Reference platform for simplifying 'smart' electric power metering

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STMicroelectronics has introduced a reference design platform for the electronic power meter market. Electronic energy meters are replacing traditional electromechanical meters because their versatility and low-cost allows manufacturers to implement many features that were impractical with the older mechanical designs.

For example, an electronic design can protect against meter tampering and theft of service. It can also measure and record energy usage at different times of the day, so utilities can bill based on time of usage. Also, automatic meter reading (AMR) can be enabled, transmitted information to the utility over a power line communications link.The reference platform provides a modular solution that can be adapted by software to meet particular needs.

It comprises two PCBs, one dedicated to the mains power measurement functions and one implementing sophisticated computational and supervisory functions. The measurement board supports all current measurement technologies, from the most accurate Rogowski coils to inexpensive shunt resistors. It can monitor both Live and Neutral current for tamper detection and complies with international standards for metering equipment (AC).

The Measurement Board is based on ST's STPM01 power metering chip, which includes all necessary signal conditioning, processing, data conversion, input/output signals and voltage reference. The STPM01 can be used as a standalone device in 1-phase kWh meters or as a peripheral in microprocessor-based 1- or 3-phase energy meters, in which case active, reactive and apparent energy, Vrms, Irms, instantaneous voltage and current, and line frequency readings are available through the SPI bus. The Control Board is based on an ST7 microcontroller and is supplied with a library of C-code software, with many additional software routines (available free from the ST website).

The microcontroller communicates with the STMP01 ASSP via SPI interface, allowing easy customisation of metering functions with included PC software. The reference design also includes the M41ST87 realtime clock chip, a 256 Kbit serial SPI bus EEPROM and a dedicated 32-character alphanumeric LCD with on-glass driver.