Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/0084—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours provided with safety means
  • B01D46/0086—Filter condition indicators
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
  • B01D46/42—Auxiliary equipment or operation thereof
  • B01D46/44—Auxiliary equipment or operation thereof controlling filtration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2273/00—Operation of filters specially adapted for separating dispersed particles from gases or vapours
  • B01D2273/26—Making use of optical waves, e.g. for measurements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
  • F24F11/00—Control or safety arrangements
  • F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
  • F24F11/32—Responding to malfunctions or emergencies
  • F24F11/39—Monitoring filter performance

Definitions

• This invention relates to air filters and more particularly to devices fpr determining when air filters have become clogged.
• HVAC heating, ventilation and air conditioning systems
• U.S. Patent 5,141,309 discloses an optical system for detecting clogging of a specific type of vacuum cleaner dust filter which employs a pleated fabric filter. This patent shows a forked light unit having one arm carrying a light emitter and the other carrying a receiver so that a pleat of the filter may be placed between the arms in position for the light to be passed through the filter twice.
• both arms are located on the same side of the filter so that access to the opposite side of the filter is not required.
• This patent also disclosed a forked light device with one arm disposed on one side of a flat filter and the other arm on the opposite side so that Hght passes through the filter and another embodiment wherein both the emitter and the receiver are located on the same side of a flat filter and Hght is directed against the filter surface to obtain a measure of filter loading with dust based on changes in the intensity of the reflected beam.
• U.S. Patent No. 3,985,528 discloses an optical system incorporated as a control means for an "automatic roU-type filter” assembly, with a "photoceU” indication when to advance clean filter material across the air duct. Placement of arms of a support element on opposite sides of the filter material for passing of light through the material is also disclosed.
• Peripheral framework for these filters typically comprises a U-shaped border made of flexible cardboard strips which would not provide enough rigidity to allow component support arms to be supported by this framework in a fixed position, as is required once the components are placed in proper aHgnment. A more stable base is therefore needed for securing of supports to which monitoring components are attached.
• detector systems including other features and characteristics would be desirable.
• such features would include use of miniaturized electronic components to compensate for the Hmited ava ⁇ abiHty of space and providing programmable chips for performing such functions as caHbrating the system and preparing a schedule for monitoring services.
• the present invention is directed to clogged filter detection systems comprising an optical transmitter adapted to transmit a beam of Hght through the body of a filter at least once, a receiver including a sensor and positioned to receive the transmitted light directly or from a reflector, a processing assembly for receiving signals from the sensor and communicating a perceptible indication when the level of obscurant reaches a predetermined value and a component supporting structure comprising support elements secured to brackets disposed at the periphery of the filter and engaged with filter receptacle framework.
• the systems may also include additional components and measures taken to avoid adverse effects of reflection of light by the surface of the filter and to aHgn components of the system in a manner such as to obtain measurements which are not unduly effected by shadowing of portions of the filter at the point being monitored.
• the invention may take the form of several embodiments which vary from one another in placement of the transmitter and receiver and in inclusion of other components required for a specific embodiment, in particular, a reflector, polarizing filter and quarterwave retarder.
• an optical transmitter and a receiver are situated on the same side of the filter, and a reflector is placed on the opposite side. Light from the transmitter is directed to the reflector and passes through the filter twice, once on the way to the reflector and a second time after being reflected and directed to the receiver. Upon reaching the receiver and the processing assembly, the reflected light is used to obtain a signal dependent upon an obscurant level in the filter. While other types of reflectors may be used, a retroreflector coupled to a pair of polarizing filters and a polarization rotating element such as a quarter wave plate is preferred to avoid adverse effects of reflection of Hght from the surface of the filter, especially fore more dense filters.
