Compact particle sensor

• US 6,876,305 B2
• Filed: 04/27/2001
• Issued: 04/05/2005
• Est. Priority Date: 12/08/1999
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Pattok, Greg R., Kadwell, Brian J.
• Primary Examiner(s): Lieu, Julie
• Application Number:
  US09/844,229
• Publication Number:
  US 20010038338A1
• Time in Patent Office: 1,439 Days
• Field of Search: 340/630, 340/628, 340/632, 356/338, 356/342, 250/573, 250/574, 250/575
• US Class Current: 340/630
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 17/113 Constructional details
• CPC Class Codes: G08B 17/125 by using a video camera to detect fire or smoke
• CPC Class Codes: G08B 29/043 of fire detection circuits
• CPC Class Codes: G08B 29/24 Self-calibration, e.g. compensating for environmental drift or ageing of components

Abstract

A compact particle sensor for fdetecting 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.

Claims

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 within 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.

2. The sensor of claim 1, wherein the light source is one of a coherent and a non-coherent light source.

3. The sensor of claim 1, wherein the light source is one of a light-emitting diode (LED) and a laser diode.

4. The sensor of claim 1, further including:

an aperture for limiting the width of the light beam supplied by the light source.

5. The sensor of claim 1, wherein the plurality of optical elements includes a plurality of 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.

6. The sensor of claim 1, wherein the plurality of optical elements includes three non-planar mirrors that are utilized to reflect the light beam from the light source to the receiver.

7. The sensor of claim 6, 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 receiver is at least about seven inches.

8. The sensor of claim 1, wherein the plurality of optical elements includes five non-planar mirrors that are utilized to reflect the light beam from the light source to the receiver.

9. The sensor of claim 8, 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 receiver is at least about fourteen inches.

10. The sensor of claim 9, wherein the five non-planar mirrors are spherical mirrors.

11. The sensor of claim 1, wherein the plurality of optical elements includes seven non-planar mirrors that are utilized to reflect the light beam from the light source to the receiver.

12. The sensor of claim 11, 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 receiver is at least about twenty-one inches.

13. The sensor of claim 1, wherein the plurality of optical elements includes a plurality of 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.

14. The sensor of claim 13, wherein the plurality of planar mirrors includes three planar mirrors that are utilized to reflect the light beam from the light source to the receiver.

15. The sensor of claim 13, wherein the plurality of planar mirrors includes five planar mirrors that are utilized to reflect the light beam from the light source to the receiver.

16. The sensor of claim 13, wherein the plurality of planar mirrors includes seven planar mirrors that are utilized to reflect the light beam from the light source to the receiver.

17. The sensor of claim 1, wherein particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

18. The sensor of claim 1, further including:

a controller coupled to the light source and the receiver, wherein the controller is configured to alter the sensitivity of the particle sensor; and

at least one of a temperature sensor providing a temperature output signal responsive to a sensed temperature and a chemical sensor providing a chemical output signal responsive to a sensed chemical presence, wherein the controller alters the sensitivity of the sensor by lowering an alarm threshold in response to exceeding at least one of a predetermined temperature, a predetermined rate of change in temperature, a predetermined chemical level and a predetermined rate of change in a chemical level.

19. The sensor of claim 1, further including:

a controller coupled to the light source and the receiver, wherein the controller is configured to alter the sensitivity of the particle sensor; and

at least one of a temperature sensor providing a temperature output signal responsive to a sensed temperature and a chemical sensor providing a chemical output signal responsive to a sensed chemical presence, wherein the controller alters the sensitivity of the sensor by varying the intensity of the light beam supplied by the light source in response to exceeding at least one of a predetermined temperature, a predetermined rate of change in temperature, a predetermined chemical level and a predetermined rate of change in a chemical level.

20. The sensor of claim 1, wherein the plurality of optical elements are a plurality of mirrors each including a reflective surface that reflects the light beam from the light source to the receiver, and wherein each of the plurality of 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.

76. The sensor of claim 1, wherein the light beam travels a non-planar path from the light source to the light receiver.

77. The sensor of claim 76, wherein the plurality of optical elements includes a plurality of non-planar mirrors.

78. The sensor of claim 77, wherein the plurality of non-planar mirrors are spherical mirrors.

79. The sensor of claim 77, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the light source to the light receiver.

80. The sensor of claim 79, 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 fourteen inches.

81. The sensor of claim 80, wherein the five concave mirrors are spherical mirrors.

82. The sensor of claim 76, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

83. The sensor of claim 1, wherein the light beam crosses itself when travelling from the light source to the light receiver.

