Abstract:
An air filter housing ( 1 ) has at least one filter chamber ( 2, 3 ) for receiving at least one filter unit (F), the filter chamber having an inlet end and an outlet end, and elements ( 18, 19 ) for measuring particle concentration in the air leaving the filter chamber. The measuring elements ( 18, 19 ) include a row of several particle detectors ( 20 ) affixed to a common support ( 21 ), members ( 23 - 31 ) for moving the support in a direction perpendicular to the row of detectors, and members for connecting each of the detectors to a counter.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an air filter housing having at least one filter chamber for receiving at least one filter unit, said filter chamber having an inlet end and an outlet end, and means for measuring particle concentration in the air leaving the filter chamber. 
       BACKGROUND OF THE INVENTION 
       [0002]    Filter housings according to the introduction are known from filtering devices for certain laboratories or the like in which there is a risk that the ambient air will be contaminated. In order to prevent air from such environment to leak out, such laboratories often are set under sub-pressure. The function of the filter is to capture all infectious particles or other contaminations, such as bugs or other air carried infectious organisms, in the circulated air. It is thus essential that each filter functions properly and the integrity of the filters is therefore continuously (periodically?) checked. 
         [0003]    It is known to use a particle detector being movable over the outlet area of a filter chamber to check if particles are present in the air leaving the filter in order to detect a leak in the filter media and where such a leak is located. A problem with such an arrangement is that the mechanism for moving the detector will have a complicated construction and be hard to manoeuvre. 
         [0004]    An objective of the present invention is to provide means for measuring particle concentration in the air leaving the filter chamber in a filter housing of the kind mentioned above which means are of a simple construction and easy to manoeuvre. 
       SUMMARY OF THE INVENTION 
       [0005]    This objective is accomplished by an air filter housing having at least one filter chamber for receiving at least one filter unit, said filter chamber having an inlet end and an outlet end, and means for measuring particle concentration in the air leaving the filter chamber, characterised in that said measuring means includes a row of several particle detectors affixed to a common support, means for moving said support in a direction perpendicular to said row of detectors, and means for alternately connecting each of said detectors to a counter. 
         [0006]    According to a preferred embodiment said moving means are a screw and nut mechanism. Especially, said support is a bar having holes with an inner thread in opposite ends thereof and said means for moving said bar are rods with an external thread fitting into said holes in said bar, said rods being rotatably mounted in the filter housing, and drive means for synchronously rotating said rods. Said drive means can be an electric motor coupled to one of said rods and a belt in engagement with drive wheels on both of said rods. A belt tensioner is advantageously disposed in the pass of the belt between the two drive wheels. 
         [0007]    In a variant, each rod can be driven by a separate electric motor. 
         [0008]    Said detectors are preferably mounted on said support moveable between a first and a second position in a direction parallel to the flow direction in the filter unit, whereby the detectors are biased by springs to the first position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention shall now be described with reference to the enclosed Figures, of which; 
           [0010]      FIG. 1  schematically discloses a perspective view of an air filter housing according to a preferred embodiment of the invention with the doors for the access openings to the two filter chambers being opened, 
           [0011]      FIG. 2  schematically discloses a side view partially in section of the air filter housing in  FIG. 1 , 
           [0012]      FIG. 3  a sectional view along line II-III in  FIG. 2 , and 
           [0013]      FIG. 4  schematically discloses a side view partially in section of a part of the air filter housing in  FIG. 1 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0014]    In  FIG. 1 , a schematic perspective view of an air filter housing  1  according to a preferred embodiment of the present invention is shown. In the preferred embodiment, the housing includes two filter chambers  2 , 3  in each of which an air filter unit F is disposed. Access to filter chambers  2 , 3  is gained by access openings  4 , 5 . These access openings are closable by doors  6 , 7  shown in their open position in  FIG. 1 . 
         [0015]    In  FIG. 2 , the filter housing  1  is shown in a partially sectioned plan view seen from the side of the housing  1  containing the access openings  4 , 5 . The doors  6 , 7  are not shown in  FIG. 2 . As can be seen in  FIG. 2 , each filter unit F comprises a circumferential wall surrounding the filter media and ensuring that air passing through the filter unit will not sidewise leak out of the filter unit but pass through the unit from one end to the other, i.e. in the longitudinal direction of the filter housing  1 . In  FIG. 2  the upper U and lower part L of this circumferential wall of a filter unit F disposed within filter chamber  2  are shown. When the filter is in operation, the filter units F are held in the filter chambers  2 , 3  by clamping devices  8  and  9 , respectively. 
