Calibration principles and underlying theory

AN2299

8/26

Rev2

If the system is not immune to the external influences, it can only be operated under very

special conditions and the results are impossible to reproduce in other locations, where

there may be a different measuring set-up. Also short time repeatability due to noise and the

resulting statistical effects will be bigger.

The external influences on total system accuracy can be as big as or even bigger than the

basic specified error.

Note:

Please note that the voltage front end handles voltages of considerable amplitude, which

makes it a potential source of noise. Disturbances are readily emitted into current

measurement circuitry, where it will interfere with the actual signal to be measured.

Typically, this shows as a non-linear error at small signal amplitudes and non-unity power

factors. At unity power factor, voltage and current signals are in phase and crosstalk

between voltage and current channels merely appears as a gain error, which can be

calibrated. When voltage and current are not in phase, crosstalk will have a non-linear effect

on the measurements, which cannot be calibrated. Crosstalk is minimized by means of good

PCB planning and the proper use of filter components.