GB317120A - Improvements in and relating to automatic and semi-automatic telephone systems - Google Patents

Abstract

317,120. Standard Telephones & Cables, Ltd., Wright, E. P. G., Baker, J. H. E., and Cameron, A. H. May 10, 1928. Automatic exchange systems.-A single-motion group selector controlled by a common marking switch has access to a number of groups in excess of ten. In the embodiment described, the selector has two sets of wipers and has access to 19 groups, 9 of which are marked by the control switch in response to a first digit other than 2, and the remaining 10 are marked in response to the first digit 2 followed by a second digit, the first digit 2 merely serving to connect up an alternative marking bank of the control switch. The set of wipers of the selector to be used is determined by whether the first digit other than 2 or the second digit if the first digit is 2 is odd or even. Operation when first digit is other than 2. When the selector is taken into use, relay KA energizes in series with relay D in the marking switch, and associates the common marking switch with the selector, extending the loop to the impulse relay A. Relay D removes its lower lowresistance winding from the test circuit to mark busy all the selectors associated with the marking switch. Relay A locks relay D and connects up relay C, and repeats dialled impulses to magnet SCDM, while as soon as the marking switch moves off-normal, a circuit is closed for the selector magnet SDM. Stopping relay H is connected to the control wipers CA, CB so that the selector cannot get ahead of the marking switch. At the end of the impulses, relay C (which was held at back contact 3 of A) relapses and shortcircuits contact 1 of H to allow hunting over the marked group. Relay H energizes when the marked group is reached, and when an idle line is found, test relay HA or HB (according as the dialled digit was odd or even) energizes and switches through. Relay KA falls back and the marking switch is restored to normal. Upon release, relay HA or HB relapses and completes the restoring circuit for magnet SDM. Operation when first digit is 2. In this case, relay F energizes over bank SC2 of the marking switch and locks when relay C falls back, and the selector continues to step until the normal position is reached, when relays H, I energize in series over wipers CA, CB in parallel. A restoring circuit is also closed for magnet SCDM, and in the normal position relay B energizes, locks and releases relays F, H, I. The marking ground is now connected to bank SC5, and in response to a second digit one of the remaining ten groups is marked as described above. Permanent loop. After a certain time, relays E, G become energized over a periodically earthed lead TP, and relay HA operates, releasing the marking switch and lighting an alarm lamp. The selector is released by means of key PGK. All trunks busy. If no idle line is found in the wanted group, the selector continues to step until the normal position is reached, when relays H, I energize in series, and busy tone is connected up.