OPTICAL TRANSMITTER FOR PRODUCING AN OPTICAL SIGNAL INDICATIVE OF TEMPERATURE

摘要

An optical transmitter (16) for converting a thermocouple voltage into an optical pulse train and a low pass input filter (30) are contained in respective spaces (28, 30) in a soft magnetic housing (22). The input filter (30) is in lead wires (32, 34) from a thermocouple whose hot junction is embedded in the tip of the insulator of a spark plug (10) of an internal combustion engine. The housing (22) itself forms part of or is connected to the H.T. lead to the centre electrode (12) of the spark plug. The housing (22) is surrounded by insulating material (42) which is itself surrounded by an earthed screening casing (44). The low pass filter (30) is symmetrically constructed, both electrically and mechanically. The filter (30) prevents interference from reaching the circuitry of the optical transmitter (16) and the housing (22) and the casing (44) prevent the generation and transmission of radio interference.