Patent GB-877005-A (GB)
Title: Terminal control circuit
IPC: H04M1/65
Filed: 1958-10-08
Abstract: 877,005. Electric selective signalling systems. ROBSONIC NATIONAL INDUSTRIES CORPORATION. Oct. 8, 1958 [Oct. 23, 1957], No. 32091/58. Class 40 (1). [Also in Group XXXIX] In an arrangement for the remote control of apparatus over a transmission circuit also used for transmitting other signals, e.g. a subscriber's telephone line, the substation equipment includes a multi-position switch to which current is supplied in response to a calling (e.g. ringing) signal, and which is then advanced step-by-step, from its starting position to its final position in which it completes a circuit for the apparatus, in response to the application to the transmission circuit of a predetermined sequence of signal and nosignal conditions, each condition being present for a predetermined time. Operation in response to correct sequence.- Incoming ringing current operates R1 whereupon the uniselector SR is stepped from position 1 to position 2, R1 being thereupon disconnected from the line by means not shown. The sequence of incoming signals required to operate the apparatus consists of periods of sound and silent intervals, each of about three seconds duration. The sequence is predetermined by setting the coding selection switches 2 to 7 ; setting of a switch to its lower position requiring a period of sound at the relevant time, and to its upper position a period of silence. As shown, the required sequence is sound, silence, silence, sound, silence, sound. Incoming sound currents are fed via amplifier 6 to rectifier 8 and a delay network 9 and, after persisting for about half a second, fire the thyratron 12, the anode current of which operates relay R2 over bank B of the uniselector. With the coding switch 2 in its lower position a circuit is then completed from B+ over bank C, front R2, and back R3 to charge capacitor 23 via resistor 22. After about three seconds the tube 24 fires, thus operating R4 which energizes the stepping magnet SRM to step the uniselector to position 3. The stepping action opens the anode circuit of thyratron 12 whereupon R2, tube 24, and R4 are restored. With no incoming sound (silent period) a circuit is completed from B + over bank C, coding switch 3 in its upper position, back R2 and back R3 to charge capacitor 23, and after about three seconds relay R4 is operated as before and the uniselector steps to position 4. Operation continues in like manner, the reception of the correct sequence finally resulting in the circuit to the apparatus being completed over contact 8 of bank A. Operation in response to incorrect sequence.- Assuming that no sound is received with the relevant coding switch in its lower position, R2 remains unoperated and capacitor 35 is charged over back R2 after about two seconds. The next sound received results in the operation of R2, whereupon capacitor 35 discharges through R3 which operates. The contact of R3 is mechanically latched in the open position so that the charging circuit for capacitor 23 is opened and the uniselector cannot be stepped on. Relay R3 must be manually released and the uniselector restored to its initial position before the equipment may again be used. If a sound is received with the relevant coding switch in its upper position, R2 will be operated and will interrupt the charging circuit for capacitor 23 so that the uniselector cannot be stepped on.  Modified arrangement.-An arrangement is described with reference to Fig. 2 (not shown), in which provision is made of a homing circuit which operates after a delay of about 25 seconds to home the uniselector if it has been stopped in an intermediate position by an incorrect signal sequence. Relay R3 is not provided, the charging circuit of capacitor 23 being opened by incorrect operation or non-operation, respectively, of relay R2. The controlled apparatus may be a machine tool, a lighting installation, domestic electrical apparatus, or a telephone answering installation.