Patent GB-549047-A (GB)
Title: Improvements in electrical signalling systems utilising trains of impulses for control purposes
IPC: H04Q3/00
Filed: 1941-04-28
Abstract: 549,047. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. T. April 28, 1941, No. 5514. [Class 40 (iv)] In a group or final selector, the end of a train of impulses is determined by a timing device, such as a condenser in association with a neon tube, which is started by the first impulse and is reset at the beginning of each succeeding impulse until, after the last impulse, its continued operation brings about a circuit change after a given time fixed by the slowest allowable impulsing speed. The usual dialling relay is not required, and the release relay is held positively during impulsing. In the group selector, Fig. 4, of the rectangular release type described in Specification 391,123, the charging circuit for the condenser QB is made at the first vertical step, and a discharge circuit is made at each relapse of line relay A until the consequential response of the vertical magnet VM. The striking voltage of the neon tube NT is reached after a continuous charging period of about 120 milliseconds, which added to the magnet operating time of say 20 milliseconds, gives a total period of about 140 milliseconds as the longest complete impulse that is permissible. The operation of change-over relay H in series with the tube NT therefore occurs about 140 milliseconds after the beginning of the last impulse. The rotary magnet RM steps in the usual manner, relay H being held over the test wiper as long as busy outlets are encountered. The relapse of H when an idle outlet is found connects up switching relay HR, which makes a fresh circuit for H. Release relay B which has so far been locked is shunted out when line relay A relapses, and H remains held over the test wiper. Release takes place by the resumption of the rotary movement. If all the outlets are busy, switchthrough occurs in the eleventh position which is wired back to line relay A and a busy signal is given, release being under the control of A. If the calling party hangs up before dialling, the wipers cut in on the first level since the relapse of A produces the same effect as an impulse, and release immediately follows switch-through. In the final selector, Fig. 5, of backward release type, the charging circuit of the condenser QA is made at the first vertical step as before and its discharge through the neon tube NT after the last impulse operates relay C which connects up change-over relay E. The latter opens the original charging circuit and prepares a fresh one which is completed at the first rotary step, and in due course, relay C operates a second time and locks for the remainder of the connection. The wanted line is tested before E falls back, and ringing takes place or a busy signal is given in the customary manner. Release relay B is locked except when C is up, and therefore should the calling party hang up without completing dialling, the operation of C which results from a spurious impulse brings about release. With the circuits shown, a minimum impulse break period is imposed by the operating time of the magnet, but this limitation may be removed if the reoperation of line relay A after it has once relapsed is made dependent on make contacts of the responding magnet. Specification 549,074 also is referred to.