84. The sensor of claim 83, wherein the plurality of optical elements includes a plurality of non-planar mirrors.

85. The sensor of claim 84, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the light source to the light receiver.

86. The sensor of claim 85, 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 fourteen inches.

87. The sensor of claim 85, wherein the five concave mirrors are spherical mirrors.

88. The sensor of claim 83, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

21. 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 such that any portion of the light emitted by the light source that is reflected off of particles suspended in the test chamber and received is proportional to the amount of high reflectivity particles present in the test chamber;

a light receiver positioned to receive light emitted by the light source that is reflected off of particles suspended in the test chamber; and

an ionization detector for providing a control signal whose level is responsive to the amount of low reflectivity particles present in the test chamber, wherein the control signal is utilized to alter the sensitivity of the sensor.

22. The sensor of claim 21, wherein the sensitivity of the sensor is altered by varying the intensity of the light emitted by the light source.

23. The sensor of claim 21, wherein the sensitivity of the sensor is altered by modifying an alarm threshold to occur at a different high reflectivity particle level.

24. 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 first light source positioned for supplying a light beam within the test chamber, wherein the first light source is utilized in sensing the amount of particles present in the test chamber;

a first light receiver positioned to receive the light beam supplied by the first light source; and

a plurality of non-planar mirrors positioned within the test chamber for directing the light beam from the first light source to the first light receiver.

25. The sensor of claim 24, wherein the first light source is one of a light-emitting diode (LED) and a laser diode.

26. The sensor of claim 24, wherein the plurality of non-planar mirrors are substantially located in a first plane and the first light source and the receiver are substantially located in a second plane such that the first light source and the receiver do not block the light beam as it is reflected between the mirrors.

27. The sensor of claim 26, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the first light source to the receiver.

28. The sensor of claim 27, wherein the sensor is contained within about a three and one-eighth inch diameter circle and the optical length between the first light source and the first light receiver is at least about fourteen inches.

29. The sensor of claim 28, wherein the five concave mirrors are spherical mirrors.

30. The sensor of claim 24, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

31. The sensor of claim 24, further including:

a second light source positioned such that any portion of the light emitted by the second light source that is reflected off of particles suspended in the test chamber is proportional to the amount of high reflectivity particles present in the test chamber, wherein the first light source is utilized in sensing the amount of low reflectivity particles present in the test chamber; and

a second light receiver positioned to receive the light emitted by the second light source that is reflected off of particles suspended in the test chamber.

32. The sensor of claim 31, further including:

a controller coupled to the first light source, the second light source, the first light receiver and the second light receiver, the controller using the amount of particles sensed using the first light source and the first light receiver to alter the sensitivity of the second light source and the second light receiver.

33. The sensor of claim 32, wherein the sensitivity of the sensor is altered by varying the intensity of the light produced by the second light source.

34. The sensor of claim 32, wherein the sensitivity of the sensor is altered by modifying a second light source alarm threshold to occur at a different high reflectivity particle level.

35. The sensor of claim 24, further including:

a second light source positioned such that any portion of the light emitted by the second light source that is reflected off of particles suspended in the test chamber is proportional to the amount of high reflectivity particles present in the test chamber, wherein the first light receiver detects the light emitted by the second light source that is reflected off of particles suspended in the test chamber, and wherein the first light source is utilized in sensing the amount of low reflectivity particles present in the test chamber.

36. The sensor of claim 35, wherein the sensitivity of the sensor is altered by varying the intensity of the light produced by the second light source.

37. The sensor of claim 35, wherein the sensitivity of the sensor is altered by modifying a second light source alarm threshold to occur at a different high reflectivity particle level.

38. 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;

a plurality of 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.

39. The sensor of claim 38, wherein the scatter emitter/receiver combination and the obscuration emitter/receiver combination share a common receiver.

40. The sensor of claim 38, 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.

41. The sensor of claim 40, wherein the controller causes the obscuration emitter to generate light only after the high reflectivity particle level crosses the initial scatter emitter threshold.

