The type of calibration required for a particular instrument can be specified using a combination of the following:

• Level of Traceability
• Calibration Test Procedure
• Calibration Interval

Level of Traceability

An understanding of the level of risk associated with the measurements made will indicate the level of calibration traceability which is appropriate.

A level of traceability for each classification of activity is suggested in the section Calibration and Measurement Traceability.

Calibration Test Procedure

The calibration test procedure will typically be defined by standards, for example BS or IEC standards. These will generally give a test procedure and sometimes suggest a calibration interval.

Examples for some items are given in: Performance Verification of Acoustical Measurement Systems : Testing Standards.

The test procedure selected will depend upon:

• The specification of the instrument, for example, IEC 61672 for some sound level meters.
• The measurements taken. For example, if frequency content measurements are of interest then the frequency response of the instrument must be checked.
• The level of traceability required. For example, the test procedure for a Level 1 fully traceable calibration at a UKAS laboratory would be different to that undertaken for a Level 3 manufacturer's check to conformance.

If in doubt, an accredited calibration laboratory will be able to give guidance as to which calibration test procedures would be suitable for a particular instrument and application.

Calibration Interval

The recommended interval between calibrations may be defined as part of the calibration test procedure or even as part of a particular measurement method used.

The UKAS document Lab 23 suggests appropriate maximum calibration intervals for many pieces of equipment. Calibration intervals must be set appropriately and it is up to the user to develop a sensible strategy to manage this as part of the overall calibration strategy.

The following table is taken from the UKAS document Lab 23 and gives suggested levels of traceability and calibration intervals for a selection of equipment.

Appropriate Calibration Strategies >>