WO2000054042A1

WO2000054042A1 - Fire detection apparatus

Info

Publication number: WO2000054042A1
Application number: PCT/GB2000/000770
Authority: WO
Inventors: Mark Philip Byfield; Gulam Mohammed Ismail
Original assignee: Marconi Applied Technologies Limited
Priority date: 1999-03-05
Filing date: 2000-03-06
Publication date: 2000-09-14
Also published as: EP1159606A1; JP2002539511A; GB2347502A; AU3173500A; GB0005269D0

Abstract

Fire detection apparatus includes an array of SAW sensors which are responsive to gases and/or vapours produced when an incipient fire occurs to give early fire detection. The apparatus is particularly applicable to detection of overheating of circuitry on PCBs, for example.

Description

FIRE DETECTION APPARATUS

This invention relates to fire detection apparatus and more particularly to

apparatus which uses chemical sensor means to detect incipient fires.

There are many different types of fire detection apparatus on the market using

different forms of technology and sensor to raise an alarm when a fire starts. For

example, smoke detectors sense smoke generated during a fire from the burning

material. Heat detectors detect changes in temperature which occur during a fire.

The present invention seeks to provide an improved fire detection apparatus.

According to the invention, there is provided fire detection apparatus

comprising: chemical sensor means including an array of SAW sensors responsive to gases and/or vapours produced when an incipient fire occurs in the environment in

which the apparatus is intended to be used, and sampling means for delivering gases

and/or vapours to the array where they are detected.

By using the invention, it is possible to detect a fire at its very beginnings

before the onset of combustion and smoke generation. The use of chemical sensor

means, for example including those arrays employed in "electronic noses", enables

gas and/or vapour molecules produced due to overheating to be detected with great

sensitivity. This permits detection of fires at an early stage, enabling appropriate

action to be taken. A SAW sensor used in an array in the chemical sensor means includes a

coating which is tailored so as to absorb particular molecules. The added mass of the

molecules absorbed onto the SAW affects the transmission of an acoustic signal at its

surface, enabling the absorbed molecules to be detected. The array of SAW sensors is

made responsive to gases and/or vapours of interest by including different coatings on

different sensors of the array, to make them sensitive to vapours likely to be produced

in the particular environment in which the apparatus is to be used. An array of SAW

sensors of this type, each being coated with a material which selectively absorbs

volatiles, gives a very sensitive detection system. The SAW coatings may be selected

to give good discrimination of gases/vapours of interest. Examples of coatings

suitable for SAWs used in detecting incipient fires includes: Poly(isobutylene):

selective for non-polar vapours (e.g. hexane, toluene, octane, etc.) Poly(phenylsulphone): selective for polar vapours (e.g. acetone, methanol, etc.).

SAW sensors offer much greater sensitivity and thus lower detection limits

than BAW (bulk acoustic wave or quartz micorbalance) sensors. For example, a 260

MHZ SAW resonator demonstrates approximately one hundred times the sensitivity

of a BAW device. Also, because SAW sensors have greater sensitivity, one may

employ much thinner sensor layers than BAWs, giving faster vapour on/off kinetics

and hence quicker responses and recoveries.

SAWs are small devices and as multi-sensor array may be laid out on a single

chip, that is, the same piece of quartz. This saves costs, permits small size arrays to

be used, suitable for handheld instruments, and aids referencing for ageing and temperature compensation and reproducibility.

SAW responses are due to comparable visco-elastic and mass based responses

whereas a BAW device only provides a mass based response. Low molecular weight

vapours give a small mass change on the SAW or BAW device but can potentially

give rise to a larger SAW response if they bring about visco-elastic changes.

The invention is particularly advantageous for applications in which the

chemical sensor means is intended to detect an incipient fire in electrical circuitry and/or cabling, for example to be responsive to gases and/or vapours produced when a

PCB overheats. It is in situations such as these that early detection is highly desirable,

particularly where the electrical equipment is used in critical applications, for

example, on board aircraft, at sea or in underground tunnels. The chemical sensor

means may be tailored so as to detect which of several possible electrical sources of a fire are involved. For example, it may be able to detect and discriminate between

overheating in wiring connected to a PCB and overheating of circuitry and

components carried by the PCB itself. This enables an engineer investigating the

problem to more quickly and accurately diagnose its location.

