GB1560731A - Radiation responsive devices - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO RADIATION RESPONSIVE DEVICES (71) We, GRAVINER LIMITED, a British Company, of Sword House, Totteridge Road, High Wycome, Buckinghamshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to the detection of smoke and flame such as caused by incipient fires and explosions.

According to the invention, there is provided flame and smoke detecting apparatus, comprising a unit incorporating both a radiation detector and a radiation emitter which are mounted in the unit in predetermined physical relationship with each other, the detector being in the form of a single cell which is adapted to be responsive to a nonvisible radiation of a predetermined type as emitted by a flame to be detected in use, the cell having a predetermined field of view extending outside the unit by which it can receive and respond radiation from the flame when the latter is in the field of view, the radiation emitter being adapted to emit radiation of the predetermined type and being mounted outside the said field of view but arranged so that the amount of radiation which it emits and which is received by the cell varies according to whether or not smoke is present within a region which is predetermined in relation to the unit, and electrical circuitry connected to the cell and producing a flame or smoke indicating output when the cell responds to the said radiation.

According to the invention, there is further provided flame and smoke detecting apparatus, in the form of a unit incorporating both a radiation detector and a radiation emitter, the radiation detector being in the form of a single cell adapted to be responsive to ultra-violet (UV) radiation and having at least one predetermined field of view externally of the unit whereby to respond to UV radiation which is emitted in use by a flame present in the field of view, the emitter being energisable to produce UV radiation and so mounted in the unit relative to the said one predetermined field of view of the detector that there is no direct path between the UV emitter and the UV detector but whereby the presence of smoke in a predetermined region relative to the unit scatters UV radiation from the emitter to the detector for detection thereby, and electrical circuitry connected to the detector which produces a flame or smoke indicating output when the detector responds to the said radiation.

Flame and smoke detecting apparatus embodying the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a diagrammatic cross-section through one form of the apparatus; Figure 2 is a block circuit diagram of the apparatus of Fig 1; Figure 3 is a schematic circuit diagram of the apparatus of Fig 1; Figure 4 is a diagrammatic cross-section through another of the apparatus; Figure 5 is a diagrammatic cross-section through a modified form of the apparatus of Figure 4; and Figure 6 is a diagrammatic cross-section through another form of the apparatus.

As shown in Figure 1, the apparatus includes a unit incorporating a detector in the form of a detecting cell 5 which is mounted in a mounting head 6 and has a field of view through an opening 8. The cell 5 advantageously comprises a photocell sensitive to ultra-violet radiation, such as a gas discharge tube. The opening 8 may comprise a window incorporating material transparent to UV radiation.

In addition, an emitter 10, which is a source of ultra-violet radiation, is mounted in a mounting head 12 of the unit and emits ultra-violet radiation through an opening defined by a slit 14. The geometry is such that there is no direct path for the ultra-violet radiation between the emitter 10 and the cell 5. Advantageously, the path betweeen the emitter 10 and the cell 5 contains an angle of the order of 1500.

The emitter 10, may for example, be a tungsten halogen or gas discharge lamp enveloped in quartz. Instead, however, it may be another cell similar in construction to the cell 5 but energised to emit ultra-violet radiation rather than to respond to it.

In use, the apparatus may be mounted on the ceiling 18 of a room in which smoke and flame is to be detected. Smoke in the room, as from a fire or incipient fire, will rise to the ceiling and pass across the apparatus in front of the cell 5 and the emitter 10. Some of the ultra-violet radiation from the emitter 10 will be reflected by the particles of smoke and will be directed onto the cell 5. Provided the operating conditions of the cell are satisfied (mainly the presence of the necessary voltage across the cell), the cell will conduct and this will be detected by circuitry to be described in more detail below.

