action on the concerns raised during audit, if any.
The laboratory shall submit Corrective Action Report to NABL Secretariat.
After laboratory confirms the completion of corrective actions, Final Assessment of the laboratory shall be organised by NABL.
Stage III
NABL Secretariat shall organise the Final Assessment at the laboratory site(s) for its compliance to NABL Criteria and for that purpose appoint an assessment team.
The Assessment Team shall comprise of a Lead Assessor and other Technical Assessor(s) in the relevant fields depending upon the scope to be assessed.
Assessors shall raise the Non-Conformance(s), if any, and provide it to the laboratory in prescribed format so that it gets the opportunity to close as many Non-Conformance(s) as they can before closing meeting of the Assessment.
The Lead Assessor will provide a copy of consolidated report of the assessment to the laboratory and send the original copy to NABL Secretariat.
Laboratory shall take necessary corrective action on the remaining Non-Conformance(s) / other concerns and shall submit a report to NABL within a maximum period of 3 months.
Stage IV
After satisfactory corrective action by the laboratory, the Accreditation Committee examines the findings of the Assessment Team and recommend additional corrective action, if any, by the laboratory.
Accreditation Committee determines whether the recommendations in the assessment report is consistent with NABL requirements as well as commensurate with the claims made by the laboratory in its application.
Laboratory shall have to take corrective action on any concerns raised by the Accreditation Committee.
Accreditation Committee shall make the appropriate recommendations regarding accreditation of a laboratory to NABL Secretariat.
Laboratories are free to appeal against the findings of assessment or decision on accreditation by writing to the Director, NABL.
Whenever possible NABL will depute its own technical personnel to be present at the time of assessment as Coordinator and NABL Observer. Sometimes, NABL may at its own cost depute a newly trained Technical Assessor as "Observer" subject to convenience of the laboratory to be accessed.
Stage V
Accreditation to a laboratory shall be valid for a period of 3 years and NABL shall conduct periodical Surveillance of the laboratory at intervals of one year.
Laboratory shall apply for Renewal of accreditation to it at least 6 months before the expiry of the validity of accreditation.
16. Who at NABL should a laboratory contact before initiating the process of accreditation...?
Enquiries for accreditation may be addressed to Director NABL or mail at info@nabl-india.org
17. What are the preparations required by a laboratory before applying for accreditation...?
Laboratory management should first decide about getting accreditation for its laboratory from NABL.
It is important for a laboratory to make a definite plan of action for obtaining accreditation and nominate a responsible person to coordinate all activities related to seeking accreditation. The person nominated should be familiar with laboratory's existing Quality System. S/he should be formally designated as the Quality Manager.
Procure all relevant NABL documents from NABL Secretariat and get fully acquainted with each of these.
Laboratory needs to ascertain the status of its existing Quality System and Technical Competence with regards to requirements for NABL Accreditation. Is the system documented and effective or does it need modification. Does it need to build the Quality System of the laboratory from scratch?
It must be remembered that Quality Manual is a policy document, which has to be supplemented by a set of other documents like Procedural Manuals, Work Instructions etc. to align the Quality System in accordance with NABL Criteria. The laboratory must ensure that the procedures described in the Quality Manual and other documents are being implemented. For preparing Quality Manual or verifying its contents, the laboratory may take help of " Guide for Preparing Quality Manual" (NABL 160). The laboratory may also get its personnel trained in NABL's training programme on Laboratory Quality System, Management and Internal Audit.
Relevant requirements for NABL accreditation should be discussed amongst concerned staff of the laboratory. This will enable them to understand their weaknesses and strengths.
Quality Manager must conduct an Internal Audit and take corrective actions before applying for accreditation.
18. Is there a publication that can guide me through the accreditation process...?
General Information Brochure NABL 100 is published by NABL to guide you about NABL accreditation and its procedure.
