GB2331172A

GB2331172A - Fire detection system

Info

Publication number: GB2331172A
Application number: GB9824618A
Authority: GB
Inventors: Robert William Gentles; Colin Bruce Mitchell
Original assignee: FPG ELECTRONICS Ltd
Current assignee: FPG ELECTRONICS Ltd
Priority date: 1997-11-11
Filing date: 1998-11-11
Publication date: 1999-05-12
Anticipated expiration: 2018-11-11
Also published as: GB9723696D0; GB2331172B; GB9824618D0

Abstract

The present invention relates to a fire alarm/detection system 1. The system comprises a control unit C coupled to a single circuit 20 provided with a power supply connection for connection of the system to a power supply 34 in use of the system. The system also comprises at least one detection device 24 and at least one warning device connected to the circuit. In a steady state monitoring condition of the system, the power supply 34 has a first signal output detectable by and useable to power the detector device 24 and in an alarm condition of the system a second signal output detectable by and useable to power the warning device 26. The first and second output signals are different from each other so as to be selectively passable by respect of filtering techniques. The detector device 24 is provided with a first filter (40) formed and arranged for selectively passing the first signal output to the detector device 24 and each alarm device 26 is provided with a second filter formed and arranged to selectively pass the second signal output from the power supply to the alarm device. In use the first signal output is used to operate the detector device 24 and the second signal output is used to operate the warning device 26. The first and second signal outputs are provided substantially simultaneously by the electrical power supply 34 in an alarm condition of the system. An addressable fire alarm/detection system is also disclosed.

Description

FIRE DETECTION SYSTZM The present invention relates to a fire detection system and in particular to fire alarm systems but not exclusively. The present invention relates also to an analogue or addressable fire alarm system.

Conventionally a fire alarm/detection system comprises a control unit or panel, a plurality of detection devices (for example heat and smoke detectors, "break-glass" points) connected to the control panel on a circuit, and a plurality of warning devices such as sounders (for example bells, sirens) or other warning devices such as strobe lights connected to the control panel in a sounder circuit. Due to the differing electrical requirements of the detectors and sounders such systems are generally wired on separate circuits or a number of different type alarm devices on a single pair of conductors arranged in a loop. Such systems will be generally know to those skilled in the art.

A disadvantage of such known systems is that at least two separate circuits must be provided requiring two sets of cabling (with twin conductors) or a single cable (with four conductors) to be run throughout an installation. Cabling is generally the most expensive item required in the installation and may account for 70% or more of the cost of an alarm/fire detection installation system. It will be appreciated therefore that it would be advantageous to put both the detectors and the sounders on a single circuit i.e. a single cable (with two conductors) then a significant reduction in the cost of the installed system would be possible.

Furthermore reduction in the time and effort required to install such a system could be realized.

United Kingdom Patent Publication No. GB1491222A discloses an arrangement whereby detection devices and warning devices may be connected to a control unit on a single circuit. The system operates by applying to the circuit electrical power in order to power the detection devices. When it is required to activate the warning devices, the polarity of the power applied to the circuit is reversed, detectors remaining active due to a bridge rectifier and the warning devices receiving power as well as the detectors. This system has the disadvantage that during fire alarm conditions, detectors, break glasses, detector removal monitoring and end of line condition cannot be monitored continuously.

United Kingdom Patent Publication No. 2281995 discloses an alarm system for use with for example fire alarms which has two operation modes. The alarm system comprises a control device coupled in parallel by means of a pair of conductive paths with a detection device and with a signaling device.

The detection device is responsive to a voltage of a first polarity across the conductive paths and the signaling device is responsive to a voltage of the opposite polarity across the conductive paths. The control device has a detection state in which it can monitor, via the conductive paths, the detection device, and a signaling state in which it can actuate via the conductive paths the signaling device by changing the polarity of the voltage across the conductive paths. There is provided oscillator means arranged cyclically to switch between the two states.

The system described above has the disadvantage that the warning devices require to be momentarily switched off and then back on again to monitor the detectors. The circuit necessary to achieve switching and sampling of the detectors is unnecessarily complex and the requirement for such additional circuitry tends to negate the cost reduction in using a single circuit (two-wire) system.

