GB814523A - Improvements in means for determining the presence or absence of a body at a particular location - Google Patents

Abstract

814,523. Electric tests. BABCOCK & WILCOX Ltd. Aug. 30, 1955 [Aug. 30, 1954], No. 25108/54. Class 37. [Also in Group XL (c)] The height of a liquid or solid fluent material in a tank is controlled by means of a probe in the tank which constitutes the termination of a. line connected to a circuit which provides pulses of high-frequency current, the arrangement being such that contact of the material with the probe suppresses the pulses, a relay being so connected as to change its state according as the pulses are suppressed or not. As shown, an alternating voltage feeds triode 17 forming part of the oscillatory circuit and a further triode 15 through the winding of relay 9. The anode circuit of triode 17 contains tuned circuit 25, 27 and is coupled to a winding 29 in the cathode circuit to produce 30 megacycles per second oscillations during alternate half-cycles of the A.C. supply. The grids of triodes 15, 17 are coupled together and earthed through a circuit 43, 45 having a time constant of 0.005 seconds. When the circuit is oscillating a negative charge builds up across the circuit reducing the current through triode 15, thereby preventing relay 9 from energizing. The oscillator load is constituted by two parallel connected transmission lines 55, 57 which terminate in probes 63, 65 inside the tank. These probes constitute, with the conductive wall of the tank, capacitors. By adjustment of capacitor 27 the oscillation frequency is such that the transmission lines length will produce a phase shift which will tend to inhibit oscillation. In operation, when the level covers the upper probe 63, the oscillation will be inhibited, the current through relay 7 will increase and will connect the second transmission line in parallel by means of its contact 71. When the level falls below the lower probe, oscillations will recommence and probe 65 will be disconnected. Further contacts operated by relay 9 may be used to give visual warning if the level is above the upper or below the lower probe. Contacts may also be provided which control valves to cut off the flow of material if the level rises above probe 63 or to introduce material if the level falls below probe 65. The Specification describes in detail (Figs. 2 and 3, not shown) two suitable probe constructions and their mounting in the tank, one (Fig. 2) consisting of a steel rod passing through two frusto-conical porcelain insulators and the other of a mild steel probe passing through discshaped insulators. Channels are provided by which compressed air is forced into the tank around the probe so as to prevent material such as damp polarized coal from clinging to the rod.