1. What are the aims and objectives of NABL...?
2. Where is NABL office located...?
3. What are the office timings of NABL...?
4. What is laboratory accreditation...?
5. Why is laboratory accreditation required...?
6. What are benefits of accreditation...?
7. How is NABL accreditation different from ISO 9000 certification...?
8. What types of laboratories can seek accreditation...?
9. Which fields of testing and calibration are covered by NABL...?
10. Which are the other organizations in India providing accreditation services...?
11. Why use an accredited laboratory...?
12. How would NABL accreditation help a laboratory reach out to the global customers...?
13. Is accreditation a one-time phenomenon...?
14. Is it mandatory for laboratories to participate in Proficiency Testing programs...?
15. What is the process for accreditation at NABL…?
16. Who at NABL should a laboratory contact for initiating the process of accreditation...?
17. What are the preparations required by a laboratory before applying for accreditation...?
18. Is there a publication that can guide me through the accreditation process...?
19. What is Mutual Recognition Arrangements (MRA) with international bodies and what are the benefits of such arrangements for the laboratories accredited by NABL...?
20. Does NABL publish periodic newsletters?
21. How can we know of the Proficiency Testing programmes organised by NABL or APLAC ?
22. What training courses are offered by NABL...?
23. How to use NABL logo...?
24. How does using an accredited laboratory benefit Government and Regulators…?
25. How do I know a laboratory is accredited by NABL…?
26. Why is a laboratory’s technical competence so critical to you as a manufacturer, supplier, exporter or customer…?
27. How does NABL determine the number of assessors that will be assigned to conduct laboratory’s assessment…?
28. What is peer evaluation…?
29. How long does it take for a laboratory to obtain NABL accreditation…?
30. What is the “Scope of Accreditation”…?
Avail free downloads
NABL Publications
Sunday, February 12, 2006
Testing labs
Ref.: 95612 May 2005
New edition of influential ISO/IEC standard on competence of laboratories
A new edition has just been published of an ISO/IEC standard acknowledged as the international benchmark for approving the competence of the testing and calibration laboratories that play a vital role in trade, in product development and manufacturing, and in protection of the consumer.
ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories, replaces the 1999 edition which has been used to "accredit" (approve) some 25 000 laboratories worldwide that test products and samples, and calibrate precision instruments. However, the influence of ISO/IEC 17025 is even greater than this figure suggests since many countries make its use a legal requirement. In addition, documents derived from it are used by laboratories in specific sectors such as medicine and microbiology.
ISO Secretary-General Alan Bryden commented: "ISO/IEC 17025 benefits business, government and society at large. Confidence in the competence of laboratories is frequently needed by businesses when testing new products, or ensuring that finished products are fit for sale, by government regulators and trade officials that require assurance about domestic or imported products before they can be placed on the market, or for ensuring the quality and reliability of testing and analysis relating to environmental, health or safety hazards."
ISO/IEC 17025:2005 contains all of the requirements that testing and calibration laboratories need to meet in order to demonstrate to customers and regulators that they operate a sound management system which puts them in full control of their processes, are technically competent, and are able to generate technically valid results. Accreditation bodies that recognize the competence of testing and calibration laboratories will use the standard as the basis for their accreditation.
"Dependable testing and calibration laboratories are ones that have been duly accredited as competent and ISO/IEC 17025:2005 is the laboratory accreditation standard that, like the edition it replaces, will be counted on by business and governments worldwide," declared Peter van Leemput, who led the ISO group of experts that carried out the work.
The new, 2005 edition results from the amendment of ISO/IEC 17025:1999 to ensure its compatibility with the requirements of ISO 9001:2000, Quality management systems - Requirements. This became necessary because of the generalized adoption of quality management systems conforming to ISO 9001:2000, including many of the organizations that testing and calibration laboratories serve.
It also seeks to clarify that while compatible, the two standards are not inter-changeable. Although both standards can be used by laboratories as a framework for providing their customers with confidence that they are managing their activities, only ISO/IEC 17025 can be used to demonstrate the technical competence specific to laboratories.
