Abstract:
A filter life sensor assembly within an air handling system is disclosed. The air handling system includes an air flow intake, an air flow exit, and a filter disposed between the air flow intake and air flow exit. The filter sensor assembly comprises a bypass connecting the air flow intake to the air flow exit, a dielectric sensor adjacent the bypass, wherein the dielectric sensor generates an electrical signal in response the air flow passing through the bypass.

Description:
BACKGROUND 
     The present inventions relates to a filter life sensor. In particular, the present invention relates to a dielectric filter life sensor. 
     Air handling systems, such as air furnaces, air conditioning systems, and room air purifiers, typically include filters to take the dust and other particulate matter out of the air. When these filters become dirty, the air flow through the filter is reduced. The filters therefore must be periodically changed or cleaned to maintain the efficiency of the air handling system. A typical recommendation is to change a filter on a household air handling system every three months. It is often difficult for users to remember to change the filter. Additionally, a recommendation for changing a filter based on a predetermined time does not factor in the actual conditions of the environment. In some instances, the filter may become clogged before the suggested three months, and in some conditions the filter may still adequately perform beyond three months. 
     Filter change sensor systems exist for measuring the end of the useful life of a filter. Such systems may include a device, such as a float, for measuring the pressure drop across the filter. These systems are generally complicated and some require sensor placement on each side of the filter for measuring the pressure drop. Some of these systems measure the air velocity through the filter. However, because the area of filters is generally large, the air velocity through a filter is quite low and measuring the actual quantity of air passing through the filter is difficult. In such cases, sensitive, specialized equipment is necessary to obtain accurate readings, which are expensive and not practical for consumer use. 
     Other systems exist that include an air bypass through or around the filter. In such systems, when the filter collects dirt and dust, the overall air flow is restricted causing more air to flow through the bypass, which in some cases is a whistle device. These systems will then whistle when the air flow through the bypass reaches a threshold level. These systems do not give a read-out, either a digital or analog signal, on the level of filter use. Additionally, these systems only indicate filter performance at the filter location and therefore do not communicate with the thermostat, which is normally placed at the location more visible to the user. Therefore, it would be desirable to have a low-cost filter sensor that is able to determine the actual end of the useful life of the filter. 
     SUMMARY 
     The present invention provides a filter life sensor that is able to determine the end of the useful life of the filter by utilizing a bypass either through a portion of the filter or through the housing around the filter and a dielectric sensor adjacent the bypass to measure the change in the air stream passing through the bypass. 
     In one embodiment, the filter life sensor is for use with an air handling system. The air handling system includes an air flow intake, an air flow exit, and a filter disposed between the air flow intake and air flow exit. The filter sensor assembly comprises a bypass connecting the air flow intake to the air flow exit, a dielectric sensor adjacent the bypass, wherein the dielectric sensor generates an electrical signal in response the air flow passing through the bypass. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an air handling system with a bypass in the housing. 
         FIG. 2  is a side view of an embodiment of an air flow filter sensor adjacent the bypass of  FIG. 1 . 
         FIG. 3  is a perspective view of an embodiment of a filter containing a bypass and an air flow sensor. 
         FIG. 4  is an enlarged, exploded view of the filter, bypass and air flow sensor of  FIG. 3 . 
         FIG. 5  is an embodiment of a circuit diagram for amplifying, rectifying, and filtering the voltage generated from the air flow sensor. 
     
    
    
     While the above-identified drawings and figures set forth embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this invention. The figures may not be drawn to scale. 
     DETAILED DESCRIPTION 
     An air flow sensor  100  is disclosed for determining the life of a filter  200 . The air flow sensor is used within a housing  300  of an air handling system  800 , such as a furnace, air conditioner, a room air purifier, or a respirator such as a powered air purifying respirator (PAPR), which utilizes a filter  200 . However, the air flow sensor  100  shown and described may be used and applied in other comparable systems where periodic changing of the filter  200  is necessary. 
