STMicroelectronics introduces energy meter evaluation boards with integrated low-cost sensors and robust electrical isolation

     STMicroelectronics' new meter evaluation board uses a low-cost anti-current shunt sensor and advanced current isolation technology to achieve excellent reliability and robustness, accelerate three-phase AC meter design, and meet the most stringent international standards for meter quality and accuracy.

     The EVALSTPM-3PHISO evaluation board integrates a high-precision STPMS2 metering front end IC with an advanced STISO621 digital isolator, as well as customizable tunable firmware running on the STM32 microcontroller for calculating metering data and power quality data. The optimized sensing circuit and PCB layout ensure that the energy meter has excellent robustness against EMI interference and excellent signal-to-noise ratio for high-precision measurement and post-processing calculations.

     The STPMS2 is a two-channel 24-bit second-order sigma-delta modulator that measures the voltage and current of each phase of alternating current via an on-board divider and shunt sensor, and then oversamples the signal using a synchronous 4MHz clock assigned by a microcontroller. The sigma delta bit stream of voltage and current is transmitted through an output pin by multiplexing technology. A three-phase meter system requires the use of three STPMS2 to collect voltage and current data for each phase.

     The meter firmware supplied with the board utilizes the sigma-delta modulated digital filter (DFSDM) integrated with the STM32 microcontroller to convert the six-bit stream into 24-bit voltage and current values and compute all metering data in real time every 200µs. The firmware also implements a virtual communication port for accessing internal parameters, reading metering data, modifying internal configurations and calibrating the board.

     The STISO621 dual-channel digital isolator, the first in a new family of isolation ics, uses ST's 6kV thick oxidation current isolation technology to transfer data between isolation domains for a variety of industrial applications. The STISO621 features two independent channels with Schmidt trigger inputs that ensure high immunity and keep pulse distortion below 3ns. With a maximum data transfer rate of 100Mbit/s, pulse withstand voltage (VIOTM) of 6000V, and maximum repetitive isolation voltage (VIORM) of 1200V, STISO621 ensures faster data transfer, longer service life, and higher reliability than traditional optical isolators.

     STMicroelectronics' energy meter evaluation boards comply with EN 50470-x, IEC 62053-2x and ANSI12.2x AC meter standards. The application solution provides broadband, fundamental, reactive and apparent power and energy data for each phase or cumulative active energy or power; Reach the IEC 62053-22 three-phase active/apparent power measurement accuracy level 0.5 and IEC 62053-21 three-phase reactive power measurement accuracy level 1, can perform RMS calculation and THD distortion calculation (optional) for each voltage and current signal, and direct current measurement, Line period, phase shift and phase voltage delay are also measured.