GB750858A - Electronic level-sensitive apparatus - Google Patents

Abstract

750,858. Electric indicating systems. GILBERT & BARKER MANUFACTURING CO. April 1, 1954 [April 22, 1953], No. 9558/54. Class 40(1) [Also in Group XXXV] In order to indicate the level of a liquid, a wire 1. Fig. 9, mounted within a belltype shild 9 is suspended vertically with its end just immersed in the liquid. When out of contact with the liquid, wire 1 is arranged to be electrically resonant at the frequency of a high frequency thermionic valve oscillator 46 to which it is coupled through a screened feeder 41 and loops 35 and 50. The oscillator is modulated at 50 c/s by the output of a mains transformer 84 and the voltage developed in wire 1, which decreases owing to the dielectric effect of the liquid as the depth of immersion increases, is demodulated by a crystal diode rectifier 36 the 50 c/c output of which is transmitted through feeder 41 and conductor 68 to a thermionic valve amplifier 73. Amplifier 73 is associated with a 50 c/s supply from a mains transformer 97 so that for a given depth of immersion there is a zero output applied through a transformer 95 to one winding 103 of a two-phase servomotor 5. Deviation in either sense from this depth produces an output from the transformer 97 of the phase sense necessary to run servomotor 5 in the appropriate direction to operate a level indicator while moving wire 1 to maintain a constant depth of immersion. A weighted pulley tensioning device (Fig. 1, not shown) is arranged to take up any slack in feeder 41. The end of wire 1 may be bent to increase sensitivity and if the liquid is conductive the tip of wire 1 is insulated to prevent conduction effects.