     Generally, the filter  200  includes a filter media  210  surrounded and contained by a filter frame  220 . The entire filter  200  may be disposable, the filter media  210  may be disposable such that the filter frame  220 , or the entire filter  200  may be reusable. 
     The filter media  210  may be constructed of paper; porous films of thermoplastic or thermoset materials; nonwoven, such as melt blown or spunbond, webs of synthetic or natural fibers; scrims; woven or knitted materials; foams; electret or electrostatically charged materials; fiberglass media, or laminates or composites of two or more materials. A nonwoven polymeric web of polyolefin, polyethylene or polypropylene is suitable, for example. Filter media  210  may also include sorbents, catalysts, and/or activated carbon (granules, fibers, fabric, and molded shapes). Electret filter webs can be formed of the split fibrillated charged fibers as described in U.S. Pat. No. RE 30,782. These charged fibers can be formed into a nonwoven web by conventional means and optionally joined to a supporting scrim such as disclosed in U.S. Pat. No. 5,230,800 forming an outer support layer. Alternatively, filter media  210  can be a melt blown microfiber nonwoven web, such as disclosed in U.S. Pat. No. 4,813,948 which can be joined to a support layer during web formation as disclosed in that patent, or subsequently joined to a support web in any conventional manner. 
     The filter frame  220  generally entirely surrounds the filter media  210 . The filter frame  220  may be constructed of paper, chipboard, cardboard, paperboard, boxboard, film, metal or plastic. In an entirely disposable filter, the filter frame  220  typically will be constructed of a paper product. In a reusable filter frame  220 , the filter frame  220  typically will be constructed of plastic or metal. 
     The filter  200  is inserted into a housing  300 . Particularly, a supporting slot  312  is included in the housing to closely engage the filter frame  220  of the filter  200 . Depending on the air handling system, the housing  300  may be a portion of a furnace, an air conditioner, or a room air purifier. Within the housing  300  is a fan  310  for pulling air through the filter  200  such that there is air in  500  the filter and air out  510  of the filter and into the housing  300 . 
     As the air in  500  passes through the filter  200  and is then pulled out of the filter as air out  510 , the filter media  210  clogs with dirt, dust, or debris, and air flow through the filter  200  becomes limited and the pressure drop across the filter  200  increases. However, due to the size of the areas of the filter  200  it is difficult to measure the air flow change. Further, although it is possible to measure the pressure drop across the filter  200 , such systems must include delicate sensors. 
     Disclosed is a bypass  400  shown either in the housing  300  ( FIGS. 1 and 2 ) or in the filter  200  ( FIGS. 3 and 4 ), which allows for a narrow path of bypass air flow  520  not passing through the filter media  210 . A detailed description of  FIGS. 1-4  is given below. Due to the constricted size of the bypass  400  and therefore increased air velocity of the bypass air flow  520 , the bypass air flow  520  is easier to measure. It is understood that the bypass  400  may be included in other locations of the housing  300  or various positions on the filter  200  including on the filter media  210  or the filter frame  220 . 
     An air flow sensor  100  is included to measure the bypass air flow  520 . As the filter  200  becomes clogged, the fan still continues to pull air through the filter  200  and bypass  400 , however the pressure drop across the filter  200  and bypass  400  is greater and therefore the bypass air flow velocity  520  increases. A threshold level may be preset and when the bypass air flow  520  reaches that threshold level, an indication can be made to change the filter  200 . The air flow sensor  100  shown is a piezoelectric sensor. However, generally the air flow sensor  100  is a dielectric sensor, which can be a sensor such as piezoelectric sensor, piezoresistive sensor, actuator sensor, capacitive sensor, and/or combinations thereof. The dielectric sensor can be one sensor or an array of sensors. The sensor  100  generates an electrical signal such as a voltage, current, or both in response to actuation caused by the bypass air flow  520 . The out put of the sensor  100  can be used to create sound, light, and/or communicate with an output such as a thermostat or a combination thereof. 
       FIG. 1  is a side view of a housing  300  of an air handling system with a bypass  400  in the housing  300  and an air flow sensor  100  adjacent the bypass  400 .  FIG. 2  is an enlarged view of the air flow sensor  100  adjacent the bypass  400  of  FIG. 1 . 
