Abstract:
A load cell with an elastically deformable membrane force transducer for receiving forces to be determined, with a sensor arrangement for detecting the deformation of the force transducer and its conversion into an electric weight signal, which is robust and can also be installed in narrow spaces and can receive and determine tensile forces as well as pressure forces, is disclosed, comprising a housing s surrounding the force transducer essentially on all sides and having an opening, through which the membrane force transducer can be acted upon with the force to be determined, wherein the membrane force transducer comprises a force introduction member arranged centrally and at the edge area an edge part projecting beyond at least one of the membrane surfaces.

Description:
[0001]     This application is a continuation-in-part of International application number PCT/EP2004/004662 filed on May 3, 2004.  
         [0002]     The present disclosure relates to the subject matter disclosed in International application number PCT/EP2004/004662 of May 3, 2004 and German application number 103 25 390.4 of May 28, 2003, which are incorporated herein by reference in their entirety and for all purposes.  
       BACKGROUND OF THE INVENTION  
       [0003]     The invention relates to a load cell (dynamometric cell) with an elastically deformable membrane force transducer for receiving forces to be determined, with a sensor arrangement for detecting the deformation of the force transducer and its conversion into an electric weight signal.  
         [0004]     A load cell with a membrane force transducer is known, for example, from DE 36 27 127 A1. This load cell is designed in the form of a load box, with which a support element resistant to bending keeps the membrane elastically deformable, wherein, in accordance with this publication, the deformation of the membrane is preferably detected with a sensor arrangement which includes a Hall generator. The membrane and the support element resistant to bending together form a load cell, in the interior of which the sensor arrangement can be accommodated.  
         [0005]     A load cell of the type described at the outset, with which the elastic deformation of the membrane is detected with a capacitive sensor arrangement, is likewise known from DE 41 32 108.  
         [0006]     The aforementioned load cells have in common the fact that they can receive only pressure forces and, in addition, can be used in rough surroundings only with minimal benefit.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     In accordance with an embodiment of the invention, a load cell is provided which is robust and can also be incorporated into narrow spaces and, in particular, can receive and determine tensile forces as well as pressure forces.  
         [0008]     In accordance with an embodiment of the invention, a load cell has a multipart housing which is resistant to bending and has an interior space for accommodating and holding the membrane force transducer and the sensor arrangement, wherein the housing surrounds the force transducer essentially on all sides and has an opening, through which the membrane force transducer can be acted upon with the force to be determined, wherein the membrane force transducer comprises a force introduction member arranged centrally and at the edge area an edge part projecting beyond at least one of the membrane surfaces. A recessed area, into which the projecting edge of the membrane force transducer can for example engage in a form-locking manner or press-fit manner (force-locking manner), is formed in the interior space of the housing.  
         [0009]     As a result of the use of a housing which is resistant to bending, accommodates the membrane force transducer and the sensor arrangement and surrounds them essentially on all sides, the load cell in accordance with the invention may be of a very robust design and used in a plurality of rough surrounding conditions. This results, in particular, from the fact that not only the sensor arrangement but also the membrane of the force transducer are accommodated in the housing in a, as it were, encapsulated manner. Only one opening in the housing is necessary so that the pressure or tensile force to be determined can act on the membrane force transducer.  
         [0010]     The production of the load cell in accordance with the invention, in particular, its assembly is simplified to a great extent due to the multipart housing resistant to bending since this accommodates the membrane force transducer with its projecting edge in a recessed area, for example, a groove, in a form-locking manner. The edge and the recessed area may be designed so as to be adapted to one another from the point of view of production engineering without the resources for this needing to be too great and so the edge of the membrane force transducer will be accommodated in the recessed area in a first housing part free from clearance.  
         [0011]     With an additional housing part, the edge of the membrane force transducer can be fixed in a form-locking and/or force-locking manner in the recessed area of the first housing part. This enables a simple exchange of the membrane force transducer to be carried out in the case where the force transducer fails during the final control process.  
         [0012]     Otherwise, the load cell in accordance with the invention can be sealed hermetically. This denotes a particularly good resistance to soiling and impairment of its functioning even in very difficult surroundings, for example, in a plurality of arrangement possibilities in an automobile, in particular, in its interior space, as well, in which temperature variations, dust and abrupt loads often occur.  
         [0013]     The load cell in accordance with the invention may be used, in particular, for determining weight forces acting on the seat of a motor vehicle, such as those increasingly used, for example, in conjunction with the selective activation of airbag systems. The preferred installation positions are between seat rails and floor pan of the vehicle or between seat shell and seat carcass.  
