GB373924A - Improvements in alternating-current potentiometers - Google Patents

Abstract

373,924. Potentiometers ; current meters; frequency measurements. CAMPBELL, A., Culmora, Girton Road, Cambridge. Nov. 2, 1931, No. 30267. Addition to 342,441. [Class 37.] The potentiometer claimed in the parent Specification is modified to enable the phase splitter to be correctly set without knowledge of the frequency. The phase splitter shown in Fig. 1 corresponds with that shown in Fig. 6 of the parent Specification. The ratios of the resistance R and inductance L of the loop circuit that includes the secondary winding of the mutual inductance M to the corresponding values r, l of the loop circuit that contains the variable resistance s are made equal, so that R/r = L/l = c, where c is unity or other constant. The currents i1, i2 in these two loops are passed through the circuits of a differential ammeter, or two separate ammeters, and the resistance s, or the mutual inductance M, or both are adjusted until I1 = cI2' where i1, i2 are the R.M.S. values of the currents t1, i2. The currents i1, i2 are then in quadrature, and the frequency may be deduced from the observed values of the mutual inductance M and resistance s, or these may be calibrated to read the frequency directly. The differential ammeter shown comprises heaters #1, #2 acting on opposed thermopiles or thermojunctions in series with a galvanometer, the heaters being shunted if necessary. Alternatively the piles or junctions may be in opposing coils of a differential galvanometer, or the differential ammeter may consist of two circuits carrying the currents i1' i2 tending to deflect a ferromagnetic member or an eddy-current circuit such as a plate or closed loop. Mutual inductance between the two deflecting circuits may be compensated by external opposing coupling. The in-phase and quadrature components vb, va of the unknown voltage may be determined by including potentiometric resistances in the two loop circuits, or after the setting for frequency has been carried out the loop connected to the mutual inductance M may be open-circuited and the other loop made non-inductive without altering@ts resistance, the in-phase component being determined by potentiometric sliders and the quadrature component by varying the mutual inductance M. Standardization of the voltage v2, Fig. 3, in the third coupled circuit, i. e. the circuit of the coil D shown in the parent Specification, may be effected by means of a three-way switch which in its right-hand position removes the coil #2 from its loop circuit and connects it, through an adjustable resistance z3, across a shunt s3 in a direct current circuit carrying a standard current id. Tho resistance z3 is adjusted so that s3 + #2 + z3 = s and the current i is adjusted until the current in the coil #2 is the same for each position of the switch. The voltage v2 may then be calculated from the values of the mutual inductance M, the resistance s3, and the standard current id.