374,432. Electric signalling systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool, RAYNER, T. R., 2, Stretton Avenue, Wallasey, Cheshire, BURNS, G. A., 4, Lucas Estate, Thomas Lane, Knotty Ash, and GUNNING, P. F., 10, Fairfield Street, both in Liverpool. March 7,1931, No. 7176. [Class 40 (i).] In an electrical distribution system in which a number of remote sub-stations are connected to intermediate stations which are connected to a control point, when apparatus at a remote station alters its condition, alternating current of a frequency characteristic of the remote station is transmitted to the intermediate station whence direct current signals are transmitted to the main station to indicate the remote station affected. Circuit-breakers are located at the intermediate stations and alteration in the condition of one of these is automatically notified to the control station whilst meter readings can also be transmitted. The locking relays at the intermediate point representative of the remote stations comprise wound permanent horseshoe magnets which can be reset from the main station. Telephone communication can be effected between the main and intermediate stations. General operation. A number of sub-stations, such as DSP1 .. DSP5, indicated by triangles on Fig. 10, are connected over party lines to intermediate points such as CLP1, CLP2, CLP3 whence circuits extend to the main station MS. As described a sub-station DSP1 sends an alternating current pulse of characteristic frequency to the station CLP1 which sends a train of impulses to the main station to alter the indicating apparatus thereat relative to DSP1. The indications for the circuit-breakers &c. at CLP1 are checked during this transmission. A maintenance engineer is despatched to DSP1 to correct the trouble and when an " all clear " signal is received; the main station operator selects the locking relay at CLP1 relative to DSP1 and restores it to its normal position. Meters at CLP1, which are of the type described in Specification 356,211, can be selected from MS and the reading is then transmitted to the main station. Construction of locking relay. The locking relays MLR, Fig. 7, comprise a permanent horseshoe magnet with windings on each leg. The energization of one coil assists the permanent magnetism of the magnet and the armature is attracted. The armature is held by the permanent magnetism, whilst energization of the other coil neutralizes the permanent magnetism and allows the armature to fall away. The two windings may be connected in series a shown at 1A, Fig. 1, the current being reversed in direction to effect the attraction and release of the armature. Transmission of signal to intermediate station. When apparatus at sub-station DSP1 alters its condition, current is connected to conductor 10 and relays G and A energize. Relays Band D pull up and relay G connects up the filament battery and the mains, which provide the high tension supply, to the voice frequency oscillating unit. When the oscillating unit becomes stabilized, relay S energizes completing the signalling circuit and breaking the circuit of B. Relays B and D fall away slowly in succession and when D has fully released, G is de-energized and S falls away. A pulse of 450 cycles, the characteristic frequency of the sub-station, is thus transmitted to the intermediate point for the period of the release of two slow relays. Other sub-stations on the same signalling circuit have characteristic frequencies of 250, 350, 600 and 800 cycles respectively. If electric means are not available the high tension supply may be generated by a small generator driven from the filament battery. Transmission of signal from the intermediate to the main station. The apparatus at the main station is indicated in Figs. 1, 5 and 6 whilst that at the sub-station is shown in Figs. 2, 3, 7 and 8. The incoming signal from the sub-station is received on transformer 1XFR and energizes the relay C connected in the plate circuit of the circuit tuned to 450 cycles. Relay CX is operated and the magnetic locking relay MLR attracts its armature. A circuit is thus completed for relay CH which energizes RSR, Fig. 2, and this latter relay shoots out the high resistance winding of CH to allow BRS to hunt for another position of equilibrium. The switch BRS serves one magnetic locking relav and three circuit breakers CBR1, CBR2, CBR3, the alteration in position of any one of which causes CH to energize. Relay SE pulls up and locks, CH relapses, CO energizes to prevent CH re-energizing, and relay E interacts with BSM to step BSS over its contacts and to impulse over the signalling conductors 14, 15. Relay RV is connected to wiper 2b of BSS and controls the direction of current flow to the main station. As the first terminal wiped by 2b is disconnected the first pulse delivered always energizes polarized relay O. Relay OUT pulls up and P energizes, completing a circuit for H which holds up during