Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1981-07-15
1984-07-03
Crosland, Donnie L.
Communications: electrical
Condition responsive indicating system
Specific condition
340506, 340508, 340510, 340590, 340588, 340653, 169 23, 169 61, G08B 2100, A62C 3718
Patent
active
044582390
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fire extinguishing apparatus and more particularly to an electrical circuit for actuating fire extinguishing devices such as sprinkler heads.
2. Description of the Prior Art
One way of actuating a sprinkler head is for each head to be provided with an electrically actuable single shot actuator which is used to rupture a seal, for example the quartz bulb, of a sprinkler head to cause water or other fire extinguishing fluid to be discharged from the head. One such actuator is sold under the trade name Metron by Nobel's Explosives Company Limited of Ayshire, Scotland. Individually, these actuators operate satisfactorily but when used in large numbers and especially when it is desired to actuate a plurality of such actuators using a single trigger signal problems can arise due to the fact that when actuated the actuators can end up either in open circuit or a short circuit state in a random manner. This means that it is possible that only some of the desired number of actuators will actually be actuated which could have disasterous consequences.
In order to ensure that each actuator of a plurality of actuators is operated, one could wire the actuators in parallel but this is an expensive operation and causes difficulties in providing a trigger signal which will meet the manufacturer's specification for a drive signal which is for example, a current of 2 amps with a rise time of 100 microsecs.
Wiring the actuators in series would avoid the problems of cost and drive signal specification but does not itself solve the problem that some actuators may be in an open circuit mode after actuation and before the drive signal current can actuate any further actuators.
SUMMARY OF INVENTION
The present invention provides fire extinguishing apparatus comprising a plurality of actuators each arranged to be actuated by an electrical signal, the actuators being connected in series and arranged to be connected to a device for producing the electrical signal characterised in that each actuator has connected in parallel with it, a device whose resistance decreases with increasing current through the device.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawing which shows a circuit diagram of a fire extinguishing arrangement according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The apparatus comprises an electrical circuit for the operation of a number of single shot actuators (gas generators) when connected in series. Each actuator comprises a low resistance electric fuse. The actuators may be used to rupture a seal for example the quartz bulb of a sprinkler head.
The circuit utilises an electrical supply which may typically be 50 volts DC which will operate up to ten actuators in one series chain.
The supply is used to charge a capacitor (C1) which is used to reduce the effect of source impedance. The capacitor is discharged via a semi-conductor switch in the form of a silicon controlled rectifier (SCR.1) through a ballast resistor R1 into the series chain of actuators (A1-An) when it is desired to operate the actuators. The silicon controlled rectifier is triggered by the closing of a contact (S1) which may be manually and/or automatically operated by a fire detection device such as a smoke or heat detector. Across each actuator is connected a current sensitive resistance device (RD1-RDn) with typical characteristics of high resistance when passing less than 10 milliamps and low resistance when passing 2 amperes. Such a device is a Brimistor.
In order to be able to monitor the continuity of the series chain of actuators, the series chain and ballast resistor form one leg of a D.C. bridge circuit whose other legs are constituted by a variable resistor VR1 and fixed resistors R.sub.2 and R.sub.3. The power supply for the bridge is provided by the junction between R
REFERENCES:
patent: 2693240 (1954-11-01), Glendinning et al.
patent: 3523583 (1970-08-01), Poitras et al.
patent: 3952809 (1976-04-01), Osborne
patent: 4013128 (1977-08-01), Davis
patent: 4101887 (1978-07-01), Osborne
Jolliffe Raymond
Willey Michael R.
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