An infrared telemetry technique for making piston temperature measurements

Document Type

Conference Proceeding

Publication Date



An optical telemetry technique has been developed for obtaining piston temperatures in reciprocating engines. The technique employs a transmitter mounted on the underside of the piston which transmits the temperature information as frequency modulated infrared pulses. This signal is picked up by a photodetector mounted in the crankcase which is wired to an external receiving unit. The transmitter consists of a thermocouple or thermistor, voltage-to-frequency converter, calibrating circuitry, and an infrared light-emitting-diode. The receiver consists of a phototransistor, frequency-to-voltage converter, calibrating circuitry and voltage readout. The transmitter is powered by lithium batteries. The signal has been successfully transmitted at speeds up to 4500 RPM in a 2-stroke engine and up to 5000 RPM in a 4-stroke engine. The accuracy of the infrared telemetry device using thermocouples is ±2.8°C (95% confidence level).

Publisher's Statement

© Copyright 1991 Society of Automotive Engineers, Inc. Publisher’s version of record: https://doi.org/10.4271/910051

Publication Title

SAE Technical Papers