GB579337A - Improvements relating to electrical measuring apparatus - Google Patents

Abstract

579,337. Electric meters. COSSOR, Ltd., A. C., BEDFORD, L. H., BELL, J., and LANGHAM, E. M. Nov. 30,1942, No. 20009/43. Divided out of 579,325, [Group XIX]. [Class 37] A null-voltage indicating circuit comprises a pair of similar thermionic valves 1, 2 having similar anode loads 3, 4, a direct current null indicating meter 11 connected between the anodes of said valves, a common cathode load consisting of two resistance potentiometers in parallel with each other and with a smoothing condenser 13, means to excite the anode circuit with alternating voltage, means to connect the grid of valve 2 to a tapping on one of said potentiometers 5 and means to inject the voltage to be nulled between the grid of valve 1 and a tapping on the other of said potentiometers, so selected that when said voltage is zero a null indication is obtained on the meter 11. To adjust the circuit for inequalities, switch 9 connects the grid of valve 1 to the mid point of resistance 6 and the tapping of the potentiometer 5 is adjusted until the meter 11 reads zero. A direct voltage to be measured is applied to terminals 10, put into circuit by the switch, and the movement of tapping 8 from mid position, to give a null indication, is a measure of the voltage. The tapping may be graduated or may be mechanically coupled to another instrument which it is desired to set according to the measured voltage. Another voltage applied at terminals 14 can be measured in a similar manner on potentiometer 7. An alternating voltage in phase with the source 16, can be measured by being put into series with a potentiometer connected across the secondary of a transformer supplied by the source 16, the total output being applied to terminals 15. The adjustment of the potentiometer when a null reading is obtained is an indicating of the alternating voltage.