GB2276264A - Method and apparatus for control of a fire alarm device - Google Patents

Abstract

A method of activating an alarm (6) of a fire alarm system including the steps of: (i) receiving a signal indicative of an alarm condition from a remote terminal (16) of a fire detection device (4), and (ii) activating a local fire alarm device (6) of the fire alarm system in response to said received signal. In this way, zonal control of sounders or alarms can be achieved without the need for separate control circuitry in the central control panel and/or separate wiring connecting the zone alarms to the control panel. <IMAGE>

Description

METHOD AND APPARATUS FOR CONTROL OF FIRE ALARM DEVICE The present invention relates to a method and apparatus for control of a fire alarm device, and is particularly suitable for use with an addressable fire alarm system.

A typical fire alarm system usually consists of a central controller which receives information from a number of fire detectors, such as smoke detectors, heat detectors, manuallyoperable call points, interface units and pressure switch monitors, all of which are hereinafter referred to as fire detection devices. When information is received indicating that a fire is present, the controller may trigger one or more alarm signals. These alarm signals may be audible and/or visual and may be located at a number of points throughout the area which is being monitored by the alarm system.

Fire alarm systems are known which include addressable fire detection devices and an appropriately compatible central controller. When the central control panel receives a suitable signal from a detection device indicating the presence of a fire, the panel can respond as normal by sounding the alarm(s) or sounder(s) and then sending a return signal back to the addressable detection device.

This return signal activates some type of indicator on, or associated with, the detector. The indicator is to show that it was this particular detection device in the system that triggered the alarm. Such detection devices typically have a "remote" terminal provided on them for operating a remote indicator, usually cited in a prominent position, to provide this identification. This can be useful, for example, in situations where the detection device is positioned out of sight.

A fire alarm system generally may be arranged in a number of configurations which permit the area to be monitored to be divided into zones These zones may be isolated from each other so that, for example, if there is a fault in one zone this does not affect the operation of the system in the other zones. Upon detection of a fire it is sometimes desirable to, activate the alarm signal in only one or a selected number of the zones.

Typically this involves complicated wiring arrangements and a sufficiently sophisticated control unit to select which zone or zones are to be activated.

It is the aim of the present invention to provide an easier way of achieving some local or zonal control.

Accordingly, in a first aspect, the present invention provides a method of activating an alarm of a fire alarm system including the steps of: (i) receiving a signal indicative of an alarm condition from a remote terminal of a fire detection device, and (ii) activating a local fire alarm device of the fire alarm system in response to said received signal.

A "remote terminal" as used above means a terminal or connection provided on, or associated with a detection device and usually used for indicating that the detection device has been activated.

Generally the fire alarm system may function as indicated above i.e. the central controller receives information from one or more detection device and, based on that information, may activate one or more sounders or alarms. If a detection device transmits information indicating that a fire is present, an alarm may be triggered and a signal transmitted back to the detection device to activate the remote terminal and/or a remote indicator. The signal thus provided at the remote terminal (which would conventionally be used to activate a remote indicator as described above) is then used to trigger one or more local alarms (which may, for example, be audible or visual) associated with that particular detection device.

The central controller need not necessarily transmist a signal back to the same detector that transmitted the fire alarm information originally. Any detector may have its remote terminal activated, and any number of areas or zones may be alerted by controlling the remote terminals of other devices.

In this way, zonal control of sounders or alarms can be achieved without the need for separate control circuitry in the central control panel and/or separate wiring connecting the zonal alarms to the control panel.

Power for the local sounder(s) could be derived from either a separate local supply or from the main supply associated with the central control panel (or the auxiliary supply thereof in the event of a main power supply failure).

Such a provision of local zonal control is particularly useful in fire risk monitoring situations where, in the event of a fire, not every building or part of a building would necessarily be alerted to the presence of fire. Examples of such situations are sheltered housing, developments of flats or maisonettes, and housing developments which are occupied predominantly by elderly and/or infirm persons.

In situations like these it is common for a warden to be resident and for the main control panel to be located in the warden's living quarters. In the event of a fire the area which needs to be immediately alerted (and probably evacuated) can be so alerted without the rest of the housing occupants being necessarily alerted immediately. The warden can also be alerted and can then take the required action, which for example may be to evacuate the whole building by initiating the evacuate procedure on the control fire panel which may activate the remote terminals of some or all devices in the system.

In a second aspect, the present invention provides a local fire alarm controller for use in a fire alarm system, the controller including input means for connection to a remote terminal of a fire detection device, output means for connection to a fire alarm device of the fire alarm system and control means for providing a fire alarm activation signal to said output means upon detection of a signal indicative of a fire alarm condition at said input means.

The local fire alarm controller may be housed independently of either the fire detection device (such as a smokehead) or the fire alarm device (such as a sounder). Alternatively it may be housed in conjunction with either of the two, or all three elements may be incorporated into one single unit.

In conventional addressable-type detection devices, such as may be used with the above aspects of the present invention, typically the remote terminal will be in a high impedance state when no fire has been detected and no signal has been returned from the central controller. Upon return of a signal from the central controller the remote terminal usually operates by going low impedance.

The local fire alarm controller may monitor the impedance of the remote terminal and, upon the terminal becoming low impedance, provide the necessary fire alarm activation signal to the output means. This activation signal would then operate the alarm(s) or sounder(s) associated with that particular detection device.

