GB2348031A - An addressable alarm system - Google Patents

Abstract

In an addressable alarm system with a plurality of addressable detectors and alarm indicating devices, at least one detector and one alarm indicating device share a common address, and are arranged to respond in a time displaced manner to addressing by a control unit. Address pulses 31 are received and a detector at a particular address responds with a word 32 while an alarm indicating device at the same address responds with a word 33 (which may occur at a time before or after word 32) so that a detector and an alarm indicating device with a common address can both be individually addressed.

Description

2348031 ALARM SYSTEMS This invention relates to alarm systems.

In alarm systems such as fire alarms or smoke alarms it is common to have a series of detectors connected to a central control unit, each of which detectors can independently detect when an alarm condition is present (eg fire, heat or smoke presence) and give a suitable signal to the control unit. A separate system of alarm units, typically in the form of sounders, are connected to the control unit and the control unit activates either all of these or in some systems, only selected ones of these. The sounders are adapted to emit an audible signal when triggered by the control unit to indicate the presence of the alarm.

Such a system is shown schematically in Figure I in which a plurality of detectors I are connected in a loop to a control unit 2 and a plurality of sounders 3 are activated over a separate line 4. The sounders 3 are powered from the control unit 2 and therefore fire-proof or at least fi-re-resistant cable must be used to connect the detectors to the control unit. In addition, once the system has been installed, particularly with an addressable system, it is difficult to alter the positions of the sounders as desired. It may often be desired to add more sounders or to alter the positions of sounders as use of a building changes and this can be difficult with the system of Figure 1. Also, since the sounders receive power from the control unit, if more sounders are added, the power requirement is greater and therefore the capacity of the cabling and the control unit power supply may need to be increased.

The present invention arose in an attempt to provide an improved alarm system which overcomes the above difficulties.

According to the present invention there is provided an alarm system comprising an alarm detection indication circuit extending from and to a control unit, a plurality of detectors being mounted at desired positions along the circuit and a plurality of alarm indicating devices being mounted at desired positions on the same circuit, wherein at least one detector and alarm -2indicating device share a common address for being addressed from the control unit and are arranged to respond individually, and in a time- displaced manner, to such addressing.

The alarm indicator is preferably a sounder but may be arranged to emit visual and/or 5 audible (eg voice) signals.

Preferably, the alarm indicating device and a detector are commonly physically mounted and share a common address.

Preferably, the alarm indicating device includes a battery and a charging means which preferably is adapted such that the alarm indicating means receives input voltage at a lever which is the same as that used by detectors, so that the or each sounder may be is placed on the same wire network as the or each detector in an alarm system. Typically, this will be 24V but could vary depending on circumstance and regulation. Generally, many detectors and alarm indicators will be placed on the same circuit.

According to the present invention in a second aspect there is provided an alarm system comprising an alarm detection/indication circuit extending from and to a control unit, a plurality of detectors being mounted at desired positions along the circuit, and wherein a plurality of alarm indicating devices are mounted at desired positions on the same circuit, each alarm indicating device comprising a rechargeable battery and charging means for said battery adapted to operate at the same voltage as the detectors.

Preferably, a plurality of mounting stations are provided, at each of which mounting station a detector and a sounder can be mounted, the sounder and/or detector being configured such that one of them is mounted directly upon the station and the other is mounted upon the respective other one, means being provided to allow electrical signals to pass through the first one of the sounder and detector to the second one.

The sounders and detectors may be mounted by simple mechanism, such as a bayonet -3 mechanism both to the mounting station and to each other to allow easy removal and replacement and are adapted so that any mounting station may be provided with either a sounder, a detector, both or none without effecting the operation of the components or any other components in the circuit.

Removal of devices may be sensed in some embodiments by a control panel however, to meet certain legislation.

