HK1174585B - Filter bypass - Google Patents

Description

Filter bypass technology

Technical Field

The present invention relates to particle detection. The following description focuses on smoke detectors and in particular on optical smoke detectors but the skilled person will appreciate that the invention has broader application.

For the avoidance of doubt, "particle detection" and similar words as used herein refer to the detection of solid and/or liquid particles.

Background

Particle detectors are often used to warn of the presence of smoke from a potential or incipient fire.

Smoke detectors operate in a wide variety of environments including, for example, office environments, factories and manufacturing plants, power stations and clean rooms, and the like. Each with a different background particulate material scale. The concentration of background particulates will change from time to time in certain environments.

Such smoke detection devices suffer from a problem if they are continuously exposed to relatively high levels of background air contamination that may be present in certain environments. One large-scale example in recent years is the high-level smoke pollution that frequently occurs in asian areas, due in large part to the burning of lignite.

Background contamination can cause contamination of components within the detector, leading to premature failure, for example, due to air passage blockage, or changes in optical properties of critical components within the detection chamber, etc.

The scatter detector includes a light source configured to project a light beam through the detection chamber. A photosensor is positioned such that its field of view is traversed by a portion of the beam. The photosensor receives light scattered from the light beam due to the presence of particles in the detection chamber. Dust accumulates on surfaces within the detection chamber over time and reflects light toward the photosensor, providing a false particle indication within the detection chamber. Debris may also be positioned on the light source and/or photosensor, reducing the transmission and reception of light and reducing the sensitivity of the detector.

One approach to solving these problems includes the use of an "air barrier". An air barrier is created as follows: one or more streams of clean air are directed into the detection chamber to flow over the critical components, such as the light source, photosensor, and walls within the field of view of the photosensor, to prevent dust from accumulating thereon.

Aspirated smoke detectors use a fan, known as an aspirator, to draw air to be investigated through the detection chamber. Air to be investigated enters the chamber through an inlet. One desirable implementation of the air barrier concept uses a filter to generate the clean air. The filter is positioned parallel to the inlet so that the clean air is drawn by the air extractor through the filter and into the detection chamber. A common air stream, such as from a network of pipes, can be divided into two portions-one portion being filtered to produce the clean air and the other portion entering the chamber under investigation.

Another solution to the problem of debris accumulation in the detection chamber is to take a measurement associated with the light reflected by the accumulated debris, referred to as "background light", and adjust the detection criteria applied to the signal received from the photosensor in response to the background light. A method of obtaining a background light measurement includes using a second photosensor within the detection chamber. The second photosensor is positioned so that its field of view does not contain the beam. The signal from the second photosensor is indicative of the light reflected within the detection chamber, rather than the light directly scattered by the beam.

The abstract description of Japanese patent application No.59192940 entitled "Smoke measuring Meter with purging device" describes filling a measuring device with clean air and measuring opacity in the clean atmosphere for calibration. The device comprises a dedicated blower for supplying clean air into the detection chamber. A valve controlled by a depressible switch is used to close the inlet tube to stop the flow of exhaust gas to the detection chamber prior to the purging operation.

The new zealand patent No.250497 relates to fire suppression measures being activated in response to false alarms. Which describes an operating system applicable to aspirated smoke detectors. When an alarm condition is detected, the chamber is purged with clean air and a background "" smoke "" signal is detected. If the background reading does not fall below a predetermined threshold, a detector error is indicated. If the background "smoke" value falls below the predetermined threshold, the system waits for the measured smoke level to rise above another threshold before triggering the fire suppression system.

Other attempts to overcome problems associated with operating particle detectors in contaminated environments have included dust filters placed in the air stream. Dust filters have been used to filter out particles not associated with the smoke to be detected. The smoke particles may occur in various sizes depending on the fuel used and the combustion conditions, and the type of filter is selected based on the expected type of dust particles and the type of smoke to be detected.

When conventional dust filters clog, they begin to remove more particulates from the air and eventually begin to filter out smoke particulates (or other small particles of interest). This is due to the reduction in the effective pore size of the filter as more particulates clog the filter. Certain types of filters, particularly foam filters, may begin to remove smoke particulates before the pressure drop across the filter or the flow rate through the filter changes significantly. As a result, the filter may remove an unknown fraction of smoke far before clogging of the filter can be detected using pressure and/or flow measuring devices.

In some cases, attempts have been made to modulate the air sample before it is introduced into the smoke detector, for example by diluting the sample stream with clean air. The purpose of this dilution is to deliver a sample stream to the detection chamber, the sample stream having an unaltered particle distribution but a lower concentration of particles than the original sample stream. While such dilution processes may also or alternatively solve problems associated with operation in a contaminated environment, lower particle concentrations reduce the sensitivity and accuracy of the detector.

Dilution presents problems for some air sampling smoke detectors that use a network of pipes to draw air from a monitored space, wherein the flow of dilution air introduced into the air stream entering the detector will reduce the amount of sample air drawn from the monitored area. This increases the time it takes for the sample air to travel from the monitored area to the smoke detector, known as the "transit time", and thus increases the detection time.

The applicant has proposed in its international patent application WO 2007/095675 an apparatus in which a first portion of a sample stream is filtered through a High Efficiency Particulate Air (HEPA) filter. The HEPA filter removes substantially all of the particulates from the first portion of the sample stream to form clean air. The clean air is used to dilute an unfiltered second portion of the sample stream. The diluted sample flow is then carried to a detection zone. This device effectively solves the transit time problems associated with other dilution devices and has a better "fail-safe" operation in which the detection zone will see an increased rather than decreased particle concentration if the filter is allowed to clog to a point where it becomes more fluid-restrictive. The degree of dilution may also vary due to environmental factors such as temperature and humidity. Varying the dilution ratio reduces the accuracy of the associated smoke detector.

