Patent Publication Number: US-2007107532-A1

Title: Sensor holder

Description:
THE FIELD OF INVENTION  
      The present invention refers to a sensor holder for arranging at least one sensor through the wall and into communication with the inside of a housing.  
     TECHNICAL BACKGROUND  
      It is common to use various kinds of sensors for sensing or measuring different parameters in processes, for example the amount of a certain substance, the temperature, the pressure, the flow etc. Sometimes it is needed to carry out such a sensing operation inside a closed housing. One way of performing such is to provide a throughgoing opening in the housing wall in which the sensor can be received and brought to communication with the inside of the housing. One of the issues to consider when arranging a sensor in an opening in a housing wall is the sealing between the environment inside the housing and the environment surrounding the housing. In some fields it is a necessity to provide a tight sealing between the sensor and the housing wall. However, it is sometimes not that simple to provide a throughgoing opening in the housing wall corresponding to the cross section of the sensor. For instance, if the sensor has a rectangular or squared cross section and the housing wall has a considerable thickness, it can be very difficult to achieve a corresponding throughgoing opening due to for example limitations in machining and cost-effectiveness. A failure in manufacturing a correct throughgoing opening may lead to that the housing must be scrapped. For example, when dealing with housings with thick walls it is preferred to form an oval or circular opening, as such forms can be easily achieved with drilling or milling machines.  
      Further, in hot temperature processes the sensor is sometimes exposed to considerable heat. To avoid damage to the sensor due to the heat it is often desired to provide the sensor with means acting as cooling flanges, thereby transferring the heat away from the sensor. One way of providing heat transfer is to design the sensor holder as a cooling flange. However, this raises additional demands on the design of the sensor holder. For instance, the heat transfer is among other things dependent on the size of the contact surfaces between the sensor holder and the sensor. Large contact surfaces provide for a better heat transfer than smaller contact surfaces.  
     SUMMARY OF THE INVENTION  
      Therefore, an object of the invention has been to provide a sensor holder for providing a sensor in communication with the inside of a housing, which sensor holder provides for a tight sealing between the housing and the sensor and where the cross section of the sensor may have a different form than the opening in the housing.  
      Further, an additional object of the invention has been to provide a sensor holder that provides for a sufficient heat transfer from the sensor.  
      These obejcts have been achieved by a sensor holder comprising a first and a second component, the first component being adapted to hold said sensor, the second component being provided with a first sealing surface and at least one throughgoing opening, a portion of the sensor being adapted to extend from the first component, through the opening in the second component and into communication with the inside of the housing, the envelope surface of the throughgoing opening in the second component being adapted to be tightly sealed to the sensor when pressing together the first and second component of the sensor holder, and the first sealing surface of the second component being adapted to be tightly sealed to a second sealing surface provided in the housing. when pressing together the sensor holder and the housing. Since the sensor is not sealed directly to the opening in the housing, the sensor can for instance have a rectangular form, whereby the opening in the housing can have a form made by drilling or milling machines such as an oval or circular form, the latter forms being easier to manufacture than the rectangular form if the housing wall has a considerable thickness.  
      In a preferred embodiment of the invention the throughgoing opening of the second component is conical or at least frusto conical, the conical or at least frusto conical form being widened towards a surface opposite the first sealing surface, and whereby first sealing means is provided in the conical or at least frusto conical part of the throughgoing opening. The conical or at least frusto conical form forces the sealing means into contact with both the sensor and the sensor holder which provides a tight and reliable sealing between the two. Thus, the environment delimited by the housing will not be able to escape to the outside of the sensor holder.  
      In another preferred embodiment the second sealing means is provided between the first sealing surface and the second sealing surface. In this way a further reliable and tight seal is obtained between the second component and the surface of the housing.  
      Preferably, the sealing means is a compressible sealing ring such as an O-ring. The use of conventional sealing means is above all cost effective, and shows consistent, well-defined sealing properties.  