According to the present invention in a third aspect, there is provided an alarm system comprising any one or more of the novel features herein described.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure I shows a prior art alarm system configuration;

Figure 2 shows schematically an alarm system according to the present invention; Figure 3 shows schematically a mounted sounder/ detector arrangement; Figures 4(a), (b) and (c) show a mounting mechanism and a mounted base/detector arrangement; Figure 5 shows schematically a sounder circuit; Figure 6(a) shows a block diagram of a sounder circuit; Figure 6(b) shows a sounder circuit in more detail; Figure 7 shows a pulse diagram showing address pulses according to the prior art; and

Figures 8-11 show schematically pulse diagrams showing address pulses according to embodiments of the invention.

Referring to Figure 2, an alarm system according to the present invention is based around a central control unit 2 similar to that of the prior art. A single circuit 5, eg a two wire system, comprises outward 6 and return lines 7. The lines need not be of fire proof cable nor be particularly heavy duty, as will be required in prior art alarm lines. This is because in prior art systems the capacity of the alarm line had to be sufficient to provide the required voltage for each of the sounders or other alarms on that line and as more sounders were added, the requirements increased. With the present invention, on the other hand, each sounding device is provided with its battery and therefore the wire can be of the same size and capacity regardless of the number of sounders mounted to it. The circuit 5 extends across a building and has mounted to it a plurality of detectors 1. These are positioned at suitable locations and may be fire or heat detectors, smoke detectors or other types of detectors as appropriate.

A plurality of alarm signalling devices such as sounders 3 are also connected to the same circuit line 5. In preferred embodiments, the detectors and alarm indicating devices (hereinafter "sounders" but which may also be other types of indicating devices such as ones providing a visual output) are mounted at common mounting points and superimposed one upon the other with electrical contacts between them but they may alternatively be mounted in different positions. There need not necessarily be the same number of detectors and sounders. Indeed, this will usually not be the case since there will usually be positions in a building where it is required to have detectors, but not sounders (such as parts generally unoccupied) and conversely areas where it is desired to have sounders, but not necessarily detectors.

Each sounder assembly is provided with its own independent rechargeable battery and battery charging units, schematically shown at 8. These are adapted such that the battery chargers work at the same voltages as are used by the detectors 1, which enables the sounders to be placed on the same circuits. Typically, a line voltage of 24 volts is normal for fire alarm systems but this desired voltage may of course change with circumstances and regulations. The charging circuit is therefore arranged to operate from a 24V supply. In practice, a step down circuit will generally be required to convert from the 24V high voltagellow current on the line to a low voltage/high current necessary to charge a battery. Preferred batteries are 3.6 volt 60/70 mA/hour NICAD/NiNM batteries but other types of batteries may be used such as lithium rechargeable ones.

The system may be an addressable type of system in which each of the detectors and, also preferably the sounders, are individually addressable from the control unit. Alternatively, the system may be an unaddressed one. In either case, the system is arranged such that when any of the detectors detect an alarm situation a triggering signal is passed to one or more of the sounders as appropriate and this triggering signal causes the battery to be disconnected from the charging circuit and connected to power the sounder. Thus, once the sounder is actuated, it 5 is powered by its own battery and does not rely at all on mains power from the control unit. Even if the control wire 5 bums through or is otherwise destroyed the sounder still operates from its own internal battery. A step-up circuit may be required to convert from the output voltage of the battery to a voltage required to operate the sounder.

As indicated, in a preferred feature of the present invention the detectors and sounders are mountable in the same location by being superimposed upon another. Figure 3 shows this concept schematically. A detector base 9 is mounted semi-permanently by being screwed or otherwise to a wall or ceiling 10. Normally, a detector body I would be mounted on top of the detector. In embodiments of the present invention the sounder body 3 may be mounted on the detector base and a detector body I may be mounted in turn upon the sounder.

As shown schematically by the dotted lines 11, electrical through paths are provided between the various parts which are connected to the main electrical line 5 from the control unit. The electrical connections between the components are such that they are automatically made when the components are assembled. They may be assembled together by a bayonet type of mechanism as is well known in the art or by other mechanisms.

