Why is it necessary to have true RMS power meters?
The simple averaging of meter readings only works for pure sine-waves. However, such pure sine-waves do not exist in the real world of an electrical installation. A true RMS meter works by taking the square of the instantaneous value of the input current, averaging over the time and then displaying the square root of this average. This is accurate and applicable for all waveforms. True RMS power measurement is essential in any installation where there are non-linear loads (e.g. computers, electronic ballasts, compact fluorescent lamps, etc).
The power meter should capable of measuring the following:
a) Active energy (kWh) for 1 min per interval
b) Reactive energy (kVarh) for 1 min per interval
c) Active power (kW) for 1 min per interval
d) Reactive power (kVar) for 1 min per interval
e) Power factor for each phase