Laboratories may choose to be accredited to ISO/IEC 17025, or be certified to ISO 9001:2000, or both, but the processes of accreditation and certification would still be two separate actions, although highly facilitated - both for the laboratories and the assessors - by the consistency now ensured between the two standards.
There are no essential changes to the technical requirements. The modifications relate mainly to the management requirements in the document to reflect the content of ISO 9001:2000, especially in a greater emphasis on the responsibilities of top management, on the need to demonstrate a commitment to continually improve the effectiveness of the management system, on customer satisfaction, and on internal and customer communication about the management system.
Peter van Leemput summed up: "Laboratories that have described and controlled their processes within the laboratory - as already required by the 1999 edition of ISO/IEC 17025 - will only have minor adjustments to make to their existing procedures to ensure that the new orientations in the management requirements are fulfilled."
The International Laboratory Accreditation Cooperation (ILAC) has set a transition period of two years from date of publication of the new edition - 12 May 2005 - for accredited laboratories to comply with the standard's requirements.
ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories, costs 112 Swiss francs and is available from ISO national member institutes (see the complete list with contact details) and from ISO Central Secretariat (see below). It was developed by Working Group 25 of ISO/CASCO, Committee on conformity assessment.
ISO Store: to order ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories
Enquiries about orders:Ms. Sonia Rosas FriotMarketing ServicesTel. +41 22 749 03 36Fax +41 22 749 09 47E-mail sales@iso.org
Press contact:Roger FrostPress and Communication ManagerPublic RelationsTel. +41 22 749 01 11Fax +41 22 733 34 30E-mail frost@iso.org
http://www.iso.ch/iso/en/commcentre/pressreleases/archives/2005/Ref956.html
How does ISO/IEC 17025 compare with ISO 9001?ISO/IEC 17025 includes the quality system requirements of ISO 9001 and additional requirements to demonstrate that the laboratory is technically competent and able to produce technically valid data and results.TopWhat the differences between ISO 17025 and ISO 9000?TCR Engineering Services has focused on the quality assurance and quality control of our services and is proud to have successfully accredited by the National Accreditation Board of Laboratories (NABL) against the ISO / IEC 17025 standard “General Requirements for the Competence of Testing and Calibration Laboratories.ISO/IEC 17025 includes the quality system requirements of ISO 9001 and additional requirements to demonstrate that the laboratory is technically competent and able to produce technically valid data and results.It is important to distinguish between a laboratory-specific accreditation like ISO 17025, and a general systems certification like the ISO 9000 series. ISO 17025 is based on the systems requirements of ISO 9000, but goes much further into the operations of a laboratory that are critical to its performance of tests. There are some very important differences in critical areas. Examples of these differences are highlighted in areas such as staff competence, test traceability, equipment calibration, audits and presentation of reports. ISO 17025 has extremely specific requirements in these areas whereas in ISO 9000 they are either not addressed or are presented in vague or general terms.Therefore ISO 17025 accreditation provides the customer with a high level of confidence in the laboratory’s impartiality, technical competence and the technical validity of its results, as opposed to ISO 9000 which is purely a systems certification. TCR Engineering Services is a Bureau of Indian Standards and NABL accredited laboratory. NABL approval is from Department of Science and Technology, Government of India. NABL provides laboratory accreditation services to laboratories that are performing tests / calibrations in accordance with ISO 17025.NABL is a member of the International Laboratory Accreditation Cooperation (ILAC). ILAC is an international cooperation between various laboratory accreditation schemes operated throughout the world, and is the world’s principal international forum for the development of laboratory accreditation policies and procedures. Membership of such an agreement further enhances and facilitates the acceptance of NABL accreditation worldwide.TCR’s Positive Material Identification tests are approved under No. D025 accreditation from National Accreditation Board for Laboratories.
