GB1477436A - Devices for measuring parameters of compound electric circuits - Google Patents

Abstract

1477436 Measuring impedance PENZEN POLITEKHNICHE INST 21 May 1975 21783/75 Heading G1U A circuit for measuring individual parameters of components in situ, includes a switch arrangement for inter-connecting the measuring circuit elements in different ways to measure the parameters in four types of three-terminal network, viz delta or starconnected series or parallel circuits. The embodiment has a further facility for analyzing series or parallel connected two terminal networks. The measuring circuit comprises four parts:- (a) Measuring circuitry including amplifiers 16, 22 and 1 acting as differentiator, integrator and summing amplifier and pulse amplifier respectively; a pulse shaper 12 operating an FET switch 14 for resetting the differentiator 16; a pulse frequency or period meter 2. (b) A reference unit 6, containing calibrated reference elements Ro, Co, Lo, which selectively connected into the measuring circuit by a switch 7, according to the unknown component being measured. (c) Circuitry including amplifiers 4, 24 for electrically isolating that arm of the network being analyzed, which contains the unknown components. (d) The switching network 25 having two selectors 26, 27. Selector 26 has a number of two position contacts 28-36, some of which have a third contact. By choosing the correct combination of the two selector positions a, b, the four types of circuit can be analyzed. The third position c of selector 26 is used for analyzing two-terminal networks. All six measuring circuit function in similar ways. For example with the selectors 26, 27 both set to a, the circuit of Fig. 2, is obtained wherein parallel components in a delta connected network are measured. The unity gain amplifier 24 ensures that the voltage difference across arm 52 is zero, with the arm 51 being shunted by the low amplifier output impedance, thus electrically isolating the arm containing the unknown components 48-50. For measuring C x , 50 the reference unit switch 7 is set to connect the reference capacitor C o , 10 in the amplifier 4 feedback. The output from amplifier 4 is a function of the output from amplifier 1, the capacitances C x , C o and time. The differentiated output from amplifier 16 is integrated in amplifier 22 and summed with the differentiator input signal via capacitor 19 and the amplifier 1 output via capacitor 21. With a proper choice of circuit parameters, the output from amplifier 1 can be shown to be a bi-polar pulse train of period <SP>4R</SP>11 C 23 Cx/Co By changing the setting of switch 7 R x , 48 and L x , 49 can also be measured. Circuits resulting from changes in the selector 26, 27 are given in Figs. 3-7 (not shown).