Patent GB-274133-A (GB)
Title: Improvements relating to electric measuring instruments and relays of the induction type
IPC: G01R5/20
Filed: 1927-07-12
Abstract: 274,133. British Thomson-Houston Co., Ltd., (Assignees of Kinnard, I. F., and Pratt, W. H.). July 12, 1926, [Convention date]. Alternating-current relays.-An instrument for measuring the resistance or other characteristic of an alternating-current circuit has a pair of induction-meter elements co-operating with a movable member to produce thereon opposing torques proportional to the watts and to the square of the voltage of the circuit, the movable member being arranged to vary the ratio of the torques as it is moved, so as to give the instrument a deflection dependent upon the ratio of the watts to the square of the voltage. An instrument is shown for indicating and recording the flow of fluid in a conduit 26, the difference of pressure of which on opposite sides of a nozzle 27 causes a column of mercury to vary a resistance 32. An armature disc 12 is reversely acted upon by two induction-meter elements 10, 11. The element 10 is wound as usual with a pressure coil 15, connected across an alternating-current supply 33, and with a series coil 16 connected in series with the source 33 and with the resistance 32, and produces a driving torque on the disc 12 proportional to the product of the voltage and current and acting in the direction shown by the adjacent arrow. The element 11 is wound with a pressure coil 10, which also acts as the primary coil of a transformer having a secondary coil 20 in series with the winding 21 of the magnet 18. A resistance 22 may be included in the circuit in order to adjust the phase of the current in the coil 21 so that the flux produced thereby is in exact quadrature with that produced by the coil 19, and may have a zero temperature coefficient to reduce temperature errors. The element 11 produces a torque on the disc 12 proportional to the square of the voltage and acting in the direction shown by the adjacent arrow, i.e. opposite to that due to the element 10. The armature 12 is formed of two parts 23, 24 of irregular shape but keyed together to form a continuous circular balanced disc. The part 23 is of nickel-silver alloy or other high-resistance metal and the part 24 of copper or other low-resistance metal. The element 10 acts only on the low-resistance part 24 of the armature. The resistance of the part of the armature acted on by the element 11 varies with the position of the armature, which determines the width of the high-resistance part 23 between the magnets 17, 18. The torque due to the element 11 is therefore a function of the deflection. In the position of equilibrium the torques are equal and the deflection is a function of the ratio of the watts to the square of the voltage, i.e. to the conductance of the resistance 32. On the shaft 25 on which the armature is mounted is fixed a pointer 35 which carries a pen marking on a chart 37. The pointer may be made hollow to provide a capillarv passage for the recording liquid from an ink well 39. A tube 40 extends from the pointer into the ink well and may be enlarged at its lower end or carry a damping vane. The invention may be applied to other instruments and meter motors, and to induction relays.