The present invention relates to a detector and in particular to an infra-red flame detector. The invention has particular, but not exclusive, application in the provision of flame detection arrangements for large spaces, such as a power station turbine hall or a boiler area.

According to the present invention a flame detector comprises a number of detection channels arranged such that each detection channel is adjacent at least one other, each detection channel providing an output, in which the output of adjacent detection channels may be summed.

Preferably, each detection channel comprises a detector pair. More preferably, each detector pair comprises a narrow band detector and a wide band detector.

More preferably the narrow band detector operates in the range 4.2 pm to 4.7 pm, more preferably substantially in the 4.45 μητι wavelength. More preferably the wide band detector operates at wavelengths greater than 5 pm, more preferably still in the range between 5 μητι and 15 pm. More preferably, the number of detection channels is eight. More preferably the detection channels are mounted on a 22.5° rotational pattern.

The invention will now be described, by way of example only, in relation to the attached Figures, in which

Figure 1 shows a plot for infra-red emission by "black bodies' of passive material at various temperatures;

Figure 2 shows a schematic diagram of a detection channel for use in a detector according to the present invention;

Figure 3 shows an arrangement of detectors making up eight channels in a detector according to the present invention;

Figure 4 shows a schematic diagram of a circuit showing the summing of adjacent channels;

Figure 5 shows a first side view of a detector in accordance with the invention;

Figure 6 shows a front view of a detector in accordance with the invention;

Figure 7 shows a second side view of a detector in accordance with the invention;

Figure 8 shows a front view of a detector corresponding to that of Figure 6 with an outer lid removed and a sensor fascia displaced; Figure 9 shows diagrammatically the benefit of the present invention; Figure 10 shows a plan schematic view of a space in which detectors according to the present invention have been located; and Figure 11 shows a side schematic view of the space of Figure 10.

Infra-red emissions of a body of material are dependent upon the source material, its temperature and its physical state or chemical process. Referring first to Figure 1, a number of peaks for passive materials at various temperatures (50°C, 150°C, 350°C and 1,000°C) are shown. Superimposed is an infra-red peak typical of CO2 formation on the combustion of hydrocarbons. As can be seen, this peak occurs over a narrow band centred around 4.3 pm, with virtually zero accumulative energy occurring in the long pass band above 5 pm.

The use of a detection channel comprising a narrow band and a wide band filter allows, by electronic analysis in relation to the various energy level parameters, each of the detection channels to reject spurious and transient emissions from the local environment.

Figure 2 shows a simplified circuit diagram in which each of a band pass filter 2 and a long pass filter 4 are connected through respective gain sets 6 to respective first inputs of first and second comparators 8. Each of respective second inputs of the first and second comparators 8 are connected to a trip set potentiometer 10. The trip levels may be varied either side of a reference bus, for example by 0.4V either side of a reference bus set at 2.5V above 0V. Outputs of the first and second comparators 8 are fed to display indicators 12,14 to indicate respectively whether a Background condition or a Flame condition is detected. A logic gate 11 is interposed between the outputs of the first and second comparators 8 and the display indicator 12 indicative of a Flame condition. The circuitry can be seen to be arranged such that long pass (background) detection blocks "band pass". The logic is such that 4.45 pm band pass detection without "long pass" is a flame condition.

Figure 3 shows an arrangement of eight such detection channel pairs 16, that is for sixteen sensors 2,4 in total. The overall field of view of the flame detector is divided so as to more readily analyse and compute background emissions. The optical viewing field of each detector pair is 30 degrees x 90 degrees. The overall arrangement is such that the eight detection channels 16 are mounted on a 22.5 degree rotational pattern to provide 360 degree coverage.

All eight detection channels 16 have a 30 degree field of view (+/- 15 degrees off the optical axis). Within a 60 degree window (+/- 30 degrees off the optical axis) a minimum of two detection channels will register. The shaded area indicates the field of view covered by at least two detection channels. A target within 90 degrees (+/- 45 degrees off the optical axis) will always be within the field of view of a single detection channel.

Flame detectors may be used to seek to monitor large spaces for flame conditions. Such spaces may be open air or enclosed. Examples of such spaces include, but are not limited to aircraft hangars, power station turbines halls, or multi-unit power stations. In such environments heat convection patterns, smoke stratification and collection profiles are such that point heat and smoke detectors are ineffective.

