EP1369835B1

EP1369835B1 - Fire detectors

Info

Publication number: EP1369835B1
Application number: EP02253889A
Authority: EP
Inventors: Fariz Khellaf
Original assignee: Cooper Lighting and Security Ltd
Current assignee: Eaton Electrical Systems Ltd
Priority date: 2002-06-05
Filing date: 2002-06-05
Publication date: 2007-05-09
Anticipated expiration: 2022-06-05
Also published as: DE60220029T2; EP1369835A1; DE60220029D1; ATE362156T1

Abstract

A fire alarm system comprises a central controller (10) controlling at least one loop/zone (20) of fire detectors (22). Each fire detector incorporates a thyristor (23), to detect a fire condition and a Shottky diode, to detect removal of the fire detector from the loop (20). The fire detector (22) also incorporates a switch (26) and is arranged to be closed when the fire detector (22) is in place and in circuit and is arranged to open when a power supply to the switch (22) ceases, or fails. <IMAGE>

Description

This invention relates to fire detectors and fire alarm systems and to a method of monitoring fire detectors.
A typical conventional fire alarm system is shown in Figure 1 and consists of a central controller 10 which is connected to a number of fire detectors 12, such as smoke detectors, heat detectors, gas detectors or manually operable call points. The fire detectors are connected along a loop or zone 13. Multiple loops or zones 13 may be controlled by one central controller 10. The fire detectors 12 typically include a thyristor and behave like a switch, whereby if a detector detects smoke the switch closes and the central controller detects the closure of the switch and causes an alarm condition.
In a normal condition, the central controller 10 only monitors the continuity of a series of fire detectors 12 by the presence of an end of line device 14, which may be of a resistor type or active type (which sends out a pulse at regular intervals), as is well known in the art. If one of the fire detectors 12 becomes faulty the fault is not detected by the central controller 10, because no monitoring takes place in conventional systems. The fault can only be detected during a test. Such a test should take place every six months or once a year.
In most cases, a conventional fire detector 12 is connected to a base 16 with the terminals numbered 1 and 2 being shorted together in order to keep a continuity along the line 13 to the end of line device 14. Sometimes a Shottky diode 18 is connected between points 1 and 2, to detect whether a fire detector 12 has been removed from its position.
If a fire detector 12 becomes faulty, whilst still remaining in position, the existing systems do not detect such a condition. There are obvious safety disadvantages in having a fire detector which is malfunctioning, but in which the malfunction has not been detected.
DE 2419919 discloses an arrangement for connecting signalling equipment, in particular smoke detectors. US 4,651,013 discloses an intelligent smoke detector system with a changeable pulse light emitting interval for monitoring purposes.
It is an object of the present invention to address the above mentioned disadvantage.
According to the invention a conventional fire detector as claimed in claim 1 is provided.
The fire detector with its fire detection means may be operable to detect heat, smoke or gas. The fire condition may involve levels of heat, smoke or gas above predetermined limits.
The communication means preferably comprise wiring, which preferably allows communication of the fire detector with a separate control means. Said wiring is preferably internal to the fire detector. The wiring is preferably adapted to allow connection to a zone/loop section of a separate control means.
The fire detection means may be heat detection means or may be smoke or gas detection means.
The fire detector advantageously has monitoring functions to allow a conventional, non-"intelligent" fire detector to indicate a malfunction of a fire sensor to a control means. Typically the control means would be a control panel, which controls a plurality of zones, each having a plurality of fire detectors.
The second section may be adapted to signal to a control panel. The monitoring means is preferably adapted to draw a different amount of current from the fire detection means on detection of a failure of the monitoring means.
The monitoring means may additionally include a further switch which may be adapted, preferably in an alarm condition after triggering of the fire detection means, to open and close repeatedly on detecting a failure in the fire detection means. The further switch may be a transistor.
The further switch may latch in an open position on detecting a failure in the fire detection means.
The monitoring means, or at least the further switch, is preferably programmable by means of control panel of a fire alarm system to which the fire detector is, in use, arranged to be attached.
The invention extends to an alarm system comprising a central controller, at least one alarm system loop/zone and at least one fire detector according to the invention.
The fall in power consumption may be a fall below a predetermined threshold. The fall in power consumption may be a fall in current drawn by the fire detection means.
The first monitoring section may comprise a switch operable to open on detecting a fall in a power supply below a predetermined limit or malfunctioning of the fire detection means.
The second monitoring section may comprise a further switch, or preferably a transistor, which detects failure of the fire detection means during a fire condition.
Specific embodiments of the present invention will now be described, by way of example, and with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a prior art conventional fire alarm system; and
Figure 2 is a schematic diagram showing a fire alarm system according to the present invention.

