Verification of the accuracy of measuring devices for Power-Quality
Power-Quality-measuring instruments are divided into accuracy classes A and S according to IEC 61000-4-30.
The norm defines the basic measurement methods as well as the accuracy requirements.
The type testing of the PQ-measuring devices with the underlying test points and signals is described in IEC 62586, so that the PQ-measuring devices of classes A and S have a proven accuracy.
An additional accuracy test may also be useful for the following situations:
- Routine testing for quality assurance
- Deviating operating conditions
- New acquisition of a fleet of measuring instruments
Within the scope of a routine test, the accuracy of the measuring instruments can be checked after a certain period of operation in order to exclude an increasing measurement error due to possible drift. For this purpose, measuring instruments are often calibrated in an external laboratory and are thus not available for a longer period. However, this is not always possible. In the case of permanently installed PQ measuring instruments, which serve the verification obligation and therefore must not be out of service for a longer period, such calibration in an external laboratory is not practicable. For this reason, an on-site check of the PQ measuring instruments is advisable.
If a PQ measuring device is operated under conditions for which the accuracy specified in the data sheet does not apply, an accuracy check is strongly recommended. An example of this is when the input voltage at the PQ measuring device is lower than the unit test according to IEC 61000-4-30.
Also, when purchasing a suitable PQ measuring device, it can be useful to compare different devices with regard to both their accuracy and their software before making the investment, in order to decide on the best device.