         [0014]     The force introduction member is preferably arranged coaxially to the opening of the housing and, in addition, preferably designed such that it is of an essentially complementary design to the cross section of the opening so that the opening of the housing is, as it were, filled essentially by the force introduction member which, in this case, preferably projects at least partially into the opening. A minimum gap must, of course, be provided between force introduction member and opening in order to be able to have the force introduction member transfer the force acting on the load cell to the membrane essentially free from friction. Gaps of between approximately 0.1 to approximately 0.5 mm have proven to be successful in practice. In this respect, it may be provided for the opening of the housing to be acted upon with a plastic covering, for example, in the form of a sleeve, wherein the plastic material is selected with a view to as low a coefficient of friction as possible.  
         [0015]     Alternatively, it may also be provided for the force introduction member to be designed such that it protrudes beyond the surface of the housing and for a screening sleeve consisting of a flexible material which essentially does not influence the force acting on the force introduction member to be provided for sealing the gap between opening and force introduction member.  
         [0016]     In addition, the load cell according to the invention will preferably have an integrated mechanical overload protection. Such a mechanical overload protection may be provided for tensile and/or pressure forces and means that in the case of any action of an excessively large force, i.e., a force no longer admissible for the safe functioning of the load cell this cannot act unhindered on the membrane. For this purpose, it is provided for one or several stop surfaces to be formed in the interior of the housing, these surfaces limiting an elastic deformation of the membrane force transducer when acted upon by tensile and/or pressure forces. In this respect, the force introduction member can then be supported, for example, on one stop so that the maximum deformation of the membrane force transducer remains limited and, as a result, any mechanical damage due to overload is precluded.  
         [0017]     In the case of several stop surfaces, at least one of the stop surfaces will undertake the function of the overload protection with respect to pressure forces and another an overload protection with respect to tensile forces.  
         [0018]     The countersurface interacting with the stop surfaces may be formed either on the membrane force transducer itself or, however, on the force introduction member. For example, the force introduction member may have a projection which interacts with one or other of the stop surfaces or the several stop surfaces in the sense of limiting tensile and/or pressure forces which can act on the membrane force transducer.  
         [0019]     The force introduction member itself is often of an essentially cylindrical design and so the opening of the housing is, accordingly, also of a cylindrical design. In one preferred embodiment, the force introduction member supports an annular flange which acts as a projection in the sense of the aforementioned overload protection. Alternatively, it may also, of course, be provided for the force introduction member to have a recess, into which a projection which is arranged securely on the housing engages and provides for a limitation of the possible movement of the force introduction member in this way.  
         [0020]     The annular flange of the force introduction member can, however, also advantageously undertake an additional function, namely of connecting the force introduction member to the membrane. In this respect, the connection between membrane and annular flange is preferably configured such that the annular flange protrudes beyond the membrane surface on both sides of the membrane so that the annular flange can cooperate with stop surfaces of the housing above and below the membrane in the sense of an overload protection.  
         [0021]     The membrane and the force introduction member may be designed in one piece in the case of several embodiments, i.e., membrane and force introduction member are worked from the solid material.  
         [0022]     Alternatively, it may also be provided for the membrane to be welded to the force introduction member, in particular, to its annular flange.  
         [0023]     The membrane is preferably designed as a circular disc. For the purpose of the secure and defined attachment of the membrane in the housing, the projecting edge is designed as an annular collar or as annular collar segments arranged at regular angular distances on the circumference, and the housing again has an annular groove in its interior, into which the annular collar or rather the segments of the membrane can be inserted during the assembly of the load cell.  
         [0024]     This allows a very simple and, nevertheless, very exact mounting of the membrane in the housing resistant to bending. The housing resistant to bending is preferably closed by a base part which acts on the free surface of the annular collar of the membrane and presses it into the annular groove.  
         [0025]     The force introduction member is, on the one hand, as already mentioned, secured to the membrane itself and has, in addition, a free end which preferably comprises a screw thread which is accessible through the opening of the housing or even protrudes out of it.  
         [0026]     As a result, the load cell with the force introduction member is very easy to install and, for example, can also be used as a screw bolt as installation means directly at the place where it is to be used.  
         [0027]     In the latter case, the housing will preferably, with respect to the plane defined by the membrane, have a screw bolt located opposite the opening or a screw thread oriented coaxially to the opening. As a result, the load cell may be installed very easily at the location of its use by means of screw connections on both sides.  
         [0028]     The force introduction member may also extend, in a preferred embodiment, through the plane of the membrane, wherein the first free end of the force transducer extends in the direction towards the opening of the housing and a second free end extends in the interior of the housing away from the membrane on its other side and ends in the interior of the housing.  
         [0029]     This free end will preferably support an element of the sensor arrangement while an additional element of the sensor arrangement is mounted securely on the housing.  
         [0030]     In general, it may be ascertained that the membrane is to be designed as a regular polygon with a center of symmetry, at which the force introduction member is then arranged.  