      In a preferred embodiment the throughgoing opening in the second component of the sensor holder and the sensor have rectangular forms. It is easier to provide for sufficient heat transfer from a sensor having a rectangular form than from a circular sensor since it is possible to provide a larger contact surface between the surfaces of a rectangular sensor and its surrounding surfaces, by for instance clamping, than around a circular form, which is more difficult to clamp around. The larger area that is in contact with the “cooling flanges” the better heat transfer can be achieved.  
      Advantageously, the throughgoing opening in the housing has an oval or circular form. In housings with considerable wall thicknesses it is difficult to manufacture rectangular or square openings since the size of the drill or mill tools needed to be able to treat the material renders creation of right-angled corners impossible.  
      It is an advantage if the first sealing surface being provided with a groove for receiving the second sealing means, the groove having an oval or circular form. By this groove the sealing means can be easily fitted to the surface of the sensor holder, which will in turn facilitate assembling to the housing. Further, the risk of having the seal misplaced during use is minimised.  
      In a preferred embodiment the first portion is provided with a groove adapted to receive at least a portion of the sensor. This is a simple and efficient way of placing the sensor in the sensor holder, while at the same time provide for large contact surfaces between the sensor and the sensor holder.  
      Advantageously, the groove is rectangular and has a depth less than the length between two opposite sides of the sensor whereof one of said sides is facing the bottom of the groove. In this way it is secured that at least one surface of the sensor can be brought into contact with the bottom of the groove and the opposite surface of the sensor can be acessed by another part, thereby enabling necessary heat transfer.  
      Preferably, the first component further comprising a second portion and that the first and second portions being adapted to be clamped together by first fastening means. By clamping together the two portions of the first component the sensor is held in a stable and reliable way providing necessary heat transfer. This clamping of two portions also makes it possible to use simple fastening means, which in turn facilitates exchange of the sensor.  
      In a preferred embodiment it is provided second fastening means for tightening the first and second components to each other. The force acting on the first sealing means can thereby be optimised independently of the force with which the sensor holder is tightened to the housing.  
      In another preferred embodiment it is provided third fastening means for tightening the sensor holder to the housing.  
      Preferably, the fastening means is a screw joint. Screw joints are well known, have consistent and well-defined fastening properties and are cost effective. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the following, a presently preferred embodiment of the invention will be described in greater detail, with reference to the enclosed drawings, in which:  
       FIG. 1  shows an exploded view in perspective of a sensor holder according to the invention and a portion of a housing to which the sensor holder is adapted to be fastened,  
       FIG. 2  shows an exploded view in perspective of an assembled sensor holder according to  FIG. 1 , ready to be fastened to the housing portion,  
       FIG. 3  shows a view in perspective from “inside the housing” showing how the sensors extend through the throughgoing opening and into the housing space, and  
       FIG. 4  shows a view in perspective of the sensor holder when the first and second components have been tightened to each other. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT  
      In  FIG. 1  is shown a sensor holder, which has been denoted with the reference numeral  10 . The holder comprises a first component  12  being a clamping device  12  and a second component  14  being a housing interface portion  14 . The clamping device  12  and the housing interface portion  14  are adapted to be pressed against each other and are each provided with a respective surface  16 ,  18 . The surfaces  16 ,  18  are adapted to face towards each other when the clamping device  12  and the housing interface portion  14  are pressed together.  
      The clamping device  12  has the form of a block, which is divided into a first and a second portion  20 ,  22  each having a clamping surface  24 ,  26  facing. the other. The division is made so that the surface  16  adapted to face towards the housing interface portion  14  is split into two parts.  
      In the described embodiment the first and second portions  20 ,  22  of the clamping device  12  are adapted to be clamped to each other by first fastening means  28 . The fastening means  28  can for example be a screw joint. To prevent any motion to occur in a direction perpendicular to the clamping direction, i.e. that the two portions  20 ,  22  slide in relation to each other, the first portion  20  is provided with at least one shoulder  29  adapted to cooperate with a surface  31  in the second portion  22 . A surface of the shoulder  29  and the surface  31  are located in a plane substantially perpendicular to the clamping surfaces  24 ,  26 .  
