Abstract:
The invention relates to electrical sensors, which are tight against longitudinal water, and to a process for a simple and cost efficient manufacture, with a tightly closed housing, a sensor element, at least one cable leading out of the housing, wherein the electrical conductors of the cable in the housing comprise a massive cross section without a cavity at least in one longitudinal section, a conductor seal seals the massive cross section against the lead insulation, a lead seal seals the lead insulation against the jacket of the cable, and against all other jackets, and a jacket seal seals the cable jacket against the housing.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS: 
       [0001]    This application claims priority from German Patent Application No. 10 2006 024 967.4-55 filed 29 May 2006. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not Applicable 
       INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0004]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0005]    (1) Field of the Invention 
         [0006]    The invention relates to electrical sensors. 
         [0007]    All electrically operating sensors, independently of what is being measured by them, react to moisture present in the sensor element and/or in the processing electronic, thus generally in the sensor housing, due to the electrical conductivity of the water and its corrosion effects which causes erroneous measurements or total failure. Therefore, sealing against moisture is one of the most important prerequisite for the long-term functionality of an electrical sensor, as with any electrical device. 
         [0008]    This applies even more, the more sensitive or the lower the resistance of the electrical part of the sensor is, possibly also to the sensitive, non-electrical part of the sensor element. 
         [0009]    Since measurement signals have to be transmitted from the sensor to the outside, an electric cable for data transfer leads out of almost every sensor housing. A wireless data transmission from a hermetically sealed housing is a comparatively expensive and complicated solution. 
         [0010]    Normally, it is not a big problem to seal the housing itself and to create a sufficient seal with a long term effect between an outer circumference of a cable jacket and an interior circumference of the cable input at the housing, e.g. via typically packing sleeves and a screwed grommet. 
         [0011]    If the sensor is used in a humid environment, a substantially long-term risk for the sensor is that longitudinal water enters into the sensor housing through the cable itself. This may occur through gaps between the single lead insulations and the cable jacket or also through gaps within the lead insulation, thus between particular strands of an electrical conductor made from a plurality of strands shaped as a lead of the cable. 
         [0012]    Even when the outer end of the cable is not located in a fluid but only in humid air, a pump effect can occur through temperature variations (day-night change) and ensuing pressure differentials within the cable. The pump effect can transport mid term and long term damaging amounts of moisture, also in the form of gas from the surrounding air, into the housing of the sensor. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    It is the object of the present invention to provide an electric sensor which is sealed against longitudinal water and to provide a process for simple and cost efficient manufacture of the sensor. 
         [0014]    Through combining various sealing measures, water is prevented from penetrating into the sensor element, thus into the interior of the housing. 
         [0015]    Through redesigning the electrical conductors of the cable, at least in a certain longitudinal section, into a massive, cavity free cross section, e.g. through soldering of the previously singular strands of the conductor into a massive cross section, water is prevented from penetrating in longitudinal direction between the single strands of the cable. In case the electrical conductor is already made from a massive material, a respective redesign is not necessary. Through sealing this massive cross section of the conductor radially against the surrounding lead insulation, no water can penetrate between the conductor and lead insulation. 
         [0016]    Through sealing the lead insulation relative to the jacket of the cable and relative to the other leads, or a core material between the leads, the penetration of water in the area between the single strands and within the cable jacket is avoided. 
         [0017]    Through sealing between cable jacket and the interior circumference of the housing, the penetration of water between the cable circumference and the housing is avoided. 
         [0018]    A particularly simple solution to design this seal includes encasing a longitudinal section having all of the cavity free cross-sections within an encasement material. The encasement material works like a gasket and preferably is made from a hardening encasement material. 
         [0019]    Instead of only encasing the respective longitudinal section where the bared, massive conductor cross sections are located, the entire interior of the housing can be also encased, thus including the sensor element, in case this is not damaging to the sensor element for other reasons, e.g. due to the reaction heat generated during the hardening of the encasement material. 
         [0020]    In case the electrical conductors of the cable or cables are being run to the sensor element, the longitudinal area in which the conductors are reconfigured into a massive cross section without a cavity can be located at any location within the sensor housing. Under certain conditions, it can also be the connection location towards the sensor element, wherein the sensor element then almost inevitably has to be encased integrally. 
         [0021]    If this is not desired, the leads of the cable would have to be stripped off the cable jacket in this case, and also of the lead insulation over a certain length at a location sufficiently far in the rear of the interior of the sensor housing so that the encasement material can penetrate to the electrical conductors. 
         [0022]    Since this is difficult to do manually on an uncut cable, and in addition, at the employed sensor elements or electronic components of the processing circuit in the sensor housing rather very thin electrical conductors are being used as primary conductors, then primary conductors through thicker leads run in via a cable, the location of the solder joint between primary and secondary conductors is being used as an area, in which also the strands themselves are already compacted into a massive cross section due to the soldering of the strands amongst each other. 
