GB1392050A - Digital voltmeter - Google Patents

Abstract

1392050 A/D Converters C MICHEL 19 July 1972 [20 July 1971] 33732/72 Heading G4H Apparatus for supplying a digital measurement of a continuously variable voltage which is affected by A.C. interference comprises a comparator 7 to which are fed the unknown voltage at an input 4 and a voltage derived via A/D converter 8 representing the count at a counter 1, 2 the difference voltage then being applied to both inputs of an AND gate 11 controlling a clock 5, firstly through a threshold device (not shown) and secondly through an integrator 13- 15 and then through a second threshold device (not shown), the outputs of each threshold device also being taken via respective inverters 16, 17 as inputs of a second AND gate 12 controlling a clock 6, the arrangement being that while both inputs 11A, 11B at gate 11 are activated, i.e. when the instantaneous and the integrated difference outputs from 7 are greater than the threshold level, the counter is incremented by the clock 5 and while AND gate 6 is activated, the counter is decremented by clock 6. Thus A.C. interference is prevented from actuating either clock source since the time integral of this approximates to zero.