GB510885A - Improvements in or relating to electrical measuring instruments - Google Patents

Abstract

510,885. Automatic control systems. BANNER, E. H. W. Feb. 9, 1938, No. 4032. [Class 38 (iv)] [Also in Group XXXVI] Electromotive force.-Apparatus for measuring or recording small fluctuations from a normal alternating-current voltage comprises a meter connected in a continuous-current bridge circuit between the rectified fluctuating voltage and a source of substantially constant voltage. Shunt or series resistors can be used with the meter for giving a less sensitive range of response. In Fig. 1, a supply through transformer 1, 2 is rectified at 3, smoothed at 4, 5 and the direct-current volts are taken from a tapping on resistor 6, 7. The constant voltage source 8 is applied to resistor 9, and may include a cell 15 for standardising purposes. The sensitive voltmeter 20 is connected between the two sources and is protected by interrupters 18, 19. A barretter and limiting resistor can be connected to the main direct-current for keeping the source 8 constantly charged. Fig. 3 shows another arrangement having a barretter 22 connected to the main source, two rectifiers 3, 23 supplying the sensitive voltmeter 20. In other arrangements, the constant voltage is supplied by a neon or other gas discharge tube, and in these circuits a constant current device can also be employed. Constant voltage devices connected in opposition can be used to increase the instrument deflection due to line voltage fluctuations. The instrument can be scaled in percentage change from normal volts, and can be provided with contacts for performing known control or regulating operations.