GB674113A - Improvements in or relating to liquid level sensitive apparatus - Google Patents

Abstract

674,113. Liquid level measurement; capacitance and inductance measurement; electric condensers. WHEELCO INSTRUMENTS CO. Feb. 24, 1948 [May 3, 1939], No. 29861/50. Divided out of 674,034. Class 37. In a liquid level indicating device (Fig. 1) a sealed bifurcated glass tube 45 immersed in the liquid contains the parallel electrodes 43, 44 of a capacitance having the liquid for dielectric which is connected across the grid inductance of an oscillator tube 50, whose anode circuit is tuned by a parallel inductance-capacitance circuit 57, 58. The anode current flows through one winding 60 of a differential relay whose other winding 61 is energized from a D.C. source through a resistance 64 variable by a split-field D.C. motor 72. When the liquid is at datum level, the oscillator grid circuit is tuned to a predetermined frequency, differing from that of the anode circuit such that the relay is balanced in its neutral position. Changes in liquid level in either sense vary the grid capacity so that the grid circuit resonant frequency approaches or recedes from the anode frequency, whereby the anode current decreases or increases and the relay contact 76 is deviated to contact 78 or 79 to drive the motor in a direction which readjusts the resistance 64 to restore the relay contact to its neutral position. The motor drives a recorder and level indicator and an ammeter 63 in the neutralizing circuit indicates liquid level. The liquid level variable capacitance is replaceable by a similarly variable inductance, Fig. 2 (not shown). Hunting is prevented by an interrupter 85, 86 in the motor control circuit which is operated at timed intervals by cam 83. Specification 674,034 is referred to.