Smart power-meter-IC family offers alternative to current transformers
Utility power meters often must rely on a current transformer for polyphase applications. Current transformers have drawbacks, however. They are relatively expensive and require additional copper wiring. Power thieves can also tamper with the devices using large permanent magnets. Shunt current sensors are often simpler and less expensive, but they work only for single-phase, single-element systems. The voltages they measure across phases are too high for the subsequent electronics and also for maintenance personnel (see “Tamper-resistant smart power meters rely on isolated sensors,” EDN, March 19, 2009, pg 29).
Teridian takes a different approach to the problem with its new SOC (system-on-chip) smart-metering product family, which includes the 71M6541x and 71M6xx1. The family features digitally isolated current sensors that the company based on its proprietary MicroDAA (data-access-arrangement) isolation technology. The 71M6541x stand-alone meter SOC targets use in single-phase systems. For multiphase systems, designers can eliminate the need for a current transformer and its associated copper wiring by using an inexpensive pulse transformer to interface the 71M6541x to the 71M6xx1 isolated sensor IC, which then connects to a current-sensing shunt element. The 6541 sends a signal to the pulse transformer, which provides a communication signal and has enough power to energize the sensor IC with accuracy to ANSI 200A Class 0.2.
The 71M6541x comes in 64-pin LQFPs with 32- or 64-kbyte flash-memory options; prices start at $2 (10,000). The 71M6xx1 isolated sensors come in eight-pin SOIC packages for prices starting at $1.50 (10,000), depending on current and accuracy range.
This article originally appeared as an entry in the PowerSource blog. Please click here to view that article.