Temp. monitoring circuit for engine crankshaft - uses thermistor coupled to coil to amplitude modulate carrier for detection and comparison with reference values

摘要

A coil (3) is attached to a probe connected to a crankshaft where a thermistor senses the temp. This coil passes between transmitting a(1) and receiving (2) coils so that it attenuates the transmitted carrier amplitude. This modulates the carrier to a depth depending on the temperature. The receiving coil output is amplified (8) and demodulated (9) to obtain a continuous voltage corresponding to the temperature. A voltage-to-current converter (10) enables a current corresponding to the temp. to be applied to a galvanometer (15) for indication. Comparators (11,13) provide alarm thresholds for high and low temp. values. An open circuit thermistor fails safe by appearing as a low temp. to activate the low temp. comparator to issue an alarm signal.