GB1149827A - Improvements in or relating to liquid level sensing devices and liquid level indicators - Google Patents

Abstract

1,149,827. Liquid level indicators. ROSEMOUNT ENG. CO. Ltd. Feb.12, 1968 [March 10, 1967], No. 11343/67. Heading G1H. [Also in Division H1] A liquid level sensing device comprises a capsule 20 containing an electrically conducting liquid 21, a flexible support 26 of polymeric material for supporting the capsule 20 from a point electrical connections 28 extending into capsule 20, from the mount for the capsule, the connections being embedded in the polymeric material of the flexible support 26, the capsule 20 being arranged so that the electrical impedance between the connections thereto depends on the angle of tilt of the capsule and capsule 20 and support 26 being arranged so that the capsule is buoyant in a liquid to be sensed but is not buoyant in the air or other gas above the liquid. As shown the capsule has a pair of electrodes at each end and mercury 21 connects together one pair or the other pair depending on the angle of tilt. Capsule 20 is surrounded by expanded polystyrene 29 to give the required buoyancy. Support 26 comprises four copper strips 27, Fig. 2 (not shown) embedded between two layers of a halogenated polymer such as fluorinated ethylene polymer and the assembly of polystyrene 29 is heat-sealed with the polymer 30. A terminal block 33 is provided and a perforated guard tube 34. A number of capsules are mounted vertically beneath each other on a probe inserted from the top or bottom of a tank and the electrode inter -connected to provide an output in binary digital form depending on the liquid level, Fig. 3. The exhausts are shown in their lowest position. If a potential is applied to lead X, that potential will also appear on output leads A, B, C, D. As the liquid level rises, the lowest capsule floats and the output potential disappears from lead D. When the second capsule floats, the output potential is removed from lead C. When the next capsule floats the output potential will reappear on lead D. Thus the potential on leads A, B, C, D will be a reflected binary code in which the presence of the potential is zero and the absence of potential one. Instead of containing mercury the capsule may contain an electrolyte 53, Fig. 8 (not shown) the circuit being broken when an air bubble surrounds one of the electrodes. A changeover switch may be constructed by using a further electrode. A capsule may be used which instead of making and breaking a circuit changes the impedance between two electrodes. The lead wires are connected to thin film metal on metal oxide tracks 63, 64, Fig. 5 (not shown) fixed on to the inside of the capsule and these are bridged by a mercury globule so that the resistance depends on the position of a globule along the tracks as the capsule tilts.