Patent GB-213676-A (GB)
Abstract: 213,676. Relay Automatic Telephone Co., Ltd., and Johnson, B. B. Jan. 5, 1923. Automatic and semi-automatic exchange systems; metering.-Metering is effected by the discharge of a condenser which is charged during conversation. The condenser MC, Fig. 2, is connected up upon energization of the feed relay B<1>, and is discharged through a relay ME when the line relay A falls back upon release. In the case of a toll call set up by an operator, a relay MCO is energized to open the charging circuit and prevent metering, and this relay also acts to maintain the connection after the calling subscriber hangs up until the operator clears. In the case of all calls made through an operator, means are provided whereby the junction tests busy until the operator clears. If the operator extends the call to a busy back device, the condenser MC is insufficiently charged to effect metering. The system described is of the type described in Specification 213,678, in which distinctive potentials are placed on the a and b wires according to the nature or condition of the wanted line to control the subsequent operations. Call to automatic subscriber. When an idle feed relay group is seized, the line relay A, Fig. 2, operates and connects up relays G, GX, establishing a holding circuit 3 over relays CO, LC, LB, OTC, Fig. 1, differential relay R and resistance HR. Relav R is balanced and does not operate, nor does the meter magnet SM in parallel with relay CO. Relay GX also energizes relays IC, BB and closes a circuit 12 which initiates the operation of an idle impulse recorder (not shown). Relay IC releases relay A and substitutes the impulse relay I, and the recorder operates to mark the wanted line. If the line is busy or is unassigned, a distinctive signal is sent back as described in Specification 213,678, over contact bb or nu of relay BB. If the line is idle, relays IS, ICO become energized and relay BB short-circuited by earth on the b wire, so that feed relay B<2> energizes, releasing relay IC, switching through the connection and substituting relay A for relay 1. When the called subscriber replies, feed relays B<1>. B<2> are energized over his loop, and condenser MC is connected up over circuit 10 and charges during conversation. Upon release, relay A falls back and condenser MC discharges through a relay ME in circuit 10', while relays G, GX relapse, short-circuiting resistance HR. Relay ME locks, and meter magnet SM operates over circuits 3<1>, 3 and shunts one winding to unbalance relay R, which operates and releases relay ME, breaking circuit 3. Call to a manual subscriber by dialling special number, e.g. 0. The b wire is earthed as in the case of a call to an automatic subscriber. When the recorder marks out, relays OTM, Fig. 3, and JM, Fig. 4, energize, connecting up relay OLM which closes the test circuit 11 over relay GS, which energizes and operates relay SS. Circuit 11<1> is thus closed for relay OJM which marks out the junction. Relays OLC, OJC energize over circuit 12 and operate relay OJH over circuit 13, whereupon relay OJB energizes and marks the junction busy by opening the test circuit 11. Relays GS, OJM, SS release, and relays JM, OTM fall back upon release of the recorder. The operator's line relay OLE energizes and lights the calling lamp CL. When the connection is completed by the operator, feed relays CB', CB<2> energize over the called subscriber's loop, short-circuiting a resistance JBR, so that relay B<1> energizes in series with relay A<2> and condenser MC is charged as before. If the called line is busy, the operator plugs into a busy-back jack, and relay B<1> is only energized momentarily so that condenser MC is not charged sufficiently to effect metering. If the calling subscriber hangs up first, when relay GX opens circuit 13, relay OJH, Fig. 4, falls back, but the junction continues to test busy since relay OJB holds over circuit 16 in series with relay A<2> and resistance JBR. Toll call by dialling special number, e.g. 9. Battery is connected to the a wire and earth to the b wire, so that relays IC, ICO, B<1> are operative at the same time and relay MCO energizes, locks and opens circuit 10 to prevent charging of condenser MC. When the calling subscriber hangs up, the connection is maintained since relay G is held over contacts of relays MCO, B<1>, and the junction tests busy until the operator clears.