It will also be apparent that, if a flame occurs in the room within the field of view of the cell 5, the ultra-violet radiation emitted by the flame will have the same effect on the cell. Therefore, the presence of smoke or flame (or both) will cause conduction of the cell 5. The arrangement of the apparatus by which it is responsive both to direct and scattered radiation considerably improves the signal to noise ratio. It should be noted, however, that the apparatus is able to respond fully to smoke alone.

Instead of the slit 14 the emitter 10 may emit its radiation through an opening as wide, for example, as the window 8 so as to give sensitivity to scattering over a wide range of angles including the value of 1500 already mentioned.

Figure 2 shows the circuit of the apparatus in block diagram form.

As shown, a voltage source 30 is arranged to apply periodic voltage pulses across the photocell 5, these pulses being of the order of, say, 300 volts and being such that the tube will conduct during these pulses in the presence of sufficient ultra-violet radiation. Conduction of the cell is detected by means of a line 32 which controls a pulse shaper circuit 34. Each pulse output by the pulse shaper 34 and corresponding to conduction of the cell is fed into a rate measuring circuit 36. This produces an output to trigger an alarm unit 38 only when the pulses from the pulse shaper 34 occur at at least a predetermined rate.

The circuit is shown in more detail in Figure 3. As shown, a voltage regulator circuit is energised from a positive supply line 42 through a diode 44. A transistor 46, whose conduction is controlled by a second transistor 48 and a zener diode 50, provides a stabilized supply to an oscillator circuit 52 which drives a transformer 54. The resultant high voltage is fed across a full wave rectifier 56 to a potential divider consisting of resistors 58 and 60 and a switching transistor 62.

The gas discharge cell 5 is connected across resistor 60 and transistor 62 via a resistor 64 and a resistor 66.

The second part of the circuit for sensing the output of the cell 5 and for controlling the switching transistor 62 in a manner to be described, is fed with stabilized d.c. via a line 68 and the supply is stabilized by a zener diode 70 in parallel with a capacitor 72.

Conduction of the cell 5 is sensed by the pulse shaper circuit 34 which consists of a transistor 74 whose base-emitter junction is connected across resistor 66.

The pulse shaper 34 controls a retriggerable monostable circuit 78 which produces a positive output on a line 80 as long as pulses are fed to its input at least once every second.

Line 80 is connected through a resistor 82 to charge a capacitor 84. The charge on the capacitor controls the conduction of a transistor 86 whose emitter-collector path is connected in parallel with that of a second transistor 88 whose base is fed from an adjustable tapping on a resistor 90 which forms part of a potential divider connected across the supply. Transistor 86 controls the conduction of an output transistor 92.

The switching transistor 62 is controlled by a square wave oscillator 94 operating at a frequency of, say, 5 kHz.

In operation, the d.c. output voltage of the full wave rectifier 56 is 300 volts, and the resistances of the resistors 58 and 60 are in the ratio of 2:1. Therefore, when the transis tor 62 is turned on by the oscillator 94, the voltage across the cell 5 and its series resis- tances falls from 300 to 100 volts.

Each conduction of the cell 5 (in response to detection of u.v. radiation) turns on transistor 74 and feeds a negative pulse to the retriggerable monostable circuit 78. Provided that the circuit 78 receives a pulse at least once every second, a positive voltage will exist on line 80 and will charge capacitor 84. When the base of transistor 86 reaches the same voltage as that set on the resistor 90, transistor 86 turns on, turning on transistor 92 to produce a positive voltage warning signal on a line 96.

If the time between two consecutive conductions of the cell 5 exceeds one second, line 80 will fall to zero and capacitor 84 will quickly discharge through a diode 98. This switches off transistors 86 and 92.

In the foregoing example, the cell 5 is energised for only 50% of the total time.

However, in order to increase the sensitivity of the system, the circuitry may be modified so that the cell is energised for almost all the time.

Figure 4 shows another form of smoke and flame detecting apparatus including a unit incorporating a detecting cell 5 which is mounted in a mounting head 6 and has a wide conical field of view delineated by the lines A and B. In addition, the mounting head 6 has a gap 97 which gives the detecting cell 5 a more limited field of view in the reverse direction, looking into an area 98 defined by gauze 99.

