Patent GB-649284-A (GB)
Title: Improvements in and relating to electrically controlled locks and switches
IPC: G07C9/00
Filed: 1948-04-13
Abstract: 649,284. Electrically controlled fastenings. CHURCHILL. A. April 13, 1948, No. 10214. [Class 44] '[Also in Groups XXXVIII and XL(c)] In an electrically controlled lock or switch, a master electro-magnetic switch or lock inserted in the power supply circuit is connected in series with a number of switches operated by corresponding relays, each of which is operated by an oscillator coupled to an absorption tuned circuit, the tuned circuits having differing frequencies, and comprising impedances, preferably capacitors, arranged to be readily connected in and disconnected from the circuits, the means effecting this connection and disconnection constituting a key, in the form of a plug, which enables the operating circuit of the lock or switch to be closed. The circuits may be arranged to give an alarm signal in case of any attempt to tamper with the lock &c. The installation comprises a number of valve oscillators a<1>, a<2>, &c., independently screened, and each of different frequency. Each oscillator circuit is coupled to an inductance c<1>, c<2> &c. adapted, when connected to a capacitor d<1> d<2> &c., to form an absorption circuit tuned to the frequency of the oscillator circuit, these capacitors being housed in a plug g constituting the operating key. Relays e<1>, e<2> &c. are included in the anode circuits of the oscillator valves, and the increases in the anode currents when the absorption circuits are brought into tune by insertion of the plug g causes contacts f<1>, f<2> to be closed. These contacts are in series and also in series with the spring-loaded electro-magnetically operated lock A. The plug g is inserted in a multiple socket housed in a metal case m outside the locked area, and having a lid m<1> secured by a lock n. A shortingt link d is provided in the key-plug g to cause the power supply circuit to be connected to the power pack i for the oscillators. A stepdown transformer q, permanently connected to the local supply mains r, has in its low tension secondary circuit a coil s, which on the closing of the circuit, through cables p, by the link d, closes contacts s<1> to complete the power supply to the power pack i. As shown, the lock bolt v is withdrawn against a spring w by a coil u when energized on the lifting of an armature t<1> . by current through the relays f<1>, f<2>, &c. A spring catch x is provided to hold the bolt retracted when rquired to be left unlocked. The plug may then be withdrawn, cutting off the power supply to the power pack. The system may be associated with a circuit arranged to give an alarm signal if the lock is tampered with. This circuit comprises a radio transmitter 13 and an audiosupply unit 14, radiating a warning through an aerial 15, the energy being supplied from the mains r through switches f<1>1, f<2>1 &c. on the relays e<1>, e<2> &c. These switches make contact while the valves oscillate, but as soon as the oscillations are quenched 'and the relays energized ,they are opened and the transmitter cut off from the mains. A key switch 1 is connected in series with a number of trip switches 2. with a reset test switch 3, which is bridged by an impulse switch 4, and with a coil 5 energized by the standing low tension supply from the secondary of the transformer q. The impulse coil 4 reconnects the circuit in case of temporary failure of main supply. Coil 5, which is only energized when switches 1, 2, 3 and 4 are all closed, i.e. when the system is set for warning operation, holds contacts 11 open, and contacts 12 (retaining contacts for the coil), closed. If then one or other of the trip switches 2 is opened, coil 5 is de-energized, and contacts 11 close, connecting coil s to the low tension supply, so closing contacts s<1> and connecting power pack i to the mains. The valves then oscillate, but since the key plug is not in position, the radio transmitter is started and gives the alarm. On the other hand, any movement of the bolt v caused by tampering with the lock closes contacts thereon which connect a coil 10 to the low tension supply, closing contacts 21 and so energizing coil s to connect power pack i to the mains, and, as before, giving the alarm signal.