GB2376548A

GB2376548A - Alarm system

Info

Publication number: GB2376548A
Application number: GB0106934A
Authority: GB
Inventors: Fariz Khellaf
Original assignee: Cooper Lighting and Security Ltd
Current assignee: Eaton Electrical Systems Ltd
Priority date: 2001-03-20
Filing date: 2001-03-20
Publication date: 2002-12-18
Anticipated expiration: 2021-03-20
Also published as: GB2376548B; GB0106934D0

Abstract

An alarm system (10) has a control unit (12), two or more detection units (22), such as smoke detectors, heat detectors, gas detectors or call points, and two or more alarm indication units (26), such as sounders. The detection units (22) are individually addressable by characteristic signals sent from the control unit (12), thereby allowing the control unit (12) to issue/receive a particular message to/from a particular identified detection unit (22). The control unit is also capable of sending a first signal to the alarm indication units (26) which are each switchable from a standby state to an alarm state by the same first signal. A voltage monitoring unit monitors the alarm system for circuit breakages and for informs the control unit (12) of detection of such.

Description

ALARM SYSTEM The present invention relates to an alarm system and a method of operation therefor. In particular, the invention is suitable for use with and/or in a fire alarm system.

A typical fire alarm system consists of a central controlling unit, a number of detectors and a number of alarm indicating units. Usually, the separate parts are connected together electrically. The detectors may be smoke detectors, heat detectors, gas detectors, manually operable call points, interface units and/or pressure switch monitors. The central control unit receives information from the detectors. When information is received indicating that a fire is present, the central control unit may trigger an alarm signal. The alarm signals are transmitted to occupants of a building, for example, via the alarm indicating units. The alarm may be audible and/or visible. The alarm indicating units may be located at a number of points throughout an area monitored by the fire alarm system.

A typical, modern fire alarm system is addressable.

In such systems, each device attached to the system has a unique address. Using a particular address, the control unit can send signals to and receive signals from specific devices, respectively. This type of system is a digital type system.

Based on the information received from individual devices attached to the system, the control unit may activate one or more alarm indication units by sending a command or a series of commands with specific addresses which indicate which alarm indication unit (s) is (are) to be activated. However, the alarm indication units in such

a system must be capable of decoding addresses and also must have a facility to set a particular, unique address for each unit. These units are costly due to the internal electronics required for the decoding of the addresses and the setting of a unique address. Using such alarm indication units also requires an installer to set a particular, unique address for the unit. This can be time consuming and requires highly skilled installation expertise.

Typically, each detector and alarm indication unit must be checked periodically to ensure continuing satisfactory operation. The maximum time between checks is set by British and European standards. In conventional digital systems, each device is checked by the control unit by periodical polling. Of course, each polling action requires that the control unit sends a unique address to the device being polled. Again, the setting up of such a polling programme is time-and labour-intensive.

The present invention aims to address some or all of the above problems.

Accordingly, in a first aspect, the present invention provides an alarm system having a control unit, two or more detection units, and two or more alarm indication units, wherein the detection units are individually addressable by characteristic signals from the control unit, and the control unit is capable of sending a first signal to the alarm indication units, the alarm indication units each being switchable from a standby state to an alarm state by the same first signal. In this system, the detection units are selectively addressable, but the alarm indication units used here typically are not. Therefore, analogue sounders may be used which are less costly and less complex than their digital counterparts. Accordingly, installation of

such an alarm system is less costly and less time-consuming than installation of a fully digital type alarm system.

Preferably, the alarm indication units are switchable from the alarm state to the standby state by the same second signal from the control unit. This allows the alarm indication units to be re-set to the standby state from the alarm state without the use of individual, unique addressing.

Typically, the alarm indication units are switchable from the standby state to a testing state by the same third signal from the control unit.

Preferably, the control unit has means for producing addressed signals and means for producing non-addressed signals. The signals may be analogue signals or digital signals. Typically, the addressed signals are digital signals and the non-addressed signals are analogue signals.

Preferably, the alarm system includes a break in a circuit connecting the alarm indication units to the central control unit, the system further including voltage monitoring means to monitor the voltage across the break to give an indication of the status of the alarm indication units.

Preferably the alarm system is a fire alarm system.

In a second aspect, the present invention provides a method of operation of an alarm system including the steps of: (i) individually addressing one of two or more detection units using a characteristic signal from a control unit, and (ii) switching two or more alarm indication units from a standby state to an alarm state using a first signal from the control unit, the switching of

each claim indication unit being achieved with the same first signal.

