797,109. Electric selective signalling systems. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 20, 1955 [Dec. 30, 1954], No. 36436/55. Class 40 (1). Relates to selective signalling systems of the type wherein coded inpulses of predetermined frequencies are superimposed upon power lines for the selective control of the energization status of remote units of apparatus connected to the power lines, and consists of a control apparatus comprising means for producing coded impulses for the selection of the remote units to be operated and further means for producing a further impulse for controlling the energization status of the units selected. The apparatus includes programme means for automatically initiating the production of the several impulses at predetermined times or alternatively, the selection may be made by manual switches. A master clock is provided to control the operation of the programme means and determine the timing of the initiation of the impulses, and may also control a number of secondary clocks in a clock system. The selective response of the receiving units depends both on the frequency of the transmitted signal and upon the time characteristics of the impulses. Provision is made for controlling forty groups of units by forty channels A, B, C, and D, having frequencies of 3510, 4200, 5010 and 6000 c.p.s. respectively. The code consists of a " start " pulse followed by one or more group selection pulses, a final or " on " pulse determining the character of the control for the groups selected during that cycle. A complete - cycle of operation has a duration of 60 seconds. Automatic operation. The programme devices are stepped by minute clock impulses appearing across wires 50A, 50B, Fig. 2B, by the closure of master clock contacts 52 from the 56th to the 58th second of the previous cycle, to energize magnets 60 of the programme units. Assuming that an " on control is scheduled for the third group in channel " C " contacts 73, Fig. 3A, corresponding to the third group, contacts 83 and 84 corresponding to the " C " channel and contacts 88 for the " on " control are closed. Contacts 61 and 62 being closed for all automatic selections. For the first five seconds of every minute clock contacts 51, Fig. 2B, are closed to energize R23, thus completing a circuit from terminal 63, Fig. 3D, via cam contacts C15 (now closed), wire 64, closed contacts R2-4, R1-4, Fig. 3A, channel selection switch 2B, closed contact R23-1, contacts 61, 62, contacts 73, wire 73c, wire 73d, and contacts R3-6, Fig. 3B, to energize relays R3, R4, in parallel, the circuit being completed via contacts R27-1, R26-1, R25-1. Relay R3 and R4 are held over R3-8 and R4-8 and wire 67 is energized to supply potential to the programme unit after the " minute " impulse ceases and R23 releases. With line 67 energized and relay R23 still energized, potential is applied via plug wire 68a, contacts 88 and plug wire 88b, to wire 91 to energize relays R1 and R19 to 22, these relays being held over contact R1-1. With R1 energized relay R13 picks up and is held until C15 opens at the 59th second to disconnect all relays, When relay R23 releases, potential is applied via contacts R23-3, switches 83, 84, plug wires 83b, 84b to relays R15, R16 which are held in a similar way to R13. With R15 and R16 both energized a circuit is made for relay R7, which controls the transmission of the " C " frequency. When R13 picks up potential is applied to a synchronous motor SM to close cam contacts C in the correct sequence to produce impulses at the appropriate times in a cycle, C16 being closed for the remainder of the cycle to provide a hold circuit for SM. C14 closes to provide a three-second start impulse which energizes R11 via contact R7-11 to key the transmitters to apply an impulse of the " C " frequency to the line. Cam contacts C1 to C5 and C9 to C13 correspond to the ten groups on a channel and when cam contacts C3, corresponding to the third group of units, are closed for three seconds the keying relay R11 is operated via contacts R7-3. The final rotation of the cam-shaft closes contacts C6 to produce an " on " pulse, relay R11 being operated via contact R7-12. At the 56th second a clock impulse via 50A steps the programme units to energize R25, R26, R7, and thereby release R3 and R4. Upon the opening of C15 at the 59th second of the cycle the remaining relays release and motor SM stops when C16 opens at the 60th second. When the relay R11 is operated relay R34, Fig. 2C, is energized and applies potential to the oscillator, causing it to oscillate at a frequency of 5010 c.p.s. as determined by the addition of capacitors by contacts R34-A Similarly energization of R9, R10, or R12, will cause respective energization of R36, R33 or R35, and keying of the appropriate frequency. During the transmission of the group selection impulse, the operation of C3 causes energization of coil LP of a latch relay 123 arranged in a 4 Î 10 