Theory of Operation Register Display Board
kVA/kVAR Calculations
The Metering Chip calculates a +90 degree, phase-shifted current signal. The result is multiplied
by the voltage signal to calculate reactive power (kVAR). The accumulation of reactive power
over time provides the reactive energy (kVARh) measurement.
The Metering Chip measures the instantaneous RMS current and voltage signals and multiplies
them together to create apparent power (arithmetic) samples. These samples are then
accumulated over time to provide the apparent energy (kVAh) measurement (arithmetic).
The meter’s main processor on the Register Display Board calculates vectorial kVAh using a
vector calculation based on kWh and kVAR values.
Data Transfer
Twice per line cycle, the meter’s main processor reads the data from all of the metrology energy
registers. This data is parsed, distributed, and accumulated in registers located on the
Register Display Board.
Once per second, the parsed data stored on the Register Display Board is transferred to
high-level tasks running on the processor’s real-time operating system. This parsed data is used
to:
• Calculate demands
• Update total billing, Time-of-Use registers (when enabled), and Load Profile
• Determine if alarm thresholds, such as Demand Thresholds and/or Reverse Power
Thresholds, have been exceeded
Calibration
The Sensor Board contains a serial EEPROM that stores the calibration constants of the sensors.
These constants are determined during the initial calibration of the meter.
Register Display Board
Main Microprocessor
Firmware running in flash memory on a 32-bit, ARM7 (RISC) processor performs the advanced,
high-level functions within the meter. The functions include:
• Processing and storage of data from metrology
• Displaying data on the LCD
• Communicating:
▪ Internally with metrology
▪ Externally by way of optional AMR modules
▪ Externally by way of the integral optical port
• Monitoring and acting on activations of switches on the face of the meter
• Maintaining time and calendar functions
• Keeping status information updated
• Maintaining a historical log of events
Version 1.0 Theory of Operation 5-3
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