Patent GB-231335-A (GB)
Title: Improvements in or relating to telephone systems employing selecting devices
IPC: H04Q3/00
Filed: 1924-04-26
Abstract: 231,335. Siemens Bros. & Co., Ltd., Patterson, W. G., and Christian, D. A. April 26, 1924. Addition to 203,759. Automatic and semi-automatic exchange systems.-The connector described in the parent Specification, in which a relay connected to a compound extra wiper causes the selector to hunt when set to the first line of a Private Branch Exchange group but not when set to a line other than the first, is modified to allow the extra wiper to be of simple type. First lines are marked in the extra bank by a direct ground, last lines and ordinary lines are left dead, and intermediate lines are grounded over a resistance Z large enough to prevent the hunting-controlling relay PR from energizing. On energizing, relay PR cuts in a second winding or short-circuits a resistance in its initial circuit to enable it to be held over the resistance Z. Arrangements are made to disconnect the busy wire during the reception of impulses in case the subscriber should dial while it is connected up. Operation for ordinary and intermediate lines. Line relay A and release relay B. pull up, and the tens digit is repeated to vertical magnet VM and series (relay C. Vertical springs k<1>, k<2>, change over and when relay C falls back at the end of the digit, relay G pulls up, and cuts in the rotary magnet RM, which responds to the units digit, after which relay C falls back and connects up the test relay H. Busy test and signal. If the line, is busy, relay H does not operate and owing to the changeover of rotary springs w<1> the relapse of relay G follows shortly on that of relay C. A short-circuit across winding 2 of relay F is thus removed and busy tone and flash are sent out from BBT and CI. Relay A is held over its winding 1 while battery is connected to the b-wire and over winding 2 while winding 1 is shunted by the low-resistance busy-transformers. Should the subscriber dial during the busy signal, a circuit, is made over a<1>, C (2), VM. The winding C (2) which is shortcuited except when relay F is operated is of highresistance and prevents the vertical magnet from operating, but relay C pulls up and disconnects the busy wire. Supply of ringing current. If the line is idle, relay H pulls up, and prevents the relapse of relay G, ringing current is sent out from RG over winding 1 of ring-tripping relay F and ring- ing signal is sent back from RS. When the called - party replies, relay F pulls up, removes a shortcircuit from its winding 2 to hold itself and completes the talking circuit. The energization of supervisory relay D reverses the current in the calling loop, and releases relay G to cut off the ringing signal. Release. When the calling party hangs up, relays A. B, H, F, D, fall back in succession and the release magnet MM is energized. If the called party hangs up first the relapse of relay D lights the lamp CSH. Operation for first lines of P.B.X. groups. If the first line is busy and relay H therefore fails to operate, relay PR pulls up to the direct ground on wiper D‹. cuts in its winding 2, and disconnects relay F. and when relay G falls back a circuit is made for the rotary magnet RM and series relay C over k<1>, pr<4>, g<2>, pr<2>. At the end of the stroke, contact rm is closed to energize relay G which releases the rotary magnet and relay C. The relapse of relay C releases relay G which, after an interval in which the line is tested, remakes the rotary circuit if necessary. When an idle line is found or when the last line of a group is reached, relay PR is disconnected (at h<6> or D‹) and ringing current or busy signal is sent as in the case of ordinary lines. According to the Provisional Specification the extra terminals may be situated in the same bank as the speaking and testing terminals.