Despite these various advances in the art, the known filtration devices and dilution devices result in a reduced concentration of particles reaching the detection zone and reduce the sensitivity and accuracy of the particle detector. It is of course desirable that a smoke detector should be sensitive and accurate. It is also preferred that if a filter is used, its condition should be known, in particular whether it has become clogged to such an extent that particles of interest (e.g. smoke particles) are removed.

Objects of the invention include providing improved particle detection, an improved particle detector and components thereof, or at least alternatives relating to particle detection.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that prior art forms part of the common general knowledge in australia or any other jurisdiction or that prior art could reasonably be expected to be known, understood and regarded as relevant by a person skilled in the art.

Disclosure of Invention

One aspect of the present invention provides a filter arrangement for a particle detector for detecting particles in an environment, the particle detector comprising one or more sensors for analysing fluid in a detection region to produce a sensor output, the filter arrangement comprising structure defining a flow path for conveying fluid from the environment towards the detection region, comprising a first flow path and a second flow path, the first flow path comprising a filter and the second flow path bypassing the filter; a mechanism for controlling the relative flow rates of fluid through the first and second flow paths; and a controller configured to receive sensor outputs corresponding to at least two relative flow rates and to apply logic thereto to generate an output indicative of the condition of the filter.

The sensor output is preferably indicative of the particulate concentration.

In preferred forms of the invention, the mechanism is configured or controlled (e.g. by the controller) to vary the relative flow rates, and the controller is configured to generate an output indicative of the condition of the filter periodically (e.g. at fixed time intervals, randomly intermittently, or according to a predetermined schedule) and/or in response to a sensed change in particulate concentration.

The controller may be configured to generate a fault signal if the condition of the filter exceeds a predetermined threshold.

The mechanism is preferably configured or controlled to vary the relative flow rates in accordance with a predicted contamination metric in the environment to control the concentration of contaminants reaching the detection zone.

Another aspect of the invention provides a filter arrangement for a particle detector for detecting particles in an environment, the particle detector comprising one or more sensors for analysing fluid in a detection region to produce a sensor output, the filter arrangement comprising structure defining a flow path for conveying fluid from the environment towards the detection region, comprising a first flow path and a second flow path, the first flow path comprising a filter and the second flow path bypassing the filter; and a mechanism for controlling the relative flow rates of fluid through the first and second flow paths; the mechanism is configured or controlled to vary the relative flow rates based on a predetermined level of contamination in the environment to control the concentration of contaminants reaching the detection region.

In a preferred form of the invention, varying the relative flow rates according to the predicted contamination scale includes varying the relative flow rates according to a repeating schedule. Preferably the schedule comprises a night mode in which a relatively low proportion of fluid is passed through the first flow path to obtain relatively high detector sensitivity, and a day mode in which a relatively high proportion of fluid is passed through the first flow path to obtain reduced detection zone contamination.

Optionally, the mechanism is configured or controlled to periodically temporarily increase the relative flow rate through the second flow path to periodically increase the sensitivity of the detector such that the average time that the detection region is exposed to fluid from the second flow path on average and the carry-over of contaminants is reduced to reduce contamination of the detection region.

Another aspect of the invention provides a filter arrangement for a particle detector for detecting particles in an environment, the particle detector including one or more sensors for analysing fluid in a detection region to produce sensor output, the filter arrangement comprising: structure defining a flow path for conveying fluid from the environment towards the detection region, comprising a first flow path containing a filter and a second flow path bypassing the filter; a mechanism for controlling the relative flow rates of fluid through the first and second flow paths; and a controller configured to control the mechanism to periodically temporarily increase the relative flow rate through the second flow path to periodically increase the sensitivity of the detector such that the average time that the detection region is exposed to fluid from the second flow path is increased and entrained contaminants are reduced to reduce contamination of the detection region.

In a preferred form of the invention, the relative flow rate through the second flow path is temporarily increased one or more times per minute.

Preferably, the means is configured or controlled such that substantially all of the fluid is delivered through the second flow path during each periodic temporary increase in the relative flow rate through the second flow path. Preferably the means is configured or controlled such that substantially all of the fluid is delivered through the first flow path between each periodic temporary increase in the relative flow rate through the second flow path.

The structure may include a flow splitting device for receiving a common fluid flow from the environment and directing portions of the common flow to the first and second flow paths. Preferably, the structure comprises a fluid combining means to receive fluid from the first and second flow paths and to deliver a combined fluid flow towards the detection zone.

The mechanism may comprise a valve, for example a solenoid valve. In a preferred form of the invention, the mechanism comprises an electromechanical device.

Preferably, the structure and mechanism together impart a fluid restriction that is substantially greater than the fluid restriction imparted by the filter, such that the relative flow rates through the first and second flow paths are substantially independent of the condition of the filter. Preferably, the filter is a HEPA filter.

In a preferred form of the invention, the second flow path is configured such that the entrained fluid is substantially free of particles of interest to be filtered.

Another aspect of the present invention provides a particle detector for detecting particles in an environment, comprising: a structure defining a detection region; one or more sensors to analyze fluid in the detection region to generate a sensor output; and the filter device is arranged to convey the fluid from the environment to the detection area and is matched with the sensor to operate.

Preferably, the particle detector comprises a controller having a purge mode wherein the controller controls the mechanism to deliver fluid to the detection zone substantially only from the first flow path to purge fluid from the second flow path in the detection zone; and a detection mode in which the controller controls the mechanism to deliver at least some of the fluid from the second flow path to the detection region; and configured to apply logic to the sensor output obtained from the detection mode to generate another output; and if necessary, adjust the logic based on the sensor output obtained from the purge mode to compensate for contamination of the detection zone.