As before, the cell 5 may advantageously comprise a photocell sensitive to ultra-violet radiation, such as a gas discharge tube.

Mounted to one side of the area 98 in a housing 100 of the unit is an emitter 10 which is a source of ultra-violet radiation. The housing 100 and the emitter 10 are so positioned that the emitter 10 emits ultra-violet radiation into the area 98, but the geometry of the head 6 and the housing 100 is such that there is no direct path for the ultra-violet radiation between the emitter 10 and the detector cell 5. Again the emitter 10 may, for example, be a tungsten halogen or gas discharge lamp enveloped in quartz, or a cell similar to cell 5 but operated as an ultra-violet radiation emitter.

If desired, the housing 100 may support a suitable optical system, such as a focussing lens 101, capable of handling ultra-violet radiation. A protecting grid 102 may be placed over the cell 5.

In use, the apparatus may be mounted on the ceiling 18 of a room in which smoke and flame is to be detected. Smoke in the room, as from a fire or incipient fire, will rise to the ceiling and pass into the area 98 through the gauze 99. Some of the ultra-violet radiation from the emitter 10 will be reflected by the particles of smoke and will be directed onto the cell 5. As before, provided the operating conditions of the cell are satisfied, the cell will conduct and this will be detected by circuitry which can be as described with reference to Figures 2 and 3. Similarly, if a flame occurs in the room within the field of view of the cell 5 as delineated by the lines A and B, the ultra-violet radiation emitted by the flame will have the same effect on the cell.

Therefore, the presence of smoke or flame (or both) will cause conduction of the cell 5.

In Figure 5 items corresponding to items in Figure 4 are correspondingly referenced. It will be seen that the emitter 10 emits ultraviolet radiation into the space 98 through a small hole 101. In operation, the cell 5 responds to ultra-violet radiation produced by a flame in the field of view embraced by the lines A and B. In addition, the cell responds to ultra-violet radiation emitted into the area 98 through the hole 101 from the emitter 10, when this radiation is scattered by the presence of smoke in the area 98 and passes through the hole 97. A sheild 101A prevents any direct path for radiation between the emitter 10 and the detector 5.

The arrangement of Figure 5 has been found to perform particularly well with the following characteristics: 1. Emitter 10 and detector 5,47 mm apart.

2. Emitter aperture 101, lmm wide and 10mm long.

3. Detector aperture 97, 6mm wide and 10mm long.

4. Detector 5 at 100 to the line of sight of the emitter 10.

5. Mask 101A, 13mmwide, placed along the line of sight of the emitter 10.

Use of an ultra-violet sensitive cell 5 in the apparatus described with reference to Figures 1, 4 and 5 means that the detector is not normally affected by ambient light. For example, the intrinsic properties of the cell are such that it will not be affected by sunlight or by radiation from tungsten or fluorescent lighting and the like. Cosmic radiation will affect the cell but conduction of the cell due to cosmic radiation will be statistically rare and the circuitry (requiring a minimum frequency of conductions before a warning output is produced) will minimise the possibility of a false warning output signal being given in response to cosmic radiation.

Use of ultra-violet responsive device for the cell 5 is advantageous because the short wavelength of the ultra-violet radiation enhances the scattering effect and makes the apparatus more sensitive to the presence of small aerosols.

The arrangements of Figures 1, 4 and 5 may be modified by providing an additional cell which is positioned adjacent to the cell 5 so as to be able to respond to flame in the area under surveillance but to be arranged to be unresponsive to the effect of smoke. The additional cell will respond similarly to the cell 5 in the presence of flame and serves as a check on the response of the cell. By means of a suitable gating circuit, therefore, it is possible to distinguish the response of the cell 5 to flame from its response to smoke.

