Patent Application
20100305871
The present invention relates to a filter system for particle detectors. In particular, the present invention relates to a method and system for determining particle transmittance of a filter, for example, for use with a smoke detection system of the kind in which a detector produces an electrical output indicating the concentration, in the air, of particles produced by smoke or fire. In one form, the invention relates to a device and a method of providing a filter warning for aspirated smoke detection systems, and it will be convenient to hereinafter describe the invention in relation to that application. It should be appreciated, however, that the present invention is not limited to that application, only.
Throughout this specification the use of the word “inventor” in singular form may be taken as reference to one (singular) or all (plural) inventors of the present invention.
Fire protection and suppressant systems may operate by detecting the presence of smoke and other airborne pollutants or, in general, particles. 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 property damage and also environmental damage may also be caused by operation of the fire suppression system and subsequent removal of the suppressant may be quite hazardous. 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 suitably sensitive system, a warning provided at that very early stage may allow the problem to be detected and rectified, or equipment turned off for example, before the fire actually starts.
Aspirated smoke detection systems may incorporate a sampling pipe network consisting of one or more sampling pipes with sampling holes installed at positions where smoke or pre-fire emissions may 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. Although there are a number of different types of smoke detectors which may be used in a system as outlined above. Optical scatter detectors, have been found to provide suitable sensitivity at reasonable cost. Optical scatter detectors operate on the principle that smoke particles or other airborne pollutants when introduced into a detection chamber and subjected to a high intensity light beam will cause light to scatter. A light sensor senses the scattered light. The greater the amount of smoke particles within the sample introduced into the detector chamber the greater will be the amount of light scatter. The scatter detector detects the amount of scattered light and hence is able to provide an output signal indicative of the amount of smoke particles or other pollutant particles within the sample flow.
A difficulty arises in operation of aspirated smoke detector systems of the above kind in that most atmospheres where smoke or fire detection is required contain dust which may interfere with operation of the system. A filter may therefore be incorporated into the system for the purpose of keeping dust away from sensitive optical surfaces and to prevent dust from artificially affecting the detection of particles indicative of the presence of fire and/or smoke. For example with optical scatter type detectors, the presence of dust may seriously affect the detector output since dust particles may be generally larger than the particles which are indicative of the presence of smoke or fire and produce more scattered light than those particles.
Over time a filter used to reduce dust transmittance into the detection chamber will eventually fill with dust, which may prevent passage therethrough of not only dust particles, but also smoke particles. This causes the effective sensitivity of the detector system to drop. Attempts have been made in the prior art to alleviate this difficulty, for example, see granted U.S. Pat. No. 6,052,058 entitled Filter Integrity Monitoring System in the name of the present applicant, the contents of which are incorporated herein by reference.
When detecting smoke in a given environment, it is important to discriminate between smoke particles and dust particles, both of which will scatter light once in the detection chamber. Ideally dust particles are removed from the airflow path and smoke particles are allowed to continue through to the detection chamber. Thus, in an ideal situation, dust transmittance through the filter would be zero, and smoke transmittance would be 100%. Unfortunately no known filter has this characteristic transmittance. One problem is that there is some overlap in sizes between smoke and dust particles, and therefore the functionality of the filter is usually a compromise between arresting all dust and unintentionally arresting some larger smoke particles thereby decreasing the apparent smoke level seen by the detector, and allowing all smoke through with some dust, thereby increasing the apparent smoke level seen by the detector. Another problem with filters is that they may block over time. If a filter blocks, it may not transmit smoke particles to the detection chamber, thus reducing the effectiveness of the smoke detector. For this reason it is desirable to be able to detect filter blocking before it causes problems in smoke detection.
Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material formed part of the prior art base or the common general knowledge in the relevant art on or before the priority date of the invention disclosed herein or, any claims defined herein.
In one aspect the present invention provides a method of determining particle transmittance of a filter in a particle detection system, the method comprising the steps of:
In essence the present invention stems from the realisation that an empirical measure of a filter's smoke particle transmittance, due to at least first particles having a size indicative of smoke particles may be achieved by way of integrating a level of such first particles passing through a particle detection system over time to determine the proportion of smoke particles arrested by a filter. Using this method it is not necessary to determine the actual “filter load” per-se. The “filter load” is a measurement of the actual particle mass trapped in the filter.
