464,109. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Hatton, W., and Lardot, C.) Oct. 11, 1935, Nos. 28128 and 32742. [Class 40 (iv)] In an electric signalling system, particularly a telephone system, employing A.C. for signalling, the A.C. is supplied to transmitting equipment (at a sub-station) over a simplex circuit on the line connecting it to receiving equipment (at an exchange). The A.C. so supplied may be used to transmit loop impulses. The invention is particularly applicable to coinbox systems by supplying A.G. ot several frequencies and selecting single or combination frequencies by means of coin contacts and filters for signalling coin values to the exchange. In such a system, a single frequency is supplied from the local exchange for calls thereto ; in the case of toll calls, however, the local A.C. supply is not connected, but A.C. of two frequencies which may be selected singly or in combination is supplied from the toll exchange which also automatically times the calls and signals the calling subscriber when further tariff payment is required, breaking down the call in the absence of such payment. Impulses of A.C. may also be transmitted under the control of fire or police alarm keys to call the desired station. The impulses set an auxiliary switch which may directly select the fire &c. station or may bring alternative call finders into operation. Multi-frequency signalling between a P.B.X. and main exchange may be controlled by keys and filters at the P.B.X. Signalling the insertion of coins at a prepayment substation. Coin - controlled contacts C 1-3, Fig. 1 (28128 /35) connect both sides of the line to earth either directly or through a circuit tuned to a frequency of 1000 or 150 cycles. Currents of these frequencies are supplied from the exchange through a transformer A. According to the contact closed, one or both frequencies pass to a receiving transformer B having a primary P connected to both sides to the line and two secondaries S1, S2 shunted by tuned circuits and controlling. relays R1, R2 through valves V1, V2. In the modification of Fig. 2 (28128 /35), the receiving transformer B has two primaries P one in each side of line and a single secondary S shunted by the tuned circuits in series. The valves V1, V2 may be replaced by rectifier bridges. A similar arrangement, Fig. 1 (32742/35) (not shown), is described for signalling between a P.B.X. and a main exchange employing four frequencies under the control of keys which connect earth to both sides of the junction through one or more tuned circuits. Alarm calling arrangement, Fig. 2 (32742 /35). Operation of a police alarm key closes contacts PC twice in succession, while operation of fire alarm key closes contacts FC three times in succession. A.C. is fed over the line from a transformer A when line relay SR pulls up, and the impulses produced by the alarm key pass through a receiving transformer B to relay BR which steps the switch S. If two impulses are received, relay P energizes, the switch S goes home, relay N pulls up and ringing current is applied to the police line PL. Upon reply, relay R responds and disconnects N to complete the connection. If three impulses are received, relay F energizes instead of P and connection is made to the fire office line FL. In the case of an ordinary call, one impulse is received from a coin-controlled contact CC and a circuit over CL allows the call to proceed in the ordinary manner. Signalling between a prepayment station CB, Fig. 1 (Comp.), a local exchange LC and a toll exchange TC. When a call is made, current of 50 cycles is applied to both sides of the line through a transformer ST. For a local call, contact 2 is operated by the coin as well as ca, cb. The 50-cycle current therefore passes through transformers TR, W and operates relay JR in a loop circuit. If a toll call is required, the subscriber dials a toll prefix and the call is extended to the toll exchange TC, where current of 50 and 100 cycles is applied through a transformer Y. Operation of contact 1, 2, or 3 by a coin allows 50 cycle current alone, 50 cycle and 100 cycle current or 100 cycle current alone to flow in the loop circuit to control relays Cn, Cnl. Modified alarm arrangements. Line relay L, Fig. 3 (Comp.) connects 50-cycle current to the simplex circuit. Operation of an alarm key closes a contact such as 2, Fig. 1 (Comp.) two or more times to send loop impulses to the exchange to step the switch ALS through relay S. At the end of this impulse train, relay J pulls up and connects up relay F in the finder individual to the alarm in question. Relay T energizes when the line is found, followed by B, C and A. The attendant is rung, and C falls back to complete the connection which is held under the control of the called attendant. If a malicious call is suspected, the attendant sends an impulse to feed relay S2 which leads to the lighting of lamp AL, and the calling party can be traced by means of