      The first portion  20  of the clamping device  12  is provided with at least one groove  30  adapted for receiving at least one sensor  32 . The groove  30  is made in the clamping surface  24  and have sides located substantially perpendicular to said surface  24 , and a bottom surface substantially parallell to and offset from the clamping surface  24 . The groove  30  extends from one side of the first portion  20  to an opposite surface  16 , said surface  16  being the above described surface  16  adapted to face the housing interface portion  14 . The relation between the groove  30  length and the longitudinal length of the sensor  32  is such that a sensing element  34  of the sensor  32  will extend a desired distance out of the groove  30 , i.e. extend in a direction out from the surface  16  when the sensor  32  has been received in the groove  30 . The distance that the sensor  32  shall extend from said surface  16  will be described in more detail later.  
      In the described embodiment there is provided two sensors  32 , thus two grooves  16  are provided in the first portion  20  of the clamping device  12 . The grooves  16  extend in a direction transverse to the direction in which the first and second portions  12 ,  14  are clamped. Thus, when clamping together the first and second portion  12 ,  14  of the clamping device  12 , the sensors  32  are adapted to be squeezed between the bottom surface of the groove  30  and the clamping surface  26  of the second portion  22  of the clamping device  12 .  
      Below only one sensor  32  will be described in more detail. The sensor  32  in this embodiment has the form of a bar with rectangular cross section. As mentioned above one of its ends is provided with a sensing element  34 . For example the sensing element  34  can be of the type sensing the amount of electrons generated by an electron. beam emitter. In the other end there is provided a cable out-feed (not shown) connected to for example a control unit or a monitoring device.  
      The groove  30  in the first portion  20  of the clamping device  12  has a cross section substantially corresponding to that of the sensor  32 . Thus, the groove  30  in this case has a rectangular cross section. However, the groove  30  is sligthly more shallow than the sensor  32 . In-other words, the groove  30  has a depth less than the length between two opposite sides of the sensor  32  whereof one of said sides is facing the bottom of the groove  30 . Preferably, the groove.  30  is also sligthly wider than the sensor  32 , i.e. the width of the groove is larger than the length between the other two opposite sides of the sensor  32 . This differences in cross section makes it possible to slide the sensor  32  into the groove  30  while leaving a small longitudinal portion of the sensor  32  outside the groove  30  in the clamping direction. Thus, when clamping together the first and second portion  20 ,  22  there will be a very close connection between on one hand a side surface of the sensor  32  and the bottom surface of the groove  30 , and on the other hand an opposite side surface of the sensor  32  and the clamping surface  26  of the second portion  22  of the clamping device  12 . Thereby, the first and second portion  20 ,  22  will act as cooling flanges for the sensor  32 .  
      The second component  14 , being the housing interface portion  14 , comprises a plate with a first sealing surface  36  and a surface  18  adapted to face towards the clamping device  12 . In addition to the surface  18  and the first sealing surface  36  the housing interface portion  14  is provided with at least one throughgoing opening  38  for each sensor  32 , through which throughgoing opening  38  the sensor  32  is adapted to extend. The throughgoing opening  38  extends from the surface  18  adapted to face the clamping device  12  and the first sealing surface  36 . The form of the throughgoing opening  38  substantially corresponds to the cross section of the sensor  32  and is therefore rectangular in this embodiment. A portion  39  of the throughgoing opening  38  of the housing interface portion is frusto conical, and the frusto conical form is widened towards a surface opposite the first sealing surface  36 .  