In the apparatus of Figure 6, two ultraviolet responsive cells 5A and 5B are provided and they are mounted in respective housings 104 and 105 at opposite ends of an area 106 defined by gauze 107. Each housing 104, 105 has a respective opening 108, 110, by which the detecting cells 5A, 6B can view the area below when the detecting head is mounted on a ceiling 112.

In operation, the cells 5A and 5B are connected in electrical circuitry which pulses the cells in the following sequence.

Initially, cell 5A is given a short high voltage pulse (450 volts for 100mS, for example). During this time, and before and after the pulse as well, the other cell 5B is held at, say, 300 volts. The high voltage, short duration, pulse applied to cell 5A causes that cell to emit ultra-violet radiation which is directed towards cell 5B. That cell, being held at 300 volts, will therefore tend to conduct, but its response will be reduced if smoke is present in the area 104, enabling the smoke to be detected.

Both cells 5A and 5B are then held at a medium voltage level, say 300 volts. Neither cell acts as a u.v. source, therefore, but either cell will tend to conduct in the presence of extraneous u.v. radiation such as from a flame in the area under surveillance by the cells, enabling the flame to be detected.

Cell 5B is then given a short high voltage pulse, 450 volts for 100mS for example. During this period, and both before and after the pulse, cell 5A is held at the medium level, 300 volts for example. Cell 5B therefore now acts as the source of ultra-violet radiation and the response of cell 5A can be monitored to detect the presence of smoke in the area 106.

Both cells 5A and 5B are then held at the medium level, 300 volts say. As before, neither acts as a u.v. source and their responses depend on the presence of an extraneous u.v. source such as a flame.

The cycle of operations then repeats.

At least with the arrangement described with reference to Figs. 1, 2, 4 and 5, using a UV responsive gas discharge tube, it may be possible to optimise the response of the cell using the technique disclosed in our copending Patent Application No. 47755/74.

(Serial No. 1515116).

The apparatus described can detect the presence of both fast and slow burning fires; this capability is not achieved effectively with other types of fire detecting apparatus. The apparatus described may have particularly advantageous performance characteristics, for example, the smoke sensitivity of an example of the apparatus of Figure 5 to a radiation attenuation level at a wavelength of 900mm of 0.3db/m (2% obscuration over one foot), was twenty counts per minute, for which the signal to noise ratio was 4:1. With this example, a flame sensitivity at least as good as a capability of responding to a 0.185m2 area natural gas flame at thirteen metres on average within five seconds was achieved. In fact, it is estimated that the response to a 0.185m2 natural gas flame at forty metres could be achieved.

Although reference is made above to the detection of smoke and flame, it will be appreciated that the detectors can also be used (modified as necessary) to detect other atmospheric effects which scatter or obscure radiation and other sources of radiation.

WHAT WE CLAIM IS: 1. Flame and smoke detecting apparatus, comprising a unit incorporating both a radiation detector and a radiation emitter which are mounted in the unit in predetermined physical relationship with each other, the detector being in the form of a single cell which is adapted to be responsive to non-visible radiation of a predetermined type as emitted by a flame to be detected in use, the cell having a predetermined field of view extending outside the unit by which it can receive and respond to the radiation from the flame when the latter is in the field of view, the radiation emitter being adapted to emit radiation of the predetermined type and being mounted outside the said field of view but arranged so that the amount of radiation which it emits and which is received by the cell varies according to whether or not smoke is present within a region which is predetermined in relation to the unit, and electrical circuitry connected to the cell and producing a flame or smoke indicating output when the cell responds to the said radiation.

2. Apparatus according to claim 1, in which the said emitter is so mounted in relation to the detector that the radiation which it emits has no direct path to the detector by the presence of smoke.

