GB516990A - Improvements in or relating to teleprinter exchange systems - Google Patents

Abstract

516,990. Telegraph exchange systems. STANDARD TELEPHONES & CABLES. Ltd., and HYDE, G. A. M. July 15, 1938, No. 21079. [Class 40 (iii)] Means such as short-circuiting contacts mc are provided to prevent the printing of undesired characters by the supervisory signals in start-stop teleprinter exchange systems. A clearing signal comprising a long space therefore has the effect of starting the teleprinter shaft; if thereafter the teleprinter is not in the stop position when the motor stops, a letter will be printed when the motor subsequently starts. Dialling impulses produce similar errors. According to the invention these are obviated by preventing the teleprinter magnet TRM from acquiring the marking condition until the teleprinter reaches the stop position. Thus, the motor M at a subscriber's station is started when polarity is put on the line either by the receipt of an incoming call or in response to an outgoing call ; in either case relays P and K pull up. According to the invention the connections shown in broken lines are added ; these include the contacts mc, which shortcircuit the receiving magnet TRM and dialling contacts ONS1 until the teleprinter, on the occurrence of a call, reaches the stop position, when the contacts mc are opened mechanically and the receiver magnet TRM pulls up and stops the teleprinter. The short-circuit is thereafter broken by the armature x2 of relay X, which holds on during-normal signalling. During dialling, however, the locking circuit of this relay is broken, and the receiver magnet TRM and relay X are short-circuited at the offnormal contacts ONS1 and ONS2 respectively ; thus the dial impulses are unable to operate the teleprinter. In a modification, Fig. 2 (not shown), the invention is applied to that described in Specification 498,428, in which the release signal comprises a long space which has a delayed action. Contacts mc, wr2 (not shown), operated respectively by the teleprinter and by a long space constituting a release signal, or part of a signal for calling in the exchange operator, disable the teleprinter receiving magnet after a long space until the teleprinter reaches the stop position. The contacts mc may be controlled by the resetting magnet of the teleprinter.