Preferably, the method further includes the step of switching the alarm indication units from the alarm state to the standby state using a second signal from the control unit, the switching of each alarm indication unit being achieved with the same second signal.

Typically, the method further includes the step of switching the alarm indication units from the standby state to a testing state using a third signal from the control unit, the switching of each alarm indication unit being achieved with the same second signal.

Preferably, the method further includes the step of monitoring voltage across a break in a circuit connecting the alarm indication units to the control unit, the voltage monitoring thereby giving an indication of the status of the alarm indication units.

Preferably, the first, second and/or third signals are all different and include voltage steps between a first voltage and a second voltage. More preferably, the general signals differ from each other in terms of the number of steps and/or the time between steps. Any or all of the signals may be, or may include, a message signal.

By"addressable", what is meant is that an addressable device can communicate with the control unit in a way which is unique to that device with respect to the other devices in the system. This is achieved by the device having a unique address (typically set by an installer) which is used to interpret messages from the control unit.

"Address"and"addressed"should be similarly interpreted.

"Signal", as used herein, refers to a communication, typically a communication of electrical or electronic origin, which is interpretable in the system. For example,

a signal sent by the control unit may be interpretable by a detector unit. Typically, the signals used are electrical in nature, consisting of variations in voltage and/or current. The signals may, for example, be of a digital or analogue type.

Preferred embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings in which :- Fig. 1 shows a schematic diagram of a first embodiment of an alarm system according to the invention.

Fig. 2 shows a schematic circuit for checking the status of a series of sounders.

Fig. 3 is a graphical representation of a schematic voltage signal for switching an alarm indication unit on.

Fig. 4 shows a graphical representation of a schematic voltage signal for switching an alarm indication unit off.

Fig. 1 shows a schematic diagram of an alarm system 10. The alarm system is for use as a fire alarm system.

The alarm system 10 includes a control unit 12 with electrical wiring loops 14,16 and wiring spurs 18,20.

Various fire alarm devices are connected between the wiring loops 14,16 and spurs 18,20.

The presence of both wiring loops 14,16 and wiring spurs 18,20 is not essential to the question of the invention, instead, both are shown to exemplify how the control unit 12 may be electrically connected to the various fire alarm devices.

In Fig. 1 are shown detectors 22, which may for example be smoke detectors, heat detectors, gas detectors, manually operable call points 24, interface units and/or pressure switch monitors. Alarm indicating units 26 are also connected between the wiring loops and spurs. The alarm indicating units in this case are sounders, i. e.

units which indicate an alarm state by emitting a characteristic sound.

The detectors 22 are digital type detectors. These are addressable by the control unit 12. The control unit 12 can send a particular message to a particular detector 22 by selecting the unique address for that detector 22 and sending a digitised message combined with that address. In this way, the particular detector of interest will act on the message. The other detectors will not act on the message since the message did not use their addresses.

Conversely, a particular detector 22 can send a unique message to the control unit 12 by appending a characteristic address to the information sent. In this way, the control unit 12 can identify from which detector 22 a particular message (e. g. a digital information stream) comes from.

When a detector 22 detects a fire, it sends this information to the control unit 12. On receipt of the information that there is a fire in the vicinity of a particular detector 22, the control unit 12 instructs the sounders 26 to emit the alarm sound.

The sounders 26 are analogue sounders. They may, for example, be identical analogue sounders. These sounders are not individually addressable. A signal from the control unit 12 to trigger a sounder to sound the alarm sound will trigger all the sounders to do the same. This is desirable since, if there is a fire in a part of a building, it is highly likely that the whole building (or the whole area covered by the alarm system) will need to be evacuated.

The use of analogue sounders in preference to digital (addressable) sounders is advantageous because analogue sounders are typically far less costly than digital

sounders. In addition, the sounders do not have individual addresses. Therefore, installation of the sounders is more straightforward than installation of digital sounders since the installer does not need to set an address on each sounder.

It is, of course, desirable to check periodically that a sounder is functioning correctly. Using the present invention, this is possible by using a voltage monitor at a break in a circuit to monitor the voltage across that break in the circuit. The circuit connects all the sounders in series. A simplified, schematic circuit is shown in Fig.

2.

In Fig. 2, the voltage monitor 30 monitors the voltage across a break 32, schematically shown as a switch. The control unit 12 applies a voltage across the circuit.