42. The sensor of claim 41, 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.

43. The sensor of claim 41, 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.

44. The sensor of claim 38, wherein the plurality of optical elements includes a plurality of 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.

45. The sensor of claim 44, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the obscuration emitter to the receiver of the obscuration emitter/receiver combination.

46. The sensor of claim 45, wherein the sensor is contained within about a three and one-eighth inch diameter circle and the optical length between the obscuration emitter and the receiver of the obscuration emitter/receiver combination is at least about fourteen inches.

47. The sensor of claim 46, wherein the five concave mirrors are spherical mirrors.

48. The sensor of claim 38, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

49. A smoke detector, comprising:

a housing providing a test chamber, the housing including at least one opening for admitting particles into a test atmosphere of 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 atmosphere and received is proportional to the amount of gray smoke present in the atmosphere;

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 black smoke present in the atmosphere;

a plurality of 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 smoke sensed by the obscuration emitter/receiver combination to alter the sensitivity of the scatter emitter/receiver combination.

50. The smoke detector of claim 49, wherein the scatter emitter/receiver combination and the obscuration emitter/receiver combination share a common receiver.

51. The smoke detector of claim 49, wherein the controller is also configured to change a smoke detector sensor cycle when a gray smoke level crosses an initial scatter emitter threshold, and wherein the rate of the smoke detector sensor cycle determines the frequency with which at least one of the scatter emitter and obscuration emitter emits light.

52. The smoke detector of claim 51, wherein the controller causes the obscuration emitter to generate light only after the gray smoke level crosses the initial scatter emitter threshold.

53. The smoke detector of claim 52, wherein a scatter emitter alarm threshold is modified to occur at a lower gray smoke level when an obscuration emitter threshold is exceeded thus altering the sensitivity of the scatter emitter/receiver combination.

54. The smoke detector of claim 52, 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.

55. The smoke detector of claim 49, wherein the plurality of optical elements includes a plurality of 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.

56. The smoke detector of claim 55, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the obscuration emitter to the receiver of the obscuration emitter/receiver combination.

57. The smoke detector of claim 56, wherein the sensor is contained within about a three and one-eighth inch diameter circle and the optical length between the obscuration emitter and the receiver of the obscuration emitter/receiver combination is at least about fourteen inches.

58. The smoke detector of claim 57, wherein the five concave mirrors are spherical mirrors.

59. The smoke detector of claim 49, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

60. A compact particle sensor, comprising:

a housing defining a test chamber, the chamber admitting test atmosphere;

at least one receiver disposed within the chamber;

a first emitter disposed within the chamber, where a received portion of the light emitted by the first emitter is proportional to the amount of high reflectivity particles present in the atmosphere;

a second emitter disposed within the chamber, where a received portion of the light emitted by the second emitter is inversely proportional to the amount of low reflectivity particles present in the atmosphere; and

a plurality of optical elements positioned within the chamber for directing the light emitted by the second emitter; and

a controller coupled to the first emitter, the second emitter and the at least one receiver, the controller using the amount of particles sensed using one of the first and second emitters to alter an alarm threshold of the remaining emitter.

61. The sensor of claim 60, wherein the controller is also configured to change a sensor cycle when a high reflectivity particle level crosses an initial first emitter threshold, and wherein the rate of the sensor cycle determines the frequency with which at least one of the first and second emitters emits light.

62. The sensor of claim 61, wherein the controller causes the second emitter to generate light only after the high reflectivity particle level crosses the initial first emitter threshold.

63. The sensor of claim 62, wherein a first emitter alarm threshold is modified to occur at a lower high reflectivity particle level when a second emitter threshold is exceeded.

64. The sensor of claim 62, wherein the intensity of the light emitted by the first emitter is increased when a second emitter threshold is exceeded thus altering the sensitivity of the sensor.

65. The sensor of claim 60, wherein the plurality of optical elements includes a plurality of non-planar mirrors that are substantially located in a first plane, and wherein the first emitter, the second emitter and the at least one receiver are substantially located in a second plane such that the first emitter, the second emitter and the at least one receiver do not block the light beam as it is reflected between the mirrors.

66. The sensor of claim 65, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the second emitter to the at least one receiver.

