User's Manual

Operation: Base Metrology
CENTRON® OpenWay™ Meter Technical Reference Guide 17
Voltage and Current Measurement
Figure 9: Voltage and Current Measurement
Watthour (Wh) Measurement
Watt-hours are measured by multiplying the instantaneous value of the voltage on each
phase times the instantaneous value of the current on the same phase.
The resulting values are added to the Wh accumulator. After the completion of two cycles,
the registers are compared to a threshold. This threshold represents 0.025 watt-hours. The
value in the accumulator is then divided by this threshold, and the registers are updated
accordingly. This means that under bidirectional measurement, if the consumption changes
from delivered to received within one second, the meter will respond correctly to the change
and accumulate in both the delivered and received registers. The CENTRON OpenWay
meter can be programmed to register watt-hours either in the delivered quadrants only, or
under bidirectional measurement, in the delivered and received quadrants. When only
delivered watt-hours are measured, any negative watthour value is ignored. This has the
same effect as a detent mechanism on an induction watthour meter.
When delivered and received watt-hours are measured, there will be one register for each
quantity available—Wh delivered and Wh received, as well as one combined register—Wh
net.
Draft