         [0016]    Clamping device  8  consists of a frame  10  which is movable back and forth in the flow direction of the air or gas passing through the filter unit F. In the preferred embodiment shown, the means for moving the frame  10  are four pneumatic cylinders  11 , of which two are shown in  FIG. 2 . These pneumatic cylinders can be disposed in the corners of the rectangular frame  10  or in pairs distanced from the corners on the upper and lower frame parts or the side parts of the frame, as is shown in  FIG. 3 . It is of course possible, but not preferred, to use more than four pneumatic cylinders and also possible to use three cylinders disposed in a triangular pattern. In  FIG. 2  the frame  10  is shown in its operative position in which the frame  10  presses the distal end of the filter unit F, i.e. the end being distal from the frame, against a first end wall of the filter chamber  2  and is itself pressed against the proximal end of the filter unit. The filter unit F is provided with sealing elements (not shown in the Figures), such as sealing rings or the like, affixed to the opposite ends of the circumferential wall surrounding the filter media. The frame  10  is biased towards the operative position by compression springs  12  acting on the piston of each cylinder  11 . The sealing elements on each end of the filter unit F is somewhat compressed due to the compressive force from the springs  12  thereby ensuring that air entering the filter housing can not leak out between the first end wall of the filter chamber  2  and the distal end of the circumferential wall of a filter unit F placed in the filter chamber or between the proximal end of this wall and the frame  10 . Each cylinder  12  also contains connections (not shown) to a pressure source for moving the pistons of the cylinders  11  against the force of the springs  12  and thereby move the frame  10  to the right in  FIG. 2  when a filter unit F placed within the filter chamber  2  is to be discharged and replaced by a fresh filter unit. 
         [0017]    A circumferential flange  14  is projecting inwardly from the outer wall of the filter housing  1  in the second end of the filter chamber  2 . In the operative position of the frame  10 , a portion  15  of the frame  10  is in abutment with the flange  14  via a sealing element. This sealing element, for example an O-ring, can be affixed to flange  14  or frame  10 . By this arrangement it is ensured that air or gas that have passed through the filter unit F placed within the filter chamber  2  can not enter the space outside the circumferential wall of the filter unit, i.e. the space to the left of flange  14  or the space between the first end wall of the filter chamber and the flange  14  in  FIG. 2 . This space contains the access opening  4  to the filter chamber. Thereby it is ensured that no contaminated air or decontamination gas will leak out of the access opening during operation of the filter or thereafter even if the sealing of the access opening is not tight. A double security is thus obtained. 
         [0018]    In order to be able to push a filter unit F towards the end wall of the filter chamber  2 , i.e. to the left in  FIGS. 1 and 2 , the frame  10  has a first tubular part  17  having an outer circumference smaller than an inner circumference of the circumferential flange  14  and a second tubular part  15  having an outer circumference larger than the inner circumference of the circumferential flange  14 , the second tubular part having a smaller longitudinal extension than the first tubular part  17  and being disposed in the portion of the frame  10  being proximal to the pneumatic cylinders  11 . Thereby, the part  17  can be moved in the longitudinal direction without being obstructed by the flange  14 . The width of the second tubular part  15  is chosen such as the O-ring affixed to the frame or the flange is compressed when the frame  10  is in operative position pressing the filter unit F against the first end wall of the filter chamber  2 . 
         [0019]    The second filter chamber  3  is constructed the same way as filter chamber  2  and includes also a clamping device  9  similar to the clamping device  10 , 11  described above. 
         [0020]    A device  18 , 19  for monitoring the integrity of the filter unit F in filter chambers  2  and  3  is mounted in the filter housing  1  at the outlet from the respective filter chamber  2 , 3 . The monitoring device  19  is identical to the device  18 . 
         [0021]    The integrity of the filter unit is monitored by measuring the particle concentration in the air leaving the filter unit in order to establish if the filter is leaking, i.e. if one or more holes in the filter media allow particles to pass through the filter media. It is also important to locate even very small leaks which means that the particle concentration in relatively small volumes of air must be studied. The monitoring device  18  therefore comprises OPC:s (Optical Particle Counter) sampling relatively small volumes of the air leaving the filter unit F. In order to cover the whole area of the filter unit, the OPC:s need to be movable so that all air leaving the filter unit will be monitored by the device  18 . 