         [0031]     A simple example for this would be a strip-like design of the membrane, wherein the force introduction member would then be arranged centrally to the longitudinal direction of the membrane strip. A triangular membrane would, for example, also be conceivable, in the same way as other polygonal shapes.  
         [0032]     In a special case of this which is, however, the most preferred case, the membrane has the shape of a circular disc, as has already been described in the above.  
         [0033]     The sensor arrangement used for the load cell in accordance with the invention may be selected from various known sensor arrangements, wherein sensor arrangements which operate free from contact are, however, clearly preferred. Nevertheless, this does not preclude the use of one or several wire strain gauges.  
         [0034]     However, as stated, the sensor arrangements for a contact-free distance measurement are preferred, such as, for example, those operating inductively as well as those operating capacitively. In addition, an optical sensor arrangement is also particularly suitable.  
         [0035]     A sensor arrangement operating inductively is particularly suitable within the meaning of the present invention, in particular, one which comprises a Hall sensor as one element and a magnet as an additional element. In the case of the magnet, a permanent magnet will be used, in particular.  
         [0036]     In the case of this particularly preferred embodiment of the invention, the magnet may be arranged on the force introduction member and the Hall sensor on the housing. A reverse arrangement, i.e., the arrangement of the magnet on the housing and the arrangement of the Hall sensor on the force introduction member is likewise possible but the first variation is preferred since this has the advantage that the signal lines of the sensor may be guided in the housing material and are, therefore, to be arranged in a very space-saving and, at the same time, protected manner. At the same time, any falsifying of the weight signal due to the presence of signal lines can be avoided.  
         [0037]     With such an embodiment, the housing of the load cell is preferably formed from ferromagnetic steel with the advantage that the sensor arrangement is encapsulated not only mechanically but also electro-magnetically. The force introduction member itself which accommodates the magnet, in particular, the permanent magnet is then to be produced, however, from a non-magnetic steel since otherwise a magnetic short circuit would result.  
         [0038]     The Hall sensor and the magnet of the sensor arrangement are preferably designed and arranged such that in the no-load state of the load cell the Hall sensor generates an electric signal with a value smaller than or equal to 1/3 of the maximum effective signal.  
         [0039]     This ensures that a sufficient reserve for amplifying the effective signal is provided for the evaluation circuit which is likewise preferably to be arranged in the interior of the load cell and an adequate signal-to-noise ratio is present.  
         [0040]     In a first variation, the magnet may be designed to act as a monopole in relation to the Hall sensor, wherein the Hall sensor comprises an even number of sensor elements which are arranged in the form of a two-dimensional matrix located opposite the monopole. In this respect, two sensor elements form each time one part of an electronic differential circuit.  
         [0041]     Alternatively, the magnet may be designed to act as a dipole in relation to the Hall sensor, wherein the Hall sensor comprises one or several sensor elements, the signals of which can be detected separately.  
         [0042]     It is conceivable, in particular, for two Hall sensors to be arranged diametrically opposite in relation to the force introduction member or rather its longitudinal direction and to be evaluated when the magnet is arranged in the force introduction member.  
         [0043]     As already mentioned above, another alternative consists in selecting an optical sensor arrangement.  
         [0044]     In this respect, the sensor arrangement will preferably comprise a light source and a slot diaphragm, on the one hand, and a differential photodiode, on the other hand. In one arrangement, the light source and the slot diaphragm are held together on the force transducer, for example, on the force introduction member whereas the differential photodiode is arranged on the housing so as to be stationary.  
         [0045]     Alternatively, the sensor arrangement can have the light source and the slot diaphragm arranged, on the one hand, so as to be secured to the housing whereas the differential photodiode is arranged on the force transducer, i.e., in particular on the force introduction member.  
         [0046]     These and additional advantages of the present invention will be explained in greater detail in the following on the basis of the drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0047]      FIG. 1 : shows a sectional view through a first embodiment of a load cell in accordance with the invention;  
         [0048]      FIG. 2 : shows a sectional view through a second embodiment of a load cell in accordance with the invention;  
         [0049]      FIG. 3 : shows a sectional view through a third embodiment of a load cell in accordance with the invention;  
         [0050]      FIG. 4 : shows a sectional view through a fourth embodiment of a load cell in accordance with the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]      FIG. 1  shows a load cell provided altogether with the reference numeral  10  in a first embodiment. The load cell  10  comprises a housing  12  which is resistant to bending and has a hollow-cylindrical cover part  14  closed on one side and a base part  16  closing the cover part  14 . The cover part  14  forms with the base part  16  an interior space  18  which communicates with the surroundings of the load cell  10  merely via an opening  20  in the cover part  14 .  
         [0052]     The interior space  18  is essentially in the shape of a circular disc and is limited on the side of the cover part  14  by an end wall  22  which is essentially designed in the shape of an annular disc and borders on the opening  20  in its center.  
