Optically powered sensor signal telemetry system

Abstract

A novel remote transducer telemetry system utilizing an optical link for electrical isolation and EMI (electromagnetic interference) immunity has been developed. This echo sensor telemetry system encodes information by a variable-pulse-width technique. The time between two echo pulses is proportional to, or a function of, the parameters being measured. At the sensing end the relatively intense incoming optical pulse (or series of pulses) is converted to a voltage by an array of photovoltaic cells. The cells power the electronics at the sensing end. The system is capable of interfacing resistance-, capacitance-, and voltage-type sensors. The power converter unit, micropower circuit, optical subsystem, and command and processing unit making up the system are detailed. An overall system accuracy of 1% and repetition rate between 500 and 1 kHz have been obtained experimentally. Using a 5-mW laser diode as a source, approximately 300 mu W of electrical power is available at the output of photovoltaic cells. The encoder circuit developed consumed less than 30 mu W of power. Additionally, a high-peak-intensity light transmitter operated at 1-V supply. Based on this single-echo sensor system, extension to a sensor network is outlined. >