GB878292A - Improvements in electrical systems comprising mutually controlled oscillators and moving coil instruments - Google Patents

Abstract

878,292. Electric tests. SANGAMO WESTON Ltd. Oct. 24, 1957 [Dec. 27, 1956], No. 39318/56. Class 37. In an automatic control, detection or measuring system, deflection of the coil in a D.C. moving-coil instrument controls a reactive element in a transistor oscillator to vary the amplitude of the oscillations therein, and a current or voltage dependent upon the amplitude is developed which tends to balance the input current or voltage to the moving coil, the movement of which is thereby opposed. The moving coil of a D.C. instrument M is connected, in series with input terminals 1, 2, across a cold end compensating bridge network R2, R3, R4, R5, a thermocouple W being connected across the terminals 1, 2; and a ferrite plug f carried by the moving coil controls the L and Q values of a coil L incorporated in an oscillator driven by transistor T1, thereby varying the amplitude level of the oscillatory output. An applied E.M.F. from thermocouple W unbalances the bridge network, and the resulting deflection of the moving coil varies the amplitude level of the oscillatory output of T1 which causes the D.C. potential between the base and the emitter of T2 to vary, and the resulting collector current of T2, as indicated by instrument K3, provides a measure of the thermocouple E.M.F. The bridge components are arranged to supply a counterbalancing E.M.F. to terminals 1, 2 so that no current is drawn from the thermocouple. The input to the moving coil may be arranged to produce either an increase or decrease in the amplitude level of oscillation of T1. In modifications, the moving coil may carry a metal vane to vary the Q value of the tuned circuit L, C1; or the capacitance of C1 may be varied; and the instrument K3 may be replaced by a relay for automatic control or detection purposes. Specifications 700,643 and 786,481 are referred to.