Existing infra-red detectors are limited in their range of detection making their use impractical in certain circumstances. Also, the limitation in their range requires higher numbers of such detectors to be used increasing the maintenance burden to the operator.

The present invention is based upon the realisation that by summing the input of two adjacent channels 16 the sensitivity in the field of view covered by two or more detection channels 16 may be increased, thereby increasing the range of the flame detector. In an embodiment of the present invention, the user can select the output of each detection channel 16 to be summed with the output of the adjacent channel. In an alternative embodiment, the user can select the output of selected detection channels 16 to be summed with the output of an adjacent detection channel. This summing increases the sensitivity in the field of view of the detector 30 covered by two or more detection channels 16. An example of such a circuit showing such summed detection channels is shown in Figure 4. The initial arrangement is similar to Figure 2 in which the output from each pair of sensors 2,4 or detection channel 16 is used to generate signals corresponding to Flame and Background conditions. These outputs are in turn fed though a pair of logical logic OR gates 20 to produce a first logic OR gate output 24 corresponding to an alarm condition and a second logic OR gate output 26 corresponding to a fault condition. The second logic OR gate output 26 is fed through a time delay device 22 prior to confirming the existence of a Fault condition.

Thus, any detection channel 16 producing a flame condition gives a first logic OR gate output 24 corresponding to an Alarm and if any detection channel 16 (or combination of detection channels 16) gives a background signal for more than a set time delay (determined by the time delay 22) - such that there has not been a period when all channels have been enabled for flame detection - a second logic OR gate output 26 corresponding to a Fault condition is generated. The Alarm condition may be utilised to actuate an alarm to warn individuals in the area covered to evacuate and to trigger fire extinguishing media in the vicinity of flame detection . In a preferred embodiment duplex coverage of the area is provided to provide a "double knock" regime prior to actuation of fire extinguishing media .

Figures 5 to 7 show somewhat schematic side views of a flame detector 30 in accordance with the present invention . In Figures 5 and 7 the flame detector 30 is shown both in an upright position (bold) and in an angled position (ghost).

The flame detector 30 comprises an inner enclosure 32 located within an outer housing 34. The inner enclosure 32 has a removable fascia 44 incorporating windows 40 for the sensors 2,4. The windows 40 and the fascia 44 are normally sealed in use to provide a high environmental rating. The outer housing 34 is connected to an air blower by way of an air hose 36 secured in place by any suitable means such as a hose clip 38 to ensure a positive air pressure around the sensor windows 40 of the flame detector 30. A pressure switch (not shown) is provided to monitor the air flow. A fault is signalled on failure of the air flow. The outer housing 34 is connected to an adjustable bracket 42 to permit alignment in both vertical and horizontal planes.

The inner enclosure 32 may be accessed for maintenance and set-up by removal of a lid 46 forming part of the outer housing 34 and also the fascia 44 of the inner enclosure 32 (Figure 8). A plurality of display indicators 48 are provided corresponding to each of the sensors and enabling dynamic status indications to be provided for each of the eight detection channels. Conveniently the display indicators 48 comprise LEDs. The inner enclosure 32 is also provided with a push button reset 52 to allow reset of the device during maintenance or set-up.

The rear of the fascia 44 is provided with a six pole program switch 50 for setting the sensitivity level and zoom characteristics of the device by selecting the channels to be summed.

Example settings for the six poles of the switch 50 are shown in the following table

The fascia 46 (and the six pole program switch 50) is connected to the inner enclosure 32 (and to the circuitry within the inner enclosure 32) by a ribbon cable 54.

Figure 9 shows a diagram indicating the effective increase in focal length produced by summing of the detection channels.

Figures 9 and 10 illustrate an example layout of such flame detectors. In practice, as will be understood, the exact location of the flame detectors will depend upon the dimensions of the space to be covered, the flame hazard (potential flame type and/or size) and the preset characteristics of the flame detector.

The flame detectors should ideally be directed toward the centre of the area to be protected and ideally have an unobstructed view of all hazards, though as this would be an unusual occurrence, final positioning will take into account obstructions to the field of view. In Figure 10 as may be seen the flame detectors are placed at low and high levels to reduce blind spots, due to for example mezzanine floors and machinery. In some cases the overall space may need to be subdivided into zones to provide effective coverage.

It will be understood that more detection channels or fewer detection channels may be utilised in each flame detector, with appropriate separation as required.