Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1998-10-28
2001-09-04
Hofsass, Jeffery A. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S628000, C340S286080, C340S629000, C340S521000, C340S586000
Reexamination Certificate
active
06285291
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system for the detection of airborne pollutants. More particularly the invention relates to a system for detecting smoke and other airborne pollutants as may be generated in the event of a fire or in circumstances which can lead to a fire.
BACKGROUND OF THE INVENTION
Fire protection and suppressant systems which operate by detecting the presence of smoke and other airborne pollutants are well known. Upon a threshold level of smoke being detected, an alarm may be activated and operation of a fire suppressant system may be initiated. While the fire itself will cause damage, considerable damage can also be caused by operation of the fire suppression system, and subsequent removal of the suppressant can be quite hazardous. Many traditional suppressants, such as halon, are also ozone depleting making this use environmentally undesirable. A detection system which is sufficiently sensitive to detect an abnormal condition prior to the onset of a fire is very advantageous as it enables action to be taken at a very early stage before the onset of actual fire conditions. For example, when most substances are heated, even before heating occurs to a point at which a fire commences, emissions will be generated and if these can be detected by a very sensitive system, a warning provided at that very early stage may allow the problem to be detected and rectified, or the equipment turned off, before the fire actually starts.
It is also desirable for the detection system to have a wide dynamic range of operation whereby it is effective not only at low levels of smoke and other airborne pollutants as may be generated prior to the onset of actual fire conditions as discussed above, but also is able to detect a range of higher threshold levels of smoke and other pollutants. High levels of smoke will indicate a greater likelihood of there being a fire and the higher thresholds can trigger alarms to shut down air conditioning, close fire doors, call a fire fighting service, and eventually trigger a suppression system if the smoke level becomes sufficiently high.
It is known for detection systems to incorporate a sampling pipe network consisting of one or more sampling pipes with sampling holes installed at positions where smoke or pre-fire emissions can be collected. Air is drawn in through the sampling holes and along the pipe by means of an aspirator, or fan, and is directed through a detector at a remote location. Conventionally, the detector is in series with the aspirator and the pressure drop associated with the detector reduces the pressure drop across the pipe network and hence reduces overall flow through the pipes. Also, the flow through the detector tends to vary with ambient conditions and from installation to installation, and contaminants flowing through the detector can alter the detection characteristics over a period of time. Accordingly, it is difficult with prior sampling systems to achieve a constant high sensitivity which is repeatable from installation to installation and which is maintained over a substantial time.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a smoke detection system comprising an inlet for connection to one or more sampling pipes, aspirator means for drawing sampling air through the inlet, a smoke detector having a detector chamber for receiving sampling air discharged from an outlet of the aspirator means via flow control means, an outlet from the detector chamber being connected to said inlet, said flow control means permitting a small portion of the outlet flow from the aspirator means to be drawn through the detector chamber for detection purposes with substantially the entirety of the sampling air flow drawn through the inlet from the or each sampling pipe being discharged to exhaust from the outlet of the aspirator means, and optional filter means for filtering that part of the sampling air flow which is drawn into the detector chamber.
In accordance with the invention therefore and as will be explained in greater detail herein, the arrangement of the components as defined above results in a substantial pressure drop across the sampling pipe network which results in a substantial sampling air flow via the or each sampling pipe and which is substantially unaffected by the presence of the filter, if present, and the detector chamber. A commensurately large pressure drop is also subtended across the filter and detector chamber which provides advantages as will be discussed later.
In a preferred embodiment of the invention the filter provides a coarse filtering stage to remove dust particles from the sampling air flow and a fine filtering stage to provide a substantially clean air flow which is directed into the detector chamber to prevent contamination of critical components within the chamber which is likely to reduce the sensitivity of the detector.
The flow control means may comprise an orifice at the inlet to the filter, and/or at the outlet from the filter, and/or at the inlet to the detector chamber.
Preferably the filter is provided by a replaceable filter cartridge.
When the system is required also to detect the presence of specified gases, one or more gas sensors can to advantage be incorporated to sense the presence of such gases within the clean air flow downstream of the filter.
In an alternative embodiment of the invention a fine filtered clean air flow can be generated by a second aspirator independently of the sampling air flow.
In a preferred embodiment of the invention the detector is an optical detector and advantageously a detector of the type which operates by detection of optical scattering in the presence of smoke particles. In that case the fine filtered clean air is introduced into the detector chamber at positions to prevent contamination of the light source, and/or a scattered light detector, and/or a light absorber, with the fine filtered clean air being introduced into the chamber at a rate which is sufficient to prevent particles of smoke and other contaminants from settling on the components.
According to another aspect of the invention, there is provided a replaceable filter cartridge for a filter as defined above, said cartridge including a coarse filter stage in which coarser particles of dust and other contaminants are removed, an outlet leading from the coarse filter stage for coarse filtered air for sampling purposes, a fine filter stage for receiving a portion of the air flow filtered in the coarse filter stage and for fine filtering that portion to produce a substantially clean air flow, and an outlet for said clean air flow.
Preferably, the coarse filter stage is such as to remove dust and other particles of a size in excess of approximately 20 microns and preferably the fine filter stage is operative to remove substantially all particles in excess of approximately 0.3 microns. The coarse filter stage may include a filter medium formed by an open cell foam and the fine filter stage may comprise a filter medium formed by an ultra-fine filter cloth or filter paper.
Although a smoke detector with provision for introduction of clean air into the detector chamber to prevent contamination of critical parts of the detector is a particularly preferred feature of the detection system in accordance with the invention as defined above, such a smoke detector can, to advantage, also be incorporated in conventional detection systems.
Accordingly, in accordance with another aspect of the invention, there is provided a smoke detector having a detector chamber, an inlet for introducing an air flow to be sampled into the chamber, an outlet for said air flow from the chamber, means within the chamber for detecting the presence of smoke particles within the air flow, and means for introducing into said chamber clean air substantially free of smoke and other particles to prevent contamination of components of the detecting means by settling of smoke particles and other particles.
Preferably, the smoke detector is an optical detector,
Knox Ronald
Ryan Christopher T.
Stevenson Hugh
Hofsass Jeffery A.
Nguyen Hung
Vision Products Pty. Ltd.
Wolf Greenfield & Sacks P.C.
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