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3 Phase Meter Eval Kit Has 24bit ADC And Measurement

ST is aiming at compliant 3 phase watt meters with an evaluation kit built around the STPMS2 double channel 24bit second-order ΣΔ modulator.

Called EVALSTPM-3PHISO, it measures through a voltage divider and current shunt for each phase. “Sensing circuitry and PCB layout are optimised to maximise signal-to-noise ratio for accuracy,” said the company. The STPMS2 oversamples signals using a 4MHz clock and outputs voltage and current sigma-delta bit-streams, multiplexed on the same pin.”

6kV galvanic isolation (up to 100Mbit/s and <3ns distortion) between ADC and host microcontroller is provided by the company’s STISO621W chip, which uses inductive transfer internally. Measurement bandwidth is 5kHz. Creepage and clearance are 8mm.

A virtual com port is implemented through which to: read metrology data, modify the internal configuration and calibrate the board – amplitude, power offset and samples offset for DC measurement is available through the latter.

Accuracy is Class 0.5 according to IEC 62053-22 on 3-ph active-apparent power measurement and Class 1 to IEC 62053-21 on 3-phase reactive power.

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The EVALSTPM-3PHISO product page is here. Brevity is taken too seriously in the associated data brief – fingers crossed for more in Rev 2 as the shunts look interesting.

Source: electronicsweekly

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