Another aspect of the invention provides a particle detector for detecting particles in an environment, comprising structure defining a flow path for conveying fluid from the environment towards a detection region, comprising a first flow path including a filter and a second flow path bypassing the filter; a means for controlling the relative flow rates of fluids through the first and second flow paths; and one or more sensors for analyzing the fluid in the detection region to produce a sensor output; and a controller having a purge mode wherein the controller controls the mechanism to deliver fluid to the detection region substantially only from the first flow path to purge fluid from the second flow path in the detection region; and a detection mode in which the controller controls the mechanism to deliver at least some fluid from the second flow path to the detection region; and configured to apply logic to the sensor output from the detection mode to generate another output; and if necessary, the logic is adjusted based on the sensor output from the purge mode to compensate for contamination of the detection region.

Preferably, the controller is configured to periodically (e.g., at fixed time intervals, randomly intermittently, or according to a predetermined schedule) transition between the purge and detection modes. Preferably, the controller is configured such that the change from the detection mode to the cleaning mode is regulated in accordance with the sensor output.

The controller may store a plurality of measurements based on the sensor output over a time interval when the chamber is purged. In a preferred form of the invention, the controller is configured to apply additional logic to the sensor output as the chamber is purged and to generate a fault signal if required.

The logic may include subtracting a background light measurement from the sensor output. Adjusting the logic may include calculating and replacing a new backlight measurement.

The sensor includes one or more optoelectronic devices.

Another aspect of the invention provides a particle detection system for detecting particles in an environment, comprising a conduit defining: at least one inlet to receive fluid from the environment; and at least one outlet; an air extractor disposed between the inlet and the outlet for moving fluid through the conduit; and the particle detector described above, configured to receive fluid downstream from the aspirator and deliver the fluid upstream from the aspirator such that the fluid is moved by the aspirator past the particle detector.

In another aspect, the invention provides a filter apparatus for receiving sample fluid and supplying fluid to be moved through a detection region of a particle detector, the filter apparatus comprising structure defining a first flow path and a second flow path, a controllable mechanism for controlling the relative flow rates of sample fluid received through the first and second flow paths, and a controller; at least the first flow path including a filter for filtering particles of the fluid traveling along the first flow path; the first and second filtered flow paths being arranged in parallel such that fluid travelling along the second flow path bypasses the filter, the first and second filtered flow paths being arranged to communicate downstream of the filter with the detection region; the controllable mechanism has at least two modes corresponding to different relative flow rates through the first filtered flow path and the second bypass flow path; and the controller is configured or programmed to receive at least one fluid characteristic parameter for each of the at least two modes and to apply logic to generate a filter condition signal indicative of filter condition based on the received parameters.

The at least one parameter is preferably a signal indicative of particle concentration, which is preferably received by a component of a particle detector, such as an optoelectronic device, associated with the detection region.

According to a preferred form of the invention, the first filtered flow path and the second bypass flow path converge downstream of the filter and are then in communication with the detection zone.

The controllable mechanism is preferably a valve. The controllable mechanism may be an electromechanical device. According to a preferred form of the invention, the controllable mechanism is a solenoid valve. Preferably the controllable mechanism is operatively associated with the controller such that the controller switches between the at least two modes. This allows the controller to be configured or programmed to switch between the at least two modes to generate the filter condition signal. For example, the controller may be configured or programmed to generate the filter condition signal periodically, such as once per week.

The controller may be configured or programmed to switch between the modes depending on actual or predicted contamination metrics to control the concentration of contamination reaching the detection zone. For example, one mode in which substantially all of the received sample fluid is filtered may be used during daytime operation (when high contamination levels are expected) in a factory environment, and a second mode in which substantially all of the received sample fluid is used during nighttime operation along the bypass line. In this way, the particle detector can operate at full sensitivity at night, but can be protected from day-time contamination. The controller may have three or four modes corresponding to different filter scales.

Alternatively, the controller may be configured or programmed to switch between modes to generate the filter condition signal in response to a signal indicative of a change in particulate concentration, e.g. if a rapid increase or decrease (such as a 50% decrease) in particulate concentration is detected, the controller may control the controllable mechanism to obtain said filter condition signal and to determine whether the rapid increase or decrease is associated with a change in the received sample fluid or a change in the filter condition. The controller may also be configured or programmed to change between modes in response to a signal indicative of particle concentration to achieve increased sensor sensitivity or increased contamination protection.

Preferably, one of the at least two modes, referred to as a filter check mode, corresponds to substantially all of the received sample fluid being run along the second bypass flow path.

In accordance with preferred embodiments of the present invention, in at least one of the at least two modes, the structure and/or the controllable mechanism imparts a flow restriction that is substantially greater than a flow restriction imparted by the filter, such that the relative amounts of fluid flowing through the first filtered flow path and the other flow paths are substantially independent of filter conditions.

The controller of the preferred form of the invention is configured or programmed to apply logic to generate a fault signal if the filter condition signal exceeds a predetermined threshold.

The structure may include a flow splitting device configured to receive a common sample fluid flow, e.g., via a common opening, e.g., from a common conduit associated with a network of conduits, and direct each of the common sample fluid flow into the first filtered flow path and the second bypass flow path.

This aspect of the invention also provides a particle detector comprising the filter means and a detection region, the filter means being in communication with the detection region for supplying fluid thereto.

This aspect of the invention also provides a method of detecting filter conditions of a filter upstream of a particle detector, the method comprising: causing a first fluid flow to pass through at least one of the filter and a bypass provided to bypass the filter upstream of the particle detector; measuring at least one first parameter associated with the first fluid flow; varying the relative flow rates through the filter and the bypass to produce a second fluid flow; measuring at least one second parameter associated with the second fluid flow; and applying logic to the measured parameters to determine filter conditions.