     As shown, a standard filter  200  with a filter media  210  surrounded by a filter frame  220  is included to capture dirt, dust and debris being pulled through the housing  300  of the air handling system. The bypass  400  is an unobstructed opening through a portion of the housing  300 . In this embodiment, the bypass  400  is just below the support slot  312  that holds the filter  200 . It is understood that any opening, connecting the air in  500  to the air out of the filter  510  (preceding the fan) without passing through the filter media  210  would be appropriate and that any one particular position of the bypass is not required. 
     The air flow sensor  100  shown a piezoelectric sensor (described in more detail below) and is positioned adjacent the bypass  400 . In this embodiment, the air flow sensor  100  is positioned on the downstream end of the bypass air flow  520 . In other words, the air flow sensor  100  is within the housing  300  directly adjacent the bypass  400 . It is understood that the air flow sensor  100  may be positioned anywhere such that the bypass air flow  520  is being measured. For example, the air flow sensor  100  may be positioned adjacent the bypass  400  on the upstream end of the bypass air flow  520  to measure the pull of the bypass air flow  520  as opposed to the push of the bypass air flow  520 . Additionally, the air flow sensor  100  may be positioned within the bypass  400 . 
       FIG. 3  is a perspective view of an embodiment of a filter  200  that includes a bypass  400  and an air flow sensor  100 .  FIG. 4  is an enlarged, exploded view of the filter  200 , bypass  400 , and air flow sensor  100  of  FIG. 3 . The filter  200  depicted in  FIGS. 3 and 4  would typically be used in the housing  300  of an air handling system that itself does not contain a bypass  400 , because the bypass  400  and air flow sensor  100  is included as part of the filter  200 . It is understood that the air handling system that the filter  200  of  FIGS. 3 and 4  is placed in includes a fan to generate an air in the filter  200  and an air out of the filter  200  such as that shown and described with respect to  FIG. 2 . An axial fan is shown; however, other types of fans can be used such as a centrifugal or an vane axial fan. Therefore, through the bypass  400  is a bypass air flow  520 , cylinder 
     As shown in  FIG. 3 , and in the exploded view of  FIG. 4 , a tube  110  and a cover  111  for the tube  110  encloses the air flow sensor  100  and includes the bypass  400 . As shown, the tube  110  is positioned within and across a portion of the filter media  210 . However, it is understood that the tube  110 , or other enclosing structure, could be placed across the filter frame  220 . Additionally, the tube  110  may be place outside of the filter frame  220  or filter media  210 , while the bypass  400  still passes through the filter frame  220  or filter media  210 . The tube  110  is shown to be generally circular; however, because the tube  110  serves simply as an enclosing structure for the air flow sensor  100  and includes an opening for the bypass  400 , the tube  110  may be of any shape such as square, rectangular, oval, triangular. 
     Contained within the tube  111  is the air flow sensor  100 , which as described above with respect to the embodiment depicted in  FIG. 2 , is a piezoelectric sensor. An exemplary piezoelectric sensor that may be used is MiniSense 100 Vibration Sensor available from MSI Sensors of Hampton, Va. 
     The piezoelectric air flow sensor  100 , described above with respect to  FIGS. 1-4 , includes a base  102  that in  FIGS. 1-2  attaches the air flow sensor  100  to the housing  300  or as shown in  FIGS. 3-4  attaches the air flow sensor  100  to the tube  110 , voltage leads  104  (not visible in  FIG. 4 ), a bending arm  106 , and a weighted end  108  at the end of the bending arm  106  and aligned with the bypass air flow  520  path exiting the bypass  400 . It is understood that voltage lead  104  may not be necessary, for example when the output signal is transmitted remotely. On the bending arm  106  is the piezoelectric material. As shown in both embodiments, the air flow sensor  100  is positioned on the down stream end of the bypass  400  to measure the push of the bypass air flow  520 . It is understood that the air flow sensor  100  could be positioned up stream from the bypass  400  or within the tube  110  to measure the bypass air flow  520 . 
