Patent GB-858122-A (GB)
Title: Circuit closing and breaking arrangement for teleprinters
IPC: H04L12/12
Filed: 1957-02-28
Abstract: 858,122. Telegraph exchange systems. TESLA NARODNI PODNIK. Feb. 28, 1957 [Feb. 29, 1956], No. 6783/57. Class 40(3). A circuit arrangement for teleprinters, including polarized relay means by which the operative circuit of the teleprinter motor can be closed when the line to a connection is free, or opened when transmission is to be ended, is such that two such arrangements are utilized to effect the simultaneous starting or stopping of the motors of two directly connected teleprinters, and that the same circuit arrangement, apart from modified internal connections of the elements provided in said circuit arrangement, is employable as an individual teleprinter station connected to, and operating with a manual or automatic telegraph exchange. When the circuit is employed for the direct connection between subscribers a plug or switch connects terminals 6 and 7, 4 and 8 and 10<SP>1</SP>, 12<SP>1</SP>. The distant subscriber is called by depressing the calling key which at its contacts vt2 completes a circuit from the terminal of rectifier network # extending through the winding of a relay A at the distant station, operating a relay C which at contact c3 prepares a circuit equivalent to that effected by the closure of vt2 to operate the relays A at both stations. Operation of each relay A closes at contact a a circuit for a relay C which operates and at contact c2 closes a circuit for relay D from the terminals of the rectifier network α. At contacts dl, d2 of the relays D the motor M at each station is connected to the power supply. At contact c4 the signal circuit is completed, bypassing the resistor 10 K via contacts kt2, kt3, and the signal intensity, which can be varied by an adjustable resistor 3K2, can be checked by a millimeter MA normally short-circuited by contacts tl. When transmission has been completed, the connection is broken by operating a circuit-breaking key which opens contacts kt2, kt3, and at contacts kt4 a circuit is completed for relay B which at contacts b4, b5, reverses the direction of the current through the A relays which release. Relay C de-energizes followed by relay D, and at the opened contacts d1, d2 the motor M is disconnected. The released contact cl allows the calling operation to be effected if the contacts a, b of the teleprinter transmitter should accidentally be open. Operation when a subscriber is connected to a manual or automatic exchange. For an exchange connection, the terminals 7, 4 and 9, 11<SP>1</SP> are connected, and in the inoperative condition a small current flows through relays A, E and the lines to the exchange at which the calling circuit is not yet in operation. When the calling key is operated a circuit though contact vtl, terminals 9, 11<SP>1</SP> contacts kt4 and relay B is completed. Relay B operates, locks up over contact b2 and at contact b1 allows the line current to increase to effect the calling operation at the exchange. At a manual exchange the insertion of the answering plug reverses the line polarity so that relays A, C, D, operate in succession to switch in the motor. At an automatic exchange, the operation of a line finder effects a break in the line current and relay E falls off extinguishing lamp SL2 to provide an indication that dialling can commence. If the desired connection is free, the exchange apparatus reverses the polarity on the calling line so that relay A operates followed by relay C which at contacts cl, c4, completes the signalling circuit, and relay D which at contacts d1, d2 switches in the motor M. If the connection is to be broken before the exchange has answered, the circuit-breaking key is operated and contacts kt4 open the locking circuit of relay B which releases and cancels the calling condition at the exchange. For the release of the connection, the release key is operated and the opening of contacts ktl, kt2, kt3 operates the clearing lamp at a manual exchange so that the operator can remove the connecting plugs from the subscriber's jacks. At an automatic exchange the clearing signal operates the selectors to break the connection and reverse the line polarity, so that relay A releases followed by relays C, D. When a connection has been established but the motors are not running, visual signalling in the Morse code may be carried out by operation of the calling key controlling at contact vt2 the circuit of relay E which at contact e2 illuminates and cuts off the lamp SL2.