Patent GB-311307-A (GB)
Title: Improvements in or relating to apparatus for indicating electrically the value of a quantity at a remote point
IPC: G01R17/08
Filed: 1928-02-09
Abstract: 311,307. General Electric Co., Ltd., and Garrard, C. C. Feb. 9, 1928. Tell-tale apparatus.-Relates to a system for indicating electrically at a station the value of a quantity at a remote point, in which the force exerted in an instrument by the quantity under measurement is balanced by a variable, force under the control of means at the station so that with the aid of a second instrument located at the station and adapted to be controlled simultaneously by the balancing force, the value under measurement may be repeated. As shown in Fig. 1, instruments 1, such as voltmeters, ammeters, power meters, &c. may be selectively associated with a pair of pilot wires 6, 7 by. switches 12, 13, 14 which are under the control of apparatus at the control station 11. The spindle of the instrument 1 carries a coil 3 which is under the control of a potentiometer 15 at the control station and is adapted to provide a force which balances the force acting on the instrument in order to restore the instrument to zero position. When it is desired to obtain the reading of the instrument 1, switch 12 is closed and a gradually increasing voltage is applied to the wires 6, 7 by means of the adjustable contact 17 of the potentiometer resistance 15 until the force generated by the coil 3 balances the force experienced by the instrument 1 and thus returns the instrument to zero position and closes contacts 4, 5 which connect the secondary winding 22 of a transformer to the pilot wire 7. Alternating current is thereby transmitted over the wire to operate a relay 27 which closes the following circuits (1) that of a brake magnet 50 which depresses the armatures 51 into engagement with a wheel 54 mounted on the shaft 43 of a moving coil instrument at the station 11 to lock the instrument in a position which is indicative of the value of the quantity being measured; (2) the circuit of a lamp 48 which illuminates a translucent screen 47 of the indicating pointer 45, Fig. 2; (3) the circuit of a relay 37 which completes a holding circuit for the lamp 48 and brake magnet 50 independently of the contact 28. These circuits are completed over contact bars 19, 20 and an auxiliary adjustable contact 18. After the necessary indication is obtained, the contacts 17, 18 are released and are thereby allowed to break contact with the potentiometer and bars 19, 20. The station 11 may be connected to a plurality of substations by different pairs of pilot wires and the indicating instrument at the station may be selectively associated with any pair of wires. Furthermore, a separate instrument for each quantity to be measured may be provided at the control station. The contacts 4, 5 of the measuring instrument may control a relay which applies the alternating current to the pilot wire. In a modified arrangement, a relay at the station 11 is operated by alternating current upon the occurrence of a balanced condition to connect an unbraked indicating instrument to the pilot wires. In a further modification the contacts 4, 5 are adapted, when balance is obtained, to intercept the balancing current in the pilot wires. This causes a continuous interruption of the line circuit and a vibration of the pointer of the indicating instrument at the station 11. The indicating instrument may be separately calibrated for giving the values of the different quantities corresponding to the several instruments at the substation. The Provisional Specification states that a bell or buzzer may be used to indicate the condition of balance.