The measured parameter is preferably the particle concentration and is preferably measured at the particle detector.

The varying preferably comprises actuating at least one electromechanical valve.

According to a preferred form of the invention, the first and second fluid flows are conveniently caused by selectively preventing and allowing fluid flow through the bypass.

In another aspect of the invention, there is provided a filter device for receiving sample fluid and supplying fluid to be moved through a detection region of a particle detector, the filter device comprising: structure defining a first flow path and a second flow path, a controllable mechanism for controlling the relative flow rates of received sample fluid through the first and second flow paths, and a controller; at least the first flow path including a filter for filtering particles of the fluid traveling along the first flow path; the first filtered flow path and the second flow path being arranged in parallel such that fluid travelling along the second flow path bypasses the filter, the first filtered flow path and the second bypass flow path being arranged to communicate with the detection region downstream of the filter; the controllable mechanism has at least two modes corresponding to different relative flow rates through the first filtered flow path and the second bypass flow path; and the controller is configured or programmed to switch between the modes to control the concentration of contamination reaching the detection zone based on actual or predicted contamination metrics.

This aspect of the invention also provides a particle detector comprising the filter means and a detection region, the filter means being in communication with the detection region to supply fluid thereto.

This aspect of the invention also provides a method of controlling the concentration of contamination in a fluid supplied to a detection region of a particle detector, the method comprising the steps of: causing a fluid flow through at least one of a filter and a bypass configured to bypass the filter; directing the fluid stream to the detection zone; and varying the relative flow rates through the filter and bypass according to an actual or predicted contamination scale to control the concentration of contamination reaching the detection zone.

In broad terms in another aspect the invention is directed to a method of monitoring an aspirated smoke/particle detector (in a contaminated environment) comprising: providing a first flow path between a sample air output and a detection region of the smoke/particle detector, the first flow path having a filter; providing a second flow path between the sample air output and the detection zone that bypasses the first filtered flow path; obtaining a first signal associated with the concentration of particulates in the first filtered flow path; diverting the sample air through the second flow path; obtaining a second signal associated with the concentration of particles in the second flow path; a measurement indicative of the condition of the filter is obtained based on the first and second signals.

The present invention further provides a method of operating an aspirated particle detector, comprising: monitoring an aspirated smoke/particle detector (in a contaminated environment) includes: providing a first flow path between a sample air output and a detection region of the smoke/particle detector, the first flow path having a filter; providing a second flow path between the sample air output and the detection zone that bypasses the first filtered flow path; switching between the first and second flow paths in response to a signal indicative of the generation of non-representative particles, such as dust particles.

The signal indicative of the generation of the non-representative particle may be, for example, a time signal or a detection signal.

In another aspect of the invention, a particle detector is provided, comprising a detection region; one or more sensors for detecting and providing a signal indicative of particles in the detection zone; a structure defining a probing fluid flow path for delivering a probing fluid to the detection region; a controllable mechanism for controlling the flow rate along the exploratory fluid flow path; and a controller configured to control the controllable mechanism to selectively move a probe fluid through the detection region to expose the detection region to the moving probe fluid and entrained contaminants to reduce contamination of the detection region.

Preferably the structure further defines a sample fluid flow path for conveying a sample fluid stream withdrawn from a sample space, and the controllable mechanism is configured to direct at least a portion of the sample fluid stream along the probing fluid flow path, the portion of the sample fluid stream forming the probing fluid.

In accordance with a preferred embodiment of the present invention, the structure further defines a first filtered flow path, the probe fluid flow path forming a second bypass flow path; the first filtering flow path and the second bypass flow path are both communicated with the detection area.

The particle detector preferably comprises an air extractor downstream of the detection region for creating and moving said fluid flow.

The second bypass flow path is preferably substantially unfiltered, such that the probe flow is substantially unfiltered.

The first filtered flow path is preferably configured to filter substantially all contaminants from the fluid traveling therealong. For example, the first filtered flow path may be spanned by a HEPA filter.

Preferably the controller is configured to move the probe fluid through the detection region about 20% of the time. It is best to explore that the flow system is moved through the detection area one or more times per minute. For example, the detection zone may be alternately exposed to filtered fluid from the first filtered flow path for 4 seconds and substantially unfiltered fluid from the second bypass flow path for 1 second.

The controller may be configured to receive the representative signal and apply logic to generate another signal. Preferably, the controller is configured to receive the indication signal as the probe fluid is selectively moved through the detection zone and, if necessary, to compensate for the contamination of the detection zone.

This aspect of the invention also provides a method of operating an aspirated particle detector having a detection region, the method comprising: intermittently introducing a new sample stream to the detection chamber; selectively moving a probe fluid through the detection zone; and studying the probe fluid in the detection zone to generate a signal indicative of the particle concentration; the detection zone is selectively exposed to the moving probe fluid and entrained contaminants to reduce contamination of the detection zone.

The selective transfer preferably includes periodically directing at least a portion, and more preferably substantially all, of a flow of fluid drawn from a sample space to reduce transit time. Said periodic directing preferably comprises directing said portion of the fluid from a first filtered flow path to a second bypass flow path; wherein the first filtering flow path and the second bypass flow path are both communicated with the detection area; the fluid traveling along the second bypass flow path will form the probed fluid. The method preferably comprises actuating an exhaust fan downstream of the detection zone to create and move said fluid flow.

The second bypass flow path is preferably substantially unfiltered such that the probe flow is substantially unfiltered.

The first filtered flow path is preferably configured to filter substantially all contaminants of the fluid traveling therealong. For example, the first filtered flow path may be spanned by a HEPA filter.