         [0022]    The device  18  comprises a row of several detectors (OPC:S)  20  mounted on a tubular bar  21  with a rectangular cross-section. The inlet end of each detector  20  comprises a funnel  22  having circular cross-sections and the row of detectors comprise as many detectors as needed for the funnels to cover the whole length of a side of the outlet area of filter chamber  2 . In the disclosed embodiment four detectors are present in the row of detectors  20 . The numbers of detectors needed is of course dependent on the length of the side of the area to be covered but also on the size of the funnel  22  which means that both more or fewer detectors can be used within the scope of invention. The term “several” means in this context “at least two”. 
         [0023]    In order to cover the whole area of the outlet from the filter chamber, the row of detectors is movable from one side of the outlet area of the filter chamber to the opposite side thereof. To accomplish this, two rotatable rods  23 , 24  having an external thread over the major part of their length are threaded into holes  25 , 26  in the respective ends of bar  21 , said holes  25 , 26  having an inner thread. Thus, by rotating the rods  23 , 24  in one or the other direction, the bar  21  and thereby the detectors  20  will move towards or away from the side of the outlet area of the filter chamber, i.e. to the left or right in  FIG. 3 . The rods  23 , 24  are rotatably mounted in opposite side walls of filter housing and drivingly in connection with each other via a belt  27  acting on drive wheels  28 , 29 . The end of rod  23  is connected to the output shaft of an electric motor  30 . Rotation of rod  23  by the motor  30  is thus synchronously transmitted from the drive wheel  28  to rod  24  via the belt  27  acting on the drive wheel  29 . 
         [0024]    A belt tensioner  31  is preferably arranged in the path of the belt  27 . Said tensioner is schematically shown in  FIGS. 3 and 4  and comprises a spring device (not shown) biasing the middle of the three rollers disclosed in  FIG. 4  to the right in  FIG. 4  as indicated by an double-arrow in this Figure. However, any type of belt tensioner can be used. 
         [0025]    By appropriate control of the electric motor  30 , the row of detectors  20  can thus be moved from one side to the other side of the outlet area of the filter chamber and back again. During a movement from a first side to the opposite, second side of the outlet area of the filter chamber only one of the detectors  20  is connected to a central counter (not shown) which calculates the particle concentration based on the number of signals from the detector and the flow rate of the air flowing through the detector and stores the values calculated this way. When one detector  20  has traveled from one side to the other side of the outlet area of the filter chamber, the central counter switch from this detector to the next detector  20  in the row and registers the values of the particle concentration from the latter detector during the return travel of the row of detectors from the second side to the first side. Thereafter, the next detector in the row is connected to the central counter and during the return travel of the row of detectors the last of the detectors  20  is connected to the counter. 
         [0026]    Since each detector  20  only travels in a straight line, the moving mechanism for the detectors can be of extremely simple construction and be both accurate and reliable. Reliability is a very important factor for a filter housing used in a contaminated environment. 
         [0027]    As is evident from  FIG. 2 , the openings of the funnels  22  of the detectors  20  lie in the same plane as the right edge of the frame  10  and portions of the funnels are also extending over said frame. In  FIG. 2 , the frame  10  is shown in its operative position clamping the filter unit F but when a used filter unit is to be discharged and substituted by a fresh one, the frame  10  is moved to the right in  FIG. 2  with the aid of the pneumatic cylinders  11 . In order to allow such a movement of the frame  10 , the detectors  20  are movably attached to bar  21  so that they can follow the movement of the frame  10  from operative to inoperative position. This is for example accomplished by mounting the detectors slidable within holes in the bar  21 . Preferably, the detectors  20  are biased towards the operative position of frame  10  by springs. 
         [0028]    The described embodiment can of course be modified in several ways without leaving the scope of invention. For example, the funnels  22  can have another cross-sectional shape than circular, e.g. rectangular or square, and other conicity than shown in  FIG. 2 . The bar  21  can also have another cross-sectional shape than rectangular, for example circular or oval, in order to have a more aerodynamic shape. The belt drive of rod  24  can be deleted and this rod be without an external thread in which case the hole  26  will be without inner thread. The movement of the bar  21  will then be performed only by the electric motor  30  and the rod  24  will only function as a guide rod. It is of course also possible to use one electric motor for each of the rods  23 , 24 . Other types of detectors than OPC:s can be used. Furthermore, the central counter can be programmed to simultaneously read the signals from all of the detectors instead of only one detector at a time. The present invention should therefore only be restricted by the content of the enclosed patent claims.