GB1361237A - Method and apparatus for testing electrical circuits - Google Patents

Abstract

1361237 Voltage measuring ROSEMOUNT ENG CO Ltd 16 Oct 1972 [15 Oct 1971] 48069/71 Heading G1U In an arrangement for sequentially sensing the voltages occurring on a set of point 100, Fig. 9, for example points of a printed circuit board, and effectively comparing them with a corresponding set of ranges set by upper and lower target potentials, each sensed voltage is passed via a switch 106, an over-voltage protection circuit 107, and a buffer amplifier 108 to a potential divider 109 which is set firstly so that if the lower target voltage were applied to it, it would produce a standard voltage Vs, and secondly so that if the upper target voltage were applied to it, it would also produce the standard voltage Vs, and the voltages that actually occur with these two settings of the potential divider are amplified 111 and compared 112 with a reference voltage V R , which should be respectively exceeded and fallen short of, so that a logic unit 113 can actuate an alarm indicator 114 when a sensed voltage does fall outside its corresponding range. The potential divider 109 is constituted by a three-decade binary-coded-decimal arrangement of series connected resistors Fig. 1 which are selectively shunted by read contacts A, B, ..., M, so that the application of the target voltage at Vin produces the standard voltage Vs across a precision resistor PR. Two sets of threedecade stores 120, Fig. 9, to store the appropriate settings of the potential divider 109 corresponding to each pair of upper and lower target voltages are provided, and as each point 100 is sensed first the lower target voltage store is rendered operative, under the control of a master clock 115 and sequencing devices 104, 103, 116, 117, 118, and then the upper target voltage store is rendered operative. The stores take the form of plug boards PB, Fig. 7, having three groups of ten vertical conductors 72, which are selectively connected by diodes 75 to common terminals T1, T2, ..., Tn, which are sequentially energized, during a testing segmence, to read the numbers stored, by the selective diode connections, to decimal-to-binary converters 71, 73, which, at the appropriate times, control the potential divider read contacts. Comparison of the voltage produced by the potential divider 109, Fig. 9, with the reference voltage V R , is effected by a conventional differential amplifier 112, its output being strobed at the appropriate times and examined for polarity. The test cycle could be halted when a faulty point is indentified.