3. Apparatus according to claim 1, in which the emitter is so mounted in relation to the detector that the radiation which it emits has a direct path to the detector so that the radiation reaching the detector along this path is obscured and varied by the presence of smoke in the path, and including means for reducing substantially to zero, for spaced intervals of time, the radiation reaching the detector via the direct path, whereby the detector can detect the presence of a flame in its said field of view during the said intervals and the presence of smoke in the said path between the said intervals.

4. Apparatus according to claim 3, in which the said emitter is in the form of a second single cell of similar type to the detector, and in which each cell is electrically energisable to act alternatively as a detector of ultra-violet (UV) radiation and an emitter of UV radiation, and including means mounting the second cell to have a respective field of view extending outside the unit by which the second cell can receive and respond to radiation of the predetermined type emitted by a flame in its field of view, there being no direct path between the two cells via their first-mentioned fields of view; and in which each cell has a respective second predetermined field of view; the second predetermined fields of view being in direct alignment with each other; and including control means for imposing a sequence of energisation on the two cells such that during each of two cycles of the sequence, a respective one of the cells acts as a UV emitter and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. the pulse as well, the other cell 5B is held at, say, 300 volts. The high voltage, short duration, pulse applied to cell 5A causes that cell to emit ultra-violet radiation which is directed towards cell 5B. That cell, being held at 300 volts, will therefore tend to conduct, but its response will be reduced if smoke is present in the area 104, enabling the smoke to be detected. Both cells 5A and 5B are then held at a medium voltage level, say 300 volts. Neither cell acts as a u.v. source, therefore, but either cell will tend to conduct in the presence of extraneous u.v. radiation such as from a flame in the area under surveillance by the cells, enabling the flame to be detected. Cell 5B is then given a short high voltage pulse, 450 volts for 100mS for example. During this period, and both before and after the pulse, cell 5A is held at the medium level, 300 volts for example. Cell 5B therefore now acts as the source of ultra-violet radiation and the response of cell 5A can be monitored to detect the presence of smoke in the area 106. Both cells 5A and 5B are then held at the medium level, 300 volts say. As before, neither acts as a u.v. source and their responses depend on the presence of an extraneous u.v. source such as a flame. The cycle of operations then repeats. At least with the arrangement described with reference to Figs. 1, 2, 4 and 5, using a UV responsive gas discharge tube, it may be possible to optimise the response of the cell using the technique disclosed in our copending Patent Application No. 47755/74. (Serial No. 1515116). The apparatus described can detect the presence of both fast and slow burning fires; this capability is not achieved effectively with other types of fire detecting apparatus. The apparatus described may have particularly advantageous performance characteristics, for example, the smoke sensitivity of an example of the apparatus of Figure 5 to a radiation attenuation level at a wavelength of 900mm of 0.3db/m (2% obscuration over one foot), was twenty counts per minute, for which the signal to noise ratio was 4:1. With this example, a flame sensitivity at least as good as a capability of responding to a 0.185m2 area natural gas flame at thirteen metres on average within five seconds was achieved. In fact, it is estimated that the response to a 0.185m2 natural gas flame at forty metres could be achieved. Although reference is made above to the detection of smoke and flame, it will be appreciated that the detectors can also be used (modified as necessary) to detect other atmospheric effects which scatter or obscure radiation and other sources of radiation. WHAT WE CLAIM IS:

1. Flame and smoke detecting apparatus, comprising a unit incorporating both a radiation detector and a radiation emitter which are mounted in the unit in predetermined physical relationship with each other, the detector being in the form of a single cell which is adapted to be responsive to non-visible radiation of a predetermined type as emitted by a flame to be detected in use, the cell having a predetermined field of view extending outside the unit by which it can receive and respond to the radiation from the flame when the latter is in the field of view, the radiation emitter being adapted to emit radiation of the predetermined type and being mounted outside the said field of view but arranged so that the amount of radiation which it emits and which is received by the cell varies according to whether or not smoke is present within a region which is predetermined in relation to the unit, and electrical circuitry connected to the cell and producing a flame or smoke indicating output when the cell responds to the said radiation.

