Patent GB-684062-A (GB)
Title: Improvements in liquid level indicators
IPC: G01F23/24
Filed: 1951-03-09
Abstract: 684,062. Electro indicating systems. SOC. DE BREVETS POUR LES APPLICATIONS DE L'ELECTRONIQUE. March 9, 1951 [March 16, 1950], No. 5771/51. Class 40 (i) [Also in Group XXXVI] To indicate the liquid level in a tank T, a support S is driven by a follow-up motor 5 through shaft F and screw 3 to follow variations in the level, the direction of the motor drive being determined by two separate circuits, one circuit including a reference reactor (inductor or capacitor) 8 always immersed in the liquid and a similar reactor 1 mounted on the support so as normally to be immersed, and the second circuit including a reference reactor 9 always above the liquid and a similar reactor 2 carried by the support and also normally above the liquid. The two circuits C, Ca Fig. 4 are identical. In circuit C. for example, equal potentials are normally applied from an A.C. source 21 through the " measuring and reference capacitors 1, 8, to the grids of valves 22, 23 respectively connected to a normally blocked triode 25. Should the liquid level fall the dielectric of capacitor 1 is altered and the phases or tne grid voltages on triodes 22, 23 correspondingly altered to produce an output from triode 25 which is amplified at 36, detected at 37 and causes a normally blocked tube 40 to conduct which through a relay 42 actuates the motor to drive the support S in the follow up direction. The motor also drives a level indicator D1 Fig. 1 the dials of which may drive a further indicator 15 to 18 through Selsyns. The circuit Ca functions similarly to drive the motor when the liquid level rises. Transmitter construction. The capacitors 1, 2 may each comprise grid-electrodes 26. 27, Fig. 3, mounted on insulating supports 29 carried on the perforated base 28. Alternatively, one plate electrode 41, Figs. 6, 7 may have a plurality of metallic prongs 43 extending through an insulating plate 44 and an earthed screen 45 towards the second perforated electrode plate 47, the whole structure being held by insulated bolts. The two capacitors 1, 2 may be mounted within a fluid tight vertical insulating chamber 50, Fig. 8 mounted in the tank so that the electrodes do not contact with the liquid and the capacitance variation effect of the liquid may be enhanced by providing a float of dielectric material surrounding the chamber, Fig. 9 (not shown). The sensitivity of the Fig. 8 arrangement may be increased by surrounding the chamber 50 by a further insulated electrode Fig. 10 (not shown). Fig. 11 shows the two capacitors 1, 2 formed by electrode pairs 53-54, 55-56 adapted to be moved helically by operation of the screw 3 within a helical square slot 50a formed by the wall of the chamber. In this way the liquid dielectric outside the chamber 50 passes between the electrodes. The capacitors 1, 2 may alternatively consist of parallel plates 57-58, 59-60, Fig. 12 longitudinally slidable along radial guide slots 61, 62 in the tube 50. In another arrangement, Fig. 13, the two capacitors are located outside the tank the liquid level in which is communicated to a flat vertical tube t, the plates of the condensers being located on either side of tube t and driven simultaneously by screws 3a. In this case also the liquid passes between the electrodes. Figs. 14 to 16 (not shown) illustrate simple inductive reactor elements carried by the support S.