http://www.tcreng.com/faq/faq.php?s=9
USEFUL LINKS
http://www.fasor.com/iso25/
tired of reading all this heavy stuff?
go here for some laffs on consultants http://managementconsultant-tqmcintl.blogspot.com/ ....
tqmcintl Industry: Consulting Location: Mumbai : Maharashtra : India ISO 9001 QMS ISO 13485 ENGINEERING NEWS UP-DATE ISO 22000 Explosion protected not Flame proof WTO CRO ISO TQM Information Security Management and ISO 27001 Software QA ISO 17025 CE Marking ISO 14000 GMP requirements SA 8000 ISO 20000 COBIT COPC STANDARD Lean Six Siqma ISO 17021 5 S Energy Manager boiler and pressure vessels eSCM useful Reference tables ERP Management Consultant hotels and restaurants Fami QS Food borne diseases and infections storing food grains Halal and Kosher wet tissues ready made garmets marking Inspection, measuring and testing equipment
New edition of influential ISO/IEC standard on competence of laboratories
A new edition has just been published of an ISO/IEC standard acknowledged as the international benchmark for approving the competence of the testing and calibration laboratories that play a vital role in trade, in product development and manufacturing, and in protection of the consumer.
ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories, replaces the 1999 edition which has been used to "accredit" (approve) some 25 000 laboratories worldwide that test products and samples, and calibrate precision instruments. However, the influence of ISO/IEC 17025 is even greater than this figure suggests since many countries make its use a legal requirement. In addition, documents derived from it are used by laboratories in specific sectors such as medicine and microbiology.
ISO Secretary-General Alan Bryden commented: "ISO/IEC 17025 benefits business, government and society at large. Confidence in the competence of laboratories is frequently needed by businesses when testing new products, or ensuring that finished products are fit for sale, by government regulators and trade officials that require assurance about domestic or imported products before they can be placed on the market, or for ensuring the quality and reliability of testing and analysis relating to environmental, health or safety hazards."
ISO/IEC 17025:2005 contains all of the requirements that testing and calibration laboratories need to meet in order to demonstrate to customers and regulators that they operate a sound management system which puts them in full control of their processes, are technically competent, and are able to generate technically valid results. Accreditation bodies that recognize the competence of testing and calibration laboratories will use the standard as the basis for their accreditation.
"Dependable testing and calibration laboratories are ones that have been duly accredited as competent and ISO/IEC 17025:2005 is the laboratory accreditation standard that, like the edition it replaces, will be counted on by business and governments worldwide," declared Peter van Leemput, who led the ISO group of experts that carried out the work.
The new, 2005 edition results from the amendment of ISO/IEC 17025:1999 to ensure its compatibility with the requirements of ISO 9001:2000, Quality management systems - Requirements. This became necessary because of the generalized adoption of quality management systems conforming to ISO 9001:2000, including many of the organizations that testing and calibration laboratories serve.
It also seeks to clarify that while compatible, the two standards are not inter-changeable. Although both standards can be used by laboratories as a framework for providing their customers with confidence that they are managing their activities, only ISO/IEC 17025 can be used to demonstrate the technical competence specific to laboratories.
Laboratories may choose to be accredited to ISO/IEC 17025, or be certified to ISO 9001:2000, or both, but the processes of accreditation and certification would still be two separate actions, although highly facilitated - both for the laboratories and the assessors - by the consistency now ensured between the two standards.
There are no essential changes to the technical requirements. The modifications relate mainly to the management requirements in the document to reflect the content of ISO 9001:2000, especially in a greater emphasis on the responsibilities of top management, on the need to demonstrate a commitment to continually improve the effectiveness of the management system, on customer satisfaction, and on internal and customer communication about the management system.
Peter van Leemput summed up: "Laboratories that have described and controlled their processes within the laboratory - as already required by the 1999 edition of ISO/IEC 17025 - will only have minor adjustments to make to their existing procedures to ensure that the new orientations in the management requirements are fulfilled."
