Patent GB-339234-A (GB)
IPC: H04M11/00
Filed: 1930-05-29
Abstract: 339,234. British Thomson-Houston Co., Ltd., (Assignees of Fitzgerald, A. S.). May 29, 1929, [Convention date]. Tell-tale apparatus. - An electric signalling system, particularly suitable for reading meters at a remote station, comprises a movable object adapted to assume any one of a number of different selected positions, a selective frequency-responsive device for each position, means at a remote point for transmitting currents of different frequencies to these devices, and means responsive to the position of the object and the operation of the device corresponding to that position, for sending a signal to the remote station. In the construction shown, apparatus at the central station and a meter at a remote station are connected through the existing telephone circuit. The apparatus at the central station comprises an audio-frequency generator employing thermionic valves and adapted to transmit currents of different frequencies over the circuit 11 to the telephone exchange and thence to any one of a number of stations, each equipped with a meter 13. Each meter is provided with differently-tuned reeds 14 associated with the meter dials, one reed for each graduation. The reeds are carried by four members 37, corresponding to the four dials shown, and secured to a core 36 which is supported on springs 45. The core is located within a coil 35 and between permanent magnets 47, 48, whereby it is caused to vibrate in response to different currents through the coil, and thereby each reed can vibrate responsive to its selected frequency. Each meter dial pointer is connected through a forked arm 39<a> with a shaft 38 carrying ten contact fingers 38<a> corresponding to the ten indications on the dial, and spaced so that as the pointer indicates successively the different numbers on the dial each finger in turn comes opposite a reed 14. Contact between a reed and a finger only takes place when the reed is vibrating. Such contact shortcircuits the coil 35 and causes a sharp click to be heard in a telephone receiver 40 connected through a transformer to the line 24. The apparatus at the central station for transmitting different frequency currents to cause the vibration of the different reeds 14 comprises a fixed oscillator 30, Fig. 2, a variable oscillator 31, a beat oscillator 32 and an amplifier 33 feeding the output circuit through switch 19. Four variable condensers 20 - - 23 provided with dials shown in Fig. 1, correspond, respectively, to the four meter dials. The arrangement is such that when the apparatus is calibrated, operation of a pointer to indicate a number on one of the dials at the central station, for example, the thousands dial, causes vibration of a reed corresponding to the same number on the thousands dial at the meter. To calibrate the apparatus switch 19 is operated to connect the output circuit to a reed 25 tuned to vibrate at a predetermined frequency, and switch 17 is operated to connect variable condenser 23 in parallel with condenser 18, and with the pointer of dial 23 at zero. Condenser 18 is then varied to set reed 25 into vibration. The operator at the central station then in succession turns each of the dials associated with the condensers 20 - - 23 until he hears a click in the telephone receiver, the positions reached indicating the meter reading.