Particulate detector

1. A particulate detector comprising:

a radiation source arranged to emit radiation in at least first and second predetermined wavebands towards a sampling region; and

a detection element arranged to detect radiation from the sampling region at at least first and second instances;

wherein the radiation source is such that the emissions in the at least first and second predetermined wavebands temporarily overlap;

wherein the detector is such that, at the instances at which the radiation is detected, the relative contributions from the emissions in each predetermined waveband are distinguishable, thereby allowing characteristics of particulates in the sampling region to be determined;

wherein the radiation emitted in the first predetermined waveband is emitted in a pulse; and

wherein the first instance occurs after the start of the pulse but before the end of the pulse, and the second instance occurs after the end of the pulse.

2. A detector according to claim 1 , wherein the pulse is a square pulse.

3. A detector according to claim 1 , further comprising a processor arranged to process information about the radiation received by the detection element.

4. A detector according to claim 1 , wherein the radiation source comprises a light emitting diode for emitting radiation in the first predetermined waveband.

5. A detector according to claim 4 , wherein the light emitting diode is arranged to emit radiation having a waveband in the range 450 nm to 500 nm.

6. A particulate detector comprising:

a radiation source arranged to emit radiation in at least first and second predetermined wavebands towards a sampling region; and

a detection element arranged to detect radiation from the sampling region at least first and second instances;

wherein the radiation source is such that the emissions in the at least first and second predetermined wavebands temporarily overlap;

wherein the detector is such that, at the instances at which the radiation is detected, the relative contributions from the emissions in each predetermined waveband are distinguishable, thereby allowing characteristics of particulates in the sampling region to be determined; and

wherein the radiation source further comprises a phosphor layer arranged to absorb a proportion of the radiation in the first predetermined waveband, and to emit radiation in the second predetermined waveband.

7. A particulate detector comprising:

a radiation source arranged to emit radiation in at least first and second predetermined wavebands towards a sampling region; and

a detection element arranged to detect radiation from the sampling region at least first and second instances;

wherein the radiation source is such that the emissions in the at least first and second predetermined wavebands temporarily overlap;

wherein the detector is such that, at the instances at which the radiation is detected, the relative contributions from the emissions in each predetermined waveband are distinguishable, thereby allowing characteristics of particulates in the sampling region to be determined;

wherein the radiation source further comprises a second light emitting diode for emitting radiation in the second predetermined waveband; and

wherein the radiation source is arranged such that radiation emitted in the first redetermined waveband is used to power the second light emitting diode.

8. A detector according to claim 1 , further comprising an optical bleed channel for enabling radiation emitted by the radiation source to pass directly to the detection element.

9. A detector according to claim 1 , wherein the detector is a scatter detector.

10. A detector according to claim 1 , wherein the detector is a transmission detector.

11. A detector system comprising a control unit and a plurality of particulate detectors, each particulate detector comprising:

a radiation source arranged to emit radiation in at least first and second predetermined wavebands towards a sampling region; and

a detection element arranged to detect radiation from the sampling region at least first and second instances;

wherein the radiation source is such that the emissions in the at least first and second predetermined wavebands temporarily overlap;

wherein the detector is such that, at the instances at which the radiation is detected, the relative contributions from the emissions in each predetermined waveband are distinguishable, thereby allowing characteristics of particulates in the sampling region to be determined; and

wherein the radiation source further comprises a phosphor layer arranged to absorb a proportion of the radiation in the first predetermined waveband, and to emit radiation in the second predetermined waveband.

12. A system according to claim 11 , wherein the control unit is arranged to supply power to, and receive signals from, each detector.

13. A system according to claim 11 , wherein the control unit is arranged to receive signals from at least one additional detection device.

14. A system according to claim 13 , wherein the control unit is arranged to combine information received from the or each additional detection device with information received from at least one of the detectors.

15. A system according to claim 13 , wherein each additional detection device is one of the following group: a heat sensor; a gas sensor; a moisture sensor.