Patent GB-418975-A (GB)
Title: Improvements in or relating to electric selective remote control systems
IPC: H04Q9/04
Filed: 1933-03-03
Abstract: 418,975. Distant - control systems. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET, Vasteras, Sweden. March 3, 1933, No. 6531. Convention date, March 5, 1932. [Class 40 (i).] In a system of electric control of selectors at a plurality of substations from a remote central station, impulses are reverted to the control station intermediate of the control impulses sent out from the control station to check the synchronous working of the selectors. The Figure shows diagrammatically the equipment at a control station S and two substations I, II connected over a common line circuit. To effect a desired selection at a substation, a corresponding button 6 is operated to mark a contact in the bank 1b of a step-by-step switch and open the normally closed circuit over relay coil 5s. De-energization of 5s energizes stepping magnet coil 1s over contacts 5a and self-interrupting contacts 1d. Operation of contacts 1d causes stepping of the switch until the marked contact is reached when relay coil 5s is again energized over button 6, lamp 7 and marked contact in bank 1b to open the driving circuit. During stepping, impulses are transmitted over the line circuit, by a wiper engaging contacts in bank 1a. Each impulse operates a polarized line relay 11s at the first substation, the line circuit terminating over the bank contacts 10a of substation switch and contact 11a. Upon operation of relay 11s, the short-circuit across station II is opened at contact 11a and the line circuit is extended to line relay 21s. Similar operations take place in the event of the provision in the line of more than two stations. The relays 11s, 21s operate the stepping magnets 10s, 20s which step forward the corresponding switches at the end of each transmitter impulse. At the end of each impulse the contacts 10d, 20d are mechanically operated by the switches and a series circuit is thereby closed over the line wire to transmit a checking impulse back to the control station. At the control station, a relay 2s energized simultaneously with the stepping magnet closes the checking circuit at contact 2a and a polarized relay coil 3s<1> is energized to close contacts 3a which are opened by the energization of relay coil 3s<2> at the termination of a step of the switch. Normally, the time between the opening of the contacts 3a by the switch and their closing by a checking impulse reverted from the substations is sufficiently short to prevent release of slow relay 4s. If, however, the operation of the substation switches is not synchronous, a checking impulse is not reverted and the relay 4 releases and opens at contact 4a the circuit of the relay 5s to permit continuous stepping of the switch. The switch mechanically operates contacts 1c to re-energize relay 4s on the final step. The transmitting switch thus sends out impulses to operate the receiver switches and in the final position of the transmitter switch a long impulse, due to a long contact, is sent to pull up slow relays such as 12s, 22s in the substations. In the event of one of the switches being out of synchronism, the transmitter continues to send out impulses to operate the receiver switches into their final positions where they wait due to the opening of magnet contacts such as 10b, 20b, until the lagging switch also moves into its final position. When the transmitter switch reaches its final position the long impulse is sent to operate relays 12s, 22s which at contacts 12a, 22a again operate the magnets 10s, 20s to initiate operation of the switches and open contacts 10c, 20c to allow a checking impulse to be reverted to the transmitter. Synchronism is thus again restored and the switches continue to operate until the selected position, as determined by the depressed button 6, is reached. A lamp 8 is flashed by magnet controlled contact 2d if the switches are in synchronism but remains dark if an out-of-synchronism condition exists. Groups of stations connected in independent line wires may be provided. Instead of D.C. impulses, high frequency A.C. impulses may be employed, the driving and checking impulses being of different frequencies. When A.C. impulses are employed the line wires may constitute power transmission lines, in which case the line short-circuiting arrangements at the receivers embody impedances which offer high resistance to power currents but low resistance to the checking impulses.