      Between the envelope surfaces of the sensor  32  and the envelope surface of the throughgoing opening  38  in the housing interface portion  14 , first sealing means  42  is provided. The sealing means  42  is located in the frusto conical portion  39  of the throughgoing opening  38  and for instance the sealing means  42  is a compressible sealing ring such as an O-ring  42 . The size of the sealing means  42  is choosen such that when pressing together the clamping device  12  and the housing interface portion  14 , the sealing means  42  will bear on at least the frusto conical surface, at at least one point and thus forming an abutment line extending around the opening  38 , and the envelope surface of the sensor  32 , at at least one point, and thus forming an abutment line extending around the sensor  32 .  
      To be able to tighten the housing interface portion  14  to the clamping device  12  the housing interface portion  14  is provided with second fastening means  40 , which in this embodiment is a screw joint  40 . The screw joint  40  is made up by a screw provided in the housing interface portion  14  and a corresponding throughgoing opening in the clamping device  12 . The screw can for instance be located between the two sensor throughgoing openings  38 .  
      The sensor holder  10  is adapted to be tightened to a housing  44 . The housing  44  is adapted to delimit a space comprising the environment to be measured by the sensor  32 . The inside of the space and the thickness of the housing wall are designed depending on the field of application. In  FIG. 1-3  only a portion of a housing  44  surrounding at least one low voltage electron beam emitter is shown and to shield off the x-rays formed during usage of the emitter (not shown), the wall thickness is considerable, for example approximately  20  mm. The housing  44  is provided with a throughgoing opening  46  through the housing wall. The centre axis of the throughgoing opening  46  is located substantially perpendicular to the housing wall. The sensing elements  34  of the sensors  32  are adapted to be brought into communication with the inside of the housing  44 , and therefore, the sensors  32  are adapted to extend through the throughgoing opening  46 . Thus, the opening  46  is made large enough for the sensors  32  to extend through it. In the described embodiment the throughgoing opening  46  has a circular form, particularly an oval form through which both sensors  32  can extend. Because of the large wall thickness of the housing  44 , the area around the throughgoing opening  46  is provided with a recess  48  for accomodating part of the sensor holder  10 . The bottom surface  50  of the recess  48  is a surface  50 , denoted second sealing surface  50 , against which the housing interface portion  14  of the sensor holder  10  is to be tigthly sealed to when the sensor holder  10  is pressed towards the housing  44 . The recess  48  can have any form suitable for accomodating the sensor holder  10 , and in  FIG. 1  it is shown a recess  48 , which is oval.  
      From the description above it can be understood that the relation between the length of the sensor  32 , its location in the groove  30  of the clamping device  12 , the depth of the recess  48  in the housing  44  and the housing  44  wall thickness should be such that at least the sensing element  34  of the sensor  32  projects into the space inside the housing  44 , see  FIG. 3 . Alternatively, the sensing element of the sensor projects at least enough to form part of the housing wall so that the environment inside the housing  44  can be measured by the sensing element  34 .  
      Between the first and second sealing surfaces  36 ,  50  a second sealing means  52  can be provided to further increase the sealing. Preferably, the sealing means should be compressible. In  FIG. 4  it is shown that the sealing means  52  is a conventional O-ring  52 , which is received in a groove  54  made in the first sealing surface  36  of the housing interface portion  14 . The groove  54  is made around the sensor throughgoing openings  38 , at a suitable distance from the edges of the throughgoing openings  38 .  
      To tighten the sensor holder  10  to the housing  44 , the clamping device  12  comprises third fastening means  56 . The fastening means  56  can for example constitute a screw joint that comprises two flanges provided with screw throughgoing openings for screws. The flanges are arranged on upper and lower portions (in relation to  FIG. 1 ) of the clamping device  12  and such that their throughgoing openings are substantially perpendicular to the housing  44 . The housing  44  is provided with corresponding screw throughgoing openings above and below the recess  46  for receiving the screws.  