Information from the voltage monitor 30 is sent to the control unit 12. In Fig. 2, a series of sounders is denoted by a dotted line. Under normal operating conditions, the voltage applied across the sounders will be dropped across the break 32. The break 32 may be located inside the control panel. If there is a break elsewhere in the circuit (for example a fault in one of the sounders 26) then the voltage dropped across the break 32 will be zero, or lower than a reference voltage. Accordingly, the voltage monitor 30 sends an appropriate message to the control unit 12 which indicates to a user that there may be a fault in the system.

Since the sounders 26 are analogue sounders, they must be triggered using analogue signals. Fig. 3 shows, schematically, an analogue signal for switching the sounders on, i. e. instructing them to emit the alarm sound.

Ta and Tb denote the width of pulses in terms of time.

Typically, the sounders are held at a voltage of 24 volts,

this voltage stepping to 0 for a pulse of width Ta. The voltage then steps back to 24 volts for a pulse of width Tb. This process is repeated three times. This signal is a signal which all the sounders recognise as the signal to switch on.

Similarly, the switch off signal is shown schematically in Fig. 4. This is a single pulse of width Tc.

The sounders to be used with this invention have the following typical characteristics :- The quiescent current consumption is 100 mA maximum, the operating voltage is 14V to 28V, the sound mode in the alarm state is a warble from 800 to 970 to 1000 Hz, the maximum current required to give a sound output of 85 dBA at 1 metre is 2.5 mA, to give 90 dBA at 1 metre is 5. 5 mA, to give 95 dBA at 1 metre is 7.5 mA, and to give 97 dBA at 1 metre is 15 mA, and the operating temperature range for the sounder is from-20 C to +60 C.

Typical pulse widths for Fig. 3 are 1000 micro seconds plus or minus 10% for Ta and Tb. For Fig. 4, Tc is typically 3000 micro seconds plus or minus 10%.

The present invention has been described by way of example only. Modifications, further embodiments and modifications thereof will be obvious to the person skilled in the art and as such are within the scope of this invention.

Claims

CLAIMS 1. An alarm system having: a control unit, two or more detection units, and two or more alarm indication units, wherein the detection units are individually addressable by characteristic signals from the control unit, and the control unit is capable of sending a first signal to the alarm indication units, the alarm indication units each being switchable from a standby state to an alarm state by the same first signal.
2. An alarm system according to claim 1 wherein the alarm indication units are not individually addressable by the control unit.
3. An alarm system according to claim 1 or claim 2 wherein the alarm indication units are switchable from the alarm state to the standby state by the same second signal from the control unit.
4. An alarm system according to any one of the preceding claims wherein the alarm indication units are switchable from the standby state to a testing state by the same third signal from the control unit.
5. An alarm system according to any one of the preceding j claims which the control unit has means for producing addressed signals and means for producing nonaddressed signals.

<Desc/Clms Page number 10>
6. An alarm system according to any one of the preceding claims wherein the alarm system includes a break in a circuit connecting the alarm indication units to the central control unit, the system further including voltage monitoring means to monitor the voltage across the break to give an indication of the status of the alarm indication units.
7. An alarm system according to any one of the preceding claims which is a fire alarm system.
8. A fire alarm system substantially as hereinbefore described with reference to the accompanying drawings.
9. A method of operation of an alarm system including the steps of: (i) individually addressing one of two or more detection units using a characteristic signal from a control unit, and (ii) switching two or more alarm indication units from a standby state to an alarm state using a first signal from the control unit, the switching of each alarm indication unit being achieved with the same first signal.
10. A method according to claim 9, further including the step of switching the alarm indication units from the alarm state to the standby state using a second signal from the control unit, the switching of each alarm indication unit being achieved with the same second signal.

<Desc/Clms Page number 11>
11. A method according to claim 9 or claim 10, further including the step of switching the alarm indication units from the standby state to a testing state using a third signal from the control unit, the switching of each alarm indication unit being achieved within the same third signal.
12. A method according to any one of claims 9 to 11, further including the step of monitoring voltage across a break in a circuit connecting the alarm indication units to the control unit, the voltage monitoring thereby giving an indication of the status of the alarm indication units.
13. A method according to any one of claims 10 to 12 wherein the first and second signals are different to each other and include voltage steps between a first voltage and a second voltage.
14. A method according to claim 12 wherein the signals differ from each other in terms of the number of steps and/or the time between steps.
15. A method of operating a fire alarm system substantially as hereinbefore described with reference to the accompanying drawings.