Patent GB-559985-A (GB)
Title: Improvements relating to electrical apparatus for indicating liquid levels
IPC: G01F23/68
Filed: 1942-10-24
Abstract: 559,985. Liquid level indicating systems. EVERSHED & VIGNOLES, Ltd., and MARCHMENT, W. T. Oct. 24, 1942, No. 14960. [Class 40 (i)] A substantially cylindrical float of electrically conducting material is maintained in contact with one or more resistance elements by the tension of one or more flexible members wrapped around the float and anchored at the ends so that as the float rises and falls it rolls along the flexible members, the upper and lower portions of which coil on and uncoil from the float and vice versa. When a single resistance element is used, the part of the resistance above and below the float may be connected in series and shunt with the respective coils of a ratiometer. As shown, however, two resistance elements are tapped for operation of a three-coil resultant field receiver. The float and resistance assembly, Figs. 1 and 2, comprise coiled-wire resistance elements 1, 2 secured in a structure consisting of top and bottom members 4, 5 connected by rods 6, the resistances being tapped at four levels, as described later, at clamps 19 carried by one of the rods 6. Two flexible wires 10 for maintaining the float 7 in contact with the resistance elements are anchored to the lower member 5 and tensioned by springs (not shown) connected to the upper member, each wire being passed once around the float. The ends of resistance elements are sloped away from the wires to avoid undue stressing of the wires in the extreme positions of the float which comprises thin metal end sections 7a, Fig. 5, grooved at 12 for the wires and separated by an insulating central section 7b. The wires may be of thin piano wire or phosphor bronze and provide electrical connection to the float. The tapping clamps, Fig. 7, comprise a central portion 19a fixed to a rod 6 and carrying a tapping plate 21 on one or each side according to whether contact is required with one or each resistance element 1, 2. As shown, one plate 21 is connected to wire 20b running to the top member of the assembly, Figs. 1 and 2, and serving as the electrical lead. The clamp is completed by a pair of checks 19b. Other tapping leads are shown at 20. All electrical connections are taken to the top member which forms a terminal block. The circuits are shown in Fig. 9. D.C. is supplied to the float over the flexible guide wires 10, the float being represented by contacts 27, 28. The resistance elements 1, 2 are connected in series, at their upper ends with separate resistances 26 (shown also in Fig. 1) one fifth of the resistance of each element 1, 2. Resistance 1 is tapped at 1/5th, 3/5ths from the lower end, resistance 2 at 2/5, 3/5, 4/5ths, the tappings and end connections being interconnected as shown to provide for a 300 degree range on the resultant field receiver which may be biassed to take up an off-scale position if the supply of current to the resistances fails. In a modification, a single guide wire is used for the float which runs along conductor rails utilized for current supply to the float. Specification 512,975 is referred to. The Provisional Specification also describes (a) the flexible members as comprising bands or chains or wires of resistance material and (b) a modification in which an insulated float closes contacts at different levels to make tapping connections with a resistance element.