         [0023]    For the electrical function of the sensor, it is important that the areas with a massive cross section, which were stripped of their insulation for the compacting process, do not have any lateral contacts and short circuits between the particular conductors. 
         [0024]    This can be realized in a different manner. 
         [0025]    A very simple solution is surrounding each of these electrical conductors with a spacer sleeve which, on the one hand, is made from electrically non-conductive material and, on the other hand, allows penetration of encasement material through the sleeve to the electrical conductor and its complete encasement. For this purpose, the spacer sleeve is preferably made from a woven mesh material or woven grid material, e.g. from plastic. 
         [0026]    Another possibility is to position the particular conductors sufficiently next to each other, e.g. through arranging them in the cutouts of a laterally extending plate as spacer, and to do this close enough to the longitudinal areas where the insulation is stripped which shall be encased, so that no lateral contact can occur any more in this location. 
         [0027]    The spacer has to be configured and positioned so that it does not inhibit the complete enclosure of the electrical conductors with stripped insulation in the area with a massive cross section through encasement material. 
         [0028]    If the sensor housing has a large opening which can eventually be sealed tight with a lid, the filling of the encasement material can certainly be performed via this lid opening, at least when the lid opening is in the suitable position, thus opposite to the encasement area. 
         [0029]    If the housing does not have a detachable cover but is only comprised of e.g. of two half shells which are interlocked relative to each other once and also glued together through the encasement material, this is not possible anymore, since the two shells have to be fixed against each other before the encasement. 
         [0030]    A bubble free encasement is accomplished through the sensor housing which is ready for the encasement and filled with the respective components. The sensor housing does not only have an encasement opening for filling in the encasement material but also has a second bleed opening from which the air to be displaced can be pressed out of the interior of the sensor housing by the penetrating encasement material. 
         [0031]    Therefore, the bleed opening should be higher during the encasement and the hardening than the fill in opening or at least high enough so that in the area above no electrical components are present anymore. 
         [0032]    The sealing between the outer circumference of the cable, thus the outer circumference of the jacket, and the inner circumference of the cable input in the housing is preferably performed through a conventional cable end closure. In the cable end closure, an annular packing sleeve with a preferably conical cross section is inserted into the distance between the outer circumference of the cable and the inner circumference of the cable in feed and pressed forward in longitudinal direction through a cup-shaped, inserted and screwed down threaded grommet. The cable and closure simultaneously serves to avoid the running out of the encasement material during encasement. 
         [0033]    The encasement can also be performed in steps after the hardening of the respective preceding step, in particular, when the heat development in the sensor shall be limited in the particular steps. 
         [0034]    Since the encasement material normally shrinks during the hardening process, the volume in the bleed opening can be used as buffer volume for the shrinking of the encasement material, so that when initially filling up to the outer edge of the bleed opening, it is assured that after the hardening process the encasement material does not recede further than to the bottom edge of the bleed opening. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0035]      FIG. 1  is a longitudinal section through a sensor completed for encasement which is tight against longitudinal water. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]      FIG. 1  shows a rotationally symmetrical sleeve-shaped sensor housing  1  and an almost rotationally symmetrical sleeve packing  3 . 2  having a conically tapered front end that seals an outer circumference of a cable  4  relative to an interior circumference of a cable input  1   a  of the housing through axial impression. The axial impression is performed through a commercially available pot-shaped threaded grommet  3 . 5 . 
         [0037]    As can be seen, cable  4  is comprised of several strands that constitute primary conductors  9  and which are each provided with a particular lead insulation  9   a  which are, in turn, received within a cable jacket  4   a  spaced from each other by a cable core  4   b.    
         [0038]    In  FIG. 1 , at the upper left end of the sensor housing, a sensor element  6  is located, e.g. an electronic chip or an electrical circuit, on which the sensor element is located and from which the secondary conductors  10  lead away, one of which is respectively connected with one of the strands of cable  4  as a primary conductor  9 . 
         [0039]    In order to reliably prevent a penetration of longitudinal water through the cable into the interior, thus, into the interior space in sensor housing  1 , a sealing has to be performed at each particular lead, on the one hand, of the particular strands of the electrical conductor amongst each other and, on the other hand, of the strands relative to lead insulations  10   a ,  9   a . Furthermore, a sealing has to be performed of each particular lead relative to jacket  4   a  of cable  4  and all other leads of cable  4 , e.g. through an encasement with a sealing means, in particular, a hardening sealing means. 
