ITRON Centron, Technical Reference Manual

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Operation: Base Metrology
18 CENTRON® Meter Technical Reference Guide
This field is focused to flow through the Magnetic Core's air gap where the Hall sensor is
precisely positioned. The voltage,
Vout , which is formed on the Hall Effect device is
proportional to the input watts (see the Power Measurement Principle figure below).
The output voltage of the Hall Effect device is then:
V
hall
= Vout = GIV = GPower
G is the combined gain factor of the entire system (Voltage to biasing current, line Current
to flux density, Hall sensor).
Figure 13: Power Measurement Principle in 2S Meter
From the power information available at the output voltage of the sensor, the meter
architecture is simplified over previous designs as the multiplication has already taken place
(see the Simplified CENTRON Architecture figure below).
The Hall sensor output voltage is amplified by a differential amplifier in order to bring the
signal within the nominal level of the analog to digital converter (ADC). The output of the
ADC is integrated over time to get the energy information and generates a pulse stream that
is accumulated into a counter. When the accumulated pulses reach a threshold set by meter
calibration, a Wh pulse is emitted and the meter LED is flashed. The counter threshold is
programmed at the factory and serves as the permanent gain calibration for the life of the
product. The calibration is a digital feature and has no variation or adjustment. All the
processing steps described above are integrated into an Application Specific Integrated
Circuit (ASIC) to improve reliability and reduce cost.
Figure 14: Simplified CENTRON Architecture