matrix, via wire 203, rectifier DD33, contacts R20-11 and R11-1 and contacts R31-1. The relay R31 is energized during transmission of any signal, via a cold cathode gas tube OA4G which is rendered conductive for the duration of any of the signal frequencies on the transmission line. Relay 123 operates a signal lamp LC-3, Fig. 2A, and relay R1 via contacts R1-6, causes the " on " signal lamp to light, thus indicating that the devices in the third code group on " C " channel are on. For an automatic " off " operation the programme unit is set so that one or more of the group contacts 71 to 80 and the appropriate channel selection contacts 83 and 84 are closed and the " on " contact 88 is left open. R2 is energized instead of R1 and no pulse is transmitted when C6 is operated. Manual operation. Assuming that the same control is to be effected as was described for the automatic operation the ganged switches 1A, 1B, Fig. 3D, 2A, Fig. 3B, and 2B, Fig. 3A, are set to position C, the group selection switch GRSW3 is put in the " on " position, and the circuit selection switch SWC-3 is put in the " on position. The manual start switch, Fig. 3D, is momentarily pressed to the " on " position to energize the " on " relay R1 through the now closed cam contacts C15. R1 is held over R1-1. R13 is energized to start the motor SM as before, and through cam contacts C8, which are closed for the first eight seconds of a cycle and contact " C " of channel selection switch 1A, energizes relay R17, which in turn energizes R15 and R16 to energize the relay R7 as before. Upon closure of C14 the three-second start impulse energizes R 11 and further rotation closes C3 to provide the group selection impulse through the manually closed switch GRSW3 and relay R11. Similarly closure of C6 energizes R11 to deliver the " on " pulse, each energization of R11 keying the transmitter as before. For a manually-initiated " off " operation the manual start switch is placed momentarily in the " off " position to energize relay R2, the other circuits being the same as for a manual " on " operation. The indicator circuits are the same as for automatic operation and in the "off" " condition appropriate latch tripping coils LT of the latch relays are operated to extinguish the corresponding lamps LA &c., Fig. 2A. Preventing incorrect code transmission. It is stated that in the minute impulsed time equipment used it is necessary to transmit a succession of rapid impulses during a portion of a predetermined minute of every hour so as to advance the secondary equipment to agreement with the master clock. Such rapid advance during a cycle of operation would produce a false code transmission and to obviate this difficulty, relays R25, R26 and R27 are connected in parallel with each of the programme unit advancing motors 59. Normally theenergization of these relays from the 56th to the 58th second of a cycle for a regular minute impulse releases R3 and R4, the last group selection impulse having been transmitted from the 50th to the 53rd second. If the programme units are slow when the rapid impulses are transmitted (during the 59th minute from the 10th to the 45th second) they will be advanced and relays R25, R26, R27 will be energized for the duration of the advance. If the station is on automatic operation R3 and R4 will release to prevent the transmission of all group selection impulses after the first so that subsequent. programmes advanced into position by the rapid operation will be ineffective to control impulses during the remainder of the cycle of the control station. During the remainder of the cycle R14 also is energized to isolate the group selection switches from wires 141 to 150. The circuit will not prevent the transmission of impulses during manual operation. Preventing manual operation during the course of an automatic operation and automatic operation during the course of a manual operation. During automatic operation, when R13 is energized the arm of the channel selection switch 1B is disconnected from lines 64 by R13-4 and this disconnects the manual start switch and also prevents the operation of an instantaneous signal switch 70, Fig. 3B. The channel selection switch 1A is also isolated by the opening of R3-11 and one or more of contacts R15-1, R16-1, R17-1 or R18-1. During manual operation once the manual start switch is operated, and R13 is energized, the switch is rendered inoperative for the rest of the cycle. The switch 1B is disconnected to prevent repositioning from having any effect on the channel selection relays for the remainder of the cycle. Automatic operation is prevented in that either R2-4 or R1-4 will be opened. Preventing interference between code control signals and clock control signals in a clock system. The secondary clocks are arranged to be responsive to signals of not less than seven seconds duration and the maximum code signal duration of four seconds has no effect on the clocks. A time signal i