      During assembly of the sensor holder  10  the sensors  32  are slid into the grooves  30  in the first portion  20  of the clamping device  12 . Then the second portion  22  of the clamping device  12  is placed with its clamping surface  26  facing the clamping surface  24  of the first portion  20 , and the two portions  20 ,  22  are tightened to each other by the first fastening means  28 , thereby squeezing the sensors  32  between themselves. Afterwards, the first O-rings  42  are placed in the frusto conical portions of the openings  38  in the housing interface portion  14 , after which the housing interface portion  14  is located so that its throughgoing openings  38  are slid over the portions of the sensors  32  that extend out from the clamping device  12 . The two components, i.e. the clamping device  12  and the housing interface portion  14  are then tightened to each other by the second fastening means  40 . The envelope surfaces of the throughgoing openings  38  will then be tightly sealed to the envelope surfaces of the sensor. The next step is to put the second O-ring  52  into its groove  52  in the first sealing surface  36  of the housing interface portion  14 . The sensor holder  10  is now completed and can be fastened to the housing  44 , see  FIG. 2 . The portions of the sensors  32  extending out from the sensor holder  10  are slid through the throughgoing opening  46  in the housing  44 , see  FIG. 3 , and part of the sensor holder  10  is accomodated in the recess  48  around the throughgoing opening  46 . The third fastening means  56  can then be tightened, whereby the first sealing surface  36  is tightly sealed against the second sealing surface  50  in the housing  44 .  
      Although the present invention has been described with respect to a presently preferred embodiment, it is to be understood that various modifications and changes may be made without departing from the object and scope of the invention as defined in the appending claims.  
      A sensor holder  10  of this kind can for example be used in a device for electron beam irradiation of a web. In such a device an electron beam emitter is enclosed in a tunnel housing through which the web passes, and it is desired to sense the amount of electrons emitted from said emitter. Due to the forming of X-ray radiation during electron irradiation, the wall thickness normally large. Thus, the receiving throughgoing opening  46  for the sensor  32  and the recess  46  is preferably made with a circular form. Although only this example of a field of application is given it should be understood that the invention may be used in many other fields.  
      All the fastening means  28 ,  40 ,  56  have been described as screw joints. This is of course not the only type of fastening means that can be applicable. For example the fastening means can be an eccentric lock.  
      If the thickness of the housing  44  wall is relatively small it is not necessary to provide a recess  48  for the sensor holder  10  in connection with and around the throughgoing opening  46  in the housing  44 , instead the housing interface portion  14  of the sensor holder  10  is pressed against the housing surface, and is sealed directly to the area around the throughgoing opening  46 , the area being the second sealing surface  50 . Moreover, the throughgoing opening  46  in the housing  44  can have any other form suitable for the sensors  32 . For example, if there is only one sensor  32  the throughgoing opening  46  does not need to have an oval form, but can for example be circular instead.  
      In the example the number of sensors  32  are two, but it should be understood that the number can be any number suitable for the field of application in which the sensor holder  10  is used. For example the number can be one as well as three or more.  
      Further, the second fastening means  40  between the clamping device  12  and the housing interface portion  14  can be excluded. Instead the clamping device  12  and the housing interface portion  14  can be pressed together by the third fastening means  56 , arranged between the sensor holder  10  and the housing  44 , which at the same time will tighten the clamping device  12  to the housing interface portion  14 .  
      Moreover, in the described embodiment the throughgoing opening of the second component is partly frusto conical. Alternatively, the throughgoing opening can be conical, whereby the conical form is similarly being widened towards the surface opposite the first surface.  
      In the embodiment the first and second sealing means  42 ,  52  used are conventional O-rings. However, it should be understood that other types of compressible sealing means can be used.  
      To prevent motion between the first and second portion  20 ,  22  of the clamping device  12 , the first portion  20  is provided with a shoulder  29 . Alternatively, the shoulder can of course be located on the second portion. Another alternative is to arrange the screw hole of the second fastening means close to the clamping surface of one of the portions such that the nut of the fastening means will extend, in its radial direction, past the joint between the first and second portions, and thereby act as a shoulder.