United Kingdom Patent Publication No. GB 2293257A discloses a system which has sounders and detectors connected in a common circuit. The detectors operate within a first voltage range and the sounders operate within a second voltage range, the two ranges having the same polarity. There is a non-sounding voltage within the first range but outside the second range which does not operate the sounders. In use the system would normally supply power to the circuit at the non-sounding voltage to power the detectors. During an alarm condition the circuit is supplied with a voltage within the second range thus causing the sounders to activate.

The system described in GB 2293257A has the disadvantage that a programmable power supply or a higher, than the industry standard of 24v, supply voltage and battery are required. The use of non standard items increases the costs of installing such alarm/detector systems.

A further disadvantage of other systems is that due to the voltage drop along long cable runs. If the volts drop at some point along the line exceeds a critical threshold of for example about 6 volts then all sounder/alarm devices beyond that point may cease to operate or operate only intermittently. Furthermore alarm devices which require a high current such as strobes or bells cannot be used due to the above mentioned voltage drop problem.

The present invention relates also to an addressable or analogue fire alarm system which uses a method of communicating to and from devices on the line. Typically with an addressable system digital pulses or tones are sent along the cable to the line devices in order to communicate with them and digital pulses or tones are sent back to the control panel of the system from the line devices to communicate in the reverse direction. These systems use two conductors and are of the two wire system type. The communication signal is superimposed on a steady state voltage which is used to power the devices on the line. Typically the power available to power sounders or other alarm devices is very limited due to the limitations in the design of the data drive circuitry.

It is an object of the present invention to avoid or minimize one or more of the above disadvantages of known system and to provide a system which may be connected in a single circuit.

The present invention provides a fire alarm/detection system comprising a control unit coupled to a single circuit provided with power supply conr, vction means for connection of the system to a power supply in use of said system, and at least one detector device and at least one warning device connected to said circuit, said power supply, in a steady state monitoring condition of the system, having a first signal output detectable by and usable to power said at least one detector device and, in an alarm condition of said system, a second signal output detectable by and usable to power said at least one warning device, said first and second output signals being different from each other so as to be each selectively passable by respective filter means, said detector device being provided with first filter means formed and arranged for selectively passing said first signal output to said detector device and said alarm device being provided with second filter means formed and arranged for selectively passing said second signal output from said power supply to said alarm device.

Thus the system, in use, uses a first signal output to operate the detector devices and a second signal output to operate the warning devices, the first and second signal outputs being provided substantially simultaneously by said electrical power supply in an alarm condition of said system.

It will be appreciated that various forms of selectively filterable first and second signal outputs may be used and will be generally well known to those skilled in the art.

Preferably though for simplicity and cheapness there is used an alternating current (AC) signal and a direct current (DC) signal. Preferably there is used a square wave AC signal superimposed upon a steady state DC signal. Desirably there is used a 24v DC supply for compatibility with "off the shelf" detectors and alarms which operate at 24v DC. Said AC signal has desirably a +24v peak. Preferably said AC signal has a frequency in the range of from 10 Khz to 100khz desirably 20 80khz, advantageously about 40KHz.

It will be appreciated that the present invention provides an alarm system which can monitor detection devices continually whilst at the same time actuating a said at least one warning device. This is an aspect of alarm systems which has previously not been possible with the known prior art.

Any suitable means of selectively filtering out one or other of the two signals may be used though preferably each of said detector means has a filter means to block or to remove the first signal means for example the AC signal and each said warning device is provided with a filter means to remove or block the second signal means for example the DC and/or digital signal. Preferably said filter means are of the passive filtering type which will be generally known to those skilled in the art.

In another respect the present invention provides an addressable fire alarm/detection system comprising a control unit coupled to a single circuit provided with a power supply connection means for connection of the system to a power supply in use of said system, and a plurality of detector devices and a plurality of warning devices connected to said circuit, said power supply, in a steady state monitoring condition of the system, having a first signal output detectable by and usable to power at least one of said plurality of detector devices and, in an alarm condition of said system a second signal output detectable by and usable to power at least one of said plurality of warning devices, said first and second output signals being different from each other so as to be each selectively passable by respective filter means, each one of said plurality of detector devices being provided with first filter means formed and arranged for selectively passing said first signal output to a said detector device and each one of said plurality of alarm devices being provided with second filter means formed and arranged for selectively passing said second signal output from said power supply to one of said plurality of alarm devices each one of said plurality of detector devices having signal generating means and said control unit being provided ith detector device testing means for venerating a test signal and means for searching said signal around said circuit to said plurality of detector devices and for monitoring the response of said detector devices to said signal so as to check the status of each of said detector devices each of said detector devices being formed and arranged to issue a status signal in response to a corresponding test signal.

