A microcontroller monitors input current loop and the capacitor’s energy charge to determine transmission frequency (slower at 4 mA; faster at 20-mA input). Powered by 12 to 28 Vdc, the receiver converts RF from binary to 4 to 20-mA output to reproduce the loop’s value at the receiver.

An internal lithium battery handles emergency transmissions or when the loop is low (4 mA) for long periods. LEDs warn of low or no loop conditions.

The LPT can be DIN-rail or Velcro (in-line) mounted and connected to existing wires; specifications at 25°C and 12-mA input: 0.5% reading accuracy, 10-bit A/D resolution; 3.6 to 36- mA minimum-maximum input; 1/15 sec @ 4-mA transmission rate; battery life gives over 100 transmissions at <4-mA input; RF band is 315, 444, 868 MHz (outside U.S.) and 915 MHz for U.S.; and operates at –10 to 70°C.

Otek Corp., 4016 E. Tennessee St., Tucson, AZ 85714, (877) 227-6835, otekcorp.com

Loop-powered wireless transceiver