GB1474637A - Electrical parameter measurement devices - Google Patents

Abstract

1474637 Measuring parameters of networks L P RUSSIN 27 Dec 1974 55971/74 Heading G1U A device for measuring the transfer parameters, e.g. amplitude ratio; phase shift; response time; output frequency, of a network comprises a source of oscillations connected to the network under test, N.U.T., to a variable phase shifter, an indicator connected to the output of a difference amplifier whose first input is connected to the phase shifter and a changeover switch connecting the source output to phase shifter input and the output of the N.U.T. to the second input of the amplifier or vice versa. In Fig. 2 the N.U.T. is a control circuit 2. The test operation is as follows:- (a) switch 6 set to positions 8, 58, 59 and capacitor 27 in phase shifter 5 set to zero-, (b) indicator 4 reading taken; (c) switch 6 set to 7, 59, 60; (d) resistor R34 in one input to difference amplifiers 3, comprising inverter 32 and adder 33, adjusted until indicator 4 reads the same as in (b), the channel gains are now equalized and the value of R34 indicates the ratio of input to output amplitudes; (e) switch 6 set to 7, 8, 59 and capacitor 27 adjusted until indicator 4 is a minimum (f) the phase shift across the circuit 2 is then calculated from the values in phase shifter 5; if the phase-shift is greater than - 180 degrees, the channels are reversed by setting switch 6 to positions 9, 10, 60 at step (e). To measure response time a squarewave generator is used for source 1 in place of a sine source. The frequency of the source is measured by using a differtiating circuit of known frequency dependence for the N.U.T. 2. The network may also comprise inductance or capacitance combined with resistance, Figs. 3, 5 (not shown), whose values can be calculated from the aforementioned parameters. To improve noise response, filters may be added between the amplifier 3 and indicator 4. This output may also be detected and displayed on a D.C. meter, Figs. 6-8 (not shown).