Metrological assurance can be defined as the set of activities necessary to guarantee the metrological reliability of the processes. The main purpose is to guarantee the proper functioning of the equipment required in each specific area, meeting current legal requirements through the development of preventive and corrective maintenance activities and equipment calibration.
All equipment used for the development of the specific activities of each area that have a significant effect on the results, must be included in a metrological assurance system and must comply with the requirements in its verification process, calibration, its operation and authorization of its commissioning or use.
Correct calibration and the implementation of an adequate equipment maintenance plan provide the security that the products or services offered meet the required specifications. In addition to the above, the calibration of the equipment guarantees the reliability and traceability of the results.
In the same order of ideas, calibration laboratories must strive to maintain their calibration equipment in optimal conditions with adequate maintenance periods to ensure the validity of the calibration results for their clients.
Ensuring the validity of results in calibration laboratories
Calibration laboratories accredited by the National Accreditation Body of Colombia, ONAC, as stipulated in the NTC-ISO/IEC COLOMBIAN TECHNICAL STANDARD 17025:2017, “must have a procedure to monitor the validity of the results.
The resulting data should be recorded so that trends are detectable and when possible, statistical techniques should be applied to review the results. This monitoring should be planned, reviewed and should include, where appropriate, but not limited to:
Use of alternative instruments that have been calibrated to obtain traceable results:
Alternate calibrated and traceable instruments should be available, apart from those normally used in daily calibrations in order to reduce the load of equipment uses. The use of a single piece of equipment to perform calibrations brings with it more workload, mechanical stress and therefore lack of reliability.
Functional checks of measuring equipment:
Calibration equipment must undergo periodic maintenance and calibration to ensure its functionality and reliability in its measurements.
Use of verification patterns or work patterns with control charts, when applicable:
Control charts are a very good tool for analyzing the results of verifications or calibrations and determining calibration periods.
Intermediate checks on measuring equipment:
Intermediate checks of the measuring equipment are necessary to check the status of the calibration instruments between calibration periods.
Repeat calibrations using the same or different methods:
Repeat calibrations can help us determine how much of the variability in the measurement system is caused by the measurement device.
Recalibration of retained items:
Preserved items or retained objects is a good method to check the condition of calibration equipment by performing periodic calibrations of these and comparing them.
Review of reported results:
Results must be reviewed and authorized before release.
Likewise, calibration laboratories must track their performance by comparing it with the results of other laboratories. This monitoring must be planned, reviewed and the results analyzed:
- Intralaboratory comparisons:
Comparing results of the same item with other laboratories helps us verify and evaluate the performance of laboratory operators in a calibration, it also provides a periodic evaluation of the equipment and in general of the entire laboratory.
The intralaboratory comparison program also provides a means to establish and demonstrate the reliability of analytical methods and detect training needs.
- Participation in aptitude tests:
Most accreditation bodies in the world require participation in proficiency testing. They are an external quality control tool that allows participating laboratories to compare their performance with respect to other similar laboratories; and, where appropriate, implement any corrective action that is necessary, for continuous improvement in its procedures.
It is the most important tool to demonstrate competence since they have wide recognition through the ILAC and are a key element in ensuring the validity of the results.
When participating in proficiency testing you are measuring yourself against other laboratories, remember that this is the best scenario to evaluate precision, accuracy and uncertainty.
Proficiency testing is the world championship of laboratories
It is important to clarify that both intralaboratory comparisons and proficiency tests are comparisons between laboratories, the difference is that a proficiency test is organized and administered by an independent third party. Additionally, a proficiency test includes the participation of a reference laboratory and uses its results to determine the performance of the participants. An Intralaboratory comparison does not require the use of a reference laboratory or coordinating body. Therefore, participating laboratories only compare performance between the group of participating members.