Evaluation board combination computes metrology and power-quality data

The EvalSTPM-3Phiso evaluation board from STMicroelectronics combines the STPMS2 metering front-end IC and the STISO621 digital isolator, with customisable turn-key firmware running on an STM32 microcontroller to compute metrology and power-quality data. The sensing circuitry and PCB layout are optimised to ensure robustness against electromagnetic interference and a strong signal-to-noise ratio, for high-accuracy measurement and post-processing computation.

This evaluation board, a two-channel 24-bit second-order sigma-delta modulator, measures voltage and current for each phase through an on-board voltage divider and a shunt current sensor. It then oversamples the signal using a synchronised 4MHz clock distributed by the microcontroller and multiplexes voltage and current sigma-delta bitstreams on a single output pin. Three STPMS2 are used in the 3-phase system to collect voltage and current data from each phase.

The provided firmware leverages digital filters for sigma-delta modulators integrated in the chosen STM32 microcontroller to convert the six bitstreams into 24-bit voltage and current values and computes all metrology data in real-time every 200-micro seconds. The firmware also implements a virtual com port that provides access to internal parameters for reading metrology data, modifying the internal configuration and calibrating the board.

The STISO621 dual-channel digital isolator is the first in a new series of ICs that leverage ST’s 6kV thick-oxide galvanic-isolation technology to transfer data between isolated domains in a variety of industrial applications. The isolator features two independent channels with Schmitt-trigger inputs that ensure high noise immunity and keeps pulse distortion below 3ns. There is a maximum data rate of 100 Mbits per second, 6000V impulse withstand voltage and 1200V maximum repeating isolation voltage.

ST’s metering evaluation board meets EN 50470-x, IEC 62053-2x, ANSI12.2x standards for AC watt meters. The application provides active wideband, active fundamental, reactive and apparent power and energy data, both per-phase and cumulative, reaching accuracy Class 0.5 according to IEC 62053-22 on 3-phase active/apparent power measurement and accuracy Class 1 according to IEC 62053-21 on 3-phase reactive power measurement. It performs RMS and optional distortion calculations for each voltage and current signal, as well as DC measurements, and line period, phase shift, and phase-voltage delay for each phase.


Latest News from Softei

This news story is brought to you by softei.com, the specialist site dedicated to delivering information about what’s new in the electronics industry, with daily news updates, new products and industry news. To stay up-to-date, register to receive our weekly newsletters and keep yourself informed on the latest technology news and new products from around the globe. Simply click this link to register here: Softei Registration