What is accreditation and certification?

An ISO calibration is always subject to the self-commitment of the laboratory, whereas UKAS calibrations are regularly checked and monitored by the UK Accreditation Service (UKAS) in terms of form, structure and content. This ensures that accredited calibration laboratories have both the technical competence and equipment and an appropriate management system. Calibrations which are carried out outside an accreditation (ISO/factory calibrations) are not subject to these controls - in this case the customer must monitor the quality.

Accreditation is the confirmation and recognition of professional competence for the accredited scope by a third body. Certification (by a third party) confirms that certain requirements (e.g. of standards) for processes, products or services are met. The difference between the two activities, which seem similar, is that accreditation focuses on formal recognition of competence. In the United Kingdom, the United Kingdom Accreditation Service (UKAS) is responsible for this. In the case of certification, the main objective is to establish conformity with a standard or normative basis. Certification can be applied for at approved certification bodies (e.g. TÜV, Dekra, DNV GL, BSI, ...).

Accreditation & Certification

UKAS calibration certificates are suitable for all users of measuring instruments who require a particularly high level of assurance. In addition, in some industries it is a normative requirement to have accredited calibrations performed. For example, factory standards, i.e. measuring instruments with which other test equipment is calibrated, are often "secured" with a UKAS calibration certificate. UKAS calibration certificates are also often required for measuring instruments in the automotive or pharmaceutical industries. ISO calibrations are suitable for users who are certified according to DIN ISO 9000 and follow further industry specific quality guidelines. For all directives and standards, the introduction and maintenance of test equipment calibration and monitoring is required and must meet the requirements of the various standards and be traceable to national standards.

If the client wishes a statement on the suitability of his measuring instrument, then an objective pass/fail evaluation is necessary in regard to the metrologically determined characteristic features of the calibration object. Such an assessment is called a conformity assessment.

Decision rules define the criteria for how measurement uncertainty is to be taken into account in conformity assessment.    

Quantitative control limits in the form of guard bands are introduced, which can reduce the acceptance range compared to the permissible deviation. During conformity assessment, the uncertainty of measurement is added to the measured deviation and a fictitious maximum deviation is generated. This must be within tolerance for the device to conform. 

There are standards and directives which require verifiable competence of the external service provider when outsourcing calibration tasks. DIN EN ISO/IEC 17025:2018 is a common standard for demonstrating the competence of testing and calibration laboratories whose calibrations are recognised worldwide. In the United Kingdom, this is referred to as UKAS accreditation, in Germany as DAkkS, in Switzerland as SCS and in Austria as ÖKD.