Out in Front

Isolated A/D converter eases motor-current measurements

Using this two-chip set from Hewlett-Packard and an external current-sensing resistor, you can measure full-scale currents from less than 1A to more than 100A with isolation and transient immunity greater than 15 kV. The HCPL-7860 sigma-delta modulator and HCPL-7870 digital interface allow you to select trade-offs between resolution and speed with maximum resolution of 15 bits (12-bit linearity) and minimum 1-msec conversion time. The chip set targets measuring motor-phase currents in precision closed-loop ac servo-drive systems.

The serial interface between the converter pair and system microcontroller is compatible with the Serial Peripheral Interface (SPI), Queued SPI , and Microwire Synchronous Bus standards. The isolated front-end IC meets relevant UL and CSA requirements; VDE approval is pending. The HCPL-7860 comes in eight-pin DIP and surface-mount packages and costs $6.52 (1000); the HCPL-7870 is available in various 16-lead packages and costs $2.77 (1000).—by Bill Schweber

Hewlett-Packard Co, Palo Alto, CA. (800) 537-7715, ext 3131, http://www.hp.com.