Sounder circuits may conventionally be operated by reversing the polarity of the voltage across the sounder. A polarising diode is provided in such a sounder and, when the polarity across the diode is reversed, current may flow and the sounder may be operated. This operation can possibly provide some compatability problems between a local fire alarm controller and the sounder circuitry.

To overcome such problems an isolating device, such as an optical coupler, is preferably used to couple the local fire alarm controller circuit to the sounder or alarm.

An embodiment incorporating aspects of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a schematic diagram of a first embodiment of the present invention connected to a typical detection device and sounder; and Fig. 2 shows a schematic diagram of a second embodiment of the present invention connected to a typical detection device and sounder.

Fig. 1 shows a local fire alarm controller, generally indicated by 2, connected between a typical detection device 4, such as a smoke or heat sensor, and a sounder or alarm 6. The fire alarm controller 2 is incorporated into a single unit with the sounder 6.

The detection device 4 is connected into a loop circuit 8 which connects it to the rest of the fire alarm system, typically comprising of other detectors and/or manual call points and a central controller (not shown). This loop circuit also provides the power for the detection devices (in this case 24 volts DC) and this power supply is also used to power the zonal fire alarm controller 2.

A typical remote circuit 10 is shown inside the detection device 4, which consists of a transistor 12 and associated remote resistor 14. The remote circuit 10 is connected between one of the loop supply connections and the remote terminal 16.

In the quiescent state, i.e. with clean and cool air in the region of the detection device, the remote terminal is high impedance relative to the 0 volts loop circuit, i.e. transitor 12 is off. If smoke or heat (as appropriate to the sensor) are detected, a message is sent to the central panel accordingly.

The software program in that panel will then send messages to one or more sensors, operating their remote terminal(s). This causes transistor(s) 12 to turn on taking the remote terminal low impedance, relative to OV loop.

An optical coupler 24 is incorporated within the controller and sounder unit. This consists of a light-emitting diode 26 (LED) and an associated transistor 28. When transistor 12 is on, this causes current to flow in the light emitting diode 26 of the optical coupler 24 and transistor 28 turns on.

This in turn turns on a transistor 30 which is biased by resistor circuit 32. Transistor 30 is a power device and controls the local sounder or sounders 34. Power 36 for the sounder(s) is provided either by a local supply or from the central panel. If the sounder unit was separate from the local controller then it may include some or all of the transistor 30, resistor 32 and diode 38.

The diode 38 is associated with the sounder 34 since circuit continuity for sounder circuits is conventionally achieved by reversing the polarity in the quiescent state. A change in polarity reverse biases diode 33, and the current drawn by an end of line resistor (not shown) can be sensed, verifying circuit continuity.

Fig. 2 shows a local controller 2, detector 4 and sounder 6 similar to the arrangement shown in Fig. 1. The local controller 2 also includes additional circuitry indicated generally by 3. This additional circuitry 3 may be included in the same housing as either the detector 4 or the controller/sounder unit or may be separate as shown.

When the remote terminal becomes low impedance, current will then flow in the base of the transistor 18, the collector of which will go high. The capacitor circuit 20 connected to the collector of transmitter 18 is designed to smooth out any pulsing which may be present on the remote terminal. The base of transistor 22 then "sees" a smooth waveform and the transisitor 22 turns on. The optical coupler then operates in the same manner as that of Fig. 1.

The above description is only of a single embodiment of the invention and as such is not intended to be limiting.

Alternative means for achieving the appropriate control of the sounder or alarm will be apparent to a person skilled in the art. Equally alternative coupling circuitry may be used.

Claims (10)

1. A method of activating an alarm of a fire alarm system including the steps of: (i) receiving a signal indicative of an alarm condition from a remote terminal of a fire detection device, and (ii) activating a local fire alarm device of the fire alarm system in response to said received signal.

2. A method of activating an alarm according to claim 1 further including the additional steps of transmitting a first signal indicative of an alarm condition from a first fire detection device to a central controller, and subsequently transmitting a second signal from the central controller to a second fire detection device, said second signal causing the remote terminal of the second fire detection device to produce the alarm condition signal of step (i).

3. A method according to claim 2 wherein the first and second fire detection devices are the same device.

4. A method according to claim 2 or claim 3 wherein said central controller transmits a plurality of said second signals to a corresponding plurality of said second fire detection devices.

5. A method of activating an alarm of a fire alarm system substantially as herein described with reference to the accompanying drawings.

6. A local fire alarm controller for use in a fire alarm system, the controller including input means for connection to a remote terminal of a fire detection device, output means for connection to a fire alarm device of the fire alarm system and control means for providing a fire alarm activation signal to said output means upon detection of a signal indicative of a fire alarm condition at said input means.

7. A local fire alarm controller according to claim 6 wherein said signal indicative of a fire alarm condition is produced by a change in impedance of said remote terminal.

8. A local fire alarm controller according to claim 5 or 6 including coupling means connected between said control means and said output means.

9. A local fire alarm controller according to claim 8 wherein the coupling means is an optical coupling.

10. A local fire alarm controller substantially as one of the embodiments herein described with reference to either Fig. 1 or Fig. 2 of the accompanying drawings.