GB401488A - Improvements in and relating to electrical measuring circuits and apparatus therefor - Google Patents

Abstract

401,488. Phase difference measurements ; electrostatic meters. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, BRAY, G. R. R., 86, Dunchurch Road, and WILKINSON, K. J. R., 16, Vernon Avenue, Hilhnorton Paddox, both in Rugby. Oct. 26, 1932, No. 30015. [Class 37.] An electrical circuit for determining whether the alternating potential differences between three or more points are in phase comprises an electrometer 1 having its fixed electrodes A<1>, B<1> excited to alternating potentials such that upon connection of two of the points O, P in succession to the movable electrode X a null response is obtained, and such that if the potential differences between each of the points O, P and a third point Q are in the same phase, a null response is also obtained on connecting the point Q to the movable electrode. The arrangement is applicable to the measurement of the power factor or loss angle of samples of insulating material, the sample to be tested being used to make up a condenser 4 in series with a standard condenser 5 and resistance 6, one or both of the latter being variable. In one arrangement, Fig. 1, the voltage for the fixed electrodes is obtained by a bridge circuit made up of resistances 8, 9 and condensers 10, 11, all of equal impedance, connected as shown across the points O, P. On connecting these points successively to the movable electrode X a null response should be obtained. The electrode X is then connected to the point Q, and the power factor of the branch Q P is adjusted until the electrometer again gives a null response ; the power factor of the condenser 4 is then equal to that of the branch Q P. In a modification, Fig. 3, the voltage of the fixed electrodes A<1>, B<1> is obtained from the secondary winding of a mutual inductance M in series with a resistance R, the series circuits 4, 5, 6 being connected across the resistance, as shown. Vector diagrams for the two arrangements are given. The electrometer may be a quadrant electrometer, or an electroscope of the form shown in Fig. 5 may be used. This electroscope comprises adjustable electrodes 12, 13, with a gold leaf 16 suspended symmetrically between them and supported by an adjusting screw 17 mounted in a metal case 18. The case may be adjusted horizontally on the base 19 by means of another adjusting screw 20.