GB857510A - Improvements in or relating to electrical analogue to digital converters - Google Patents

Abstract

857,510. Electric selective signalling systems. SOC. NOUVELLE D'ELECTRONIQUE. Feb. 20, 1959 [Feb. 28, 1958], No. 6008/59. Class 40 (1). In a device for digitising an amplitude significant voltage derived from a sliding potentiometer of the type in which the voltage to be digitised is compared with a linearly increasing voltage from a time-base circuit and in which clock pulses are counted for the period from when the time-base circuit is triggered until equality of the two voltages is detected, means are provided for periodically adjusting the reference voltage that is applied to the sliding potentiometer to such a value that when the slider of the potentiometer is in its extreme position equality between the voltage then produced and the time-base voltage occurs when the counter has just reached its maximum capacity. This ties the entire system to the source of clock pulses and compensates for any drift in the circuit parameters. The circuit for effecting this periodic adjustment is shown in full lines in Fig. 2, the dotted lines being connections required only for the actual digitisation, and an adjustment is effected as follows: a pulse 4 is applied to trigger the time-base and to cause clock pulses to be applied to the counter. When the counter reaches its maximum capacity it stops the clock pulses and causes the time-base circuit to apply the voltage it has then reached to a circuit 13, via a diode 12, where this voltage level is clamped, and from the clamp this voltage is applied via a unity-gain amplifier to the sliding potentiometer 7. In the actual embodiment described, a plurality of potentiometers 7 have their outputs multiplexed.