In a preferred feature, the mounting mechanism of the sounder and of the detector I is the same so that, if desired, a detector body I can be mounted immediately upon detector base 9 without an interposed sounder. Alternatively, a sounder can be used without a detector on top. A blanking cover may then be placed on the sounder. Thus, complete flexibility is achieved as to the positioning of detectors and sounders. In some locations both a detector and a sounder may be mounted whereas in others only a detector or a sounder can be mounted. Alternatively, some positions may be left blank without detector or sounder. In an addressable 30 system, the various addressable units preferably provide details to the control unit, when -6addressed, indicative of their type and identity such that when detectors or sounders are moved or removed, the system is automatically configured to recognise the change.

In some applications it may be necessary to 'lock' detectors onto their mounting so that they can only be removed with a tool. A locking mechanism may be incorporated onto both or only one of the sounder and detector, allowing one or both to be locked in position or for a detector to be locked onto a sounder ensuring that they are removed together.

As shown in Figure 3, the detector unit I is provided with a series of indentations 22 or other means at its distal edge and these can engage with a disconnecting means such as a 'cherry picker' type which comprises manipulatable arms which engage into these recesses 2 to enable rotation thereof and thereby remote removal or replacement of the detector.

Figure 4(a) illustrates schematically how a bayonet mechanism may be used for mounting the components. A plurality of circumferential apertures 12 are formed in the base and/or top of a sounder detector or mounting base unit. Each of these is provided towards one end with a pair of inwardly directed lips 12a, forming a channel portion. Electrical contact fingers 13 are mounted in each aperture, electrically connected to circuitry on the unit or to electrical connection parts on the other side of the unit. Electrical mounting contact pins or bosses 14 are provided on a unit to be mounted to the first one, which pins have enlarged heads 14a and reduced diameter stems 14b. The pins may be spring-loaded. The pins engage into respective apertures 12 at their widened (lipless) parts and the units are relatively rotated so that the enlarged heads 14a of the pins are held captive within the channels by lips 12a, preventing axial removal. The pins act against the resilience of contact fingers 13 to provide electrical contact therewith as shown in Figure 4(b). The fingers may be secured at one end by a screw 13a as shown in Figure 4(b), or by other means so that their distal ends have a resilience. They may be spring loaded or be otherwise resilient. Locking tabs may also be used which, when a unit is fully inserted are sprung into a location position where they must be manually manipulated to enable release by turning in the opposite direction.

In some embodiments, both pins and apertures may be provided on each surface to be joined.

One of the units to be joined is provided with a plurality of arcuate flange portions 40 of different lengths, forming arcs of a circle as shown in the figure. The other unit is provided with a circumferential groove 41 into which the flanges extend when mounted.

Radial ribs 42 are mounted in the groove 41, spaced so that the flange 40 can only enter groove 41 in one relative disposition. This ensures that the correct contacts are made between the pins 14 and fingers 13, since a particular pin can only be placed against a particular finger.

Figure 4(c) shows, in cross-section, a detector I mounted upon a mounting base 9. The figure shows flanges 40 in groove 41, with the wall 43 of the detector lying generally flush with the wall 44 of the base. Pins 14 are shown with their head 14a through apertures 12. The detector shown includes an ionisation chamber 45 mounted upon a plate 46. A lower plate 47 mounts the circuit board for the detector. In embodiments of the invention, a sounder can be placed between the detector and base, or the detector iemoved and a sounder and cover mounted on the base.

Figure 5 shows schematically part of an alarm system including a power/communications line 5 extending from a control unit 2. Mounted to this line are a plurality of detection/alarm stations 15 at which a detector and/or a sounder may be mounted.