Preferably, remote monitoring means is included for communicating with the

SAW array. This is particularly advantageous as it permits fire detection in

dangerous, hazardous and/or inaccessible areas. It is advantageous in less dangerous

environments but where fixed links between the SAW array and a remote processor or

monitor, for example, would be difficult or inconvenient to install. An antenna may be mounted on the SAW oscillator to transmit over short

distances, say of the order of tens of metres, at the actual operating frequency of the

device, say 260 MHZ . The response from the SAW array may include an identifier

code, which is particularly useful where several SAW arrays are included in the

system.

In a particularly advantageous embodiment, the array is contained within a

sensor module. Also it is preferred that sampling means is included in a sampling

module. The sampling module may be simply a flexible tube and pump located to

acquire a sample which is then transmitted to the array or a more complex sample

acquisition arrangement. The modular system permits optimisation of the fire

detection apparatus as a whole for a particular environment in which it is installed.

For example, typically, electrical apparatus will be housed in separate cabinets, each

cabinet including many PCBs, for example. A sampling module or modules may be

included in each cabinet and arranged to acquire a sample from the cabinet and

transmit it to a sensor module. The sensor module may be located outside the cabinet

or may also be included within the cabinet. A plurality of sensor modules may be

included in the cabinet, each having its own sampling module attached thereto. In

other embodiments, a single sensor module may be included in or near a cabinet and

arranged to receive the outputs from several sampling modules, either serially or

simultaneously. Samples may be acquired continuously, as discrete samples or as batched samples, for example.

The modular approach may also be implemented by having a processor module which is arranged to accept inputs from one or more sensor modules. The

processor module may be located in a physically remote region from the sensor

modules which, to minimise the transfer path of the volatiles to be sensed, are located

in or near the environment which is being monitored. The use of a separate processor

module provides a powerful tool to a user. It enables a large physical area to be

monitored by the fire detection apparatus. When an incipient fire is detected, an

operator may be alerted as to its physical location and even to a particular component

or components likely to be the seat of the incipient fire. Even where a large number

of PCBs, say, are included in a cabinet, it may be possible to distinguish which one or ones of these are likely to be the source of the problem. Different PCBs may have

different characteristic volatiles produced when they overheat and the coatings of the

array of SAW sensors may be tailored so as to distinguish between these.

An added benefit of the present invention is that it enables earlier detection of

fires than conventional smoke detectors, together with the ability to distinguish fires

from normal background gas signatures, reducing the number of false alarms and

increasing user confidence in the system. Algorithms may be used for analysing the

outputs of the arrays or array. This may be achieved through pre-training of the fire detection apparatus with standard samples or by programming it with known fire

"signatures".

The fire detection apparatus may include a display module for presentation of

information to an operator. This may take the form, for example, of a NDU. In addition, or alternatively, there may be means to provide a control signal to initiate shutdown of a region at which a fire has been detected. This is particularly applicable

to electrical systems. This enables the benefits of early detection achievable using the

present invention to be realised. Shutdown may be implemented before combustion

and smoke production occur, thus saving other parts of the electrical system from

additional damage.

Some ways in which the invention may be performed are now described by

way of example with reference to the accompanying drawings, in which:

Figure 1 schematically shows fire detection apparatus in accordance with the

invention;

Figures 2 and 3 are an explanatory diagrams relating to the operation of the

SAW array included in the apparatus of Figure 1; and

Figure 4 schematically illustrates another apparatus in accordance with the

invention.

With reference to Figure 1, a fire detection apparatus is set up to monitor electrical

circuitry enclosed in three housings 1, 2 and 3 distributed around a room and some

additional circuitry 4 which is not enclosed within a housing. The circuitry comprises

stacks of PCBs which carry various components and conductive tracks together with

connections thereto and cabling encased in PNC and other plastics material. The

detection apparatus is modular in format and comprises a plurality of sensor modules 5, 6, 7, 8 and 9. Each sensor module comprises an array of SAW sensors, each array

consisting of between five and eight coated sensors and may also include within the

sensor module an uncoated SAW sensor as a reference, a temperature sensor and a

relative humidity sensor, these permitting changes in ambient conditions to be

accommodated.

