Patent GB-682242-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M3/32
Filed: 1949-07-25
Abstract: 682,242. Automatic exchange systems. DEHN, S. G. (Automatic Electric Laboratories, Inc.). July 25, 1949, No. 19525/49. Class 40 (iv). An attendant at a test desk connected to a busy line may connect a power source to the line to remove the busy condition (e.g. release the finder-selector link), but is automatically prevented from connecting the power source to an idle line. The test desk may be at an exchange remote from that to which the lines under test are connected. Connection of test desk to an idle subscriber's line. The test equipment is connectable by keys, such as key 160, Fig. 1, to trunks, e.g. C14 ... C17, each terminating in a test distributer, Fig. 2, in the same or another exchange. Operation of a key 160 brings up relays 125, 150 and a lamp 108 is lit. The impulsing relay 220 operates and relays 230, 230<SP>1</SP>, 240 prepare the distributer to receive the digits. At the end of the first digit, relay 240 releases to change over the impulsing circuit from the vertical magnet 248 to the rotary magnet 264. Relay 245 is operated for the duration of the second digit and on. release disconnects relay 230<SP>1</SP>. If the selected test connector 300, Fig. 3, is busy, the release of 230<SP>1</SP> is followed by the operation of relay 280 which reverts busy tone. If idle, the release of 230<SP>1</SP> is preceded by the operation of switching relay 290. The third and fourth digits are repeated by relay 220 over conductor C33 to the connector 300. During the fourth digit, relays 245, 280 pull up, and earth from the connector over conductor C34 energizes relay 265 which locks up to differentially energize the two windings of 270 to actuate contact 278. If the line 305, to which the connector is set, is free, relays 245, 265, 280 fall back and 270 operates completely. Relay 260 connects earth to conductor C35 and so energizes the cut-off relay 320 of the line 305, and relay 210 completes a metallic circuit from the test desk to line 305 and provides an alternative circuit for the impulsing relay 220 which is held over conductor C16 and the winding of 135. The normal tests may now be carried out. Resetting of connector. The testing equipment is somewhat similar to that of Specification 669,420 and as described therein the connector may be set to another line by dialling a further digit. In the present case, actuation of the off-normal dial contacts completes a circuit prepared by relay 135 to energize relays 130, 140 in series and to close an impulsing circuit over conductor C16 to the upper winding of relay 220. Connection of test desk to a busy subscriber's line. At the end of the fourth digit, test relay 250 is energized and shunts a resistance 256. Thus, when relay 270 is completely operated, relay 260 and a marginal relay 155 operate in series, the latter lighting a lamp 109 to indicate that line 305 is busy. Relay 210 pulls up but, owing to the operation of 250, the bridge 223, 224 in the talking circuit is not shunted. The attendant can now listen-in to the connection. If no conversation is present, a fault, e.g. as shown by X or Y, may be assumed, in which case the attendant throws a key 121 to connect a marginal relay 140 and relay 130 in series with a resistance 107. Relay 130 pulls up and relay 150 falls back to release 155, 260. Relay 240 operates. The release of 260 connects battery over the low resistance winding to shunt down the impulsing relay 340 of the finder-selector link 360 and to prevent line relay 310 operating when the cut-off relay 320 releases. The link 360 releases and removes the holding earth from the p-wire and relay 250 is de-energized to complete a circuit for the cut-off relay 320 and to disconnect the battery and earth from conductors C31, C32. The attendant restores the key 120, and relay 130 releases and 150 operates to energize relay 260 in series with the resistance 256. Relay 240 releases and the line is ready for testing. Should the battery and earth connected by the test distributer fail to shunt down relay 340 due to, e.g. a direct earth on one of the line wires, the current taken through the low resistance winding of relay 225 may become excessive. In this case, relay 225 operates to connect up its high resistance winding in place of the low resistance winding, thus limiting the current to a safe value. Setting up a connection over a subscriber's line by the test attendant. If, when the test connector 300 has been set to an idle line, e.g. 305, the attendant throws key 120, the operation is similar to that described above excepting that relay 310 operates and a finder-selector link is seized. Since relay 250 is back, there is a metallic connection from the dial 102 to the impulsing relay 340 of the finder-selector link, and so a connection may be set up. The finder-selector link is released by a key (not shown) in the dialling circuit.