As today’s home electronics and appliances offer ever-lower standby power, new smart-meter chips from STMicroelectronics enable utility companies to improve billing by measuring accurately down to extremely low power levels.Meters featuring ST’s new STPM32, STPM33 and STPM34 ICs will help utilities minimize revenue losses and ensure consistent billing for even the most frugal customers. Although existing meters are highly accurate at current levels typically down to 50mA, errors at lower currents can bring about up to megawatt-hours of lost billings across a large customer base. The STPM3 devices prevent such losses by keeping the meter accuracy down to just a few milliamps, comparable to the current drawn by an LED television in standby.
ST’s new chips also enable the development of more economical meters that help utilities reduce their operating costs. By performing power-quality calculations on-chip, including RMS voltage and current measurement, apparent-energy computation, and under-voltage/over-voltage detection, the chips can offload the meter’s host processor thus simplifying software. Neutral-phase tamper detection in the STPM33 and STPM34 helps further simplify the design and enhance system security. The STPM34 can also calculate apparent power in single- and multi-phase systems.
The STPM3 devices integrate key functions that simplify hardware design, saving external components and pc-board size. These include a voltage regulator, a temperature-compensated voltage reference supporting long-term accuracy, and a SPI/UART host connection allowing low-cost isolation for immunity to DC magnetic fields. True single-point calibration also streamlines meter manufacture and helps reduce field-servicing overheads. The ICs can measure frequencies down to DC, while their wide bandwidth allows accurate measurement of harmonic content for power-quality assessment.
The STPM32, STPM33 and STPM34 provide two, three or four independent channels respectively, for single- and poly-phase AC applications. They are fully compliant with applicable International Electrotechnical Commission (IEC) and American National Standards Institute (ANSI) standards as adopted by regulatory authorities worldwide, and exceed State Power Grid Corporation of China (SGCC) requirements.