User's Manual

Operation: Base Metrology
16 CENTRON® OpenWay™ Meter Technical Reference Guide
Surge Protection
Surge protection for the electronics in the CENTRON OpenWay 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 OpenWay meter superior
performance when exposed to extremely high-voltage surges.
Sampling
The analog-to-digital converter samples each phase voltage and current signal (independent
of the line frequency) and sends the digital values immediately to the microprocessor. Each
time a new set of digital samples are received by the microprocessor, it calculates all of the
selected metrological quantities.
Figure 8: Sampled Waveform
At this sampling rate, harmonics to the 15th are measured. The high rate of the sampling
enables the CENTRON OpenWay 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.
Draft