Performance Verification of Acoustical Measurement Systems - Technical Guide: Verification of acoustic systems
Verification of acoustic systems
Verification is the demonstration, by application of a series of tests, that a measuring instrument or system conforms to a set of requirements.
The purpose of performance verification of a measurement system is to assure the user that the complete systems characteristics are understood in terms of the individual parts, that the system has not changed significantly, and is fit for the intended measurement application.
Calibration of acoustic systems
A basic tool for ensuring traceability of a measurement is instrument calibration. Calibration may be defined as a set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or system, and corresponding values realised by standards. This calibration involves determining the measurement characteristics of an instrument by direct comparison with standards.
Reasons for calibration include:
- To ensure readings from an instrument are consistent with other measurements
- To determine the accuracy of the instrument reading
- To establish the reliability of the instrument
Results of calibration are:
- Assignment of values of things being measured - or determination of corrections that need to be applied
- Determination of the effects of influence quantities
- Recorded in a calibration certificate and report
The calibration of an individual acoustical instrument is linked to the primary standard by a chain of calibrations descending down through the NMS hierarchy. Measurements made using that instrument are then said to be traceable to national standards maintained at NPL.
Testing laboratories
In the UK acoustical calibration laboratories are accredited by the United Kingdom Accreditation Service (UKAS) [National Accreditation Council for Certification Bodies (NACCB) and National Measurement Accreditation Service (NAMAS) were merged in 1995 to form the United Kingdom Accreditation Service]. The relevant national metrology institute is the National Physical Laboratory (NPL).
Frequency of verification
Periodic verification should be undertaken at appropriate intervals determined by the measurement application. For example in the case of a sound level meter, it is recommended that verification occurs at least every two years.
The system should always be verified after a part of the measurement system has undergone repair that is likely to affect it's performance.