An analogue-digital converter with long life

An instrument has been developed for converting small voltages representing a measured parameter into a digital representation of the parameter. Features of the instrument include a high input impedance, extremely long service-free life (due to lack of any moving parts), accuracy of 0.1 per cent. of full scale deflection, and conversion time of 25 milliseconds or less. The instrument is unusual in that conversion is performed at the input level, thus eliminating the necessity for a d.c. amplifier with stable gain, and circuits have been designed to ¿linearize¿ the outputs from copper-constantan or chromel-alumel thermocouples so that the output is in degrees centigrade rather than in thermocouple e.m.f. Some observations are made on the problems of switching low-level signals. Suggestions are made as to suitable uses for such converter.