In one embodiment the estimated smoke particle transmittance is compared to a first threshold value at which it is predetermined that the transmittance of smoke particles by the filter has reached a first level and indicating a first level filter warning when the estimated smoke particle transmittance is less than, or equal to the first threshold value.
Preferably, the method further comprises the steps of:
The method may further comprise the steps of:
The method may still further comprise the steps of:
The method may yet further comprise the steps of:
The first and/or second particles may either be detected prior to entering the filter of the detection system or after exiting the filter.
In another aspect, the present invention provides apparatus adapted to determine particle transmittance of a filter of an aspirated particle detector system comprising:
Preferably, the predetermined weighting operation is a multiplication operation performed by a multiplier which, may be further adapted for use with a look up table.
Furthermore, in another aspect the present invention provides apparatus adapted to determine particle transmittance for a filter of an aspirated particle detector system, said apparatus comprising:
In a further embodiment the present invention provides apparatus for monitoring a filter in a particle detection system, the apparatus comprising:
In another embodiment, the apparatus for monitoring a filter in a particle detection system further comprises:
In yet another embodiment, the apparatus for monitoring a filter in a particle detection system further comprises:
The apparatus for monitoring a filter may still further comprise:
The apparatus for monitoring a filter may yet further comprise:
The comparator for comparing the estimated smoke particle transmittance to the first threshold value and the comparator for comparing the estimated smoke particle transmittance to the second threshold value may be one and the same apparatus.
The comparator for comparing the estimated combined particle transmittance to the first threshold value and the comparator for comparing the estimated combined particle transmittance to the second threshold value may also be one and the same apparatus.
The indicator for indicating the first level filter warning and the indicator for indicating the second level filter warning in the case of either the estimated smoke particle transmittance or the estimated combined particle transmittance may be one and the same apparatus.
In another aspect the present invention provides apparatus for monitoring a filter of a particle detection system, the apparatus comprising:
Preferably, the predetermined weighting operation may comprise multiplying the integrated smoke hours value by a given multiplier value, for example, a multiplier value obtained from a look up table. The predetermined weighting operation will depend, however, on the material properties of a given filter and will vary accordingly from filter to filter. Further, various filter designs and materials may be expected to demonstrate various relationships between the smoke level to which they are exposed and the rate of reduction in smoke particle transmittance that they suffer, including either linear or non-linear relationships. For example, an underlying function employed by the present invention may be of the form:
x=∫(a(bSc+dS)dt Eqn 1
Preferably, for each filter design envisaged, accelerated levels of smoke are used to obtain the empirical testing data.
The above integral function applies to measurements where the flow rate of air in a detector system is not taken into account. In a given aspirated particle detector system the flow rate of air passing through the detector system may be taken as a constant. In practice and of more general application, flow rates may vary within a given detector system or from system to system. With various environmental changes or changes to system configurations, such as sample pipe network changes, the flow rate may not necessarily be considered as a constant, at least in an interval of time corresponding to a determination of integrated smoke hours. The inventor has realised that in these circumstances, the flow rate is a significant factor in the determination of a filter's smoke particle transmittance. Accordingly, in another aspect, which takes into account a given constant flow rate, the present invention provides a method of determining particle transmittance of a filter in a particle detection system, the method comprising the steps of:
Further, in yet another aspect, which takes into account a varying flow rate, the present invention provides a method of determining particle transmittance of a filter in a particle detection system, the method comprising the steps of:
In one embodiment the following integral function applies to a measurement involving constant flow rate:
x=∫(a(bSc+dS))dt x eFR Eqn 2
The following integral function applies to a measurement involving varying flow rates of air in the detector system:
x=∫(a(bSc+dS)x eFR)dt Eqn 3
The “integrated smoke hours” value defined above is, generally, a measure of cumulative filter blockage over time by smoke like particles and that general measurement is referred to hereinafter as “integrated smoke hours”. It is empirically a measure of a given amount of ambient smoke detected and recorded by a smoke detector system and integrated over the time of exposure of the smoke detector system to the ambient smoke. “Smoke like particles” refers to particles, being either smoke or otherwise, which have a particle size in the order of that of smoke particles, for example, smog and other ambient air pollutants. Owing to their size, these smoke like particles display similar properties to actual smoke particles. In particular, they scatter light in a similar fashion to smoke particles and as a result, their characteristic output from a light scatter detector is accordingly similar to a scatter detector's output produced by smoke particles.