2. Apparatus according to claim 1, in which the said emitter is so mounted in relation to the detector that the radiation which it emits has no direct path to the detector by the presence of smoke.

3. Apparatus according to claim 1, in which the emitter is so mounted in relation to the detector that the radiation which it emits has a direct path to the detector so that the radiation reaching the detector along this path is obscured and varied by the presence of smoke in the path, and including means for reducing substantially to zero, for spaced intervals of time, the radiation reaching the detector via the direct path, whereby the detector can detect the presence of a flame in its said field of view during the said intervals and the presence of smoke in the said path between the said intervals.

4. Apparatus according to claim 3, in which the said emitter is in the form of a second single cell of similar type to the detector, and in which each cell is electrically energisable to act alternatively as a detector of ultra-violet (UV) radiation and an emitter of UV radiation, and including means mounting the second cell to have a respective field of view extending outside the unit by which the second cell can receive and respond to radiation of the predetermined type emitted by a flame in its field of view, there being no direct path between the two cells via their first-mentioned fields of view; and in which each cell has a respective second predetermined field of view; the second predetermined fields of view being in direct alignment with each other; and including control means for imposing a sequence of energisation on the two cells such that during each of two cycles of the sequence, a respective one of the cells acts as a UV emitter and

the other acts as a UV detector whereby the cell acting as the detector responds to the obscuring effect of smoke in its second field of view on UV radiation emitted by the cell acting as the emitter, and in a third cycle of the sequence both cells act as UV detectors and respond to UV radiation emitted by a flame in their respective first-mentioned fields of view.

5. Apparatus according to claim 1, 2 or 3, in which the radiation of the predetermined type is ultra-violet (UV) radiation.

6. Flame and smoke detecting apparatus, in the form of a unit incorporating both a radiation detector and a radiation emitter, the radiation detector being in the form of a single cell adapted to be responsive to ultra-violet (UV) radiation and having at least one predetermined field of view externally of the unit whereby to respond to UV radiation which is emitted in use by a flame present in the field of view, the emitter being energisable to produce UV radiation and so mounted in the unit relative to the said one predetermined field of view of the detector that there is no direct path between the UV emitter and the UV detector but whereby the presence of smoke in a predetermined region relative to the unit scatters UV radiation from the emitter to the detector for detection thereby, and electrical circuitry connected to the detector which produces a flame or smoke indicating output when the detector responds to the said radiation.

7. Apparatus according to claim 6, in which the UV emitter and the UV detector are so positioned relative to each other that smoke in the said region scatters radiation from the UV emitter to the detector via its said one field of view.

8. Apparatus according to claim 6, in which the UV detector has a second predetermined field of view and in which the UV detector and the UV emitter are so positioned relative to each other that the presence of smoke in the said region scatters radiation from the emitter to the detector via its second field of view.

9. Apparatus according to any one of claims 1,2 and 6 to 8, including an additional detector responsive to the said radiation and having a predetermined field of view which includes at least part of the said one predetermined field of view of the firstmentioned detector but which is such that it cannot receive any radiation from the emitter either by direct or by indirect path, and means for gating the responses of the two detectors to enable the response of the first-mentioned detector to radiation arising from a source within its said or its said one predetermined field of view to be disting uished from its response to radiation from the emitter.

10. Apparatus according to any preced ing claim, in which the or each said cell is a gas discharge tube.

11. A smoke and flame detector, substantially as described with reference to Figure 1 of the accompanying drawings.

12. A smoke and flame detector, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.

13. A smoke and flame detector, substantially as described with reference to Figure 4 of the accompanying drawings.

14. A smoke and flame detector, substantially as described with reference to Figures 2 and 4 of the accompanying drawings.

15. A smoke and flame detector, substantially as described with reference to Figure 5 of the accompanying drawings.

16. A smoke and flame detector, substantially as described with reference to Figure 6 of the accompanying drawings.