The International Laboratory Accreditation Cooperation (ILAC) has set a transition period of two years from date of publication of the new edition - 12 May 2005 - for accredited laboratories to comply with the standard's requirements.
ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories, costs 112 Swiss francs and is available from ISO national member institutes (see the complete list with contact details) and from ISO Central Secretariat (see below). It was developed by Working Group 25 of ISO/CASCO, Committee on conformity assessment.
ISO Store: to order ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories
Enquiries about orders:Ms. Sonia Rosas FriotMarketing ServicesTel. +41 22 749 03 36Fax +41 22 749 09 47E-mail sales@iso.org
Press contact:Roger FrostPress and Communication ManagerPublic RelationsTel. +41 22 749 01 11Fax +41 22 733 34 30E-mail frost@iso.org
http://www.iso.ch/iso/en/commcentre/pressreleases/archives/2005/Ref956.html
How does ISO/IEC 17025 compare with ISO 9001?ISO/IEC 17025 includes the quality system requirements of ISO 9001 and additional requirements to demonstrate that the laboratory is technically competent and able to produce technically valid data and results.TopWhat the differences between ISO 17025 and ISO 9000?TCR Engineering Services has focused on the quality assurance and quality control of our services and is proud to have successfully accredited by the National Accreditation Board of Laboratories (NABL) against the ISO / IEC 17025 standard “General Requirements for the Competence of Testing and Calibration Laboratories.ISO/IEC 17025 includes the quality system requirements of ISO 9001 and additional requirements to demonstrate that the laboratory is technically competent and able to produce technically valid data and results.It is important to distinguish between a laboratory-specific accreditation like ISO 17025, and a general systems certification like the ISO 9000 series. ISO 17025 is based on the systems requirements of ISO 9000, but goes much further into the operations of a laboratory that are critical to its performance of tests. There are some very important differences in critical areas. Examples of these differences are highlighted in areas such as staff competence, test traceability, equipment calibration, audits and presentation of reports. ISO 17025 has extremely specific requirements in these areas whereas in ISO 9000 they are either not addressed or are presented in vague or general terms.Therefore ISO 17025 accreditation provides the customer with a high level of confidence in the laboratory’s impartiality, technical competence and the technical validity of its results, as opposed to ISO 9000 which is purely a systems certification. TCR Engineering Services is a Bureau of Indian Standards and NABL accredited laboratory. NABL approval is from Department of Science and Technology, Government of India. NABL provides laboratory accreditation services to laboratories that are performing tests / calibrations in accordance with ISO 17025.NABL is a member of the International Laboratory Accreditation Cooperation (ILAC). ILAC is an international cooperation between various laboratory accreditation schemes operated throughout the world, and is the world’s principal international forum for the development of laboratory accreditation policies and procedures. Membership of such an agreement further enhances and facilitates the acceptance of NABL accreditation worldwide.TCR’s Positive Material Identification tests are approved under No. D025 accreditation from National Accreditation Board for Laboratories.
http://www.tcreng.com/faq/faq.php?s=9
USEFUL LINKS
http://www.fasor.com/iso25/
tired of reading all this heavy stuff?
go here for some laffs on consultants http://managementconsultant-tqmcintl.blogspot.com/ ....
tqmcintl Industry: Consulting Location: Mumbai : Maharashtra : India ISO 9001 QMS ISO 13485 ENGINEERING NEWS UP-DATE ISO 22000 Explosion protected not Flame proof WTO CRO ISO TQM Information Security Management and ISO 27001 Software QA ISO 17025 CE Marking ISO 14000 GMP requirements SA 8000 ISO 20000 COBIT COPC STANDARD Lean Six Siqma ISO 17021 5 S Energy Manager boiler and pressure vessels eSCM useful Reference tables ERP Management Consultant hotels and restaurants Fami QS Food borne diseases and infections storing food grains Halal and Kosher wet tissues ready made garmets marking Inspection, measuring and testing equipment
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