Patent GB-230173-A (GB)
Title: Improvements in and relating to a safety-device in alarm-apparatus
IPC: E05G1/10
Filed: 1923-12-05
Abstract: 230,173. Litwin, S., and Kassenfabrik St. F. & M. Litwin vorm. B. Hesky & Co. und S. Wertheimer Ges. Dec. 5, 1923. Burglar alarms. - An alarm device for safes and the like of the type having an electric current passing in two branches over a relay in such a way that the currents in the relay normally neutralise each other, is provided with a clockwork arrangement which causes, a lever to make contact at regular short intervals to avoid undue consumption of current. On cutting a wire, or making contact with the alarm device, the balance is destroyed and the relay energizes a solenoid to sound an alarm. Current normally flows from the positive terminal 9 of supply mains 30, 32 round the solenoid 12 of the magnet 24 to a terminal 56 protruding from a glass tube 52 mounted in a holder 45 carried by a rod 44 fixed to the armature 43 of the magnet 24. A. mercury ball 53 makes contact between the terminals 56, 57 when the armature 43 is in the position shown in Fig. 1, i.e. when current is passing round the solenoid 12, so that current can pass from the terminal 9 to the terminal 12 of the relay circuit B where it divides and flows round two equal and oppositely wound coils 1, 2 surrounding a soft iron core 3. The current from coil 1 passes through a resistance C to the negative pole 10 of the current supply main 32 and the current from coil 2 passes down the lead 17 through a resistance D. equal to the resistance C, up a lead 18 to the terminal 10. In this condition the currents in the coils 1, 2 balance each other so that the core 3 is not magnetized. An alarm contact A is placed in parallel with the resistance D. This contact is shown in the set position in Fig. 3 and comprises a metallic rod 27 with a concave top 31 containing a mercury ball 11 and a needle 38 reaching almost to a metal cap 40. A metal tube 37. insulated by a sleeve 28, is formed with a funnel shaped top 39. The tube 37 and cap 40 are connected to one terminal and the rod 27 to the other and the device A placed or attached to the safe so that movement or percussion caused by attempts to force the safe cause the mercury ball 11 to drop into the funnel 39 and make contact between the rod 27 and tube 37, or inversion causes it to drop into the cavity 41 and make contact between the needle 38 and cap 40. This short circuits the resistance D and disturbs the balance of current in the coils 1 and 2, causing the core 3 to become magnetized to attract the armature 4, pivoted at 5, and release the switch arm 6 to cause a direct and continuous current to flow from the terminal 9 via terminals 57, 14, 13, round the bell E and back to the terminal 10, giving the alarm. If the wires 17 or 18 are cut, the coil 2 is cut out of the circuit and the coil 1 only has current, so that the core 3 attracts the armature 4 with the same result as before. If the current supply wires 30, 32 are cut, no current flows round the solenoid 12, and the magnet 24 fails to release the armature 43 in the position shown because a weight 48 carried on an arm 54 on the shaft 44 attached to the armature drops until held by the stop 55, partially rotating the carrier 45 and causing the mercury ball to " break " contact between terminals 56, 57 and to " make " contact between terminals 57, 58, putting an auxiliary battery 19 in circuit so that the alarm can still function, the current then passing from terminal 20 to terminal 35, across the arm 22 to terminal 36, to terminal 58, across the mercury ball 53 to terminal 57 and round the relay circuit as before. As the current supply is now a storage battery, a clockwork mechanism G is incorporated for causing the current supply to be made in regularly spaced short-lasting flows so as to prolong the life of the battery. When the rod 44 is turned by the weight 48, a catch 46 carried by it releases the pendulum 49 of the clockwork mechanism G the ratchet 42 of which commences to actuate a cam disc 51 on an axis 50 to raise and lower the pivoted rod 22 by engaging the projection 23, so as to regularly " make " and " break " the contact between terminals 35, 36. The throw-over switch F may be used as a transformer. In this case, the coil 12 acts as the primary coil and is connected to the main terminals 9, 10, and the secondary coil (not shown in Fig. 1) is connected to terminals 56, 21. The contact device A, after being actuated, is reset by pulling down the rod 27 until the mercury ball faIls on to the top surface 31 thereof and raising it again into the position shown.