Thus with an addressable system according to a second aspect of the invention it is possible to check the status i.e. on/off or working/not working of each of the detector devices on the circuit.

For use with an addressable or analogue system preferably there is used a square wave AC signal superimposed upon a steady state DC signal which may be modulated by digital signals. The alarm drive frequency though has to be much higher as it has to be above the bandwidth of the data signal so that the line filtering can separate the two signals.

Preferably said AC signal has a frequency in the range of from 10khz to 1Mhz, desirably 100Khz - 1Mhz, advantageously about 500Khz depending on the frequency of the digital transmission selected. It will be recognised though that a very high frequency will cause unwanted radiation from the line and will have greater losses and so is undesirable.

Preferably said addressable detection system is configured as a loop wherein both ends of the line are connected to a said control unit. Preferably there is provided power supply means at each end of the line to verify the integrity of the loop.

This feature acts as a fail safe system in the event that one or other of the power supply means should fail or there is a break in one of the circuits in the line.

Further preferred features and advantages of the present invention will appear from the following detailed description given by way of example of a preferred embodiment illustrated with reference to the accompanying drawings in which Fig. 1 is a circuit diagram of a conventional fire alarm system; Fig. 2 is a schematic diagram of a fire detection system according to the invention; Fig. 3 shows a diagram of a circuit for use in a detector device of a fire detection system according to the invention; Fig. 4 is a circuit diagram for use in a sounder device of a fire detection system according to the invention; Fig. 5 is a circuit diagram for use in a detector monitor of a fire detector system according to the invention; Fig. 6 is a circuit diagram of a fire detection system power supply system according to the invention; Fig. 7 is a circuit diagram for use in a detector device for use with a second embodiment of fire protection system according to the invention; and Fig. 8 is a circuit diagram for use in an addressable fire detection according to the invention.

With reference to Fig. 1, a conventional fire detection system comprises a control unit C connected to a circuit 1 and to two sounder circuits 2, 4.

The circuit comprises a pair of wires 6 to which a DC signal is supplied by the control units C. In the circuit 1, various detection devices 8 are connected between the pair of wires 16. These devices 8 may include fire, smoke and heat detectors and manual call points such as "break glass" points.

The final device on the circuit is an end of line monitor 10 which sends signals to the control unit whereby a fault in the circuit 1 may be detected.

The sounder circuits 2, 4 each comprise wire pair 12, 14 across which is connected a plurality of warning devices 16 including such things as bells, electronic sounders and strobe lights. The last component of each sounder circuit 2, 4 is an end of line resistor 18 which interconnects the wires of the wire pair, whereby the control unit can detect open or shcrt circuit conditions within the sounder circuit 2, 4.

In use the control unit C monitors the current flowing in the circuit 6 and if this changes due to one of the detectors 8 detecting an emergency condition, the control unit applies electrical power to one or both sounder circuits 2, 4 to activate the warning devices connected thereto.

In the present invention, as illustrated in Fig. 2, there is provided a control unit C to which is connected a circuit 20.

The circuit 20 comprises a wire pair 22 across which are connected two detectors 24 and two sounders 26 and at that the end of the circuit there is an end of line (EOL) resistor 27.

The control unit C houses sounder drive circuitry 28, a detector monitor 30 and an EOL monitor 32 together with a power supply 34.

The detectors are connected to the line via a detector interface 36 and the sounders are connected to the line via a sounder line interface 38.

In use, the control unit C monitors the current flowing in the circuit and if this changes and drops due to a detector drawing current as a result of detecting an emergency condition, the control unit C actuates the power supply to supply a +24v peak AC voltage to be superimposed upon the 24v DC power supply for the detectors.

The system therefore allows the use of a direct current to monitor the detectors, and any removal of the detector or the end of line unit and to use an alternating current to power the sounders. The AC and DC components at the detectors and sounders can be separated using passive filtering techniques which are described in more detail below and with reference to Figs. 3 to 6.

