Patent GB-293027-A (GB)
Title: Improvements in and relating to means for indicating at a distance electrically
IPC: G08C15/10
Filed: 1928-06-19
Abstract: 293,027. British Thomson-Houston Co., Ltd., (Assignees of Fitzgerald, A. S.). July 1, 1927, [Convention date]. Tell-tale apparatus.- In a method of indicating at a distance the readings of a series of meters &c. 2 - - 6, the moving parts are associated with frequency-varying means, such as condensers, which are successively connected, as by a distributor 7, 7<1>, to an alternating current source 1 to control the frequency thereof, and at the indicating station a corresponding series of indicators 12 - - 16 is supplied in succession with currents having a frequency dependent on that of the source 1. The currents of variable frequency may be transmitted over wires to the distant station, or they may be caused to modulate a high-frequency current, as described in Specification 291,092. The distributors 7, 7<1>, 20. and 18, 21 are driven step by step by periodic interruptions of the carrier current, and are synchronized at the end of each cycle by a long interruption. The period of association of each meter with the line, and of the long interruption at the end of each cycle, is determined by the time of discharge of a condenser 31 in the grid circuit of a valve 29. and the period of the short interruptions is determined by a slow release relay 26. The operation in further detail is as follows.- At the beginning of each cycle, the relay 28 is energized over the distributor arm 20 and opens the keying circuit 34, 40 of the transmitter 1, and the relays 24, 25, 26 are de-energized owing to the negative charge on the grid of the valve 29. After a time determined by the discharge of condenser 31 through a resistance 30, the valve passes current and the relays 24, 25, 26 energize in succession, relay 25 closing the circuit of the motor magnet 22, which is opened shortly after by the slow-acting relay 26. The magnet 22 moves the distributor to its first contacts, connecting the condenser associated with meter 2 to the transmitter 1, thereby determining the frequency impressed on the line 10, the keying circuit 34, 40 being completed over contacts K<11>, K<1>. The relay 26 also connects battery 32 to condenser 31, thereloy making the grid of valve 29 negative and opening the circuits of relays 24, 25, 26. When the condenser 31 has discharged, relays 24, 25, 26 again energize, the motor magnet 22 moving the distributor to the next contacts. During the interval between the energization of relays 25, 26, the keying circuit is interrupted at both contacts K, K<1>, and a relay 52 at the indicating station causes the de-energization of relay 53 and a slow-release relay 54, thereby momentarily closing the circuit of the motor magnet 23 controlling the distributor 18, 21. The operation is repeated until the wiper 20 reaches one of the strapped contacts connected to a relay 27, which closes a self-interruption circuit for the motor magnet 22 and indirectly produces a long interruption of the carrier current, whereby the two distributors are returned to normal, thus ensuring synchronism at the commencement of each cycle.