Preferably the method comprises moving a probe fluid through the detection zone for about 20% of the time. It is preferred to explore that the fluid is moved through the detection zone one or more times per minute. For example, the detection zone may be alternately exposed to filtered fluid from the first filtered flow path for 4 seconds and substantially unfiltered fluid from the second bypass flow path for 1 second.

The method may include applying logic to the representative signal to generate another signal; and may also include receiving the indicative signal during selective movement of a probe fluid through the detection region and compensating for the contamination of the detection region if desired.

In another aspect of the invention, a particle detector is provided, comprising a detection region; one or more sensors for detecting particles in the detection zone and providing a signal indicative of the particles; a controller; a structure defining a first flow path and a second flow path for delivering the received sample fluid to the detection zone; and a controllable mechanism for controlling the relative flow rates of sample fluid received through the first and second flow paths; at least the first flow path including a filter for filtering particulates from the fluid traveling along the first flow path; the first and second filtered flow paths being arranged such that fluid traveling along the second flow path bypasses the filter; the controllable mechanism has: a purging mode in which the detection zone receives substantially only filtered fluid from the first filtered flow path to purge the detection zone of unfiltered fluid; and a detection mode wherein the detection region receives at least some fluid from the second bypass flow path; the controller is configured or programmed to receive the representative signal and apply logic to generate another signal when in the detection mode; the controller is configured or programmed to receive the indication signal when the detection region is purged of unfiltered fluid and adjust the logic in response thereto, if necessary, to compensate for contamination of the detection region.

The controller is preferably operatively associated with the controllable mechanism to control the transition between the purge and detection modes. The controller may be configured such that the transition from the detection mode to the purge mode is regulated in accordance with the indication signal. For example, the detector may be configured not to enter the clear mode if the indication signal is at or above a threshold. The threshold at which purging is initiated preferably corresponds to a particle concentration that is less than an alarm threshold, and preferably about 50% thereof.

The controller preferably stores a plurality of measurements based on the representative signal over a time interval when the chamber is purged. The controller may be configured to generate a fault signal if the signal indicative of when the chamber is purged is too low, too high, too variable, and/or too different from the signal indicative of the previous purge and trim operations. The logic may include subtracting a measure of background light from the representative signal. The logic may be adjusted to include averaging the stored representative signals to calculate a new background light measurement.

This aspect of the invention also provides a method of operating a particle detector having a detection region, the method comprising moving a probe fluid through the detection region; investigating the probe fluid in the detection area to generate a signal indicative of the particle concentration; and applying logic to the representative signal to generate another signal; filtering the sample fluid drawn from the sample space to form a filtered fluid; moving the filtered fluid through the detection region to clear the detection region of the probe fluid; studying the filtered fluid in the detection zone to generate a second signal indicative of the particle concentration; and adjusting the logic in response to the second representative signal if necessary to compensate for the concentration of the detection region.

The flow of filtered fluid through the detection zone to clear the detection zone is adjusted in response to the indicator signal.

As used herein, the terms "comprises," "comprising," and variations thereof, such as "comprises," "comprising," and "including," are not intended to exclude other additives, components, integers or steps, unless the content requires otherwise.

Drawings

FIG. 1 is a schematic diagram of a particle detector in accordance with a preferred embodiment of the present invention;

FIG. 2A is a schematic view of a filter device in an operating mode according to a preferred embodiment of the present invention;

FIG. 2B is a schematic view of the filter apparatus of FIG. 2A in another mode of operation;

FIG. 3A is a schematic view of a filter device according to another embodiment of the present invention in an operating mode;

FIG. 3B is a schematic view of the filter apparatus of FIG. 3A in another mode of operation;

FIG. 4A is a schematic view of a filter device according to another embodiment of the present invention in an operating mode;

FIG. 4B is a schematic view of the filter apparatus of FIG. 4A in another mode of operation;

FIG. 5 is a schematic view of a filter device according to yet another embodiment of the present invention in an operating mode;

FIG. 6A is a schematic view of a filter device according to another embodiment of the present invention in an operating mode;

FIG. 6B is a schematic view of the filter apparatus of FIG. 3A in another mode of operation; and

FIG. 7 is a schematic diagram of a filtration apparatus in an operational mode according to yet another embodiment of the present invention.

Detailed Description

FIG. 1 illustrates a particle detector 12 according to a preferred embodiment of the present invention. The particle detector 12 includes a filter 10, a detection chamber 30 and an air pump 14.

The air extractor 14 draws air from a network of pipes 18. This air is referred to as "sample air". The sample air is exhausted from the aspirator 14 to the outlet 16 via an exhaust tube 46. A sampling tube 48 branches from the exhaust tube 46 and extends to the filter device 10 to conduct the filter device 10 and the exhaust of the exhaust blower. A conduit 40 connects the filter device 10 and the detection chamber 30. The detection chamber 30 is in communication with the pump inlet via a conduit 50. Thus, sample air from the aspirator exhaust is driven through the filter assembly 10, through the detection chamber 30, and back to the aspirator inlet. This device is called a sub-sampling loop.

The filter apparatus 10 includes structure 42, the structure 42 defining a first flow path 22 and a second flow path 24. The flow paths 22 and 24 are arranged in parallel and extend between a manifold space 20 and a plenum 28. Sample air discharged from the suction fan is received in the manifold space 20 where it is distributed to first and second flow paths 22 and 24. The flow paths converge and the fluids combine within the plenum 28. The combined fluid is then delivered to the detection chamber 30.

A filter 26 is disposed along the first flow path 22.

The manifold space 20 contains a valve that forms a controllable mechanism for varying the relative flow rates through the first and second flow paths. The valve may be a simple flapper valve or butterfly valve, such as flapper valve 120B shown in FIGS. 2A and 2B. By varying the operation of the valve, the relative proportions of filtered and unfiltered air reaching the plenum chamber 28, and the composition of the mixed air reaching the sensing chamber 30, can be controlled.

