1534280-A is referenced by 49 patents.
1534280 Testing thermocouples SOLARTRON ELECTRONIC GROUP Ltd 27 Feb 1976 [28 Feb 1975] 8369/75 Heading G1U In a method of testing a thermocouple, firstly the resistance of the thermocouple is measured and stored at an instant when the thermocouple is known to be in good working condition, and secondly the resistance is measured later and compared with the first measurement, any deviation outside a present range indicating an abnormality in the thermocouple. The method is described embodied in a system in which a plurality of thermocouples 14, each having hot 16 and cold 18 junctions, are sequentially scanned.; Each thermocouple is tested, under the control of a sequence controller 70, by first measuring its resistance when it is known to be good, this being effected by- (a) with the switches in their positions shown, measuring the output voltage of the thermocouple and storing it 40, (b) closing switches 28, 30 so as to apply a constant current 36 through the thermocouple, and (c) changing over a contact 38 so that the resulting voltage from the thermocouple when the constant current is flowing (this voltage being the sum of the thermoelectric voltage and the I-R drop across the junction) has subtracted 44 from it the first measured voltage from the thermocouple, and storing 56 the difference which represents the resistance of the thermocouple.; Having established the "good" resistance of the thermocouple, at some later instant a contact 52 is changed over, a further measurement of resistance - using steps (a) and (b) above is made - and the further measurement is compared 60 with the "good" resistance, any deviation that is too large producing an output 66. To test every thermocouple in the system, one store 56 per thermocouple will be required, and either the resistance measuring section can be repeated or it can be time shared.