Version 1.6.1
David Trew
Consulting Ltd
3 Calibration and Maintenance of Equipment
Clause 6.4.7 of the 2017 edition of the ISO 17025 International Standard requires laboratories to establish a calibration program. It is recommended that the laboratory identifies all measuring equipment requiring calibration. A suitable calibration interval needs to be established and specifications for each piece of equipment and the associated calibration procedures. The quality plan should also include a schedule for calibration and maintenance activities.
3.1 Equipment Classification
If the laboratory has many measuring instruments, it is suggested that equipment is classified into different categories, this will help the laboratory make important decisions concerning the calibration and maintenance interval together with decisions regarding the extent of calibration and maintenance necessary to maintain confidence in the accuracy and precision of measuring equipment. Two schemes of equipment classification which could be used are discussed below.
3.1.1 Equipment Quality Criticality Classification
This scheme, equipment is classified according to its capability to impact the quality of the results, for example, using the following criteria:
1. Quality Critical Equipment is all equipment used to make measurements or produce results reported to the customer, including the computers that control or collect and process data from such equipment.
2. Quality Non – Critical Equipment is all equipment that, although not used to make measurements or produce results reported to the customer, is used to assure the quality of the results reported to the customer.
3. Non – Quality Equipment is all equipment not used to make measurements or produce results reported to the client or to assure the quality of the results reported to the customer.
The Equipment Quality Criticality Classification is useful in making decisions regarding calibration intervals.
3.1.2 Laboratory Equipment Classification
The second scheme classifies equipment according to its respective complexity.
1. Category A includes standard equipment with no measurement capability or usual requirement for calibration. Examples of equipment in this group are nitrogen evaporators, magnetic stirrers, vortex mixers, and centrifuges.
2. Category B includes standard equipment and instruments providing measured values and equipment controlling physical parameters (such as temperature, pressure, or flow) that need calibration. Examples are balances, melting point apparatus, light microscopes, pH meters, variable pipets, refractometers, thermometers, titrators, viscometers, muffle furnaces, ovens, refrigerator-
3. Category C includes instruments and computerised analytical systems, where user requirements for functionality, operational, and performance limits are specified for the analytical application. Examples are gas and high-
The laboratory equipment classification is useful in making decisions regarding the extent of qualification and routine maintenance required. Also, the laboratory equipment classification is useful in determining how calibration and maintenance should be recorded. For example, the requirements for calibration and maintenance of equipment in category B could be recorded in the respective equipment procedure. In contrast, the requirements for calibration and maintenance of equipment in category C would probably need to be recorded in a separate document.
3.2 Calibration and Maintenance Intervals
The intervals at which equipment calibration and maintenance are carried out will often attract significant scrutiny from assessors. The International Laboratory Accreditation Cooperation secretariat has published a guidance document on the topic4. The initial calibration interval should be based on an assessment of the risks associated with the equipment and considering the following criteria:
1. The instrument manufacturer’s recommendation;
2. Expected extent and severity of use;
3. The influence of the environment;
4. The required uncertainty in measurement;
5. Maximum permissible errors (e.g. by legal metrology authorities);
6. Adjustment of (or change in) the individual instrument;
7. Influence of the measured quantity (e.g. high-
8. Pooled or published data about the same or similar devices.
The rationale for selecting the calibration and maintenance interval should be recorded in the quality plan.
3.3 Content of the Equipment Calibration and Maintenance Section of the Quality Plan
It is recommended that you discuss the rationale for selecting the extent and frequency of calibration activities. Also, it is recommended to prepare a table containing the following information about each piece of equipment that requires either calibration or maintenance:
1. Laboratory asset reference
2. Equipment type
3. Manufacturer
4. Make
5. Model
6. Serial number
7. Calibration interval
8. Maintenance interval
9. Calibration protocol number
10. Maintenance protocol number
11. Calibration due date(s)
12. Maintenance due date(s)
13. Calibration completion date(s)
14. Maintenance completion date(s)
This information could be conveniently recorded either in an Excel spreadsheet or an Access database. In either case, it would probably be convenient to establish an audit trail to conveniently conform with the requirements of Clause 7.5 of the ISO 17025:2017 International Standard.
4 Laboratory Performance Monitoring
Clause 7.7 of the ISO 17025:2017 International Standard requires laboratories to carry out performance activities, including the following:
1. Use of reference materials or quality control materials;
2. Use of alternative instrumentation that has been calibrated to provide traceable results;
3. Functional check(s) of measuring and testing equipment;
4. Use of check or working standards with control charts, where applicable;
5. Intermediate checks on measuring equipment;
6. Replicate tests or calibrations using the same or different methods;
7. Retesting or recalibration of retained items;
8. Correlation of results for different characteristics of an item;
9. Review of reported results;
10. Intralaboratory comparisons;
11. Testing of blind samples.
Also, laboratories are required to compare their results with the results obtained from other laboratories; this can either be in the form of proficiency testing (PT) activities or other forms of interlaboratory comparison.
