Accredited or In-House Calibration? Deciding Which Instruments Go Where

Not every instrument in a factory needs the same treatment. A sound calibration programme sorts equipment into three groups.

Group 1: Reference and critical instruments

These include:

• master gauges, reference weights, reference thermometers and other standards used to check other instruments
• instruments whose readings decide product release, safety or legal compliance
• instruments named in customer contracts, GMP requirements or regulations

ISO 9001 itself requires traceability. The accredited calibration is the simplest way to demonstrate traceability: the laboratory’s competence has already been assessed by EGAC. Regulators, notified bodies and many multinational customers expect it. For laboratories that are themselves accredited to ISO/IEC 17025, ILAC P10 makes accredited calibration the normal route.

Group 2: Working instruments

Many organisations calibrate their working instruments internally against reference instruments that have accredited certificates. This is legitimate and economical, provided that:

• a written procedure defines the method, points and acceptance criteria
• the reference instrument’s uncertainty is suitable for the tolerance being checked
• the environment is controlled where it matters
• staff are trained and their competence is recorded
• records show the instrument ID, date, reference used, results, uncertainty or acceptance criteria, and who performed the work

Group 3: Indication-only instruments

Instruments never used to make a product decision may not need calibration at all. Label these clearly “for indication only” so they are never used to make a product decision.