Patent GB-195209-A (GB)
Abstract: 195,209. Western Electric Co., Ltd., and Deakin, G. Jan. 27, 1922. Manual exchange systems.-In establishing inter-exchange connections, an A-operator depresses a key OK<1> corresponding to the wanted exchange, whereupon switches OLS, JS select an idle trunk terminating at a B-operator's position at the distant exchange, and the number of the selected trunk is automatically indicated to the A-operator by lamps SL, JL. The A-operator inserts her plug in the jack JK of the trunk indicated, thus putting the calling subscriber into direct communication with the B- operator who completes the connection by means of the plug CP. The switch OLS comprises a number of brushes O<1> moving over separate levels, one level being assigned to each exchange, and the appropriate brush being connected up by a relay O'R in response to the depression of the key OK<1>. The switch JS is of similar construction, the outgoing trunks, however, from all the levels of the same switch leading to the same exchange. Provision is made by which any B-operator having a call in hand may receive one more (waiting) call, and then is marked busy; and any trunk which has been taken into use continues to be marked busy at its outgoing end until it has been released at both ends. The jacks JK of the outgoing trunks are arranged in numbered strips of 10 each, lamps SL connected up by brushes OL<1>, OL<2> indicating the number of the strip, whilst the lamps JL indicate the particular jack in that strip. Each set of lamps is arranged in two groups, corresponding to the even and odd-numbered strips respectively. Each trunk is provided with a relay OBR which remains energized as long as the trunk is in use. The various contacts operated by a relay are indicated in the drawing by small. letters a, b, &c., and are denoted in the following description by the designation of the relay followed by the appropriate small letter, for example, O<1>Ra indicates contact a controlled by relay O<1>R. In response to the depression of key OK<1>, relay O<1>R energizes over contacts OK<2>b, OSTRd, CRKRd to connect up the brush 0', light the lamp IPL<1> and energize the stepping magnet OS of the switch OLS. The terminals engaged by the brush O<1> lead over relays L<1>R and over parallel-connected back contacts of relays OBR of idle trunks to a front contact of a relay CAR<3>. When a B-operator's position is occupied, a key TJ is closed and relays CAR<2>, CAR<3> are energized as long as the position has not more than one call in hand. When wiper O<1>, therefore, reaches a terminal associated with a level of an idle switch JS which has access to an idle trunk at an available B-operator's position, test relay OSTR energizes in the circuit CRKRd, O<1>Ra, O<1>, L<1>R, CAR<3>c to break the circuit of the stepping magnet OS. Relay OSTR remains energized over this circuit until an idle trunk is selected unless, in the meantime, all the B- operator's positions accessible over the selected level become busy, in which case relay OSTR falls back, and magnet OS is energized again to re-start the switch OLS. Relay L'R energizes in series with relay OSTR to connect up the brush L<1> and to close the starting circuit for the stepping magnet JS<1> of the switch JS over contacts JRRf, JTRd which at present short-circuit relav JRR. When the wiper L<1> reaches a terminal corresponding to an idle trunk at an available B- operator's position, test relay JTR energizes in series with relay JHR and clcses the circuit of its low-resistance left-hand winding to mark the selected trunk busy. This busy condition may beremoved at will by means of common release key CRK which de-energizes relay CRKR and is employed in case of error. Relay JHR is connected in parallel with a non-inductive resistance and does not at first energize over the test circuit, but the decrease in resistance produced by the operation of the test relay causes this relay to energize and lock up, at the same time opening the circuit of the parallel resistance and so increasing the resistance of the test circuit that two relays JTR in parallel cannot simultaneously remain energized. Double connection is thus prevented. Relay JTR also removes the shortcircuit from high-resistance! relay JRR which now energizes in series with the stepping magnet JS<1> to prevent its furtlier operation and also energizes relays LH<1>R, LH<2>R which maintain the holding-circuit of relays OSTR, O<1>R.. L<1>R independently of relay CkR<3>, thus preventing premature release in case all the B-operator's positions become busy before the A-operator has time to insert her plug. Relay JRR also lights indicator lamps SL, JL. Upon the A-operator plugging into the indicated jack JK of the selected trunk, sleeve relay OAR energizes and locks up relay OBR to mark the trunk busy and also to break the holding circuit for relay JTR which deenergizes. Relay JRR is again short-circuited and extinguishes the lamps SL, JL and releases relays LH<1>R, LH<2>R which in turn cause relays OSTR, O<1>R, L'R to release and restore the switches OLS, JS to normal. The insertion of the plug also energizes relay BR at the B-operator's position to light the lamp CRL in series with relay CAR<1> which energizes to mark the pcsition busy. The B-operator throws her listening key LK, temporarily extinguishing lamp CRL and de-energizing relay CAR<1> so that the position may receive one more call, and, on learning the desired number, inserts the plug CP to complete the connection. Sleeve relay CT energizes over low resistance R<2> to disconnect permanently the relay CAR<1>. When the called subscriber replies, supervisory relay SR completes a short-circuit round the high-resistance lefthand winding of relav BR through the low-resistance left-hand winding of relay AR. The decreased resistance in the trunk circuit causes the supervisory relay at the A-operator's end to energize and extinguish the calling supervisory lamp. Relay AR energizes to extinguish lamp CRL and locks up. When the called subscriber hangs up, relay SR falls back and the increase of resistance in the trunk circuit causes the A-operator's supervisory lamp to light. When the A-operator removes the plug, relay OAR falls back, but relay OBR remains locked up to mark the trunk busy until the plug CP also is taken down. Relay BR also releases and the disconnect lamp DL lights up in series with relay CT. Upon the removal of the plug CP, relay CT falls back and completes a circuit for relay OCR which unlocks relay OBR and completes the release of the trunk. A supervisory lamp ABPL lights un when all the B-operators have. received one waiting call and the number of times this occurs may be registered on a meter ABSM.