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A compact particle sensor for detecting suspended particles includes a housing, a light source, a light receiver and a plurality of optical elements. The housing provides a test chamber and includes at least one opening for admitting particles into the test chamber, while simultaneously substantiall

A compact particle sensor for detecting suspended particles includes a housing, a light source, a light receiver and a plurality of optical elements. The housing provides a test chamber and includes at least one opening for admitting particles into the test chamber, while simultaneously substantially preventing outside light from entering the test chamber. The light source is positioned for supplying a light beam within the test chamber. The plurality of optical elements are positioned to direct the light beam from the light source to the receiver, which is positioned to receive the light beam supplied by the light source.

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What is claimed is: 1. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the

What is claimed is: 1. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and at least three optical elements positioned to direct the light beam from the light source to the receiver, wherein at least one of the at least three optical elements is a mirror. 2. The sensor of claim 1, wherein the at least three optical elements include at least three non-planar mirrors, and wherein the non-planar mirrors are substantially located in a first plane and the light source and the receiver are substantially located in a second plane such that the light source and the receiver do not block the light beam as it is reflected between the mirrors. 3. A compact particle sensor for detecting suspended particles comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and at least three optical elements positioned to direct the light beam from the light source to the receiver, wherein the sensor is contained within a three and one-eighth inch diameter circle and the optical length between the light source and the receiver is at least about seven inches. 4. The sensor of claim 3, wherein the optical length between the light source and the receiver is at least about fourteen inches. 5. The sensor of claim 3, wherein the optical length between the light source and the receiver is at least about twenty-one inches. 6. The sensor of claim 1, wherein the optical elements are spherical mirrors. 7. The sensor of claim 1, wherein the at least three optical elements include at least three planar mirrors, and wherein the planar mirrors, the light source and the receiver are substantially located in a single plane, and wherein the light source and the receiver are positioned to not block the light beam as it is reflected between the mirrors. 8. The sensor of claim 1, wherein the at least three optical elements include three planar mirrors that are utilized to reflect the light beam from the light source to the receiver. 9. The sensor of claim 1, wherein the at least three optical elements include at least three mirrors each including a reflective surface that reflects the light beam from the light source to the receiver, and wherein each of the mirrors includes at least one of a hydrophilic coating on the reflective surface and a heater positioned to substantially prevent fogging of the reflective surface due to humidity. 10. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and a plurality of optical elements positioned to direct the light beam from the light source to the receiver, wherein the sensor is contained within no greater than about a three and one-eighth inch diameter circle and the optical length between the light source and the receiver is at least about seven inches. 11. The sensor of claim 10, wherein the optical length between the light source and the receiver is at least about fourteen inches. 12. The sensor of claim 11, wherein the optical length between the light source and the receiver is at least about twenty-one inches. 13. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and at least two non-planar optical elements positioned to direct the light beam from the light source to the receiver, wherein at least one of the at least two non-planar optical elements is a mirror. 14. The sensor of claim 13, wherein the at least two non-planar optical elements include three non-planar mirrors, and wherein the non-planar mirrors are substantially located in a first plane and the light source and the receiver are substantially located in a second plane such that the light source and the receiver do not block the light beam as it is reflected between the mirrors. 15. The sensor of claim 13, wherein the optical elements are spherical mirrors. 16. A compact particle sensor, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while substantially preventing outside light from entering the test chamber; a scatter emitter/receiver combination positioned such that any portion of the light emitted by the scatter emitter that is reflected off of particles suspended in the chamber and received is proportional to the amount of high reflectivity particles present in the chamber; an obscuration emitter/receiver combination positioned such that any portion of the light emitted by the obscuration emitter that is received is inversely proportional to the amount of low reflectivity particles present in the chamber; at least three optical elements positioned to direct the light emitted by the obscuration emitter to the receiver of the obscuration emitter/receiver combination; and a controller coupled to the scatter emitter/receiver combination and the obscuration emitter/receiver combination, the controller using the amount of particles sensed by the obscuration emitter/receiver combination to alter the sensitivity of the scatter emitter/receiver combination. 17. The sensor of claim 16, wherein the scatter emitter/receiver combination and the obscuration emitter/receiver combination share a common receiver. 18. The sensor of claim 16, wherein the controller is also configured to change a sensor cycle when a high reflectivity particle level crosses an initial scatter emitter threshold, and wherein the rate of the sensor cycle determines the frequency with which at least one of the scatter emitter and obscuration emitter emits light. 19. The sensor of claim 18, wherein the controller causes the obscuration emitter to generate light only after the high reflectivity particle level crosses the initial scatter emitter threshold. 