the train. CB energizes and locks, completing an interacting circuit for F, FR to provide pulsating current and a circuit to the alarms ALB, ALP. Relay P completes a circuit to magnet MRM so that when the pulse ceases and P falls away, switch MRS steps on to its next contact. On the second contact wiper 2b encounters positive so that RV energizes. The next pulse received at the main station therefore energizes I and IN pulls up. P operates to complete the circuit for MRM and as MRS is now connected with the indicator representing MLR, which has changed over, a circuit is completed over 2c for 1B. Relay 1B locks in series with Z and completes a circuit for magnetic locking relay 1A which pulls up in parallel with P. Lamp WSP, representing DSP1, is connected to pulsating current and flashes. When the pulse ceases MRS and BSS move on. The next contact of 2b connects with CBR1 and for this two lamps RIL, GOL, are provided at the main station. If CBR1 has altered since the last indication relays 2B and 2A, which are similar to 1B and 1A but are not shown, are energized to alter the lamp indication and connect the lamp to the pulsating current. If no change has taken place the lamps remain unaltered. A train of impulses is thus transmitted to the main station which checks the indicator positions relating to all apparatus and magnetic locking relays at the intermediate station. When the signalling cycle is completed MRS and BSS will be on their home positions, P remains de-energized for a prolonged period and H falls away. The alarms ALB, ALP remain in circuit however until the attendant operates key ARK to release CB. CB breaks the alarm circuits, releases FR and the operated B relays to change the flashing signals to steady glows. Automatic repeat after incorrect transmission. Should the switch MRS not be in its home position when the impulse transmission ceases, a circuit is completed on the release of H for 1CH. Relay 1CH completes a homing circuit for MRS and transmits a signal to the intermediate station to operate polarized relay 1A thereat. Relay 1A energizes CRM in series with 1G so that when 1CH falls away, on MRS homing, 1A releases and CRS moves into its second position. Relay 1G energized 1H and as no further pulse is received these relays fall away slowly in turn. When 1H has fully restored a circuit is completed over 1e of CRS for RSR which initiates the transmission of impulses as before described. The transmission of the signal back train can be initiated by the operation of CHK which energizes 1CH to reproduce the circuit operations just described. Telephone arrangements. To call the intermediate station from the main station ringing current is connected to conductors 16, 17. Relay. AC, which is a direct current relay bridged by a metal rectifier MRC, responds and energizes relay T which connects current to the signalling circuit to energize relay 1B at the intermediate station. High pass filter HPF prevents the ringing current from reaching the signalling conductors. At the intermediate station relay 1TC, Fig. 2, pulls up starting up the ring- ing generator over 18 and connecting conductors 19, 20, over which ringing current is fed, to the telephone set on 21, 22. Speech takes place over conductors 14, 15. To call the main station from the intermediate point, ringing current is connected to 21, 22 to energize 1AC and 1T pulls up to connect potential to 14, 15. At the main station 1 responds, followed by 1N and TC pulls up. Ringing on 23, 24 is connected over 16, 17 to operate the calling signal. Keys TCO and 1TCO are provided to extend the conductors to special telephones. The speech circuit is extended at springs TCO1 and 1TCO1 whilst springs TCO2 and 1TC02 enable special calling signals to be operated from the normal calling circuit. The calls are initiated by keys TCK and 1TCK at the main and intermediate stations respectively. Remote control of magnetic locking relays. The magnetic locking relays are reset from the main station. The relative key SLKl .. SLK23 is operated at the main station, removing potential from the relative contact of 1d of SLS and energizing KR and 1RV in parallel. KRX energizes and 1E and SLM interact to step SLS, the impulses being repeated to the intermediate station. After the first impulse, a circuit is completed over 3d and 1/ to MCM, and MCS steps round with SLS. At the intermediate station 1A responds and repeats the impulses to CRM which steps CRS. When wiper 1d reaches the marked contact, 1RV relapses and the next impulse is of reversed polarity, so that 1B responds and, as CRS is off normal, CCM instead of CRM is energized to step CCS. The release of 1RV breaks the circuit of MCM, so that MCS does not step and when 1RV reoperates on the next contact of 1d, the circuit of MCM is not again completed. The reoperation of 1RV restores the polarity in the signalling circuit and 1A responds, but as CCS is off normal the remaining impulses of the train are