266,026. Standard Telephones & Cables, Ltd., Baker, J. H. E., and Hardwick, J. R. Nov. 4, 1925. Semi-automatic and manual exchange systems; metering; coin and check-freed systems.-In a system in which calls for a manual exchange are made over automatic switching apparatus to a two-wire junction leading to an operator's position, a relay group at the outgoing end of the junction in response to a decrease in the resistance of a forward loop across the incoming end effects the application of booster current to the release wire to initiate metering. The decrease in the loop resistance which is brought about by - shunting a low-resistance winding of a relay across a bridged high-resistance winding of the same relay, causes the response of a marginal relay at the outgoing end of the junction. The booster battery is momentarily applied once only during the progress of a call, ground being maintained on the release wire to mark the junction busy until the calling party has hung up and the operator has taken down the connection at her end. The operator is provided with means whereby she may prevent automatic metering and ticket the call in the case of calls to distant exchanges. A drawing accompanies each of the five provisional Specifications, and for convenience in abridging these drawings have been indicated Figs. 1 to 5 respectively. Fig. 1 shows a repeater and an associated relay group at the outgoing end of a junction which terminates in an operator's cord circuit, Fig. 2. Fig. 4 shows a modified repeater which operates similarly to that shown in Fig. 1, with the exception that release of the automatic part of the connection is under the control of the operator instead of the calling party. In Fig. 5 is illustrated a modified cord circuit for use in a coin-box system. Calls are automatically metered as before to provide a check on the contents of the coin-boxes. In the modification shown in Fig. 3, the incoming junction terminates in a jack at the operator's position and the operator uses an independent cord circuit. This arrangement may be used with the outgoing repeaters shown in Fig. 1 or Fig, 4. System using the repeater, Fig. 1, and the cord circuit, Fig. 2. When the junction shown in Fig. 1 is seized over an automatic switch train, the line relay A energizes relay B. which grounds the release wire RT, connects a tone signal to the upper speaking conductor, connects earth over relay D and battery over the lower winding of relay C to the lower and upper outgoing conductors respectively, and energizes a relay F. A circuit is completed over the lower conductor for relays D, Fig. 1, A, M, Fig. 2, but only the relay A responds and energizes relay AA which lights a calling lamp at the operator's position over wire LC. The operator throws her talking key T, thereby connecting up her talking set over wires T1, T2, and energizing a relay B. which locks up and connects the high-resistance lower winding of relav A across the incoming junction. The relay C, Fig. 1, now responds and cuts off the tone to the calling party, who states his requiremenfs. The operator tests with the tip of the plug which is connected to the third wire T3 of her set, and plugs into the wanted line jack. The substation circuits are so arranged that both speaking conductors are grounded at switch-hook contacts when the receiver is on its hook. The relay D, Fig. 2, is therefore energized over one conductor and its lower winding but only actuated its armatures 5 and 8, closing a circuit for a relay 5 over the grounded sleeve. Relay S locks up, disconnects the calling lamp, and connects the plug tip to the upper winding of relay D. which now operates fully. If the call is a local one the operator presses the ringing key RS and erergizes a relay F, which locks independently of the key and connects ringing current over the leads RG1, RG2 to the wanted party. If the calling party restores during ringing, relays A, B. Fig. 1, and A, AA, B, F, Fig. 2, relapse and ring- ing is cut off. When the called party answers. ground is removed from the speaking wires at the substation, the relay D relapses, and the ringing relay F is de-energized. If the call is to be metered in the automatic exchange, the talking key T is released when the plug is inserted so that between the relapse of relays D, F, the relay M is energized over its lower winding and contacts T7, 8, energizes a position meter over the wire MW, and shunts the upper low-resistance winding across the lower winding of relay A. Relay D, Fig. 1, now responds, and opens the circuit of slow-release relay F. during the relapse of which booster battery lead BB is momentarily connected to the release wire RT. When relay F has fallen away, ground is again applied to the wire RT at armature 6 and a relay F energizes, locks to the release wire, and disconnects the booster battery lead BB for the remainder of the call. If the operator does not wish the call to be