20. The sensor of claim 19, wherein a scatter emitter alarm threshold is modified to occur at a lower high reflectivity particle level when an obscuration emitter threshold is exceeded thus altering the sensitivity of the scatter emitter/receiver combination. 21. The sensor of claim 19, wherein the intensity of the light emitted by the scatter emitter is increased when an obscuration emitter threshold is exceeded thus altering the sensitivity of the scatter emitter/receiver combination. 22. The sensor of claim 16, wherein the at least three optical elements include at least three non-planar mirrors that are substantially located in a first plane, and wherein the obscuration emitter/receiver combination and the scatter emitter/receiver combination are substantially located in a second plane such that the obscuration emitter/receiver combination and the scatter emitter/receiver combination do not block the light beam as it is reflected between the mirrors. 23. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and a plurality of non-planar optical elements positioned to direct the light beam from the light source to the receiver, wherein the light beam travels a path from the light source to the receiver that does not lie a single plane. 24. The sensor of claim 23, wherein the plurality of optical elements include a plurality of non-planar mirrors that are substantially located in a first plane, and wherein the light source and the light receiver are substantially located in a second plane such that the light source and the light receiver do not block the light beam as it is reflected between the mirrors. 25. The sensor of claim 23, wherein the sensor is contained within about a three and one-eighth inch diameter circle and the optical length between the light source and the light receiver is at least about seven inches. 26. The sensor of claim 25, wherein the optical length between the light source and the light receiver is at least about fourteen inches. 27. The sensor of claim 25, wherein the optical length between the light source and the light receiver is at least about twenty-one inches. 28. The sensor of claim 23, wherein the light beam crosses itself when travelling from the light source to the light receiver. 29. The sensor of claim 23, wherein the plurality of non-planar optical elements include a plurality of non-planar mirrors. 30. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and a plurality of non-planar optical elements positioned to direct the light beam from the light source to the receiver, wherein the light beam crosses itself when travelling from the light source to the light receiver. 31. The sensor of claim 30, wherein the light beam travels a non-planar path from the light source to the light receiver. 32. The sensor of claim 30, wherein the non-planar optical elements are spherical mirrors. 33. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam within the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and at least three optical elements positioned to direct the light beam from the light source to the receiver, wherein the light beam alternately converges and diverges between the optical elements when travelling from the light source to the light receiver. 34. The sensor of claim 33, wherein the at least three optical elements includes three non-planar mirrors. 35. The sensor of claim 34, wherein the non-planar mirrors are concave mirrors. 36. The sensor of claim 35, wherein the concave mirrors are spherical mirrors. 37. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and at least three optical elements positioned to direct the light beam from the light source to the receiver, wherein a path length of the light beam between the light source and the receiver is at least about two times the smallest dimension of the test chamber. 38. The sensor of claim 37, wherein the path length of the light beam between the light source and the receiver is at least about two times the largest dimension of the test chamber. 39. The sensor of claim 37, wherein the path length of the light beam between the light source and the receiver is at least about four and one-half times the smallest dimension of the test chamber. 40. The sensor of claim 37, wherein the path length of the light beam between the light source and the receiver is at least about four and one-half times the largest dimension of the test chamber. 41. The sensor of claim 37, wherein the test chamber is circular. 42. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber, wherein an interior color of the housing that provides the test chamber is non-black; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source; and a plurality of optical elements positioned to direct the light beam from the light source to the receiver. 43. The sensor of claim 42, wherein the plurality of optical elements include at least three non-planar mirrors, and wherein the non-planar mirrors are substantially located in a first plane and the light source and the receiver are substantially located in a second plane such that the light source and the receiver do not block the light beam as it is reflected between the mirrors. 44. The sensor of claim 42, wherein the sensor is contained within a three and one-eighth inch diameter circle and the optical length between the light source and the receiver is at least about seven inches. 45. The sensor of claim 44, wherein the optical length between the light source and the receiver is at least about fourteen inches. 46. The sensor of claim 44, wherein the optical length between the light source and the receiver is at least about twenty-one inches. 47. The sensor of claim 42, wherein the optical elements are spherical mirrors. 48. A compact particle sensor for detecting suspended particles, comprising: a housing providing a test chamber, the housing including at least one opening for admitting particles into the test chamber while simultaneously substantially preventing outside light from entering the test chamber; a light source positioned for supplying a light beam in the test chamber; a light receiver positioned to receive the light beam supplied by the light source, wherein the light receiver includes a Faraday shield that shields the receiver from outside electromagnetic interference; and a plurality of optical elements positioned to direct the light beam from the light source to the receiver. 49. The sensor of claim 48, wherein the optical elements are spherical mirrors.