GB1390063A - Method and apparatus for measuring a voltage with the aid of an analogue-digital converter - Google Patents

Abstract

1390063 Analogue to digital converter G ZSCHIMMER 28 Feb 1972 [3 March 1971 11 Feb 1972] 9143/73 Heading G4H In an A/D converter comprising an integrator provided with a feedback loop, a storage device in the loop stores a voltage applied to the integrator and can be disconnected from the integrator output so that the stored voltage biases the unknown voltage and the converter input is of constant polarity. The auxiliary voltage (-U o ) is larger than the unknown voltage (U E ) and of the same polarity as the reference voltage (-U R ). The converter comprises a differential amplifier 1, an integrator 2 and a comparator or zero threshold detector 3, the output of which controls the flow of clock pulses to a counter (not shown). A capacitor 8 and switch 7 are connected between the output of comparator 3 and one input of differential amplifier 1. In operation, switches 9 and 7 are closed and the feedback loop charges capacitor 8 to (-U O ), the auxiliary voltage. This voltage is held at one input of differential amplifier 1 when switch 7 is opened. Switches 9 and 7 are opened, switch 5 closed and the unknown voltage U E is applied to differential amplifier 1, the difference between Uo and U E being integrated by integrator 2. After time (t 1 -t 0 ). switch 5 is opened, switch 6 closed and the counter is started. The input to the integrator is now U R -U O and this brings the integrated voltage at A down to zero, at which point comparator 3 stops the counter. U O is made equal to ¢U R . The counter starts at 10,000 and counts downwards and then upwards, matters being arranged so that when U E is at earth potential the count reading is zero. The counter thus provides a reading of the unknown voltage, of the count down period is indicated as negative and the count up as positive. The device may also be used for determining resistance by substitution of the unknown for R 1 or R 2 .