An air-borne temperature indicator

THIS paper describes an air-borne temperature indicator which was developed specifically for the U. S. Army Signal Corps, Belmar, N. J. While the specification indicated that the instrument should be of the electromechanical null-balance type,1 many of the required features represented significant departures from those of somewhat similar instruments used in industrial applications. Operation from a 115-volt (±10 per cent) 400-cycle (±5 per cent) power source was required, and the instrument was to have a range of ¿70 to +60 degrees centigrade (C) (4.92 millivolts for a copper-constantan thermocouple). The full-scale response time was specified to be less than 10 seconds, the minimum sensitivity 4 microvolts (0.14 C), and the limit of error ±1 C. Operation in accordance with these specifications, as well as storage without power connected, over an ambient temperature range of ¿55 to +55 C was required; this requirement precluded the use of dry batteries or standard cells. The indicator had to be small in size and weight, be sufficiently rugged to withstand severe shock and vibration, and develop sufficient torque to position a synchro transmitter.