• the transmitter and receiver are positioned on opposite sides of the filter in aHgnment with one another so that the light beam passes through the filter only once.
• the receiver and processing assembly in this case may be carried in a common housing, while the transmitter is carried in a separate housing with a wiring interconnect.
• opposing components placed in aHgned positions across from one another are preferably offset angularly away from an aHgnment parallel to air flow in order to avoid shadowing of the area being monitored. Placement of components straight across from one another would result in deposition of a non-representative amount of dust at the area of interest, particularly when one or more of the components is placed in close proximity to the filter.
• Component support structure for systems of the invention may comprise a bracket in the form of a thin but rigid base member conforming to a plate of a filter receptacle against which a side face of a border strip of the peripheral framework of the filter is removably positioned, the receptacle also having a restraining ledge integral with and at a right angle to the plate, the ledge securing filter framework from moving in the direction of air flow.
• the bracket has a first side portion connectible to the ledge with a clip or the like as well as to a first arm and in some cases, a second side portion available for attachment to a second arm.
• the arms are adapted to support components including transmitters, receivers, processing assembHes and reflectors as appropriate.
• At least one of the arms may be pivotally and/ or flexibly mounted on the ledge with an outer end free to be moved away from the middle portion of the filter in order to allow insertion and removal of the filter from the receptacle and to aUow for movements necessary to obtain proper alignment of components.
• Another object is to provide a clogged filter detector which includes means for determining and giving a perceptible indication when obscuration of the filter reaches a predetermined level.
• a further object is to provide a support structure for components of a clogged filter detection system wherein the support structure is connected to elements of a filter receptacle.
• Fig. 1 is an exploded view of an HVAC plenum with a grill, filter and filter receptacle arranged for alignment.
• Fig. 2 is a schematic of an optical assembly transmitting Hght through a filter and receiving light redirected back through the filter by a reflector assembly towards the receiver.
• Fig. 3 is a view similar to Fig. 2, but with a simplified reflector assembly.
• Fig. 4 is an exploded view of an "U" shaped bracket which fits within a filter receptor and supports detector components.
• Fig. 5 is an end view of a bracket as in Fig. 4 "U” with detector components and filter shown.
• Fig. 6 is an end view of a bracket as in Fig. 1 showing a transmitter and a receiver placed on opposite sides of a filter.
• Fig. 7 is an exploded view of a filter receptacle arrangement in use in certain
• Fig. 8 is an end view showing placement of both the transmitter and the receiver spaced apart from the filter where more space is available.
• Fig. 9 is a view as in Fig. 8 wherein a laser is used as the light source.
• Fig. 10 is an exploded partial view of a detector in which a reflector is supported adjacent to the filter on a frame attached to a grill structure.
• Fig. 11 is an exploded view of an "L" shaped bracket for use in combination with a component support as in Fig. 10.
• Fig. 12 is an end view of a detector wherein a component support member is attached directly to a griU.
• Fig. 13 is a perspective view showing a reflector component attached directly to a mesh extending across a filter.
• Fig. 14 is a schematic view showing operation of an electrical network for a transmitter/ receiver assembly.
• Fig. 15 is an end view of the detector built with and sharing parts with the filter receptacle.
• a terminal portion of a HVAC plenum 10 in dotted lines
• a filter receptacle 12 and a grill 16 connected to the receptacle by means not shown, are aligned for being placed over a filter 14.
• the filter has an external frame 18 supporting the filter body 20 which is made up of fiber glass or the like and is either self supporting or held in place by mesh 22 on both sides.
• Receptacle 12 has four side plates 24 with inner surfaces parallel to the direction of airflow and ledges 26 integral with and disposed perpendicular to the plates.
• FIG. 2 schematically depicts a clogged air filter detection system 11 positioned to monitor the obscuration level in filter 14 and to provide an indication when the level exceeds a predetermined value, signaling that the time for replacement or cleaning of the filter has come.
