4.6.3 Constraints

All computed quantities available through the Metrology firmware are integrated over a time interval equivalent to an integral number of periods of the fundamental frequency. All integration periods are approximated by the final output sample rate of the DSP filters, 4000 Hz. So, the measurement accuracy will increase using longer integration periods. One second is the recommended minimum integration period (50 cycles at 50 Hz or 60 cycles at 60 Hz), but fewer numbers of samples may still yield acceptable results.

DSP filters require a settling time before accurate measurements may be used for revenue-quality metering. It is recommended to wait at least 250 ms after start-up when testing to revenue-grade accuracy.