Patent GB-251387-A (GB)
Title: Improvements in automatic or semi-automatic telephone systems
IPC: H04M3/30
Filed: 1925-03-02
Abstract: 251,387. Standard Telephones & Cables, Ltd., and Gould, J. R. March 2, 1925. Automatic exchange systems. -In a test distributor the relapse of the dialling relay E releases a further sluggish relay TC, test relay G being connected to test wiper P<1> or P<2> when relay E falls back and disconnected on the relapse of relay TC. If the test connecter is busy, the test relay sends back busy tone as well as reversing the connections of the line relays L, A. If the line is busy the tone signal is not sent. During the busy condition the rotary magnet is disconnected to prevent any effect from further dialling. Operation of test distributor by impulses. When the test clerk plugs in, line relays L, A energize release relay B. Relay A repeats the thousands digit to the vertical magnet V, and on the relapse of series relay C (springs ON having changed over), repeats the hundreds digit to the rotary magnet R and relay E in parallel. Relay E energizes relay TC. Connector busy signal. At the end of the digit, relay E falls back sluggishly and if the connector is busy, relay G pulls up over the grounded test wiper P<2>, holds up the sluggish relay TC, sends back busy tone from BS and reverses the connections of relays L, A to give a lamp signal. Operation of test connector by impulses. When the connector becomes idle relay G falls back followed by the sluggish relay TC. Relay G is of high resistance to prevent the re-energization of the cut off relay of a busy line becoming idle while the line switch is being restored. If it is idle to begin with the relapse of relay TC follows that of relay E. In the interval between the relapse of relay G or E and that of relay TC, relay H pulls up sluggishly, locks itself up, grounds the wiper P<2> and switches over the test circuit to wiper P'. Relay A repeats the tens and units digits over the wires L-, L+. Line busy signal. If the line is busy, relay G pulls up over wiper P' when relay E falls back, holds up relay TC and reverses the connections of the relays L, A. The busy wire however is disconnected at H6. Testing. If the line is, or when it becomes idle, relay TC connects up the testing wipers T-, T+, and energizes the out off relay over L5 P<1>. To test the line apparatus from the subscriber's point of view the test clerk releases the cut off relay by grounding L- and disconnecting L+ whereupon relay L falls back but relays A, B hold up. The test connctor may be given further rotary steps by dialling, but if a line in another level is to be tested the test clerk grounds L+ and disconnects L-. Relays L, B hold up, but relay A falls back to release the line relay of the connector which then restores itself to normal. Relay A is then re-energized and the wanted number dialled. Release. Release may occur at any stage and follow the release of relay B by relays A, L. Relays E, TC pull up before relay B falls back and then fall back sluggishly. The release magnet RL is energized in series with a common alarm relay (not shown). Relay TC is sluggish enough to keep the wipers T-, T+ disconnected during the release, and relay E keeps relay G disconnected from the wiper P<2>.