Preferably, the period of time in which the above integrations may be performed ranges from the time at which the detector begins operation with a new or fresh filter until either:
Particle transmittance as referred to herein is defined as the ratio of detectable particle level output by a filter to the detectable particle level input to the filter. In operation, it is possible to utilise the above method and a smoke detection system in accordance with the invention to produce or flag a filter warning or fault condition when the estimated transmittance reaches a threshold at which a predetermined reduction of the transmittance of the filter may be deemed to indicate an unacceptable degradation in filter performance. For example, the predetermined reduction in particle transmittance may be between about 2% and about 40%, and preferably about 10%. A further critical fault condition may be flagged at a point in time when the integrated smoke hours reaches a further threshold at which a further predetermined critical reduction of the particle transmittance of the filter may be predicted. For example, the further predetermined critical reduction in particle transmittance may be between about 10% and about 70%, and preferably about 15%.
In another embodiment a method of indicating particle transmittance includes:
It has been found that smoke passing through a filter, as estimated by the smoke passing through the detection chamber, can be used to estimate the blocking of a filter. For a known filter type and design, it is possible to estimate particle transmittance of the filter by ascertaining the amount of smoke that has already passed through the filter.
In an embodiment of the present invention there is provided a computer program product comprising:
a computer usable medium having computer readable program code and computer readable system code embodied on said medium for determining particle
transmittance of a filter in a particle detection system within a data processing system, said computer program product comprising:
computer readable code within said computer usable medium for performing the method of determining particle transmittance of a filter in a particle detection system as herein disclosed.
In another embodiment there is provided a computer program product comprising:
a computer usable medium having computer readable program code and computer readable system code embodied on said medium for monitoring a filter in a particle detection system within a data processing system, said computer program product comprising:
computer readable code within said computer usable medium for performing the method of monitoring a filter in a particle detection system as herein disclosed.
In yet another embodiment there is provided a computer program product 15 comprising:
Other preferred forms, aspects and embodiments are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the invention.
Other features, disclosure, improvements, aspects and advantages of one or more preferred embodiments of the present invention will be readily apparent to one of ordinary skill in the art from the following written description with reference to and, used in conjunction with, the accompanying drawings which are given by way of illustration only, and thus are not limiting to the scope of the present invention, and in which:
Initially referring to
Filter 25, such as a volume foam filter having pores, will accumulate particles within the pores over its life. The particles appear to block the pores, reducing particle transmittance, however the exact mechanisms of filter blocking are not known. Blocked pores will not let dust or all smoke particles through, but may still let air through at flow rates and with pressure drops that are very close to the initial conditions, thus making it impractical to detect a filter which is substantially blocked to smoke by monitoring airflow or pressure drop alone. Flow sensors are typically used in aspirated smoke detectors to recognise failures of the aspirator (fan) and to recognise gross failures of the sampling pipe network such as breakage or blockage of sampling holes. Flow sensors, however, cannot determine when a filter has become significantly blocked due to the transmission of smoke particles as air will continue to pass largely unhindered through the filter medium, even if a significant proportion of the particles within the air passing through the filter are not transmitted. In most applications of filters, this is not necessarily a disadvantage, as, for example with air filters for air-conditioning units, it is desirable to remove as many particles as possible. Any measurable reduction in airflow rate only occurs long after the filter has ceased to pass particles. Nonetheless, as noted above, in accordance with embodiments of the present invention, the inventor has realised that an empirical measurement of the particle transmittance of a filter may depend upon a measurement of integrated smoke hours as well as a measurement of flow rates comprising constant and variable flow rates. An increase in flow rate over time, for a given value of integrated smoke hours, contributes in a proportional manner to a reduction in particle transmittance of a given filter.
