GB1236092A - Improvements in or relating to voltage measuring circuits - Google Patents

Abstract

1,236,092. Voltage measurement. JULIE RESEARCH LABORATORIES Inc. June 5, 1968 No. 26757/68. Heading G1U. A precision potentiometer circuit 9 incorporates a voltage source 10, a first variable resistance 11, a second variable resistance 12-15 adjusted to a standard value Rs and a voltage divider 16 having an input circuit of constant input impedance R IN ; the voltage source, first and second variable resistances and the divider input circuit being connected in a first series circuit. An adjustable output for comparison with an unknown Ex is derived from the voltage divider. To calibrate the system a standard voltage source 24, which may provide e.g. 1. 01830 volts from three standard isothermally lagged cells is connected in series with a null detecting meter 27 across Rs + R IN , and the variable resister 11 in the series circuit is adjusted until a null is derived. R IN may be 100 K# and Rs set to 1830 #, so that the voltage across R IN will then be precisely 1 volt. To reduce the effects of resistance variation on the precision of operation, Rs/R IN <2%. A switch 26 enables the meter to be subsequently connected with the unknown voltage source Ex to be measured in series opposition with the divider output. The above arrangement enables a calibrated input voltage to be applied to the divider 16. In order to calibrate the dial 20, which indicates the value of the divider output, both the scale factor for the dial 20 relative to the potentiometer system and the divider ratio calibration factor must be determined. The first is ascertained by connecting the reference source 24 in series with the meter 27 across the output circuit of the divider and a standard resistor 21 in the input energizing circuit for the divider, connected to the common input/output terminal 18. Any difference between the actual and expected meter reading represents the scaling error. The divider ratio error is determined by connecting a precision resistor chain across the divider input circuit 17, 18 and comparing the voltages tapped therefrom with supposedly equivalent output voltages obtained across 19, 18 Fig. 1A (not shown). The potentiometer may be used in association with a voltbox, of the type incorporating a resistor chain to which a large input voltage is applied, the voltage tapped across part of the chain being compared with the output of the divider. The errors in the resistor chain of the voltbox may be determined by energizing the box from a known source, so that the output from each tapping point should be of given value and comparing these outputs with outputs of the given values obtained from the divider Fig.3 (not shown). All the above arrangements may be combined in one unit incorporating one null detecting instrument and standard voltage source, appropriate switches being provided to set up the various circuit configurations Fig.4 (not shown).