At each of these stations 15, a detector, if present, receives power and communicates and a sounder module may be present. A schematic, simplified, diagram of a sounder circuit is illustrated. A battery 16 is switchably connected to either a charging circuit 17 or a sounder device 18. The charging circuit is arranged to operate via the standard voltage on line 5 and is typically 24 volts. This will generally necessitate the use of a step down circuit to convert from high voltage/low current to a lower voltage/high current signal usable to charge a battery.

This is illustrated by part l7a although in some circumstances the step down circuit may not be necessary. In normal use, that is when no alarm situation is detected, power is applied to -8charger 17 and a switch 19 is used to connect the battery to the charger such that the battery charges. With one circuit arrangement, the battery charges at a rate of 2 mA from a chargelstep down system which draws current from the line 5 at between 0.8 and I mA. With a 3.6 volt 60/70 mA hour NICAD/NiNfffl battery it has been found that this current is sufficient to fully charge the battery in about twenty four hours to give a full one hour of sounding time before the battery is discharged.

When an alarm situation is detected by any of the detectors on the line a signal is sent to a control unit 2 which sends an appropriate signal to actuate the selected one or more of the sounders on the circuit. A triggering signal is sent from the control unit to that sounder and switch 19 is switched to the position shown in the figure at which the battery is disconnected from the charger but is connected to the sounder 18 to thereby operate the sounder. At this stage, the sounding unit is powered entirely by its own battery. The switching of switch 19 is controlled by an addressable local sounder control circuit 20 which is generally addressable to receive signals from control unit 2 and act on them accordingly. It is used to switch 19 from and to the charging positions and may also be connected directly to the sounder 18 so as to be able to control functions of the sounder and to generate status reports on the sounder which can be sent to and from the control unit via addressing techniques. Addressing techniques are well known in the art. The sounder may be of the type which can generate several different types of sound or which can optionally generate a visual alarm in addition to sound and the local control unit 20 can determine which type of signal should be output at any time. Upon the cessation of an alarm situation, the local control unit can be arranged to switch back the battery to begin charging again, perhaps after a predetermined time interval has elapsed.

Figure 6(a) shows a block diagram of the sounder circuit. Addressable control unit 80 receives signals from the alarm line. A constant current source 61 is connected to the line and provides current to step down converter 62 to recharge battery 16. When the sounder 18 is to be activated, the control unit 20 sends an enable signal to step up converter 63 which receives input from battery 16 to power sounder 18 through a sounder control circuit 18a. This generates suitable signals to power the sounder and can generate different types of sounds, and other features.

Figure 6(b) shows one example of a circuit diagram of the sounder in more detail. Essentially the circuit reproduces the general function of the diagram of Figure 6(a). 5 The step down circuit utilizes a constant cur-rent source IC2 which is formed by a I mA constant current diode. Alternatively, this may be a FET or a bipolar transistor for example. A 30 volt zener diode D I I is fitted across a 22 gF capacitor C8 to protect a step down integrated circuit IC I from excess input voltage. Capacitor C8 acts a charge reservoir. A feedback signal is derived from charge current flowing in the battery with a sensing resistor R 17 of 100 ohms and this is compared with an internal 200 mV internal reference voltage on IC I, which is a LT 1073 IC made by Linear Technology. As indicated above, the preferred charging current is 2 mA at an output voltage of about 5 volts. A blocking diode D8 prevents the battery from discharging back into the circuit ICI when line power is removed so that the battery can be used to power a sounder at this time.

A large inductor Ll of 1000 gH is used, and a capacitor C9 is used because a switching oscillator is gated in sympathy with the triangular wave form developed across C9. A flywheel diode in the form ofa schottky diode D7 is provided to reduce reverse voltage across the switching transistor when it turns off. The integrated circuit has a spare internal comparator which is used to monitor the voltage across the reservoir capacitor C8. If this voltage falls below 18 volts then a transistor TR10 is turned on to force the feedback voltage to an artificially high level. This immediately switches down the switching circuit until the reservoir voltage rises above 18 volts.