The filter apparatus 10 further includes a controller 32. The controller 32 receives sensor output from the detection chamber 30 in the form of a signal 44 indicative of the concentration of particles within the detection chamber. In some embodiments, the controller may be configured to process the received signal to generate an output. In this embodiment, the controller 32 is operatively connected to valves in the manifold space 20 to control the relative flow rates through the first and second flow paths 22, 24.

The "controller" described herein may be any device that receives an input signal and processes the signal to generate another useful signal. For example, the controller may include, but is not limited to, a microprocessor, Field Programmable Gate Array (FPGA), ASIC, microcontroller, or any equivalent functional analog or digital implementation.

The controller 32 generates an alarm signal (not shown) based on the signal 44 indicative of the particle concentration when certain alarm criteria are met. As will be described, the controller 32 also applies logic to generate a signal 34 indicative of the condition of the filter 26.

The smoke detector according to the preferred form of the invention may be installed along a fire alarm circuit (not shown) through which signals 34 indicative of the filter condition are transmitted to a fire alarm control panel (FACP, not shown). The FACP may display the condition of the filter and signal an error when the filter condition exceeds a predetermined threshold, such as providing an audible signal or flashing a light on a display.

The filter 26 is configured to cause a known reduction in particulate concentration. According to a preferred form of the invention, under the influence of the controller 32, the valves in the manifold space 20 are configured such that substantially all of the received sample air is directed through the first filtered flow path 22 when in a normal detection mode. Substantially all of the air reaching the detection chamber 30 is filtered. The detection chamber 30 is protected from contamination.

The warning criteria applied by the controller 32 to the signal 44 is adjusted based on known reductions in particulate concentration associated with the filter 26. According to the preferred form of the invention, the adjustment is performed automatically by the controller 32 and the amount of adjustment is regularly updated based on the filter conditions as determined by the following procedure.

Once per week, at a fixed time of day, the controller 32 sends a signal to the manifold space 20 to change the position of the valves therein to change the relative flow rates through the first and second flow paths 22, 24 so that substantially all of the received sample air is directed through the bypass flow path 24. Substantially all of the fluid received by the detection chamber 30 is unfiltered. This case is referred to as a "filter check mode".

By comparing the signal 44 in the normal detection mode and the filter check mode, the controller 32 can make an inference of a filter condition, and in particular the degree to which the filter 26 filters particles of interest from fluid passing through the filter.

In the normal detection mode, the detection chamber 30 is protected from contamination, and the adjustment maintains an improved accuracy over other filtering devices. Nonetheless, by filtering the incoming air, the concentration of particles reaching the detection chamber 30 will be reduced, which results in some reduced sensitivity compared to unfiltered devices.

In accordance with a preferred form of the present invention, the controller 32 is operable to control valves within the manifold space 20 to vary the relative flow rates through the first and second flow paths 22, 24, thereby controlling the extent to which fluid received by the detection chamber 30 is filtered in response to actual or predicted contamination metrics. When the relative flow rates are so adjusted, the controller 32 makes a corresponding adjustment to the alarm criteria. The present invention is able to maximize the protection from contamination when the air is heavily contaminated and to maximize the sensitivity when the air is not so contaminated.

For example, the particle detector 12 may operate in a normal detection mode when the daytime operating hours of a plant, i.e., the pollution scale, is expected to be high; and reverts to a "night time" mode when the plant is at rest and the pollution scale should be low. In the night time mode, substantially all or a selected proportion of the received sample air is directed through the unfiltered second flow path 24 and a corresponding adjustment to the alarm criteria is made by the controller 32. The detection chamber 30 is protected from daytime contamination, while maximum sensitivity is maintained at night. The controller 32 may compare the signal 44 for each transition between the normal detection mode and the night mode. The filter condition can then be checked and the alarm criteria updated appropriately on a twice-a-day basis.

In accordance with some embodiments of the present invention, a portion or substantially all of the received sample air may pass through the unfiltered second flow path 24 during normal operation to maximize sensitivity. According to such embodiments, the amount of filtering may be increased when there is a contamination event (e.g., theatrical smoke released in a theater or a diesel-powered train arriving at a station). The logic applied to the sensor output may be changed as a function of the relative flow rate, for example, an alarm threshold or alarm delay may be decreased as the degree of filtering increases. The variation of the amount of filtering may be controlled by a timetable (e.g., a train timetable) or by other inputs. For example, in a simple implementation, an operator may provide an input to switch to a high filtration mode before operating a machine known to produce significant particulate contamination. Some embodiments may have more than two, e.g., four, different modes of operation, corresponding to different relative flow rates and different amounts of filtration.

The degree of filtration may be adjusted in response to the measured concentration of particulates. For example, the filter 26 may be a foam filter selected to filter dust while allowing smoke particles to pass through. In this embodiment, the controller 32 varies the relative flow rates through the flow paths 22 and 24 in response to a signal 44 indicative of increased particulate concentration so that a greater portion of the received sample fluid is filtered. By monitoring the change in the signal 44, the controller 32 can make an inference as to whether the measured increase in particulate concentration is associated with dust or smoke.

Fig. 2A and 2B schematically illustrate a structure 142 of a filter device according to an embodiment of the invention. Sample air is received into a manifold space 120A by an inlet 138. The structure defines two parallel flow paths 122 and 124. The flow path 122 is spanned by a foam filter 126. The flow path 124 is spanned by a simple pivotally mounted flap which provides a controllable mechanism for varying the flow rate through the flow path 124, as well as the relative flow rates through the flow paths 122 and 124. Figure 2A shows the flap 120B in the closed position. Figure 2B shows the flap 120B in the open position. The flow paths 122 and 124 converge so that the fluids combine in the plenum 128 and the combined fluid exits the structure 142 through the outlet 140.