Typically the pores in a filter are many times larger than the dust to be blocked; however volume foam filters have a relatively long channel for a dust particle to travel through. Particles travelling through filters with pores are frequently trapped within the filter due to their inertia and attraction to the walls of the filter as they draw close thereby, rather than completely blocking a channel. The mechanisms behind particles being trapped in filters and filter blocking are generally not well understood, and therefore reliance is often made on empirical assumptions based on anecdotal evidence. In the present invention, a distinction is made between dust particles and smoke particles, mainly on their size. In general, the majority of smoke particles encountered can be said to range in size from <0.1 microns to approximately 5 microns. The majority of dust particles range in size from 5 microns upwards.
Referring to
A controller circuit 16 is coupled to the light source controlling circuit 10 and to the light scatter detector 12. Controller circuit 16 receives signals on line 22 from the light scatter detector 12, which signal is indicative of the amount of light reaching the light scatter detector 12 from the laser light source incorporated into the light source control circuit 10, after the light has been scattered by passing through the detection chamber 14. A control signal is output from controller 16 on line 24 to light source controlling circuit 10, to control the light source controlling circuit 10.
The controller circuit 16 may control alarm apparatus, such as a suitable display 18 to indicate the level of detected smoke, based on the light level detected by the detector 12. The components of the above system may generally be formed in conventional manner. Detector 12 may be formed as shown in
Output from amplifier 124 is taken via the series connected capacitor 132 and resistor 134 to the inverting input of a second amplifier 136. The non-inverting input of this is again connected to the rail 130, whilst the inverting input and output are connected via the parallel capacitor 140 and resistor 142 shown. The photodiode may for example be of type BPW34 and the operational amplifiers may be of type LMC662. The arrangement of this circuit is such that the first amplifier stage represented by amplifier 124 and associated components generates an output signal proportional to the current from the photodiode 120 and provides a first order low pass filter to remove high frequency noises. The second stage, provided by capacitor 132, resistor 134 and the amplifier 136 and associated components, provides a high pass filter which removes DC offsets and provides additional gain. Output from amplifier 136 is applied to the controller circuit 16.
Referring to
The controller 16 may also comprise circuitry 164 for recording the steady signal indicative of fire hazard smoke particles and other non-fire hazard smoke like particles. Further to this, integrating circuitry 166 may be incorporated into the controller to integrate the measured or recorded signal of the smoke like particles over time. An estimator 168 determines either the smoke particle transmittance alone as an output with the aid of a multiplier 168A adapted for use with a look up table 168B or, the cumulative count from counter 156 may be utilised by estimator 168 and combined, for example by summer 168C, with the estimated smoke particle transmittance to produce an output estimating the combined particle transmittance. In practice the values used for predetermining the weighting operation applied to the integrated smoke hours value stem from the physical properties of a given filter and the environmental conditions in which the filter is operating. These values may be stored in the look up table 168B. The output of estimator 168 or the output of dust counter 156 is applied, via selector 162, to comparator 158 which may compare the outputs of estimator 168 or the outputs of counter 156 to given preset thresholds 170. The preset thresholds may be preset counts in the case of a dust count alone and/or preset particle transmittances in the case of either the estimated smoke particle transmittance alone or a combined estimated particle transmittance. The output 160 of comparator 158 may be used to set warning indicators based on the result of comparisons with the given preset threshold values 170.
It is possible to correlate a given particle transmittance based on a cumulative dust particle count to an equivalent estimate of a reduction in smoke particle transmittance based on the weighted integrated smoke hours. For example, see table 1 showing some empirical results:
In a particularly advantageous embodiment and referring again to
As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the present invention as defined in the appended claims. Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the present invention and appended claims. For example, with respect to the embodiment of a detection system as shown in
The present invention provides a method and apparatus for allowing continually monitoring of the condition of a filter and alleviates the need for excessively frequent testing and maintenance of a smoke or fire detection system. Accordingly, the risk of failure of the detection system to operate in the event of fire is reduced.
“Comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 203903703 | Jul 2003 | AU | national |
This is a continuation of U.S. application Ser. No. 10/564,732, filed Feb. 26, 2007, which claims priority to Australian Provisional Patent Application No. 2003903703, filed 18 Jul. 2003 and entitled “Method and System for a Filter” and, the specification thereof is incorporated herein by reference in its entirety and for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10564732 | Feb 2007 | US |
| Child | 12856953 | US |
