Patent GB-241191-A (GB)
Title: Improvements in or relating to electrical indicating mechanism, more particularly for use with flow meters
IPC: G01F1/37
Filed: 1925-10-05
Abstract: 241,191. British Thomson-Houston Co., Ltd., (Assignees of Thompson, L. W.). Oct. 7, 1924, [Convention date]. Tell-tale apparatus.-In indicating apparatus, more particularly flow meters, the pressure difference created by a flow tube 26 in a conduit 27 is caused to vary the resistance of the secondary winding of a transformer, by submerging it to a greater or less extent in a conducting liquid in a container, and so vary the current in an indicating circuit to which the primary winding of the transformer is connected. A casing 1 is formed with walls 2, 3, the walls 3 being formed integral with a bottom plate 5, whilst the walls 2 project above the walls 3 and are provided with flanges 6 to support a cover 7. Pivotally mounted at 9' at the lower ends of arms 8 depending from one end of the cover 7 is an inverted bell 10, which is sealed by mercury 11 in the chamber 4, formed by the walls 2, 8, and serves to divide the casing into a leading pressure chamber 12 and trailing pressure chamber 13. These chambers communicate by pipes 24, 25 with the two sides of the pressure difference creating device 26. At the end of the casing 1 opposite to that at which the bell 10 is hinged is a well 14 containing a. sealing liquid 15. A sleeve 16, attached at its upper end to the bell 10, depends into the well 14 and carries at its lower end a knife edge bearing 18 on which is hinged the lower end of a rod 19. The rod 19 passes up through a sleeve 17 secured to the cover 7 and having its lower end positioned within sleeve 16, the rod 19 being connected at its upper end to one end of a lever 20 fulcrumed at 21 on a bracket 22 carried by the upper end of sleeve 17. The other end of the lever 20 is connected to a copper U-shaped strip 28 having its lower open end in a cup 29 supported on a post 30 and containing a conducting liquid, such as mercury. Supported on brackets 31 on the cup 29 is a laminated transformer core 32 comprising three legs, on the middle one of which is mounted the primary transformer winding 33. The arms of the strip 28 pass down on opposite sides of the winding 33 and, when their lower ends dip into the liquid in cup 29, a closed secondary winding is formed, the resistance' ot which decreases the further the arms are submerged. The primary winding 33 is connected to a source of alternating current supply 34; an indicating ammeter 37, curve drawing ammeter 38, integrating watt hour meter 39, fixed resistance 40 and adjustable resistance 41 being connected in the circuit. Rods 43, depending from a cross-arm 42 connected to lever 20 at its fulcrum point. carry adjustable counterbalancing weights 44, whilst lever 20 is also provided with an adjustable balancing weight 45. In use, the weight 45 is arranged on lever 20 so as to hold it horizontal, the rods 43 then being vertical. On a flow taking place in the conduit 27, the pressure difference created by flow tube 26 causes the left-hand end of bell 10 to be raised and lever 20 to be turned in a clockwise direction until the weights 44 balance the differential pressure applied to bell 10. The turning of the lever 20 causes the arms of the strip 28 to be immersed in the liquid in the cup 29 thereby closing the secondary winding of the transformer and causing a flow of current in the primary winding, the value of which increases as the resistance' of the secondary winding decreases. In a modified construction, Figs. 6 and 9, the strip 28 is replaced by a rectangular coil 46, the terminals 47 of which are connected to two conductors 48, 49 of suitable resistance material coiled one on each side of an insulating frame 50. The coil 46 surrounds the middle leg of the transformer core 32a, the primary winding being shown at 33<a>. On movement of the lever 20<a>, as before described, the conductors 48, 49, which form a resistance in circuit with the secondary winding 46, are lowered into the conducting liquid in the container 29<a>, the movement of the conductors 48, 49 in the liquid having the effect of gradually putting more or less of the resistance strips into the circuit. It is also stated that a single conductor only may be used.