Figure 2A illustrates a device similar to the normal detection mode described above. The flow path 124 is closed by the flap 120B so that substantially all of the received fluid is directed through the filter 126. The filter 126 has a relatively high impedance, so that when the flap 120B is opened, as shown in FIG. 2B, substantially all of the fluid is directed through the flow path 124.

Foam filters, such as the filter 126, efficiently filter out dust particles. In their normal operating range, such filters remove only a small proportion of the smoke particles. The different treatments for smoke and dust particles will suitably allow the detection chamber to be protected from dust with a small reduction in sensitivity. One problem with these foam filters is that when they become clogged, they will begin to filter out smoke particles, and a significant portion of the smoke particles may be filtered out before there is any significant change in the pressure drop across the filter. It can be difficult to determine when the filter has become clogged to such an extent that it filters out smoke particles. As those skilled in the art will appreciate, the preferred embodiment of the present invention solves this problem by opening flap 120B to expose the detection chamber to unfiltered air.

The structure of figures 1, 2A and 2B lends itself to two other preferred modes of operation.

According to the first of these two modes, the flap 120B, i.e., the bypass 124, is periodically opened and closed. In this mode the detector receives periodic bursts of unfiltered air separated by periods of clean air. This has the advantage of extending the life of the detector by reducing the incoming contaminants in proportion to the duty cycle of the clean air. For example, if the unfiltered air is allowed to enter the detector for one second followed by four seconds of exposure to air from the filter 126, the contamination rate of the downstream detector will only be one fifth of the rate that would occur if the detector were fully exposed to unfiltered air at all times. This method would provide similar extended life benefits of the dilution apparatus as proposed by the applicant in international patent application WO 2007/095675. However, preferred versions of this time-dependent method have the advantage that they do not rely on maintaining or measuring the fluid ratio. In accordance with a preferred form of the present invention, the controller 32 will only apply normal processing techniques to the signal 44 when the chamber 30 is full of unfiltered air, and ignore the signal 44 when the chamber 30 is full of filtered air.

A second of these preferred modes of operation is particularly suited for use with a HEPA filter which is capable of efficiently filtering out substantially all of the particles of the fluid flowing therethrough. When the flap 120B is closed such that all of the received sample fluid is directed through the filter 126, quiet air (i.e., air without particles, or at least without particles of interest) is delivered to the detection chamber 30. The signal 44 provides an indication of the background light in the detection chamber when the chamber is purged of any unfiltered air and filled with clean air. This detection chamber can be used to adjust the alarm criteria. For example, a background light reading (when the chamber 30 is filled with unfiltered air) is subtracted from the signal 44 to generate another signal, and an alarm sound is generated when the other signal exceeds a predetermined threshold.

Fig. 3A and 3B schematically illustrate another embodiment of the present invention. This embodiment includes three parallel flow paths 222, 224, and 236. The flow path 222 is traversed by a HEPA filter. A second flow path 224 is unfiltered. A third flow path 236 is spanned by a flap 220B.

In a normal detection mode, the flap 220B closes to close the flow path 236, as shown in FIG. 3A. Substantially all of the sample air received into the manifold space 220A via the inlet 238 is split between the two flow paths 222 and 224. From the flow paths 222 and 224, the air is received in the plenum 228 and exits the structure 242 via the outlet 240. According to this arrangement, the relative flow rates through the flow paths 222 and 224 are determined by the relative resistances of the two flow paths.

The preferred form of the invention includes one or more structural elements, such as an apertured baffle (not shown), which is configured to control the relative resistance of the flow paths 222 and 224. The baffle preferably has a resistance that is significantly greater than the resistance of the filter 226. The relative resistance of the two flow paths 222 and 224 is determined by the shape of the baffle, so that the relative flow rates are more or less independent of the filter conditions (at least until the filter becomes extremely clogged). For example, the baffle may include a single orifice in communication with the unfiltered flow path 224 and a plurality of similar orifices in communication with the filtered flow path 222.

Also, the device provides a "fail-safe" operation in which a higher particulate concentration signal is generated when a filter becomes clogged to a point where its resistance changes appreciably (e.g., when recommended maintenance intervals have been ignored). If the filter 226 becomes clogged, the resistance of the flow path 222 increases and relatively more air flows through the flow path 224. Thus, if the filter 226 becomes clogged, the air passing through the structure 242 in the normal detection mode becomes less filtered, i.e., has a higher particulate concentration.

As in the embodiment of fig. 2A and 2B, the flow path 236 desirably has a significantly lower resistance than the flow paths 222 and 224, such that when the flap 220B is opened, substantially all of the received fluid passes through the unfiltered flow path 236. Or another flap 320C, as shown in fig. 4A and 4B, may also be provided.

Periodically, or when the detected smoke reading changes by some amount, the position of the flap 220B may be changed from the closed position of figure 3A to the open position of figure 3B. When this is done, the smoke detector is exposed to undiluted smoke and the detector records the actual sampled smoke values. By forming the ratio from the smoke scale taken in the two configurations shown in fig. 3A and 3B, the actual dilution ratio (i.e., the ratio of fluid passing through the two flow paths 222 and 224) in the normal detection mode can be determined, and the threshold scale or sensitivity gain of subsequent analytical equipment can be adjusted.

A similar "fail-safe" operation can also be achieved by using the structure of FIGS. 2A and 2B, by only partially closing the flap 120B in the normal detection mode.

