Patent GB-848701-A (GB)
Title: Improvements in or relating to fire alarm apparatus
Inventor: COCKRAM REGINALD WILLIAM JAMES
IPC: G08B17/06
Filed: 1955-12-22
Abstract: 848,701. Fire alarms. PYRENE CO Ltd. Dec. 21, 1956 [Dec. 22, 1955], No. 36811/55. Class 118 (1). Fire alarm apparatus of the kind described in Specification 632,279 employs a number of detector heads each provided with two resistor elements which are unequally affected by temperature rise or rate of rise. All the elements in the heads more affected are connected in series with one coil of a two coil alarm relay, and all the other elements are similarly connected with the other coil of the relay. The two circuits thus formed are paralleled and balanced, so that if due to temperature rise and so on the balance is lost a differential current flows in the alarm relay. In the present invention an additional sensitive relay SR is connected across the parallel circuits so that an alarm is given only when both relays operate. The coils of a fault relay FR are also in series with the resistor elements. Power is supplied from a battery 1 or mains 2 to parallel circuits PCA and PCB containing the coils of the alarm relay AR, fault relay FR, and the resistors of the heads D, and resistors 9 and 10 are provided to balance these two parallel circuits. The relay SR is in the form of a galvanometer having contacts 11, 12 on a moving pointer 13, and on a flow of unbalance current, contacts 14, 15 are bridged. The relay is provided with coils 17, 19 which protect it during normal operation and balancing, and a magnet which holds the contacts 11, 12, 14 and 15 when they are made is overcome when the energising current is removed by a resetting coil 20 and switch 21. On normal operation the contacts A1, A2 are made and current flows through a green lamp LG, but when the pointer 13 connects the contacts 14, 15 a safety relay TR across the power supply is energised to open contacts T1 and T3 and close T2 and T4. Contacts A1 and A3 are also closed by the alarm relay AR so that current may flow to energise the coil 22 of an alarm device relay AD. Part of the current flows through a red lamp LR and contacts 23 are made by the coil 22 to ring the bell 8. If, due to vibration or other accidental cause, the armature ARA closes the contacts A1 and A3 without unbalance of current, then the green lamp LG will be extinguished and a circuit will be made via contacts 27, 28 through the relay AR and the contacts T1 to earth via a blue lamp LB and a buzzer 26, but as contacts T2 are open the relay AD will not be energised and the red lamp LR and the bell 8 will not ring. Should the relay SR accidentally operate, the contacts A1 and A2 will remain closed and the contacts T2 and T4 will make and current will flow through the contacts T4 and contacts 24, 25 to light the lamp LB and sound the buzzer 26. When the contacts A1 and A3 are made the coil 22 of the alarm device relay AD is energised and causes the contacts 24, 25 to separate and break the fault alarm circuit. The relays TR and AD are heavily slugged so as to operate only on small currents, whilst the relays FR and PR operate only on serious faults when larger currents flow. If a major fault occurs, say a break in one of the parallel circuits, then the alarm will not operate but a normally centralised blade FRA will close on to either contact F2 or F3 and cause a yellow lamp LY to light and energise a coil 30 of relay FD. This causes contacts 27, 28 to break and prevent operation of the alarm, and makes contacts 27, 29 to provide a holding circuit for the coil 30. Simultaneously a switch 36 completes a circuit to a buzzer 7. A protective relay PR in series with the parallel circuits has a coil 31 which will close contacts 32, 33 if the current passing through both parallel circuits drops appreciably and cause the yellow lamp LY to light and the relay FD to operate as before. A switch RS is provided to reset the armature ARA and break the contacts 35 in the holding circuit of the relay FD. Specification 704,605 also is referred to.