Fig. 3 shows the circuitry for the detector interface 36 that is connected between the cable and a standard detector device 24. The detector interface 36 comprises a low pass filter 40 comprising a combination of an inductor L and a capacitor C.

This low pass filter prevents the high frequency alternating current voltage present during alarm conditions from reaching the detector 24 and affecting its normal operation. The low pass filter 40 does not affect the steady state direct current voltage so that the condition of the detector 24 can be monitored continually.

Fig. 4 shows the circuitry for a sounder interface 38. This is the interface that is connected between the cable line 22 and a standard sounder device 26. The sounder interface 38 comprises a capacitor Cl being used as a high pass filter to block the steady state detector monitoring voltage while allowing the high frequency alternating current voltage present during alarm conditions to pass through unaffected.

The diodes D form a bridge rectifier which converts the alternating voltage of current during alarm conditions to a direct voltage and current. A capacitor C2 is connected across the sounder to store the energy supplied by the bridge rectifier and to smooth the voltage for driving the sounder 26.

Fig. 5 shows the circuitry for the detector monitor interface.

This is the interface that is connected between the cable line 22 and the detector monitoring circuitry found in the control unit. This circuitry comprises an inductor L1 connected between the positive side of the line and positive side of the detector monitor and a second inductor L2 connected between the negative side of the line and the negative side of the detector monitor. The inductors Ll, L2 act as low pass filters to block the high frequency alternating current found during alarm conditions and to allow a steady state monitoring voltage and current to pass through unaffected.

Fig. 6 shows the circuitry of the sunder driver interface 38.

This is the interface that is connected between the alarm supply and the cable line. The circuitry comprises four electronic switches 5W1, 5W2, 5W3, and SW4 arranged in pairs, each pair being controlled by a controller - control A and control B respectively. Control A and control B are logic signals generated by an oscillator (not shown) and have an even mark space ratio. Control B is the logical inverse of control A. The mid connection point 42 of the electronic switches is connected alternately to the line supply and to zero volts. This gives an alternating voltage at the line + connection via an in-line capacitor. The second pair of electronic switches are controlled in a similar manner to produce an alternating voltage on the line - the control signals control C and control D are anti-phase to control A and control B so that the alternating voltages at line + and line - are in antiphase. This gives a push-pull alternating drive voltage at the cable line which is then used by the sounder interface to energize the sounders.

Fig. 7 shows a modified detector line interface circuitry which makes the detector "non-polarity conscious". This is a particularly desirable feature as it means operators when installing a system do not have to insure that the positive and negative sides of the detector are correctly connected to the respective positive and negative sides of the line. The modification comprises connecting a bridge rectifier 44 between the detector and the interface. The diodes D used in this bridge rectifier are of the Shottky type so as to reduce as far as possible volt drop and losses.

Turning now to Fig. 8 which is a circuit diagram for use in an addressable fire detection system according to a second aspect of invention, the addressable fire detection system comprises a control unit C connected to a loop circuit 20. The circuit 20 comprises a wire pair 22 arranged in a loop between the first alarm driver 21 and line monitoring circuitry 21a and a second alarm driver 23 and monitoring circuitry 23a. A number of detectors 24 and sounders 26 are connected across the wire pair 22. The control unit C houses sounder driver circuitry 25 and a high frequency alarm driver each of these are provided within the control unit C to act as a loop verification system and fail safe system. A low pass filter 27 and a high pass filter 29 are provided to discriminate between the test signal and the alarm drive signal.

Each of the detectors 24 is connected to the line via a detector interface 36 and the sounders 26 are connected to the line via a sounder line interface 38. In use, the control unit monitors the current flowing in the circuit and if this changes and drops due to the detector drawing current as a result of detecting an emergency condition, the control unit C actuates the power supply to supply a +24v peak AC voltage to be superimposed upon the 24v DC power supply for the detectors. The system therefore allows the use of a direct current to monitor the detectors, and any removal of the detector causes an alternating current to power the sounders.

The AC and DC components of the detectors and sounders can be separated using passive filtering techniques generally similar to that described above and with reference to Figs. 3 to 6.

