Chamber condition

1. A particle detector including:

a chamber including at least one sample inlet for receiving sample fluid, at least one clean fluid inlet for receiving clean fluid, and at least one fluid outlet;

a first aspirator for moving the sample fluid through the chamber;

a light source for projecting a light beam through the chamber;

one or more sensors for detecting, and providing a sensor signal indicative of, particles in the chamber, wherein the one or more sensors have a field of view intersecting the projected light such that the one or more sensors receive light scattered from the projected light beam by particles in the chamber;

a controller having a detecting mode and a purge mode;

a clean fluid supply for supplying clean fluid to the clean fluid inlet, the clean fluid supply and clean fluid inlet cooperating, when in the detecting mode, to direct clean fluid into the chamber to prevent contamination by dust and debris of one or more components, the contamination of which would reduce the accuracy of the particle detector; and

the controller, when in the detecting mode, receiving the sensor signal and applying logic to the sensor signal to generate a further signal, and when in the purge mode controlling substantial purging of the chamber of sample fluid with clean fluid from the clean fluid supply;

the controller receiving the sensor signal while the chamber is purged with clean fluid from the clean fluid supply and if necessary adjusting the logic in response thereto, to reduce false alarms due to accumulation of dust and debris in the chamber.

2. The detector of claim 1 wherein the clean fluid supply includes a filter, for filtering fluid to produce clean fluid, and a dedicated clean fluid aspirator for moving the clean fluid, the dedicated clean fluid aspirator being downstream of the filter to avoid exposure to unfiltered fluid.

3. The detector of claim 2 wherein, when in the detecting mode, the dedicated clean fluid aspirator is inactive and the first aspirator moves fluid through the filter.

4. The detector of claim 2 further including plumbing for dividing a stream of fluid into two or more portions, and directing one portion to the clean fluid supply to be filtered to form clean fluid, and directing another portion to the chamber to form the sample fluid.

5. The detector of claim 1 wherein the controller is configured to deactivate the first aspirator when in the purge mode.

6. The detector of claim 1 wherein the controller is configured to automatically enter the purge mode periodically.

7. The detector of claim 1 wherein the detector is an optical particle detector.

8. The detector of claim 1 being a smoke detector.

9. The detector of claim 1 wherein the logic includes an alarm threshold.

10. The detector of claim 1 wherein the controller is configured such that a transition from the detection mode to purge mode is conditional on the sensor signal.

11. The detector of claim 1 wherein the logic includes subtracting a measure of background light from the sensor signal and the adjusting the logic includes updating the measure of background light.

12. The detector of claim 1 which further includes at least one valve for preventing sample fluid entering the at least one sample inlet of the chamber when the detector is in the purge mode, and allowing sample fluid to enter the at least one sample inlet of the chamber when the detector is in the detecting mode.

13. The detector of claim 12 wherein the first aspirator additionally causes the clean fluid supply to enter the chamber.

14. A particle detector including:

a chamber including at least one sample inlet for receiving sample fluid, and at least one fluid outlet;

a first aspirator for moving the sample fluid through the chamber;

a light source for projecting a light beam through the chamber;

one or more sensors for detecting, and providing a sensor signal indicative of, particles in the chamber, wherein the one or more sensors have a field of view intersecting the projected light such that the one or more sensors receive light scattered from the projected light beam by particles in the chamber;

a clean fluid supply, the clean fluid supply including a filter, for filtering fluid to produce clean fluid, and a dedicated clean fluid aspirator for moving the clean fluid, the dedicated clean fluid aspirator being downstream of the filter to avoid exposure to unfiltered fluid; and

a controller having a detecting mode and a purge mode;

the controller,

when in the detecting mode, receiving the sensor signal and applying logic to the sensor signal to generate a further signal, and

when in the purge mode controlling substantial purging of the chamber of sample fluid with clean fluid from the clean fluid supply;

wherein the controller receives the sensor signal while the chamber is purged with clean fluid from the clean fluid supply, and if necessary adjusts the logic in response thereto, to reduce false alarms due to increased light scattering from dust and debris that has accumulated in the chamber.

15. The detector of claim 14 wherein, when in the detecting mode, the dedicated clean fluid aspirator is inactive and the first aspirator moves fluid through the filter.

16. A method of operating a particle detector;

the particle detector including:

a chamber having:

at least one sample inlet for receiving sample fluid,

at least one clean fluid inlet for directing clean fluid into the chamber to prevent contamination by dust and debris of one or more components the contamination of which would reduce the accuracy of the particle detector, and

at least one fluid outlet;

a light source for projecting a light beam through the chamber; and

one or more sensors for detecting, and providing a sensor signal indicative of, particles in the chamber, wherein the one or more sensors have a field of view intersecting the projected light such that the one or more sensors receive light scattered from the projected light beam by particles in the chamber;

the method including when in a detecting mode:

moving sample fluid through the chamber;

receiving the sensor signal to detect particles in the chamber; and

applying logic to the sensor signal to generate a further signal; and

when in a purge mode:

substantially purging the chamber of sample fluid with clean fluid via the clean fluid inlets; and

receiving the sensor signal while the chamber is purged with clean fluid from the clean fluid supply; and

if necessary adjusting the logic in response thereto, to reduce false alarms due to contamination by dust and debris.

17. The method of claim 16 further including moving fluid through a filter to produce the clean fluid.

18. The method of claim 17 wherein said purging includes activating a dedicated clean fluid aspirator, the dedicated clean fluid aspirator being downstream of the filter to avoid exposure to unfiltered fluid.

19. The method of claim 17 , further including

dividing a stream of fluid into two or more portions,

directing one of the portions to the filter to be filtered to form the clean fluid, and

directing another of the portions to the chamber to form the sample fluid.

20. The method of claim 16 further including transitioning between purge mode and detecting mode periodically.

21. The method of claim 16 wherein said purging is conditional on the sensor signal being below a predetermined threshold.

22. The method of claim 16 wherein the

detector includes a first aspirator for moving sample fluid through the chamber; and

the purging includes deactivating the first aspirator.

23. The method of claim 16 wherein the particle detector is an optical detector.

24. The method of claim 16 wherein the particle detector is a smoke detector.

25. The method of claim 16 wherein the logic includes an alarm threshold.

26. The method of claim 16 wherein the logic includes subtracting a measure of background light from the indicative signal and the adjusting the logic includes updating the measure of background light.

27. A method of operating a particle detector;

the particle detector including:

a chamber including at least one sample inlet for receiving sample fluid and at least one fluid outlet;

a light source for projecting a light beam through the chamber;

one or more sensors for detecting, and providing a sensor signal indicative of, particles in the chamber, wherein the one or more sensors have a field of view intersecting the projected light such that the one or more sensors receive light scattered from the projected light beam by particles in the chamber; and

a clean fluid supply, the clean fluid supply including a filter, for filtering fluid to produce clean fluid, and a dedicated clean fluid aspirator for moving the clean fluid, the dedicated clean fluid aspirator being downstream of the filter to avoid exposure to unfiltered fluid;

the method including when in a detecting mode:

moving sample fluid through the chamber;

receiving the sensor signal to detect particles in the chamber; and

applying logic to the indicative signal to generate a further signal; and

when in a purge mode:

substantially purging the chamber of sample fluid with clean fluid from the clean fluid supply; and

receiving the sensor signal while the chamber is purged with clean fluid from the clean fluid supply; and

if necessary adjusting the logic in response thereto, to reduce false alarms due to increased light scattering from dust and debris that has accumulated in the chamber.