         [0040]    This sealing is provided when the entire cross section is sealed between an interior circumference of housing  1  and an outer circumference of all electrical conductors  9 ,  10  and spaces between the conductors  9  and  10 . 
         [0041]    The sealing of the spaces between the strands of the conductors, in case these conductors are of the primary conductors, thus the particular leads, that do not already have a massive cross section, is performed through the penetration of liquid soldering tin, while all other seals are formed by encasement material. 
         [0042]    For this purpose, sensor housing  1  can have cable input  1   a  having an interior cross section only marginally larger than an outer circumference of the cable and long enough in axial direction to receive all longitudinal sections of the electrical conductors each having a cross section converted into a massive cross section. 
         [0043]    The manufacture of the sensor is then performed in the following steps:
       stripping the insulation of the free ends of the secondary leads  10  pointing away from sensor element  6  at a defined distance from sensor element  6  and over a defined length;   removing cable jacket  4   a  from cable  4  over a certain length;   freeing the particular leads as primary leads/conductors  9  from the cable core;   shortening the leads to certain lengths, depending on the end of the cable insulation  4   a  or depending on the end of other leads;   removing lead insulation  9   a ,  10   a  over a certain length from particular leads;   sliding a spacer sleeve  7  onto the end of each primary conductor  9  or associated secondary conductor  10 ;   tinning the ends of secondary and primary conductors  10 ,  9 , possibly using soldering sleeves;   soldering one respective primary lead  9  with a secondary lead  10 ;   subsequently sliding spacer sleeve  7  over the soldered section with a massive cross section;   inserting sensor element  6  into an interior cavity  15  of sensor housing  1  so that the cable sleeve  4   a  still reaches into cable input  1   a ; and   sliding the packing sleeve  3 . 2  into the space between cable jacket  4   a  and the beginning of cable input  1   a , axial sliding and screwing tight threaded grommet  3 . 1  onto the outer circumference of cable input  1   a.          
 
         [0055]    After positioning of the sections with the massive conductor cross section is performed in the interior of the sensor housing in this manner, and the intermediary state according to  FIG. 1  is reached, the interior space  15  is now filled with encasement material, at least in the area of the massive cross section. 
         [0056]    This is preferably performed from a cover opening, that is with a cover  11  not yet in place. The encasement material is filled through the cover opening, preferably past sensor element  6 , with the sensor housing  1  standing approximately vertical, up to the desired encasement height, thus at least beyond the connection locations between primary conductors and secondary conductors, possibly until also sensor  6  is integrally enclosed. 
         [0057]    In this case, a designated encasement opening  16  and a bleed opening  17  are not necessary, and they are only being used if the housing is substantially closed during encasement. Thus, no removable cover  11  is present, but this is a closed housing side. 
         [0058]    Preferably, the sensor housing is then positioned so that the bleed opening, which is also present in the housing, is located higher than encasement opening  16 , and beyond that interior space  15  to be encased, is laid out so that during encasement, with the liquid level of the encasement material rising, no cavities remain, which are not filled by the encasement material, and which are not vented, in which in particular electric components are located. 
         [0059]    In this manner, either only the area of cable input  1   a  or the entire interior space  15 , including the sensor element  6 , can be encased if the encasement is not mechanically detrimental for the sensor element  6  or detrimental due to the heat development during the hardening process of the encasement material. 
         [0060]    According to  FIG. 1 , cable input  1   a  comprises a hollow cylindrical interior, in whose longitudinal extension all section of the conductors converted into a massive cross section are positioned, and in whose interior circumference several annular circumferential or punctual anchor chambers  12  leading radially to the outside are provided, into which the encasement material also penetrates, and anchors in longitudinal direction  8  of the cable direction of extension, after hardening, through which a pull relief for the cable is provided. 
         [0061]    If only the cable input  1   a  is to be encased, this is performed through slanted or vertical alignment of the longitudinal cable axis with the sensor housing  1 , with the cable end closure  3  facing downward, while with complete encasement also the horizontal position during encasement and hardening can be maintained. 
         [0062]    The spacer sleeves  7 , thereby, are made from electrically non-conductive material, and reach from the area with the insulation stripped and reconfigured into a massive cross-section via soldering tin, up to the two abutting lead insulations  9   a ,  10   a  of the primary conductor  9  and the secondary conductor  10 . 
         [0063]    Preferably, each spacer sleeve  7  is thus comprised of a woven mesh, which can be permeated by the encasement material without any problems, so that it can penetrate completely up to the cross section of the conductor. 
         [0064]    In case the spacer sleeve  7  does not have this property to be permeable by the encasement material, the respective free end of the spacer sleeve  7  is sealed relative to the respective lead insulation  9   a ,  10   a  and, thereby also the penetration of longitudinal water towards the sensor element  6  is avoided.