jack AJ. If an alarm call comes in while the corresponding finder is in use, relay 0 energizes, since A is up, and an announcing device tells the calling party to wait. Ordinary local call from coin-box station. The calling line is connected by a finder F to the link circuit LC, Fig. 4 (Comp.) and a registercontroller RC is taken into use. In position 5 of the sequence switch R, 50-cycle current is connected to the simplex circuit through a transformer ST. The insertion of the coin for a local call closes contact 2, Fig. 1 (Comp.) and JR responds. Dialling takes place, and in position 7 of R a check is made that the money has been deposited. If it has not, JR is back and PG energizes and steps on the sequence switch. In passing from the ringing position 11 to the talking position 15, relay Cc energizes and connects up booster AC on lead B to operate the cashing-in magnet CIM, Fig. 1 (Comp.). The timing switch TA starts in position 15 and after six minutes closes a circuit for advancing the sequence switch R to position 16 in which the connection is broken and a tone is fed to the calling party. Toll call. The calling party dials 03 without inserting any coins. The first selector is set to a position in which contacts L10 are opened to prevent operation of PG and the call is extended to a cord circuit, Figs. 5 and 6 (Comp.), at a toll position. A cashing-in signal from the operator is received by relay Gt which connects up Cc. Sleeve relay Ta energizes and connects up Cw in series with Tb, To, whereupon Xr, Cr operate. The latter short-circuits Cw, allowing Tb, To to pull up, and starts the switch PF which associates the coin-control circuit, Figs. 7 and 8 (Comp.) with the cord circuit. Test relay Tr energizes, locks in series with Sh and connects up Ct, Cd. In the cord circuit, Er, Fr pull up, releasing Tr, Sh, followed by Se, Se1. Relay Df energizes over the b wire and connects up Rd, which bridges Sr, Sr1, across the incoming line. Calling lamp CL lights, ring-back tone being fed to the calling party, and the operator throws key LK, energizing Lr, Lr1, Dr, and Oh in the coin-control circuit. The operator asks the calling party what number he requires, instructs him to insert coins up to the appropriate value and throws key FK, which controls relay Fq to connect 50 and 100 cycle current to the a and b wires over transformer Y in the coin control circuit. Signals are returned over the loop circuit as the coins are inserted as in Fig. 1 (Comp.) and control relays Cn, Cn1, and an aggregate record is made on the switch SY. When Cn alone operates, the switch SX takes one step, whereupon the switch SY takes one step due to the relapse of Se. Relays Ip1, 2 send an impulse to advance the operator's money indicator MM and the switch SZ. When Cn, Cn1 both operate (4-unit coin), relay IF pulls up and releases Se, whereupon the switch SY advances 4 steps, when Se reoperates over a staggered cross-connection between wipers sya, sxc. Relay Ce pulls up, unlocking IF and SX advances into line with SY. The operator's indicator and SZ also advance 4 steps. If Cn1 alone operates (20-unit coin), relay 5F pulls up and SY takes 20 steps, Se being controlled over wipers sya, sxa. When the operator sees that the correct sum has been inserted, she plugs into an appropriate junction and sets up the connection by means of her keyset KS. Sleeve relay Or lights lamp SL, which is extinguished by the reply of the called party. Operation of key CK restores the money indicator and connects up Nr which starts a clock circuit CLC and energizes Ci in the coin control circuit. The switch SZ advances to a home position in which Ta, Tc pull up, and relays Ip1, 2 send impulses to step the switches SA, SZ together until the latter reaches a position marked over wipers syb, szb, when Se1 energizes. The switch SA therefore takes a number of steps arbitrarily related to the tariff. Relay Ra energizes and disconnects Tc, during the release of which Yr energizes and Tb, Fig. 5 (Comp.) releases, so that battery is connected over the test wire to operate Gt, Fig. 4 (Comp.) to send back the cashing-in signal. Relays Er, Fr fall back followed, on the restoration of key LK, by Lr, Lrl, leaving the cord circuit in the talking condition. The switches SX, SY, SZ go home and the coin control circuit is released. Should the calling party depress his switchhook while the money indicator is off normal, it is restored and lamp CL is flashed. Time control. The switch SB receives a stepping impulse every 10 seconds via Tr, and when it reaches its tenth position, the switch SC takes one step. After 2 minutes 40 seconds, a circuit is closed over wipers sbb, scb for Rc, which again associates a coin control circuit with the cord circuit. Relays Sr, Sr1 are connected to the incoming line as before, and Oh is connected to the outgoing junction, the talking circuit being maintained by Sc. Relay Cd renders the coin signalling equipment effective, and Ts energize