GB1446170A - Locking system - Google Patents

Abstract

1446170 Locks AERONAUTICAL & GENERAL INSTRUMENTS Ltd 6 Nov 1973 [6 Nov 1972] 51179/72 Heading E2A A locking system comprises a key device which comprises at least one impedance, circuitry into which the key device is insertable, the circuitry comprising at least one variable impedance, a locking device and means for releasing the locking device when the at least one variable impedance is correctly set to a value or values having a predetermined relationship with the value or values of the at least one impedance in the key device when the device is in the circuit. As shown in Fig. 1, a bridge with fixed resistors R 1 R 2 in two arms and a, fixed resistor R 3 and variable resistor R 4 in the other two arms has a current source across the bridge and terminals 1 to which the key device 8 is connected. When the variable resistor R 4 is correctly set no signal is received by the lockout 5 when a switch 2 is pressed and a trip 4 connected to a 12V. D.C. source releases the locking device 7. If a signal is in the line 3 the locking device is not released when the switch 2 is closed, and the lock out 5 may operate a relay to cut out the trip 4. As shown in Fig. 2, a tapped transformer T provides two arms of the bridge and the key device is inserted in the arm with the fixed resistor R 3 , alternatively in the arm with the variable resistor R 4 . In a modification the transformer provides two arms, and the other two arms have a variable potentiometer to provide variable resistors R 6 , R 7 which are connected in parallel with fixed resistors R 8 and R 9 connectable to the key device which has resistors R 10 , R 11 and is also connectable to one end of the transformer. The resistor R 6 is first set and the key device is inserted, the switch 11 is closed and the signal in line 3b transmitted to memory and logic circuitry, the resistor R 7 is then set and the switch 12 is closed and the signal in line 30 also conveyed to memory and logic circuitry. When both signals are zero. a signal is sent to release the locking device. A similar circuit 30 is shown in Fig. 5 with transformer 31, variable potentiometer 32, and key device with resistors 54, 55 connectable to variable resistors 35 adjustable for use with a number of different key devices, when the key is inserted and a correct zero signal is obtained successively in lines 3a, 3b, a positive signal is obtained in lines 44, 45 from circuits 42, 43 connected to the lines 3a, 3b. The lines 44, 45 convey the signals to logic circuitry with flip-flops 38, 39, 40 and 41, a positive signal in the line 44 provides an output from the flip-flop 39 which operates a timer 46 and relay 47 which then releases the lock 48 for a predetermined time. If the first attempt to release the lock is unsuccessful a lamp 49 lights, if the second attempt is successful the lamp goes out and the lock is released. If the second attempt is also unsuccessful, an output from the lower side of the flip flop 41 energises transistor 50 and switches on the warning lamp 49, and an output from the upper side of the flip flop 41 energises a solenoid 51 which actuates a switch 36 to apply a voltage Vcc to an alarm 52 which may be an electric bell, and disconnects voltage to solenoid 51 which actuates key holding mechanism 53. A D.C. power supply circuit 35 applies voltage Vcc by solenoid operated switch 36, a switch 37 is closed to apply current Cp to the logic circuit. As shown in Fig. 6, a key 60 is a plastics plate with resistors 54, 55 at one end, a plunger 66 is spring urged downwardly to engage in a hole 64 in the key, the plunger being normally held in disengaged position by a plunger 70 of the solenoid 51. Actuating the solenoid releases the plunger to engage in the hole of the key to hold it against withdrawal. The plunger breaks the circuit through contactor 72 to cut out voltage Vcc from circuitry and actuates the alarm 52. The plunger 66 is reset by a lever 75. As shown in Fig. 4 a variable capacitor 15 is connected to an oscillator 13 connected to a D.C. source. A key having a capacitor 17 is connected to the capacitor 15 and in parallel with a resistor to a line 18 connected by a switch 19 to narrow and wide band channels 20, 21, connected to the lock 7. When the setting of the capacitor 15 is connected and the key is inserted and the switch 19 closed a restricted frequency band is transmitted to release the lock.