• the system includes a Hght transmitter 32 such as a Vishay model TLCR 5100 Hght emitting diode (LED) aimed toward a reflector assembly 42 placed on the side of the filter opposite from the transmitter so that a beam 48 of Hght passes through the filter and then strikes a retrorefiector 46, typically a 3M model 3990 retroreflector. Reflected Hght is then directed to a receiver 34, such as a Vishay BPV 10 photodiode, which is coupled to a processing assembly 35 wherein a signal responsive to obscuration level of the filter is obtained.
• the receiver and transmitter may be located in a common housing 36, along with components of the processing assembly.
• housing 36 is positioned to direct the beam of light through the filter 14 at an acute angle with respect to the plane of the filter. This results in passage of light through an area 50 of the filter which is offset from reflector assembly 42 and is not subjected to shadowing or obstruction of air flow 49 through the portion of the filter being monitored. Placement of the transmitter straight across from the reflector would result in use of a non- representative sample for detection of clogging, especially where optical components are located in close proximity to the filter. Placement of the transmitter and reflector at an angle of 30 to 50 degrees with respect to the filter is preferred.
• Randomly polarized radiation is linearly polarized (in this case, perpendicular to the plane of the paper, and represented by the dot 54) via a polarization filter 38, such as a 3M HN38 filter, as it departs the transmitter 32.
• a linear polarization filter 40 again a 3M HN38, in front of the receiver 34 is oriented to receive polarization normal to that of the transmitted radiation (i.e., polarized in the plane of the paper and represented by the two headed arrow 56) such that any radiation reflected from the filter surface 58 is highly attenuated ( ⁇ 30dB) before it reaches the receiver 34 photo diode (or phototransistor).
• This is accompHshed in one of two methods: (a) by the corner cube retroreflector itself ( ⁇ 100% efficient), or (b) by a combination of quarter-wave-retarder 44, such as an Ed un Optics L54- 542 retarder, and reflective surface 46.
• the quarter wave retarder 44 converts the Hnear polarized radiation 54 to circular polarization which is converted to reverse circular as it is reflected from the reflector 46, (i.e., from right hand circular to left hand circular or visa versa).
• the reverse circular radiation is converted back to linear, but with a 90 deg (i.e., flipped) orientation 56 with respect to its original 54 polarization.
• This radiation is now of the same polarization orientation 56 as the orientation of the polarization filter 40 in front of the receiver 34.
• This polarization assembly can be estabHshed as depicted, or can be reversed with polarization of transmitted radiation 48 lying in the plane of the paper and the received radiation 52 perpendicular to the plane of the paper.
• Fig. 3 shows an embodiment as in Fig. 2 except that no polarization filters are used at the transmitter and receiver, and a retroreflector 46 is placed directly against the filter 14 without an intervening quarter wave retarder or other means for rotation of the polarity of the reflected Hght.
• This approach is adequate for less dense (and therefore less costly) filters as are commonly used in residential HVAC systems.
• Fig. 4 shows a bracket 60 of U-shaped cross section, having a bottom strip 62 and side strips 64 and 66 to which arms for supporting system components may be connected.
• Side strip 64 is secured to ledge 26 of the filter receptacle 12 by means of cHps 68 which are hooked over the ledge.
• Side 64 has an aperture 70 placed to receive a bolt or rivet extending through the arm.
• Side strip 66 also has an aperture 72 to enable connection to a second arm.
• the bracket 60 is shown in position with other components of the system.
• the bracket is secured to the ledge 26 of the filter receptacle by clips, 68 and the lower end of a first arm 74 is fixedly connected to side strip 64.
• Arm 74 extends outward at an angle away from the filter, and at its upper end is connected to housing 36, in which transmitter 32 and receiver 34 are carried.
• a second arm 76 is pivotaUy connected at its lower end to side strip 66 of the bracket 60 and at its upper end supports a retroreflector assembly (typically retroreflecting tape) 46 afigned for being contacted with Hght 48 from transmitter 32 and reflecting it back to receiver 34.
• a retroreflector assembly typically retroreflecting tape
• Fig. 6 shows an embodiment wherein transmitter 32 and receiver 34 are placed on opposite sides of the filter and transmitted light passes through the filter only once.
• Hght is converted to an electrical signal, which is carried to a processing assembly in housing 36 by means of wire 78.
• the wire may be placed between the bracket and receptacle plate as shown. No reflector is included in this embodiment.