The embodiment of fig. 4A and 4B may be modified by including a third valve 320D to selectively close flow path 224 and filter 226 being a HEPA filter, as shown in fig. 5. By closing the flow paths 224 and 236, all of the air is filtered, so that the signal from a detection chamber (downstream of the filter device shown) provides an indication of background light.

Figures 6A and 6B illustrate an alternative arrangement in which the controllable mechanism, in the form of a flap 320C ', is configured to selectively close the filtration flow path 322 to provide an indication of the condition of the filter 226' and the dilution ratio. Figure 6A shows that in normal use of this configuration, filtered air combines with bypass air, resulting in dilution of the amount of particulates in an output fluid compared to the input fluid.

In fig. 6B, fluid flow through the filter is substantially blocked, while allowing only undiluted air to pass through the outlet. By blocking the flow path 324 when desired, the actual incoming particle concentration can be measured and then compared to the concentration measured when the filtered flow path 324 is not blocked. In this way, the dilution ratio of the entire filter can be determined and the threshold scale or sensitivity gain of subsequent analytical equipment can be adjusted.

Those skilled in the art will appreciate that a number of valve arrangements may be used. Applicants contemplate that by placing a valve downstream of the filter to protect the valve from debris, such as the arrangement shown in fig. 7, wherein the valve 320E is placed downstream of the filter 226E, the life of the valve may be extended.

The invention has been described with reference to embodiments having a substantially unfiltered bypass flow path. While it is envisioned that these unfiltered bypass flow paths could be spanned by a coarse filter to filter out very large particulates, such as insects, for present purposes such a device would be considered substantially unfiltered.

Also, those skilled in the art will appreciate that some commercially advantageous embodiments do not include an unfiltered bypass. For example, referring to fig. 1, the two flow paths 22 and 24 can both be spanned by the same foam filter (which, when new, filters out dust but not smoke). In this case, in one possible configuration, one of the filters may be exposed only to fluid and generated particulates in the filter inspection mode. The filter check mode is typically short and rare compared to the usual operation in the normal detection mode. Thus, when receiving fluid to check the condition of another filter, it can be assumed that the filter is operating in a "new-like" condition.

It should be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the present invention.

Claims (20)

1. A filter arrangement for a particle detector for detecting particles in an environment, the particle detector including one or more sensors for analyzing fluid in a detection region to produce sensor outputs, the filter arrangement comprising:

structure defining a flow path for conveying fluid from the environment towards the detection region, comprising a first flow path containing a filter and a second flow path bypassing the filter;

a means for controlling the relative flow rates of fluids through the first and second flow paths; and

a controller configured to receive sensor outputs corresponding to at least two relative flow rates and apply logic thereto to generate an output indicative of the condition of the filter.

2. The filter apparatus of claim 1, wherein the sensor output is indicative of a particulate concentration.

3. A filter device as claimed in claim 1 or 2, wherein the means is configured or controlled to vary the relative flow rates and the controller is configured to periodically generate an output indicative of the condition of the filter.

4. The filter apparatus of claim 1 or 2 wherein the mechanism is configured or controlled to vary the relative flow rates and the controller is configured to produce the output indicative of the condition of the filter in response to a sensed change in particulate concentration.

5. The filtration device of claim 1 or 2, wherein the filter is configured to generate a fault signal if the condition of the filter exceeds a predetermined threshold.

6. The filter apparatus of claim 1 or 2, wherein the mechanism is configured or controlled to vary the relative flow rates in accordance with a predicted contamination metric in the environment to control the concentration of contamination reaching the detection zone.

7. The filtering device of claim 6, wherein varying the relative flow rate according to the predicted contamination scale comprises varying the relative flow rate according to a repeating schedule.

8. The filtration device of claim 7, wherein the schedule includes a night mode in which a relatively low proportion of fluid passes through the first flow path to obtain relatively high detector sensitivity, and a day mode in which a relatively high proportion of fluid passes through the first flow path to reduce contamination of the detection region.

9. The filter apparatus of claim 1 or 2, wherein the mechanism is configured or controlled to periodically temporarily increase the relative flow rate through the second flow path to periodically increase the sensitivity of the sensor such that the average time that the detection region is exposed to fluid from the second flow path and contaminants carried thereby is reduced to reduce contamination of the detection region.

10. The filtration device of claim 9, wherein the relative flow rate through the second flow path is temporarily increased one or more times per minute.

11. The filter device of claim 9, wherein the mechanism is configured or controlled such that substantially all of the fluid is delivered through the second flow path each time the relative flow rate through the second flow path is periodically temporarily increased.

12. The filter device of claim 9, wherein the mechanism is configured or controlled such that substantially all of the fluid is delivered through the first flow path between each periodic temporary increase in the relative flow rate through the second flow path.

13. A filter device as claimed in claim 1 or 2, wherein the arrangement comprises a flow dividing means for receiving a common flow of fluid from the environment and directing portions of the common flow into the first and second flow paths.

14. The filter device of claim 1 or 2, wherein the structure comprises a fluid combining means for receiving fluid from the first and second flow paths and delivering a combined fluid stream towards the detection region.

15. The filtration device of claim 1 or 2, wherein the mechanism comprises a valve.

16. The filtration apparatus of claim 15, wherein the valve is a solenoid valve.

17. The filter device of claim 1 or 2, wherein the mechanism comprises an electromechanical device.

18. The filter apparatus of claim 1 or 2 wherein the structure and the mechanism together impart a flow restriction that is substantially greater than a flow restriction imparted by the filter such that the relative flow rates through the first and second flow paths are substantially independent of filter conditions.

19. The filtration apparatus of claim 1 or 2, wherein the filter is a high efficiency particulate air filter.

20. The filter apparatus of claim 1 or 2, wherein the second flow path is configured such that the entrained fluid is substantially unfiltered of the particles of interest.