67. The sensor of claim 66, wherein the sensor is contained within about a three and one-eighth inch diameter circle and the optical length between the second emitter and the at least one receiver is at least about fourteen inches.

68. The sensor of claim 67, wherein the five concave mirrors are spherical mirrors.

69. The sensor of claim 60, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

70. 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;

a plurality of optical elements positioned to direct the light beam from the light source to the receiver; and

a controller coupled to the light source and the receiver, wherein the controller is configured to alter an on-time of the light source such that a predetermined initial condition is established irrespective of the brightness of the light source.

71. The sensor of claim 70, wherein the plurality of optical elements includes 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.

72. The sensor of claim 71, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the light source to the light receiver.

73. The sensor of claim 72, 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 fourteen inches.

74. The sensor of claim 73, wherein the five concave mirrors are spherical mirrors.

75. The sensor of claim 70, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

89. 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

a plurality of 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.

90. The sensor of claim 89, wherein the plurality of optical elements includes a plurality of non-planar mirrors.

91. The sensor of claim 90, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the light source to the light receiver.

92. The sensor of claim 91, 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 fourteen inches.

93. The sensor of claim 92, wherein the five concave mirrors are spherical mirrors.

94. The sensor of claim 89, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

95. 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

a plurality of optical elements positioned to direct the light beam from the light source to the receiver, wherein the plurality of optical elements are formed on an integral support structure.

96. The sensor of claim 95, wherein the plurality of optical elements includes a plurality of non-planar mirrors.

97. The sensor of claim 96, wherein the plurality of non-planar mirrors includes five concave mirrors that are utilized to reflect the light beam from the light source to the light receiver.

98. The sensor of claim 97, 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 fourteen inches.

99. The sensor of claim 98, wherein the five concave mirrors are spherical mirrors.

100. The sensor of claim 95, wherein the particles are suspended in one of an atmosphere, a liquid and a non-opaque solid.

101. 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

a plurality of 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.

102. The sensor of claim 101, 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.

103. The sensor of claim 101, 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.

104. The sensor of claim 101, 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.

105. The sensor of claim 101, wherein the test chamber is circular.

106. 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 such that any portion of the light emitted by the light source that is reflected off of particles suspended in the test chamber and received is proportional to the amount of high reflectivity particles present in the test chamber;

a light receiver positioned to receive light emitted by the light source that is reflected off of particles suspended in the test chamber, the light receiver providing a control signal whose level is responsive to the amount of high reflectivity particles present in the test chamber; and

an ionization detector for providing an indication of the amount of low reflectivity particles present in the test chamber, wherein the control signal is utilized to alter the sensitivity of the ionization detector.

107. The sensor of claim 106, wherein the sensitivity of the sensor is altered by modifying an alarm threshold to occur at a different low reflectivity particle level.

108. 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 gray smoke detecting means for providing an indication of the amount of gray smoke particles suspended in the test chamber; and

a black smoke detecting means for providing an indication of the amount of black smoke particles present in the test chamber, wherein at least one of the gray smoke detecting means and the black smoke detecting means provides an output that is utilized to alter the sensitivity of the other detecting means.

109. The sensor of claim 108, wherein the gray smoke detecting means includes a scatter sensor.

110. The sensor of claim 109, wherein the black smoke detecting means includes one of an ionization detector and an obscuration sensor.

111. The sensor of claim 108, wherein the sensitivity of the sensor is altered by modifying an alarm threshold associated with one of the gray smoke detecting means and the black smoke detecting means.

112. A compact particle sensor, comprising:

a housing defining a test chamber, the chamber admitting test atmosphere;

at least one receiver disposed within the chamber;

an emitter disposed within the chamber, where a received portion of the light emitted by the emitter is proportional to the amount of high reflectivity particles present in the atmosphere;

an ionization detector disposed within the chamber, the ionization detector providing an indication of the amount of low reflectivity particles present in the atmosphere;

a controller coupled to the emitter, the ionization detector and the at least one receiver, the controller using the amount of particles sensed using one of the emitter and the ionization detector to alter an alarm threshold associated with the other.

113. 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 surface of the housing is of a color other than black;

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

a plurality of optical elements positioned to direct the light beam from the light source to the receiver.

114. The sensor of claim 113, wherein at least one of the light source, the light receiver and the plurality of optical elements diffuses the light beam.