Wireless Transmitter Gets Its Power From The Loop

The Loop-Powered Transmitter (LPT) joins the more than 20 loop-powered devices—from digital panel meters to controllers—made by Otek Corp. The LPT uses a patent-pending technique, along with nanotechnology and an ASIC, to extract the loop’s current (4 to 20 mA or 10 to 50 mA) to charge a supercapacitor that powers the RF transmitter. The technique does not affect the accuracy of the loop. A microcontroller monitors the input current loop and the capacitor’s energy charge to determine the wireless transmitter’s rate of transmission. The rate is slower at 4 mA and faster at 20 mA. The receiver, which is externally powered (12 to 28 V dc), converts the RF from binary to a 4- to 20-mA (or 1- to 5-V) output to reproduce the loop’s value.

The LPT includes an internal lithium battery used for emergency transmissions or when the loop current is low for long periods of time. The battery is externally enabled prior to operation (and disabled in transit). LEDs warn the user of low- or no-loop conditions. The LPT can be DIN-rail or Velcro (in-line) mounted. At 25°C and with a 12-mA input, the transmitter’s accuracy is ±5% of reading. The analog-to digital converter’s resolution is 10 bits. The input can vary from 3.6 to 36 mA, and the transmission rate is up to 10/s at 20 mA. Frequencies available include 315, 433, and 915 MHz (and 868 MHz for outside the U.S. only).