The sensor module 5 associated with housing 1 is connected to a sampling

module 10 which comprises a tube extending into the interior of the housing 1 and a pump which continuously circulates samples of air within the housing 1 over the

SAW array. In the second housing 2, the sensor modules 6 is included within the

container itself and is connected to sampling modules 11 and 12 which takes samples

of the atmosphere within the housing 2 at two different points and then alternately

pass them over the SAW array in the sensor module 6.

Two sensor modules 7 and 8 are included within the third housing 3 being

located at different places within the housing 3. Finally, a further sensor module 9 is

located near the circuitry 4 located externally of the housings 1, 2 and 3.

The low power consumption of the SAW sensors and their ability to operate at

room temperatures means that they can be operated substantially continuously to give

complete monitoring of the environment in which they are located. The outputs of the

sensor modules 5 to 9 are applied to a processor module 13 which applies statistical

techniques to the received outputs to determine whether or not a volatile indicative of

incipient fire has been detected. In other embodiments, fuzzy logic or a neural network may be implemented. The status of the system is displayed at 14 for an

operator to monitor. In addition, when a fire is detected, an alarm signal is transmitted

to a control circuit 15 which interfaces with the various electrical systems contained

within the housings 1 to 3 and the electrical circuitry 4 outside the housing. The

control system 15 acts to shut down any region where an incipient fire is detected and

simultaneously send and alarm signal to the NDU 14 which presents a visual and audible warning to the user.

Each array of SAW sensors comprises different coatings which may for

example test for acetone, toluene and xylene vapours, which are typically generated

when over-heating in a PCB occurs. Figure 2 illustrates the normalised response of an

array having five SAW sensors, having coatings Z4, Z6, Z9, Z13 and Z19

respectively. It can be seen that each of these three vapours has a characteristic

response which readily identifies it when the outputs are considered as a combination.

Thus even with very low concentration of vapours, an incipient fire can be detected.

Figure 3 shows the response of the SAW sensors to vapours emitted from an

overloaded cable.

Figure 4 schematically shows a system having three SAW arrays 16, 17, 18

which each include an antenna for communication via a wireless link with a remote processor 19.

Claims

1. Fire detection apparatus comprising: chemical sensor means including an array of SAW

sensors responsive to gases and/or vapours produced when an incipient fire occurs in the

environment in which the apparatus is intended to be used, and sampling means for

delivering gases and/or vapours to the array where they are detected.

2. Apparatus as claimed in claim 1 wherein the array of SAW sensors is responsive to gases and/or vapours produced when an incipient fire occurs in electrical circuitry and/or cabling.

3. Apparatus as claimed in claim 2 wherein the array is responsive to gases and/or vapours

produced when a PCB overheats.

4. Apparatus as claimed in claim 2 or 3 wherein electrically circuitry and/or cabling is to be

monitored is contained within a cabinet.

5. Apparatus as claimed in any preceding claim wherein the array is contained within a

sensor module.

6. Apparatus as claimed in any preceding claim wherein the sampling means is included in a

sampling module.

7. Apparatus as claimed in any preceding claim and comprising a plurality of sensor

modules each comprising an array of SAW sensors responsive to gases/or vapours produced when an incipient fire occurs, the plurality of sensor modules being spatially distributed in a

region to be monitored for incipient fires.

8. Apparatus as claimed in any preceding claim and including a processor module for

receiving a signal from the array of SAW sensors.

9. Apparatus as claimed in any preceding claim and comprising a display unit for presenting visual information to a user.

10. Apparatus as claimed in any preceding claim and including means for initiating electrical shut-down in a region where an incipient fire is detected.

11. Apparatus as claimed in any preceding claim and including wireless communication

means for communication with the SAW array.

12. Fire detection apparatus substantially as illustrated in and described with reference to the accompanying drawings.