Elgama EPQS - Electronic Circuitry and Principles of Operation

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2.3. Electronic circuitry and principles of operation
Picture 2-5. Block diagram of the meter
2.3.1. Measurement module
The measurement module converts the electricity network voltage and current values to
corresponding analog signals.
The voltage value is converted by a resistive voltage divider, and the current value is converted by a
precise current transformer. Firmware of the central processor unit compensates a phase shift in the
current measurement circuit. The voltage and current of each phase is measured by a separate
respective measurement module (further referred to as “measurement element”).
2.3.2. Analog to Digital Signal Conversion
From the measurement module, the analog voltage and current signals further go to a 6-channel ADC
(Analog to Digital Converter) (Sigma – Delta integrator). The integrator converts the analog signals
into digital 16-bit codes 72 times during a single AC period. A logical multiplexer unit integrated in the
same chip combines signals of different phases into a single sequence of digital codes.
2.3.3. Central Processor Unit
Multiplexer unit output codes are further sent to the central processor unit (CPU) where they are
multiplied by calibration constants entered during calibration. Based on the result, the processor then
calculates square voltage and square current for each phase and voltage with 90° phase shift
(necessary for calculating of reactive energy): I²
A
, I²
B
, I²
C
, U²
A
, U²
B
, U²
C
, U’
A
, U’
B
, U’
C.-
From these values,
active, reactive and apparent powers and energies are calculated. The CPU also acts as a controller
of memory unit, LCD, and communication interfaces, generates calibration (LED) signals and
performs other functions.