Metrology Theory of Operation
5-2 Theory of Operation TM-iX0A-0805
Voltage Sensor
Voltage on each phase is measured using a precision-resistive-divider that is designed to
maintain a highly stable division ratio over temperature, humidity, and time. The signals from
the divider feed into the Metering Chip.
Inputs
The two types of meter data are:
• Real-time values (instantaneous), such as per-phase voltages and currents
• Accumulated values, such as kWh
Depending on meter form, up to six inputs (Va, Vb, Vc, Ia, Ib, and Ic) are simultaneously
sampled at a rate of 26k samples/second at 24-bit resolution. The sample streams:
• Are filtered
• Corrected for gain and offset
• Serve as the real-time values for the calculations of per-phase and poly-phase energy (Wh,
VARh, and VAh)
The calculated energy values are accumulated in the designated energy registers, and are used to
generate the test pulse signals. The K
h
(configured through iConFig) setting controls the weight
of each pulse. The test pulse signals are routed to the IR Test Pulse LED under the control of the
main microprocessor.
Power Calculations
The real-time and accumulated values are used in the calculations to determine:
• Watts and Watt-hours
• kVA and kVAR
Watts and Watt-Hours
The Metering Chip multiplies the real-time values of current and voltage to calculate power
(kW), and accumulates kW over time as energy (kWh). This calculation includes digital
calibration factors to ensure that the registration of the meter is kept within specified tolerances.
The raw energy values for each individual phase are transmitted by digital serial interface to the
Register Display Board. The interface also carries information on the RMS current and voltage
for each phase. The values are interrogated by the Register Display Board at least once per
line cycle.
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