Measurement Matters- Validation of methods

As a UKAS accredited laboratory, validation of methods is a fundamental, often extensive and ongoing task. Our engineers complete validation activities on a routine basis with frequencies ranging from daily to annually. We thought that it would be beneficial to share some more information on this important topic and its impact on the day to day running of a busy lab;

Why is method validation important?

Demonstrating a high level of technical competency is an integral part of the accreditation process both initially and on a maintained basis. Every laboratory will have developed their own methods and processes, method validation ensures that these methods are valid, fit for purpose and consistently deliver accurate results. Validation of methods also provides a ‘repeatable’ mechanism for calculating elements that are included in uncertainty budgets.

At Withnell Sensors we are committed to maintaining high standards of measurement accuracy, without a solid schedule of method validation we would not be able to deliver these accuracies with confidence. Our technicians not only offer experience in completing temperature calibrations but also offer years of experience in operating, maintaining and working with our high precision test equipment. This experience, coupled with a comprehensive validation programme ensures that we maintain some of the highest standards in our industry.

ISO 17025:2017 offers a standardised approach to the validation of methods, suggesting several ways in which a laboratory can justify and validate their processes as explained in more detail below.

How do we validate our methods?

Section 7.2.2.1 of ISO 17025:2017 outlines several techniques that can be used for validation of methods. One approach involves the comparison of results achieved with other validated methods. For example, this approach is useful when validating calibration methods using software programmes. We can often verify these results by comparison to a manual method, ensuring that the outcome is the same. This has the additional advantage of allowing us the necessary experience and documentation for a backup process in an disaster scenario.

Systematic assessment of the factors influencing results is also an approach used, almost habitually, as elements of this will be required for calculating measurement uncertainties. Our lab assesses many factors on an on-going basis, examples include temperature variation across operating ranges, bath load, fluid volume, uniformity, stability, immersion depths, bath flow, stirring as well as the individual impact of different test items. This systematic approach equips our technicians with detailed information about each piece of equipment, as well as the aforementioned validation and measurement uncertainties it allows us to build up a profile and history for each item of test equipment. This in-depth knowledge means we will always select the most appropriate calibration method for you test items which can be discussed with our engineers before a quotation is generated.

Of course we also maintain an extensive range of reference standards, we aim for a minimum double redundancy in this area but in key areas we often better this with triple or quadruple redundancy. This redundancy covers us for fluctuations in workload and allows for our reference standards to be away for calibration having several standards means we can cross reference their performance to highlight any issues. Our reference standards provide us with certainty and traceability. As well as being fundamental for calibrations they form the basis of additional intermediate control checks. Even with our high precision temperature standards we also have primary standards that can be used verify and support our chain of measurements.

Inter Laboratory Comparisons

ILC is not only a recognised approach for validation of methods, it is also a requirement of ISO 17025:2017. This activity is subject to its own schedule and means that we can monitor our own performance by comparing the results that we achieve with that of another laboratory. Results from both labs are recorded and analysed to provide the Technical Manager with valuable insights into the overall suitability of our calibration activities.