The battery voltage monitor part of the circuit is a simple window comparator which uses CMOS comparator. A "battery fail' condition is triggered if the battery voltage falls below 3 volts or rises above 4.8 volts and this results in low output conditions and 'I pulse' transistor TR3 being shut off. Integrated circuit IC3 is an addressable control circuit.

A step up circuit utilizes an integrated circuit IC6 which is a DC to DC step up voltage converter. This receives power from the NICAD battery at a level of about 4 volts or so and provides an output voltage of about 12 volts which is sufficient to power the sounders. The input current in this situation is approximately 30-40 mA. The step up circuit and sounder are normally turned off but, if a logicTis output from pin 16 of IC3 then a MOSFET TR4 is turned on which thereby causes the step up circuit and the sounder to be powered. The sounder circuit IC5 is turned on when transistor TR4 is turned on and turned off when not since the NICAD battery is then effectively in an open circuit because of the blocking diode D8.

It is known to provide addressabifity for alarm systems. Various techniques are available for doing this but one of them is illustrated in Figure 7. The system uses pulse transmission over the power lines 5. A first pulse 30 is emitted from the control unit and this in effect a timing pulse. The receipt of this pulse by each detector causes a counter to be reset and begin counting. A number of subpulses 31 are output at predetermined time intervals after counter reset pulse 30 and each one of these is associated with a unique detector address. Thus, the first subpulse 31 which occurs, say, 50 counts after the timing pulse is associated with detector 1; the second pulse, say 100 counts after the timing pulse 3 0, is associated with detector 2 and so on. Each detector receives the pulses and is arranged to transmit or receive data in the time interval immediately after its own pulse has been received. Thus, in the situation in Figure 7, the first detector receives first pulse 31 and transmit a digital word 32 to the controller. This digital word 32 immediately follows a particular one of the pulses 31 when it is received again by the control unit and the control unit can therefore identify which of the detectors it is associated with. The data transmitted by the detector may contain data representative of any or all of; the status of that detector, whether an alarm has been detected or not; its address (enabling detectors to be moved on the system and be individually addressed automatically); the actual magnitude of the alarm signal (ie amount of smoke, fire or whatever else is to be detected) and other types of data.

In embodiments of the present invention, timing pulses 30 and address pulses 31 are still produced, as shown in Figure 8, but the spacing between the address pulses 31 is - I I increased. This gives time for not only a detector at a particular station or address, to respond with a word 32 but also for a sounder to respond with a word which is time displaced 33 (either before or after word 32). Thus, where in the present invention a detector and a sounder share the same address they can both be individually addressed and can communicate with a control unit. The control unit is programmed to recognise that a word or other data received within a certain number of counts from any particular address pulse 3 1 relates to a detector at that address and a word or data received within a predetermined further count relates to a sounder at that address.

The control unit can also, of course, send communications data to each addressed detector and/or sounder.

In a preferred embodiment, the reply 32 from the detector is delayed, eg by about 2 ms, as shown in Figure 8, to enable a reply 33 from the associated sounder. Each sounder may be arranged so that when the detector at the same address triggers, indicating an emergency situation, that sounder operates to inforin persons in its vicinity of the emergency. General sound, evacuate and silence commands, for example, may still operate all the sounders in the system. Alternatively, or additionally, the sounders may be controlled in zones, in which a plurality of sounders and/or detectors comprise one zonal control area.

In preferred embodiments, different types of signal maybe applied to the devices at a single address. For example, a first set of signals may refer to one type of device (eg a detector), a second set of signals to a second type of device (eg a sounder) and a third set of signals may refer to both types of device together. Thus, address reset and address increment pulses (eg pulses 30,3 1) maybe applicable to both detectors and sounders, an analogue multibit signal may be applicable only to a detector, and a toggle pulse may be applicable only to a sounder.