• Fig. 7 shows a filter receptacle 12 located at some distance away from an end of a duct or plenum 10. Access to this type receptacle is provided by a slot 80 replacing a side plate so that the filter may be inserted from the side instead of from a downstream end position. Both arms of the sensor may extend out angularly away from the filter as shown in Fig. 8 to take advantage of the space available on both sides and rriinirnize shielding of the filter from air flow and entrained dust .
• the sensor shown in Fig. 8 has a transmitter 32 on one side of the filter and a receiver 34 on the other side, with a wire 78 extending underneath the filter as shown in Fig. 6.
• Fig. 9 The embodiment shown in Fig. 9 is similar to that of Fig. 8, except that the transmitter 32 in this instance is a laser, which produces a much narrower beam 48.
• Fig. 10, 11 and 12 show an embodiment wherein a retroreflector assembly 42 is carried on an upper corner of a rectangular metalHc (or plastic) frame 82 which is attached by magnets 84 to the frame 88 of louvered 86 griU 16.
• the outer frame 88 of the griU 16 is shown in position to be attached by fastener 90 by engaging a flange 92 extending downward from the filter receptacle plate 24.
• Arm 74 which supports transmitter 32, receiver 34 and housing 36, is connected to the side strip 64 of L-shaped bracket 63 at aperture 70.
• the bracket in turn is secured to ledge 26 of the filter receptacle by cHps 68.
• the magnetically supported frame which supports the reflector is not connected to the bracket as in other embodiments.
• Fig 13 depicts the retroreflector 42 attached to the filter support material 22 and not requiring a separate support structure. This attachment can be performed by either the filter manufacturer or in the field with adhesive. Attachment is typicafiy upstream 49 of the sensor in a preafigned position, such that the sensor aHgnment operation is required only during initial sensor instaUation.
• clogged filter detection of this invention is shown schematicaUy in Fig 14 for a filter in use.
• Elements of the processing assembly 35 are carried in housing 36 supported by one of the arms.
• An electrical signal is generated at microprocessor 94, controlled by driver 96, and converted to optical at transmitter 32.
• the resulting radiation beam 48 traverses a subject filter 14 body 20 and mesh 22 on either side thereof, impinges upon the retroreflector 42 and is reflected 52 back toward the optical receiver 34.
• At the optical receiver it is converted back to electrical form and fed into an analog amplifier 97 assembly.
• the amplified signal is digitized via analog-to-digital (A-to-D) converter 98, entered into the microprocessor 94 and stored in digital memory 100. This provides a relative measurement of the optical transmittance through the optical network including the filter body 20 and mesh 22.
• a digital calibration signal from the A-to-D converter 98 output is stored in memory 100 upon command by manual activation of momentary external switch 102.
• the microprocessor is programmed to compare the stored digital caHbration signal with a pre scheduled daily measurement of the optical transmittance through the filter mesh.
• An indication is broadcast optically 104, aurally 106 and/ or otherwise locally and/ or transmitted 108 to a remote location when the A-to-D output drops to a preprogrammed level.
• This preprogrammed level indicates that the filter 14 has clogged with dust, etc., and the optical transmittance through the filter has degraded to a pre-selected level which is a preprogrammed amount below the initial clean filter cafibration level.
• the digital value of the A-to-D output may be transmitted (108) on a scheduled basis to the remote location.
• Fig. 15 depicts the detector manufactured simultaneously with the filter receptacle 12, thereby reducing the number of parts.
• First arm 74 is attached directly to ledge 26.
• Side strip 66 is attached directly to side plate 24 by means such as welding.
• the transmitter, receiver and reflector can be mounted on either the upstream or downstream sides of the filter. More than one transmitter and/ or receiver can be used to provide more versatiHty in eHnainating obstructions due to the filter support structure.
• a corner structure may be added to the detector support bracket 62 for additional structural support. If the ledge 26 of the receptacle 12 is sufficiently strong to maintain aHgnment without any bottom strip 63, side plates 64 may be attached directly to ledge 26 without strip 63.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Filtering Of Dispersed Particles In Gases (AREA)
• Air Conditioning Control Device (AREA)

Applications Claiming Priority (3)

Publications (2)

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ID=23202222

Family Applications (1)

Country Status (3)

Families Citing this family (6)

Family Cites Families (5)

• 2002
  • 2002-08-01 EP EP02761233A patent/EP1423678A4/de not_active Withdrawn
  • 2002-08-01 AU AU2002326513A patent/AU2002326513A1/en not_active Abandoned
  • 2002-08-01 WO PCT/US2002/024760 patent/WO2003014838A2/en not_active Ceased

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