ICs Make Meter Designs Easier, Energy Theft Harder

Oct 1, 2007 12:00 PM
By David Morrison, Editor, Power Electronics Technology

Demands for greater functionality, higher reliability, and lower cost have driven the development of the latest electronic energy-metering ICs. These devices, which include both system-on-a-chip (SoC) metering chips and general-purpose microcontrollers with metering-oriented peripherals, target a range of single-phase and three-phase electricity meter applications for residential or commercial use.

Functional integration is a key feature of the new energy-metering ICs, which aim to simplify the meter design, add new features, and reduce the overall meter-design cost. Some of the new chips also incorporate special features to prevent thieves from tampering with the meter. Requirements for energy efficiency are also in evidence in some of the metering devices, which boast intelligent power-management features aimed at minimizing the energy meter’s power consumption.

A summary of the capabilities offered by the new metering ICs is provided here, as well as functional block diagrams and application circuit examples based on these components. There are also links to other vendors who offer energy-metering ICs not covered this article.

Recent Introductions

In June, STMicroelectronics introduced a family of energy-metering ICs that incorporate all of the core circuitry necessary to implement a complete meter system without any other active component. The STPM1x family of single-phase energy-metering ICs measure active energy as pulse-frequency output and feature fast digital calibration, providing meter manufacturers with a cost-effective series of power-metering chips specifically designed for low-end metering applications. 

Fully compliant with specifications for single-phase, class 0.5 static meters, the STPM1x ICs provide fast digital calibration at only one point over the whole current range. This capability allows a drastic reduction in manufacturing costs when compared to hardware calibration made using a resistor network. The mixed-signal ICs are designed for effective measurement of active energy in a power-line system using a wide variety of current sensors such as shunts, current transformers and Rogowski coils.

Analog blocks within the STPM1x include preamplifiers for signal conditioning, analog-to-digital converters (ADCs) and low-dropout voltage regulators to supply the circuitry. In the digital part of the device, the hardwired digital signal processor uses ripple-free computation algorithms to calculate the amount of consummated active energy, considerably reducing the meter’s calibration time.

Fig. 1. From STMicroelectronics, the STPM1x single-phase energy-metering IC with pulsed output and digital calibration provides all the necessary features required to build a single-phase energy meter without any other active components. click image to see full-sized figure

Fig. 2. The STPM1x provides active energy measurement in a power-line system using input from a Rogowski coil, current transformer and shunt resistors. (click image to see full-sized figure)

In addition, the active energy is available through complementary pulsed outputs that enable an easier energy measurement while directly driving stepper-motor counters in low-end applications. The device is configured and calibrated through a serial port, which exploits the one-time programmable cells for permanently storing calibration parameters, preventing subsequent tampering. Offered in the TSSOP20 ECOPACK package, the STPM1x is priced at $1.40 each in quantities of 1000.

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© 2007 Penton Media, Inc.