GB872488A - Improvements in or relating to voltage-measuring circuits - Google Patents

Abstract

872,488. Electric selective signalling systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Jan. 19, 1960 [Jan. 19, 1959], No. 1965/59. Class 40 (1). [Also in Group XXXVI] A voltage-measuring circuit comprises a trigger circuit T 1 of threshold voltage V 2 and an integrator G and a feedback connection between the integrator and an adding circuit A in the input of T 1 , input pulses of peak value V 1 triggering T 1 at each pulse and feeding a charge to integrator G and increasing the negative output voltage - v by #v each time, this output voltage being fed back to A and thus decreasing the input to T 1 in steps until it is below the threshold voltage V 2 when the T 1 will no longer trigger and the circuit is balanced, the output voltage at O therefore giving a measure of V 1 . A counter C which registers each time T 1 triggers will give a digital indication of T 1 . In order to provide for the condition V 1 < V 2 a second trigger circuit in parallel with T 1 is provided in an alternative embodiment (Fig. 2, not shown) which has a threshold voltage less than V 2 and adds a charge equal but of opposite sign to that added when both trigger circuits trigger. In a further embodiment (Fig. 3, not shown) a continuous input voltage V 1 is chopped to provide the input pulses to the trigger circuits, one of which comprises two trigger circuits in series, one of the trigger circuits triggering at every pulse and adding a charge - Q to integrator G while the other trigger circuit (consisting of two trigger circuits in series) triggers, as before, only when V 1 - v > V 2 but adds a charge + 2Q to integrator G each time it triggers. In the embodiment shown in Fig. 7 the circuit can be used as an analogue to digital converter, the digital output being in binary code. In this arrangement, the threshold voltage of the trigger circuit T 1 is changed during operation to enable balance of the circuit to be achieved more quickly. The operation is as follows. The input analogue voltage V 1 is applied to T 1 through switch contact 53 and threshold level voltage V 2 via lead 50. A capacitor 52 is connected between the output of integrator G and switch contact 53<SP>1</SP> which operates with contact 53. Assuming that 51 is originally charged, then when 53 closes, 53<SP>1</SP> will also move to connect 52 in parallel with 51 the charge therein thus being shared equally with 52. If V 1 is greater than the threshold voltage (provided by the charge on 51) T 1 will fire and contact 54 will change to discharge capacitor 52 into the integrator thus increasing the output of the latter and therefore the threshold voltage. If V 1 is less than the threshold voltage T 1 will not fire and capacitor 52 will discharge through resistor 55 and there will be no output from the integrator. Equilibrium is reached when the threshold voltage V 2 becomes equal to the input voltage V 1 , means operated synchronously with switches 53, 53<SP>1</SP> giving a record when T 1 is triggered and therefore a binary indication of the voltage V 1 .