Variable air speed aspirating smoke detector

[0001] The invention pertains to aspirating smoke detectors. More particularly, the invention pertains to such detectors which include variable speed control circuitry.

[0002] Aspirated smoke detectors use a network of pipes to sample air from a large area and use a highly sensitive central detector. One of the problems with aspirated smoke detectors is the time that it takes for smoke to travel from the sampling port to the central detector (transport time). A fan or blower is required to move the air toward the detector.

[0003] On one hand, it would be desirable to operate the blower at a high speed to reduce the transport time. However, operating the blower at a reduced speed will increase its life span and decrease power consumption. Decreased power consumption means that the system will require less battery capacity for situations when main power fails.

[0004] There is a need to take advantage of performance provided by higher fan, or blower speeds while at the same time taking advantage of longer operating life and reduced power consumption provided by operating at lower speeds.

[0008] While embodiments of this invention can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention, as well as the best mode of practicing same, and is not intended to limit the invention to the specific embodiment illustrated.

[0009] Embodiments of the invention advantageously have the capability of operating a blower, or, fan in an aspirating smoke detection system at two or more speeds. A higher fan speed decreases the time it takes for air samples to reach a central, or common, smoke detector.

[0010] In accordance with the invention, increasing the fan speed upon detection of an increased level of sensed particulate matter will speed a determination as to whether smoke is present (and persistent or increasing) or if the sensed particulate represents a short term false alarm condition.

[0011] Known aspirated systems work by establishing pre-alarm and alarm thresholds at very high sensitivities i.e., low obscuration levels. When pre-alarm levels are reached, the system will typically wait for the obscuration level to increase (indicating possible fire) or decrease (indicating a false alarm). Increasing the fan speed will speed this determination.

[0012] Increasing the system air speed once particulate is detected may aid in classifying particulate as either dust or smoke. Increasing the speed will change the behavior of larger (heavier) particles such as dust differently than lighter smoke particles. By evaluating the behavior of the particles in inertial particle separators at different speeds, size might be inferred.

[0013] In one aspect of the invention, speed of the blower, or, fan could be increased during commissioning in order to more quickly quantify the environment. Typically, aspirated systems will be installed for a period of time before firm alarm thresholds are determined. During the commissioning period a record is kept of background particulate levels and alarm thresholds are set accordingly.

[0014] Conversely, the air speed could be slowed down once particulate is persistently detected in order to allow the sensor to more carefully analyze the sample. Some aspirated detection systems are classifying the particulate in the sampled air by size. A slower speed may aid in the classification process by allowing more dwell time in the sensor i.e., more analysis on a homogeneous air sample.

[0015] FIG. 1A is a block diagram of an aspirating smoke detector 10 which embodies the invention. Detector 10 includes a housing 12 which carries a smoke sensor 16 which could be implemented as a photo-electric or an ionization-type smoke sensor without limitation. Signals from sensor 16 are coupled to control circuits 18.

[0016] Control circuits 18 could be implemented, at least in part, by a programmable processor 18a in combination with executable instructions or software 18b. Executable instructions or software 18b are stored on a computer readable medium accessible to the processor 18a.

[0017] Control circuits 18 provide output control signals 18c to a Fan/Blower Speed Control unit 22. Speed Control unit 22 responsive to signals 18c generates output control signals 22a to an aspiration unit, such as 26 which could be implemented as a fan or blower without limitation.

[0018] FIG. 1B illustrates a system 10′ where the aspirator 26′ is placed after the smoke sensor 16′ and air is pulled through the smoke sensing chamber. Air exhausts back to the monitored space R. In this embodiment, a partial representative flow can be maintained through the sensor 16′ in order to reduce contamination of the sensor 16′ by airborne particulate normally in the atmosphere. Other elements of FIG. 1B correspond to elements of FIG. 1A and have been assigned the same identification numerals and need no further discussion.

[0019] As a speed parameter of the aspirator is increased, ambient air A from a monitored, or protected space R is drawn by a pipe network, indicated generally at P, at a higher rate of speed by blower 26 into sensor 16. Conversely, as the speed of unit 26 is decreased, output ambient air flows from that unit and is coupled to sensor 16 at a lower rate. As particulate matter from a fire condition F in region R increases, the speed of unit 26, in response to signal 16a, can also be altered, or, increased as explained below relative to the method 100 of FIG. 2.

[0020] As illustrated in FIG. 2, initially unit 26 is energized, as at 102, and speed is set to a nominal value, as at 104. The aspirator 26 inputs ambient air from the region R into sensor 16, as at 106. Circuits 18 can analyze air sensed via sensors 16, as indicated by signals 16a, as at 108.

[0021] In the event that sufficient particulate material is present, as at 110, speed of the aspirating unit 26 can be increased from its initial nominal value, as at 112. In response to the increased aspirator speed, the circuits 18 can carry out an analysis, as at 118 of the incoming ambient to determine a concentration of airborne particulate matter. If particulate matter is no longer present, as at 120, aspirator speed can be returned to a nominal value, as at 104. Otherwise, speed can be reduced below nominal, as at 122.

[0022] Subsequent the particulate matter can be categorized as smoke or dust as at 124. If dust, analysis can continue, as at 118. Alternately, the particulate matter can be evaluated to determine if an alarm indicator should be issued, or not as at 128.

[0023] From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.