The fire alarm system as shown in Figure 2 comprises a central controller 10 similar to that as described in relation to the prior art system shown in Figure 1. A loop/zone 20 is shown on which a fire detector 22 is located. Only one fire detector 22 is shown for simplicity, but numerous detectors 22 would typically be placed on the loop 20 and the central controller 10 may control a number of loops in different zones. At the end of the loop away from the central controller 10 is an end of line device 14, similar to that as described in relation to the prior art and Figure 1.
Although reference is made to a fire detector 22, the device could be used to detect heat, smoke, gas or other factors which may require an emergency alarm to be triggered.
The fire detector 22 fits into the loop 20 between terminals 1 and 2, with terminal 3 being connected to a return leg of the loop 20.
The fire detector 22 incorporates a thyristor 23, to detect a fire condition (different elements known in the art are used to detect smoke and gas etc), and a Shottky diode 24, which is used to detect removal of the fire detector 22 from the loop 20, as described above. As soon as the fire detector 22 is removed from the loop 20 the Shottky diode 24 becomes in circuit, which is detected by the central controller 10 and an alarm can be raised. Normally the presence of the fire detector 22 causes shorting out the Shottky diode 24.
The fire detector 22 also incorporates a switch 26, such as a transistor, FET or any other suitable switching mechanism.
The switch 26 is used to monitor a power supply to the detector 26 during a normal (non-fire) condition. The switch 26 is arranged to be closed when the fire detector 22 is in place and in circuit and is arranged to open when a power supply to the switch 22 ceases, or fails. The opening of the switch 26 results in a non-detection of the pulse from the active end of line device 14, which non-detection is sensed by the central controller 10. Such a failure of the detector circuitry is likely to be the result of a fault in the fire detector 22.
The monitoring described above is in relation to a normal, non-fire, condition.
In a fire condition the following monitoring is used, because the thyristor 23 may fail to trigger during the fire condition.
A second transistor 25 is placed in parallel with the thyristor 23. When the thyristor 23 fails the change in power consumption is detected by the internal circuitry of the detector which results in the second transistor 25 responding as follows.
The second transistor 25 may draw a predetermined continuous current when the thyristor fails. Alternatively, the second transistor 25 may toggle between open and closed positions on detection of failure of the thyristor 23. The continuous or pulsed current is detected by the central controller 10 as a fire or a fault with the fire detector 22.
A further alternative is to clamp the voltage of the loop 20 by using a Zener diode or known reference voltage in order for the central controller 10 to detect the clamping of the voltage and hence trigger an error condition in the central controller 10.
The embodiment disclosed above in which a known current (continuous or pulsed) is drawn by the transistor 25 of the fire detector 12 can be used as an indication of failure of the thyristor 23 in the event that the thyristor 23 fails on detecting a fire. The known current may for instance may be 10mA when normally the thyristor 23 would draw 20mA. The difference in current drawn can be used as an indication by the central controller 10 that the fire detector 22, or more particularly the thyristor 23, has failed.
An addition to the monitoring devices described above would be to install a battery (not shown) in the fire detector 22 to provide power for the switch 26 and transistor 25. This allows notification to the central controller 10 that the fire detector 22 has failed.
In its simplest form the fire detector 22 uses a switch 26 which, when power is supplied to the fire detector 22, remains closed, thus allowing usual functioning of the fire detector. If no power is supplied to the fire detector 22 the switch 26 opens to indicate failure of the fire detector 22 to the central controller 10, to allow the problem to be remedied.
A further feature of the alarm system is that each of a number of fire detectors 22 on the loop 20 can be addressed in series from the central controller 10 outwards. By passing an instruction to close the switch 26 to each of the fire detectors 22 in turn it can be determined whether the fire detector 22 is functioning properly. If one of the switches 26 of a number of fire detectors 22 does not close on receiving the instruction, then this is indicative of a malfunction of that switch 26, and so of that fire detector 22. If, however, each of the switches 26 in a series of fire detector 22 on the loop 22 correctly performs the command of closing the switch 26, then it is indicative of the switches 26 in the series of fire detectors 22 are performing correctly. If one switch 26 fails then the instruction to close cannot be passed further along the loop 20.
The switch 26 is controlled by software in the central controller 10, so the continuous current or open/close options for signalling a fault can be programmed from the central controller 10 when the switch 26 is present.
The system for monitoring fire detectors 22 disclosed herein has significant advantages over standard conventional fire detectors, because the monitoring of the fire detectors 22 is achieved. The monitoring is achieved in a simple way by the use of a switch 26 in each fire detector 22, which switch responds to a loss of power by opening to indicate to a central controller that the fire detector 22 is malfunctioning. The simplicity of the fire detectors 22 which are of a conventional type, rather than an intelligent type, also has cost advantages.
Conventional fire detectors typically only have a fire/heat/smoke detecting element, which may be a thyristor or similar, which signals a fire to the controller 10 when an environmental change is detected.
Intelligent fire detectors are typically addressed separately using micro-controllers and microprocessors together with unique addressing methods.
Thus, the use of conventional fire detectors having a monitoring function is of significant advantage.

Claims

A conventional fire detector (22) comprises fire detection means (23), communication means and monitoring means wherein the fire detection (23) means is operable, on detection of a fire condition, to cause the communication means to signal a fire condition, and wherein the monitoring means are operable to monitor a power supply to the fire detection means (23) and to signal a fire detection means (26) failure to the communication means, on detecting a fall in power consumption by the fire detection means (23), wherein a first section of the monitoring means comprises a switch which is adapted to remain closed when a power supply to the fire detection means is functioning normally and is adapted to open on detecting a loss of supply to the detection circuitry and/or on detecting a fall in current drawn by the fire detection means (23), characterised in that a second section of the monitoring means (25) is adapted, during an alarm condition after triggering of the fire detection means (23), to vary a current drawn by the monitoring means (23) on detection of a fall in a current drawn by the fire detection means (23) and/or if the fire detection means fails.
A fire detector (22) as claimed in claim 1, which, with its fire detection means (23) is operable to detect heat, smoke or gas.
A fire detector (22) as claimed in either claim 1 or claim 2, which has monitoring means (23) to allow a conventional fire detector, having only detecting means and signalling means, to indicate a malfunction of the fire detector (22) to the control means (10).
A fire detector (22) as claimed in any preceding claim, in which the second section (25) is adapted to signal to a control panel (10) by drawing a different amount of current from the fire detection means (23) on detection of a failure of the monitoring means.
A fire detector (22) as claimed in any preceding claim, in which the first section of the monitoring means is programmable by means of a control panel (10) of a fire alarm system to which the fire detector (22) is, in use, arranged to be attached.
An alarm system comprising a central controller (10), at least one alarm system loop/zone (20) and at least one conventional fire detector (22) as claimed in any one of claims 1 to 5.