Patent GB-320938-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-07-26
Abstract: 320,938. Automatic Telephone Manufacturing Co., Ltd., Taylor, R., and Simpson, L. M. July 26, 1928. Automatic exchange systems.-In a final selector switch arranged to connect with groups of various sizes, the wipers test the lines in a second level if all lines in the first level are engaged and the group extends beyond the first level. In such circumstances cam springs make when the wipers step clear of the bank to complete a relay circuit which operates the release magnet circuit and completes a circuit through a resistance for the vertical magnet. The vertical magnet partly energizes in this circuit and operates immediately the rotary off normal springs make, thus preventing vertical release. The relay that initiates hunting is operated in the first place by a negative potential on the special test wiper and is subsequently energized by an earth condition, releasing when a free or a disconnected line is reached. The switch is provided with a double test bank wiped over by wipers 54 and 55 respectively. Single lines have no connection on the contact brushed by 55, whilst groups of lines have the contact of the first line connected to battery, the last line disconnected and the contacts of intermediate circuits joined to the corresponding contacts of the bank wiped by 54. The switch is operated in the usual way to step the wipers onto the contacts of the wanted line. Connection to single line. The relay G is connected through resistance 42 to wiper 54 and if the line is busy G attracts its light armature 26 to open the circuit of relay H, operating fully when C releases. Busy tone and flash is returned from 60 to the calling line whilst relay B is held during the flash periods by battery from 59. Had the line been free relay H would have operated (54, 6, 11, H, 26, 8) on the release of relay C and connected the line through. Relay E is operated at this stage and falls away after a slow release pause to connect ringing through relay F to the called line. The slow release period of E is sufficient to prevent premature tripping of the ringing. When the called party replies relay F operates and locks up at its lower armature in series with relav E and relav E switches the line through. Relay D operates to reverse the direction of the current in the calling line for metering, &c. 'This relay is disconnected at 50 until relay H operates to prevent movement during dialling. When the calling party clears, relays A and B release completing a circuit for relay Z to release the switch. Connection to auxiliary group. If the line tested is the first line of an auxiliary group battery would have been connected to wiper 55 and if the line had been busy relay HS would have operated after relay G had pulled up and before E released (8, HS, 21, 15, 38, 31, 55) completing a circuit at 34 for relav C and for the rotary magnet R to advance the wipers one step. During the switching movement G is held over its lower winding and 36 but HS releases when the wipers are centred on the next contact due to the breaking of interrupter springs 24. If this line is free G releases and H switches through as before but if the line is busy G is maintained by earth on 54 and HS re-operates from earth on 55 via front contacts of 15. Stepping continues until a free line is reached or until the last line of the group is tested when the disconnection of 55 prevents HS from re-operating and G connects busy tone as before mentioned. If the group extends to the next level HS and G both operate on the 10th contact to step the switch clear of the bank where cam springs S operate completing a circuit for relay HO which makes a circuit for Z to release the switch and for V to partially saturate through resistance 43 (V, 39, 32, 36, 43, 8). When the wipers have completed the rotary restoration springs NR close allowing V to operate and the vertical rotation of the switch is prevented. V steps the wipers up one step. Relay HC on operation broke the circuits of HS at 36 and 38 and this relay de-energized. When the vertical magnet operated, the circuit of HC was broken at 33 and after a pause HC released, completing a circuit for the upper winding of HS (24, 36, 32, NR, 8) which energized R to cut the wipers into the bank. Hunting takes place on this level as before until a free line or the last line of the group is reached. The automatic vertical step can be repeated if necessary. The rotary off normal and cam springs are preferably built in a single unit to' be operated by the same member in different positions as in Specification 321,985. Night service. If a line other than the first in the group is called, and the line is busy relay G will not operate until after relay C has released and consequently HS will not pull up and hunting will not take place. Attendants' supervisory signals. The lamp CSH lights when relays E and H are operated and relay D is back, that is after the line has switched through and before ringing has been connected, or if the connection is held by the calling party.