Operation: Base Metrology
14
CENTRON® Polyphase Meter Technical Reference Guide
Surge Protection
Surge protection for the electronics in the CENTRON POLYPHASE meter is provided by
Metal Oxide Varistors (MOVs). MOVs are clamping devices that allow voltage up to a
limit, and then increasingly conduct current to prevent the voltage from exceeding
the limit. The MOVs on the power supply board are connected directly across the voltage
inputs to the meter. Although this approach requires very large MOVs, it prevents high
voltages from appearing on or near the electronic boards giving the CENTRON
POLYPHASE meter superior performance when exposed to extremely high-voltage surges.
Sampling
The analog-to-digital converter samples each phase voltage and current signal 32 times per
line cycle and sends the digital values immediately to the microprocessor. This amounts to
32 samples per cycle at 60 Hz. Each time a new set of digital samples are received by the
microprocessor, it calculates all of the selected metrological quantities.
Figure 9: Sampled Waveform
At this sampling rate, harmonics to the 15th are measured. The high rate of the sampling
enables the CENTRON POLYPHASE meter to measure energy quantities accurately under
high harmonic distortion conditions. The sampling continues uninterrupted as long as the
meter is powered up. All other processing is done in the background between samples. From
the continuous train of digital samples on each of the six channels, current, voltage, active
energy, reactive energy, and apparent energy quantities are computed.