Proficiency testing is defined, by ISO 170435, as the evaluation of participant performance against pre-
1. Quantitative scheme — where the objective is to quantify one or more measurands of the proficiency test item;
2. Qualitative scheme — where the objective is to identify or describe one or more characteristics of the proficiency test item;
3. Sequential Scheme — where one or more proficiency test items are distributed sequentially for testing or measurement and returned to the proficiency testing provider at intervals;
4. Simultaneous scheme — where proficiency test items are distributed for concurrent testing or measurement within a defined time period;
5. Single Occasion Exercise — where proficiency test items are provided on a single occasion;
6. Continuous scheme — where proficiency test items are provided at regular intervals;
7. Sampling — where samples are taken for subsequent analysis;
8. Data Transformation and Interpretation — where sets of data or other information are furnished and processed to provide an interpretation (or some other outcome).
Proficiency testing schemes administered by bodies accredited to the ISO 17043 International Standard are considered suitable for the purposes of Clause 6.6 (Externally Provided Products and Services) of the ISO/IEC 17025:2017 International Standard.
Interlaboratory comparison (ILC) studies can be any study that evaluates participant performance against pre-
In addition to monitoring testing performance, measuring instruments’ performance should also be monitored, including monitoring the intermediate checks on equipment. This can be used to pre-
One useful parameter to monitor is the response factor for standard solutions.
Any significant changes in the response factor could indicate adverse changes are occurring, suggesting that equipment maintenance is required.
2.1 Guidelines and Policies
To promote harmonisation of the requirements for the level and frequency of participation in performance testing, the European Mutual Recognition Agreement, European Accreditations, has published a guidance document6 that discusses the criteria laboratories should consider when deciding the level and frequency of performance monitoring activities.
This guidance advocates proficiency testing based on subdiscipline. A subdiscipline is defined as an area of technical competence defined by a minimum of one measurement technique, property and product, which are related. (e.g. Determination of Arsenic in soil by ICP-
Ideally, a laboratory should participate in a specific PT for every measurement technique it uses and every property measured in every product; however, it is not logistically and economically feasible. Laboratories are recommended to identify appropriate subdisciplines. A minimum of one PT or ILC study is usually required for each subdiscipline within each four-
The level and frequency of performance monitoring activities should be determined based on assessing the risk presented by the laboratory, the sector in which it operates and the methodology being used. The level of risk should be determined, for example, by considering:
1. Significance and final use of testing/calibration data (e.g. forensic science represents an area requiring a high level of assurance)
2. Turnover of technical staff
3. Experience and knowledge of the technical staff
4. Source of Traceability (e.g. availability of reference materials, national standards, etc.)
5. Known stability/instability of the measurement technique
6. Number of tests/calibrations/measurements undertaken
The International Laboratory Accreditation Cooperation has implemented a policy6 for participation in performance testing; this requires all accredited laboratories to have a PT activities plan and specifies there shall be evidence of satisfactory participation before gaining accreditation where PT is available and appropriate. Further ongoing activity is appropriate to the accreditation scope and consistent with the PT participation plan. Many accrediting bodies have implemented policies requiring at least one PT or interlaboratory comparison to be carried out for each test or subdiscipline during each four-
2.2 Recommended Content of the Performance Monitoring Section of the Quality Plan
It is recommended the quality plan should contain the following elements:
1. Discussion of the overall strategy for performance monitoring, including aims and objectives and how the laboratory intends to achieve them.
2. An assessment of the risks presented by the: laboratory, sector in which it operates, methods used, and purpose for which testing or calibration is carried out
3. Identification of all tests for which performance will be monitored
4. If appropriate, identification of all subdisciplines, together with all applicable tests, for each subdiscipline and justification for the selection
5. Identification of the performance testing and interlaboratory comparisons activities the laboratory will participate
6. The frequency of participation for each study
7. A justification for the level and frequency of participation in performance testing or interlaboratory comparison studies
In addition to interlaboratory monitoring activities, you should discuss your internal monitoring activities. These should include:
8. The testing of reference materials or quality control materials of known analyte concentration or calibration properties
9. Comparing the results obtained from different instrumentation
10. Carry out functional checks of measuring and testing equipment;
11. Monitoring the response factors obtained from check or working standards with control charts, where applicable
12. Monitoring intermediate checks on measuring equipment
13. Replicate testing or calibrations using the same or different methods
14. Retesting or recalibration of retained items or samples Provided samples or items are sufficiently stable and do not deteriorate between the original test or calibration and the retest or recalibration.
15. Correlation of results for different characteristics of an item or sample
16. Comparison of results obtained by different members of staff on the same sample or item using the same method
17. Testing or calibration of blind samples or items.
The Role of the Quality Plan in an ISO 17025 Laboratory
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