The circuitry for the sounders interface and the detector monitor interface are as shown in Fig. 8 and they are generally similar to that described above with reference to Figs 4 & 5. Each of the devices on the line has an "address" and a digital tone or pulse may be sent down the line superimposed on the DC signal to allow the condition of the devices to be checked. In practice this is done by polling each of the devices in turn by putting an interrupt on the line and the system then goes on to check the status and condition of each of the devices. Such techniques will be generally known to those skilled in the art.

Various modifications may be made to the above described embodiments without departing from the scope of the present invention. Furchermore whilst the above description haq been restricted to the use of the present invention in a fire alarm/detection system it will be appreciated that the invention is applicable also to a variety of other applications including intruder alarms and other building and security management systems.

The above described embodiments have been described with reference to a system installed in what is referred to by those skilled in the art as a single zone system or an addressable single zone system. It will be appreciated that the above described systems could be utilized in a multi-zone or addressable multi-zone installation and there be provided different drivers to cover each zone thereby to discriminate via a control means in which zone an alarm condition has been detected.

Claims

CLAIMS 1. A fire alarm/detection system comprising a control unit coupled to a single circuit provided with power supply connection means for connection of the system to a power supply in use of said system, and at least one detection device and at least one warning device connected to said circuit, said power supply, in a steady state monitoring condition of the system, having a first signal output detectable by and usable to power said at least one detector device and, in an alarm condition of said system, a second signal output detectable by and usable to power said at least one warning device, said first and second output signals being different from each other so as to be each selectively passable by respective filter means said detector device being provided with first filter means formed and arranged for selectively passing said first signal output to said detector device and said alarm device being provided with second filter means formed and arranged for to selectively passing said second signal output from said power supply to said alarm device.
2. A fire alarm/detection system as claimed in claim 1 wherein said first signal output is in the form of an alternating current (AC) signal.
3. A fire alarm/detection system as claimed in claim 1 or claim 2 wherein said second signal output is in the form of a direct current (DC) signal.
4. A fire alarm/detection system as claimed in claim 2 or claim 3 wherein there is used a square wave AC signal superimposed upon a steady state DC signal.
5. A fire alarm/detection system as claimed in claim 3 or claim 4 wherein said direct current DC supply is a 24v DC supply.
6. A fire alarm/detection system according to any one of claims 2 to 5 wherein said AC signal has a +24v peak.
7. A fire alarm/detection system according to any one of claims 2 to 6 wherein said AC signal has a frequency in the range of from 10Khz to 100Khz.
8. A fire alarm/detection system as claimed in claim 7 wherein said AC signal has a frequency in the range of from 20-80Khz.
9. A fire alarm/detection system as claimed in any one of claims 1 to 8 wherein the first and second signal outputs are provided substantially simultaneously by said electrical power supply in an alarm condition of said system.
10. A fire alarm/detection system as claimed in any one of claims 1 to 9 wherein each of said detector means has a filter means to block or to remove said first signal means and each said warning device is provided with a filter means to remove or block the second signal means.
11. An addressable fire alarm/detection system comprising a control unit coupled to a single circuit provided with a power supply connection means for connection of the system to a power supply in use of said system, and a plurality of detector devices and a plurality of warning devices connected to said circuit, said power supply, in a steady state monitoring condition of the system, having a first signal output detectable by and usable to power at least one of said plurality of detector devices and, in an alarm condition of said system a second signal output detectable by and usable to power at least one of said plurality of warning devices, said first and second output signals being different from each other so as to be each selectively passable by respective filter means, each one of said plurality of detector devices being provided with first filter means formed and arranged for selectively passing said first signal output to a said detector device and each one of said plurality of alarm devices being provided with second filter means formed and arranged for selectively passing said second signal output from said power supply to one of said plurality of alarm devices each one of said plurality of detector devices having signal generating means and said control unit being provided with detector device testing means for generating a test signal and means for searching said signal around said circuit to said plurality of detector devices and for monitoring the response of said detector devices to said signal so as to check the status of each of said detector devices each of said detector devices being formed and arranged to issue a status signal in response to a corresponding test signal.
12. A fire alarm/detection system substantially as described hereinabove and with reference to Figs 2 to 6 and 7.
13. An addressable fire alarm/detection system substantially as described herein above and with reference to Fig. 8.