metered in the automatic exchange, she plugs in with the key T thrown, thereby preventing the energization of the metering relay M. If the call is to another exchange, the operator plugs in with the key T thrown and does not press the key RS, so that no metering or ringing is done, the call being ticketed by the operator. Resuming the description of a local call, the relapse of relay D, Fig. 2, closes a circuit for the upper winding of relay DA which only operates its armature 5 : the talking circuit is now complete. Should the calling -party hang up first, relays A, B, Fig. 1, are de-energized, but between their relapse relay F is momentarily energized and removes ground from the release wire RT for a short interval to restore the automatic switches. The opening of the loop to the operator's position de-energizes relays A, AA, Fig. 2, and a circuit is closed over wire LC for the calling lamp, but until the operator takes down, relay S maintains a ground on the upper conductor to hold relay C, Fig. 1, which in turn holds ground on the release wire RT over armatures 6, 7 and 5 of relays F, C, and B respectively. These circuits obtain to hold the junction if the operator plugs in to ring a subscriber when no call has come in over the junction. If the called party hangs up first, the replacement of ground on both speaking wires at the switch-hook causes relay D, Fig. 2, to operate and close a circuit for both windings of relay DA, which now operates fully and lights a clearing lamp over lead LS. When the operator takes down the plug, relays D, S, M, Fig. 2, and C, D, Fig. 1, de-energize, but the junction remains guarded by ground applied to the wire RT over armature 5 of relay B, Fig. 1, until the calling party restores. Modified outgoing repeater, Fig. 4. This operates in the same manner as that described with reference to Fig. 1 with the exception that the release of the automatic switch train does not take place until the operator takes down the calling plug; this permits a calling party to recall' the operator by vibrating his switch-hook. When the calling party hangs up, relays A, B, D relapse and the loop to the operator's position is opened, thereby giving a signal and causing ground to be returned over the upper conductor as previously described to hold relay C, which is rendered slow-to-release by its lower winding- having been short-circuited by the relapse of relay A, and holds the release wire RT grounded. If the calling party again removes his receiver the circuits revert to their former condition with relays A, B, D energized, the release wire grounded over armatures 8, 9, and the operator's supervisory lamp extinguished. Metering does not again take place between the energization of relay D and the relapse of relay F, since booster battery BB on the release wire is replaced by earth by relay E, which remains locked to the release wire. When the operator takes down her plug after the calling party has hung up, relay C falls away and removes ground from the release wire at armature 5. Modified cord circuit, Fig. 5, for calls from coin-box substations. On the junction being taken into use over a relay group as illustrated in Fig. 1, when the relays C, D, Fig. 1, are connected up the relay A, Fig. 5, energizes over its upper winding and the speaking wires and energizes relay AA to light a calling lamp over lead CL. The operator throws keys LBK to connect her head-set across the calling line, ascertains the wanted number, and plugs into the multiple, causing the energization of relays D, S over the ring and sleeve contacts, the speaking wires being grounded at the switch-hook as before. Relay S locks up and shunts the lower winding of the relay A around its upper winding, causing the call to be metered as before to provide a check upon the contents of the coin-box. It also connects to the tip contact the upper winding of relay D which now operates fully and energizes relay B. If the call is a local one, the operator presses her ringing key RSK to energize relay F and ring the wanted party. When the called party replies, the removal of ground from the speaking wires at the substation, causes the relapse of relay D which de-energizes ringing relay F and relay B, grounds the position meter wire MW, and operates relay DA half-way over its upper winding. The operator can now converse with the wanted party by throwing key LFK which at the same time opens the talking circuit back to the calling party. By throwing key LBK the operator can again talk to the calling party and collect the fee. When both keys LBK, LFK are restored, the two parties can converse and by pressing key MK the operator may listen in without disturbing the connection. On the called party hanging up, relay D will re-energize and cause relay DA to operate fully and light a supervisory lamp over wire SL. If the calling subscriber hangs up first, relays A, AA relapse and the calling lamp is lighted over