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The Case to Revise ISO 17025 - Part 1
Alignment of terminology: calibration and verification
"The more critical the decision, the more critical the data. The more critical the data, the more critical the measurement."
–NASA Reference Publication 1342
ISO 17025 was initially released in 1999. In 2005, it underwent minor revision to align better to ISO 9000:2000. In 2010, the standard was up for review again and rather than voting for revision, the vote was to confirm the standard as-is for another five years. In attending the 2012 ILAC joint annual meetings, it is becoming my opinion that ISO 17025 needs to be revised. This is the first of a series of blog posts that I will be making to demonstrate why the revision needs to be made.
Some definitions in ISO 17025 contradict the VIM
In order to understand and interpret a requirements document correctly, it is important to know pertinent definitions of terms and concepts. ISO 17025 was written referencing definitions in the International Vocabulary of Metrology (VIM). Since 1999, the VIM has undergone significant change and refinement in its definition of terms and concepts associated with metrology. The VIM was been revised in 2007, and had minor corrections applied in 2012. As a result, there are many terms that are used in ISO 17025 that have different and contradictory definitions than are currently understood in the VIM.
Calibration
The first term to consider is calibration itself. The VIM defines calibration as “operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.”
This is a very long way to say that the process of calibration is to compare a known reference to a device under test. Every test and measurement instrument can be calibrated using this definition. It is possible to calibrate a standard resistor, a gage block, or a digital multimeter using this definition. When ISO 17025 was written, it was this basic definition of calibration that was largely used, where for each test point a measured value and corresponding uncertainty of measurement was given.
There are two very important things that the act of calibration does not address: The first is adjustment, which is referred to as “adjustment of a measurement system” in the VIM and means just what it sounds like. Many people confuse calibration for adjustment. It is possible to calibrate all test instruments, it is not possible to adjust all test instruments.
For example, it is not possible to adjust a standard resistor, but it is possible to compare a standard resistor to a reference standard resistor to determine a measurement value and associated uncertainty. Therefore a standard resistor can be calibrated, but not adjusted. For the case of a digital multimeter, it is possible to calibrate it as per the VIM definition.
Verification
The second thing that calibration does not address is that for most customers, this is only performing half the job. Most of our customers need to know if the multimeter is meeting a technical requirement such as whether all of the measured values obtained during calibration are within the published specifications for the instrument.
The act of providing objective evidence that a given item fulfills specified requirements is defined in the VIM as verification. Again, for the case of a standard resistor there are usually no published specifications, one uses the measured value and associated uncertainty of measurement, so it is possible to calibrate a standard resistor, but not adjust a standard resistor or to perform verification.
Section 5.10.4.2 of ISO 17025 discusses making a statement of compliance with a specification. Again, by the VIM definitions, this is not calibration, but is a second step of using the calibration data to perform a verification. ISO 17025 does not differentiate what should occur between these two very important processes. The result? We have to provide calibration reports with measured values and associated uncertainty and largely avoid the process of verification. But many of our customers may not care about the calibration data at all, and really want to verify that the instrument meets a particular specification.
The Solution
The solution for this is to re-write ISO 17025 to address the process of calibration and have an additional section to address verification when a customer requests this service during the contract review process. How is this accomplished? We all need to start letting our accreditation bodies, our National Measurement Institutes, and national standards writing bodies (example: ANSI in the USA) know that it is time to revise ISO 17025.
Do you agree? Comment and share your opinion.
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Comments
I think that the arguments Jeff Gust has risen in his blog are not enough to support a revision. Jeff’s arguments are based on the “redefinition” of calibration, verification and adjustment in the VIM. His argument is that the new definitions to these terms in the VIM differ to the extend that the ISO17025:2005 requirements do not cover these entirely anymore. To summarise my arguments, I think that the clauses in the ISO/IEC17025:2005 incorporate the new definitions. If anything is needed, the blog by Jeff could be room for more guidance documents by ILAC or its members.
As to calibration, I think that the definition in the current VIM is closer to the concept of calibration as it is required by ISO/IEC17025:2005 than the previous versions of the VIM. I included some relevant clauses (or requirements) from ISO/IEC17025:2005 in the definition:
calibration : Operation (clause 5.4.1) that, under specified conditions (clause 5.3), in a first step, establishes (clause 5.4.5) a relation between the quantity values (also see clause 5.6.2.1.2) with measurement uncertainties (clause 5.6.2.1.1) provided by measurement standards and corresponding indications with associated measurement uncertainties (clause 5.4.6.3) and, in a second step, uses this information to establish a relation (5.4.7.1) for obtaining (clause 4.13.2) a measurement result from an indication (clause 5.10.1).
There are many more clauses in the ISO/IEC17025:2005 that firmly fix all the above in a coherent management system that “meets the principles of ISO9001” (section 1.6 of ISO/IEC17025:2005).
Verification is already dealt with by the ISO/IEC 17025:2005. Clauses related to these terms are in the reporting section 5.10. Verification as a term is now defined in the VIM which is not dissimilar from its definition in ISO9000:2005:
The present VIM reads that verification is the “provision of objective evidence that a given item fulfils specified requirements” ISO9000:2005 defines that verification is “confirmation, through the provision of objective evidence that specified requirements have been fulfilled”.
Adjustment is not dealt with explicitly by the ISO 17025:2005 but the quality of adjustment is confirmed by requiring calibration before and after adjustment (clause 5.10.4.3). Only if this cannot be done e.g. when the instrument failed and has been repaired, calibration results before adjustment shall not be reported.
The only subject where revision could add to the present text of the standard is where computerised systems are used for measurement and for reporting. In this respect current practice has changed when compared to practice at the turn of the century when much of the ISO/IEC 17025 was written. It strikes me as an assessor now how much the present version of the standard is still applicable to data registration and reporting even though the technology has advanced so much. I hope that changes can be dealt with through a guidance document rather than through a revision of the standard though as we do not know what changes are in store for us.
Do you agree?
Jeff, John Hurl is quite competent in this field and I very much agree with him. From my experience as an assessor I find that I can fit all (non-conformities) that need improvement in a "management system" in existing clauses/requirements of the present ISO/IEC 17025. I have substantiated my case in my blog as it is too long for an entry here.
You promise us a part 2 and I very much hope that you can find some arguments that John and I cannot object to. This would strengthen your case and make life metrology-wise even more interesting as it already is.
John, I totally agree that customer education is critical. Thanks for your comments.
Sorry, Jeff, but I disagree strongly with most of this.
Yes, the term "calibration" is often misunderstood and is taken to include adjustment, verification and the like. The VIM definition of calibration is clear and there is no conflict with the way the term is used in ISO17025.
ISO17025 permits us to make compliance with specification statements as long as the uncertainty is taken into account. Therefore it does "differentiate what should occur between these two very important processes". Quite rightly, ISO17025 does not tell us how to account for the uncertainty, as this could depend on many factors. These might include how the specification is presented (e.g., limit values or confidence intervals) or whether a means of compliance verification is described in a standard against which the calibration is conducted. General information regarding assessment of compliance is already available in documents like ILAC G8 and UKAS M3003.
There is nothing within the existing ISO17025 criteria that prevents reporting measured values, the associated uncertainties and compliance statements. Indeed, Fluke in the UK already present many of their calibration certificates in this kind of format.
The solution to all this is not to change the standard but to educate the customers!