     The bypass air flow  520  contacts the weighted end  108  to causes steady vibration of the bending arm  106 . This vibration causes the piezoelectric material on the bending arm  106  to generate an electrical signal such as a voltage, current or a combination of both. As the filter media  210  clogs with dirt, dust, and debris, the bypass air flow  520  increases causing the frequency and amplitude of the vibration of the bending arm  106  of the air flow sensor  100  to increase and therefore the voltage generated to increase. Generally, a voltage is generated that is associated with each speed of the fan  310 . To get an accurate reading from the air flow sensor  100  it is desirable to have proper air flow through the bypass  400 . Have a tube-like path (as shown in  FIGS. 1 and 2 ) for the bypass airflow  520  to pass through before contacting the weighted end  108  may assist getting proper air flow through the bypass  400 . Generally, a fan speed will cause the sensor  100  to generate an electrical signal such as a voltage. Initially, it may be desirable to calibrate the sensor  100  for the particular fan speed. If a variable speed fan is included that has for example 3 speeds associated with it, it is desirable to calibrate the sensor  100  for that speed that will be used. It may be desirable to have the fan on a single, possibly high, speed to get a repeatable output reading from the air flow sensor  100 . 
     The output voltage signal from the air flow sensor  100  may be amplified, rectified, and filtered. The output voltage signal may be transmitted to a relay box  121  that converts the voltage output into a measurement of the filter condition life. An exemplary amplification, rectification, and filtration circuit is show in  FIG. 5  for the piezoelectric sensor MiniSense  100  Vibration Sensor available from MSI Sensors of Hampton, V.A The transmission of the output signal may be through wire  122  or may be through remote transmission such as radio frequency. In the embodiment depicted in  FIGS. 3 and 4 , transmission through a remote mechanism such as radio frequency is ideal in that no wires must be connected to the tube  110 . The relay box  121  may connect with a display  123 . 
     The converted signal may then be made visible to a user. In one embodiment, a percentage used output is transmitted and is available for viewing by the user. In another embodiment, a red, yellow, or green light may be indicated, the colors corresponding to a percentage of the filter  200  used and the need for the user to replace the filter  200 . This final output may be positioned at a convenient location to a user such as at a thermostat. Alternatively, an alarm may signal. It is understood that it maybe either the output signal or a converted form of the output signal that is transmitted from the filter sensor  100  or relay box. 
     It may be necessary in some embodiments to include a power source to amplify and transmit the air flow sensor  100  output. This is particularly the case when a remote transmission mechanism is included such as a radio frequency transmitter. In such a case a battery  131  may be included. That battery may be disposable or rechargeable. Alternative, the circuit can be designed where the sensor electrical output can be stored and that stored electrical output is used to transmit the signal. For example, the continual movement of vibration of the bending arm  106  of the air flow sensor  100  may generate enough voltage to charge the battery or capacitor, if included. 
     The air flow sensor can be used for multiple applications. As described, the air flow sensor described may be used with a furnace system, room air purifier, or air conditioner. Additionally, the air flow sensor may be used with a respirator to monitor the air flow to the user of the respirator. The output signal generated may be transmitted and monitored at an external area. 
     Disclosed is an air flow sensor for providing reminder to a user of when to change a filter. It may be desirable to incorporate into the air handling system other types of sensors such as a timer or other sensors that measure the airflow through the filter or pressure drop across the filter. For example a suitable time system is disclosed in U.S. patent application Ser. No. 11/420,936 titled “FILTER TIMER” ,now issued as U.S. Pat. No. 7,621,978. 
     Although specific embodiments of this invention have been shown and described herein, it is understood that these embodiments are merely illustrative of the many possible specific arrangements that can be devised in application of the principles of the invention. Numerous and varied other arrangements can be devised in accordance with these principles by those of ordinary skill in the art without departing from the spirit and scope of the invention. Thus, the scope of the present invention should not be limited to the structures described in this application, but only by the structures described by the language of the claims and the equivalents of those structures.