Patent GB-597873-A (GB)
Title: Improvements in or relating to electric indicating systems
IPC: G01B7/04
Filed: 1943-10-05
Abstract: 597,873. Electric gauging apparatus. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 5, 1943, No. 16303. Convention date, Oct. 5, 1942. [Class 40 (i)] Variations in the position of the edge of a moving strip 10 of electrical conducting material such as a strip of hot steel in a rolling mill are detected by a pair of narrowly-separated jets 11, 12 of water or other conducting fluid which are movable to and from the strip by a servomotor 17 and are maintained thereby in a neutral position such that the inner jet strikes the strip while the outer one just misses it. By the provision at the opposite edge of a similar pair of jets 43, 44, operated by a servomotor 45, a continuous indication of the width of the strip is obtained. The servomotor 17 is a direct current motor and a pair of rectifier valves 19, 20, connected back-to-back provide for the supply of pulses of unidirectional current of either polarity to its armature to determine the direction of rotation. If both valves are operative, the forward and reverse torques balance and the motor remains stationary. The supply of A.C. to the valves 19, 20 is dependent on the condition of a corresponding pair of grid-controlled discharge-tubes 26, 27, the control grid of 26 being biassed negatively with respect to the cathode through a high resistance 33 and that of 27 being biassed positively through a high resistance 39. In addition, the control grids are connected respectively to the two liquid jets 11, 12 and the movable strip 10 is connected to the midpoint of the battery 34, the cathode tappings either side of this point. When, as shown, neither of the jets strikes the strip, the tube 27 is conductive and the motor 17 rotates to drive the jets inwardly. When the inner jet 11 strikes the strip, the control grid of 26 becomes positive and that tube also becomes conductive and the motor stops. Should the position of the edge of the strip change so that both jets strike the strip, the tube 27 ceases to conduct since its control grid becomes negative with respect to the cathode, and the motor rotates in the opposite direction to move the jets outwardly. Similar apparatus indicated at 48 controls the motor 45 driving the jets 43, 44. To compensate for any changes in the resistances of the jets, each of the resistances 33, 39 may be formed by the volume of liquid between two metal inserts 72, 73 in the rubber tube 74 through which the liquid flows to the associated jet. For indicating variations in the width of the strip, a selsyn system comprising transmitters 50, 51, 52 and a receiver 53 is employed. The rotors of 50, 52 are driven by the motors 45, 17 respectively, the stator winding of 50, 52 are connected respectively to the stator and rotor windings of 52, and the rotor windings of 52 are connected to the stator windings of 53. If the rotor of 51 is restrained therefore, the rotor of 53 rotates by an amount equal to the algebraic sum of the motions of the rotors of 50, 52 and controls an indicator 63 accordingly. In practice, the rotor of 51 is set by a knob 62a for a standard width, which is shown on an indicator 62 and the movements of the indicator 63 on either side of the zero then show the departures from standard as the strip passes through the mill. Glow tubes 64, 65 are connected across the armatures of the motors for indicating to an observer when the jets are in motion. Duplicate indicating units may be provided at remote points, as shown.