GB583981A - Improvements in and relating to electrical measuring instruments of the bridge type - Google Patents

Abstract

583,981. Inductance and capacitance measurements. ACE ELECTRONICS, Ltd., WELCH, L. C., and COOK, R. J. Sept. 7, 1944, No. 17117. [Class 37] An A.C. bridge for the measurement of capacitance and inductance, in which the conditions for balance are not dependent upon the frequency, is supplied simultaneously with two currents having widely different frequencies for the purpose of extending the effective range of measurement. The bridge network has two variable resistance arms R1 R2, a standard condenser C forming a third arm and the condenser Cx under test forming the fourth arm. A galvanometer D is connected between the junctions 1, and two sources of alternating current F1, F2 of different frequencies are connected in series between the junctions 2. For inductance measurement a standard inductance and the inductance to be measured are used in place of the condensers C, Cx. The frequency F1 may be 50 cycles and the frequency F2 5,000 cycles per second. Then, for a range of from 100 micro-farads to 10 micro-microfarads the bridge impedance at the frequency F1 varies from about 30 ohms to 300 megohms and the bridge impedance for the frequency F2 varies between about 0.3 ohms and 3 megohms. If the supply F1 were used alone the impedance of the bridge at one end of the range would be excessively high. If the source F2 were used alone the bridge impedance would be excessively low. If the two sources F1, F2 are applied simultaneously, however, the effective bridge impedance at one or the other frequency lies between approximately 30 ohms and 3 megohms.