Figure 9 shows schematically a condition in which an address increment pulse 31 is received, indicating a specific address. The normal reply 34 from the analogue detector is -12delayed by 2-3 ms, for example, giving time for a sounder to reply with a normal reply pulse 35, of 244 ps. This may indicate that all is correct with the sounder, for example. After its normal reply pulse 34, the detector issues a multi-bit analogue signal 32 giving status, etc.

Figure 10 shows schematically a condition in which a toggle pulse 36 is issued by the central control unit, at a time representative of a particular address in the addressing cycle. The toggle pulse is of 976 gs, significantly longer than the address increment pulse 31 of Figure 9, and this increased length can signal to the sounder that a toggle reply is required. The sounder accordingly replies with an elongated toggle reply 37, of 1.9 rns, and the analogue detector replies after this.

Hence, the length of the toggle reply pulse from the sounder may be used to give information, avoiding the need for the sounder to produce multi-bit messages. For example, a pulse of one length may indicate that the sounder is 'readY, whereas a pulse of a second, different, length may indicate that the sounder is 'not ready'. Other messages maybe transmitted by causing the sounder to generate pulse of other lengths, so that a plurality of different pulse lengths can indicate a plurality of different conditions. In addition, or alternatively, the detector may also output signals of different lengths.

Alternatively, or in addition, the sounder and/or detector may be arranged to provide pulses of signals of a different magnitude, or intensity, to those of the detector. Figure I I shows this schematically, indicating that a reply 32 from a sounder is of a higher amplitude current pulse than the reply 33 from a detector. By having a plurality of different amplitudes possible, a plurality of different messages may be transmitted. A different amplitude for the detector and sounder replies, respectively, can also help in identifying the source of a reply from an address.

In some embodiments voltage pulses may be used from the central control unit as addressing or control pulses, and current pulses used for replies from the devices connected to the control unit.

-13Other variations may of course be used.

In some embodiments of the invention the alarm system may be of the zoned type, in which detectors and/or alarm indicating devices are grouped together, on the same or different circuits, in zones for the detection and indication of alarm situations, so that a detected alarm causes the sounder(s) in that zone to actuate - an alarm signal may be a voltage on the zone wire set by a detector in the alarm state.

Sounders (or other alarm indicators) may be arranged so that they continue to operate even if the sounder becomes disconnected from the rest of the system when in an alarm state and may be reset to normal by a'silence/reset' signal, eg a pulse, series of pulses, a predetermined voltage or some other signal.

Claims (7)

-14CLAIMS

1. An alarm system comprising an alarm detection indication circuit extending from and to a control unit, a plurality of detectors being mounted at desired positions along the circuit and a plurality of alarm indicating devices being mounted at desired positions on the same circuit, wherein at least one detector and alarm indicating device share a common address for being addressed from the control unit and are arranged to respond individually, and in a timedisplaced manner, to such addressing.

2. An alarm system as claimed in Claim 1, wherein the alarm indicating device and a detector are commonly physically mounted and share a common address.

3. An alarm system as claimed in Claim I or 2, wherein different types of signals are output by the detector and alarm indicating device. 15

4. An alarm system as claimed in any one of Claims I to 3, wherein the detector and/or alarm indicating device is an-anged to output reply signals of a plurality of different pulse lengths or amplitudes, each different pulse length indicating a different message.

5. An alarm system as claimed in any of the preceding claims, wherein the alarm system is a zoned system in which detectors and/or alarm indicating devices are grouped together in zones for the detection and indication of alarm situations.

6. An alarm system as claimed in Claim 5, wherein each alarm indicating device responds 25 to an alarm signal which is the voltage on the zone wire set by a detector in the alarm state.

7. An alarm system as claimed in any of the preceding claims, wherein the alarm indicating device continues to operate if it becomes disconnected from the rest of the system when it is in the alarm state. 30 f -158. An alarm system as claimed in Claim 7, wherein the alarm indicating device is reset to normal by a 'silence/reset' signal.