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3-Phase Energy Meter Evaluation Board with Low-Cost Sensors and Robust Galvanic Isolation for Industrial Metering Applications

EVALSTPM-3PHISO Evaluation Board
STMicroelectronics EVALSTPM-3PHISO Evaluation Board

The EVALSTPM-3PHISO evaluation board for 3-phase AC Watt meters introduced by STMicroelectronics combines the high accuracy STPMS2 metering front-end IC and the advanced STISO621 digital isolator, with customizable turn-key firmware running on an STM32 microcontroller to compute metrology and power-quality data. The sensing circuitry and PCB layout are optimized to ensure robustness against EMI and a strong signal-to-noise ratio for high-accuracy measurement and post-processing computation.


The voltage and current for each phase are measured by a two-channel 24-bit second-order sigma-delta modulator (STPMS2) with the help of an on-board voltage divider and a shunt current sensor. The signal is then oversampled by the synchronized 4MHz clock distributed by the microcontroller, STPMS2 multiplexes voltage, and current sigma-delta bitstreams on a single output pin.


By leveraging the digital filters for sigma-delta modulators (DFSDMs) integrated into the chosen STM32 microcontroller, the firmware converts the six bitstreams into 24-bit voltage and current values and computes all metrology data in real-time every 200µs. The STISO621 dual-channel digital isolator leverages ST’s 6kV thick-oxide galvanic-isolation technology to transfer data between isolated domains in a variety of industrial applications.


The STISO621 includes two independent channels with Schmitt-trigger inputs for ensuring high noise immunity and keeps pulse distortion below 3ns. The maximum data rate of 100Mbit/s, 6000V impulse withstand voltage (VIOTM), and 1200V maximum repeating isolation voltage (VIORM) allows the STISO621 to deliver faster data transmission, longer lifetime, and higher reliability than conventional optical isolators.


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.


The EVALSTPM-3PHISO evaluation board is available from and distributors at $118.


Features of EVALSTPM-3PHISO Evaluation Board

  • 6 channels voltage and current decimated samples available @200 us
  • 5 kHz measurement bandwidth
  • RMS and THD (optional) calculation of each voltage and current signal
  • Selectable high pass filter for DC measurement
  • Line period and phase shift measurement for each phase
  • Phase voltage delays
  • Full calibration (amplitude, power offset, and samples offset for DC measurement)
  • Two configurable LED for pulsed outputs
  • Communication through USB in virtual com port mode with shell commands
  • 6 kV galvanic isolation between the phases with 8 mm creepage and clearance


Note: More technical information can be found in the EVALSTPM-3PHISO Evaluation Board’s Databrief linked at the bottom of this page and on the product page of EVALSTPM-3PHISO Evaluation Board.

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