         [0053]     Adjacent to the opening  20 , the end wall  22  is recessed in an annular shape (reference numeral  24 ). At its outer circumference, the end wall  22  merges into an annular groove  26 .  
         [0054]     The interior surface of the base part  16  has an end side  28  which is essentially designed complementary to the end wall  22  and borders centrally on a blind-end bore  30  arranged coaxially to the opening  20 . Around the blind-end bore  30 , the end side  28  has a recess  32  which is essentially designed in mirror image to the recess  24  of the end wall  22 . At the outer circumference of the end side  28 , a recess  34  is provided which extends all the way around and is essentially designed in mirror image to the groove  26  of the end wall  22 . At its outwardly located surface, the base part  16  bears a screw bolt  35  coaxially to the blind-end bore  30 .  
         [0055]     Adjacent to the base of the blind-end bore  30 , this widens to form a receiving means  36 , in which a component of a sensor arrangement of the load cell  10 , which is still to be explained, is accommodated.  
         [0056]     A membrane force transducer  38  is accommodated in the interior space  18  and this has a membrane  40  which is in the shape of a circular disc and bears at its circumferential edge an annular collar  42  which projects beyond both surfaces of the membrane  40 . The annular collar  42  is, in cross section, of an essentially rectangular design and engages without clearance in the groove  26  in the end side  22  of the cover part  14 .  
         [0057]     The membrane  40  is preferably designed in one piece with the annular collar  42  or, however, the annular collar  42  is welded to the membrane  40  at its outer circumference. In the engaged state of the annular collar  42  in the groove  26 , a gap remains between the membrane surface and the end wall  22  and this allows an elastic deformation of the membrane when acted upon with a tensile or pressure force.  
         [0058]     A force introduction member  44  is arranged in the center of the membrane  40  and this has essentially the shape of a bolt. One end of the force introduction member passes through the opening  20  and is provided with a screw thread  46  whereas the other, free end of the force introduction member  44  is accommodated by the blind-end bore  30 . The opening  20  as well as the blind-end bore  30  form a guide for the force introduction member  44  which supports the force introduction member against any tilting moments.  
         [0059]     In the area where it penetrates the membrane  40 , the force introduction member bears a circumferential annular flange  48 , via which the force introduction member  44  is connected to the membrane  40 . The force introduction member  44  may, in principle, be designed in one piece with the membrane  40  and the annular collar  42  or, however, be produced as a separate part and inserted into a passage in the membrane  40  and then welded to it.  
         [0060]     The annular flange  48  interacts with the recesses  24  and  32  as a mechanical overload protection, i.e., the elastic deformation of the membrane  40  is limited by the displaceability of the force introduction member  44  in the direction of the axis of symmetry of the opening  20  as well as the blind-end bore  30  and limits the action of tensile or pressure forces and, therefore, the deformation of the membrane due to abutment of the annular flange  48  on the recess  24  or the recess  32 .  
         [0061]     A transverse bore  50 , which makes a receiving means available for an additional element of the sensor arrangement of the load cell  10 , is provided in the end of the force introduction member  44  engaging in the blind-end bore  30 .  
         [0062]     In order, as far as possible, for the determination of the weight force acting on the load cell not to be influenced, it may be provided for the opening  20  and, where applicable, also the wall of the blind-end bore  30  to be covered with a material, for example, in the form of a sleeve  52  (cf. dash-dot illustration at opening  20 ) which has as low a sliding friction as possible.  
         [0063]     The sensor arrangement of the load cell  10  according to the invention consists essentially of a Hall sensor element  54  and a permanent magnet  56 . The permanent magnet  56  is fixed in the transverse bore  50  of the force introduction member  44  and moves together with the force introduction member  44  along its longitudinal direction away from the base part  16  or towards it during the action of tensile and pressure forces, respectively.  
         [0064]     The receiving means  36  provided in the base part  16  accommodates the Hall sensor element  54  which is connected via signal and energy supply lines  58  via a bore  51  in the base part  16  as well as a passage in a side wall of the cover part  14  which is aligned thereto.  
         [0065]     When selecting the sensor arrangement, as mentioned above, the cover part  14  as well as the base part  16  will preferably be formed from ferromagnetic steel so that an electromagnetic screen for the Hall sensor arrangement results.  
         [0066]     The force introduction member  44  is produced from a non-magnetic material, in particular, non-magnetic steel in order to avoid any magnetic short circuit. The material, from which the membrane  40  as well as the annular member  42  are formed, may be selected from different materials, for example, aluminum.  
         [0067]     Aluminum is also suitable for producing the force introduction member  44 . The membrane  40  as well as the annular member  42  may, however, also be produced from steel.  
         [0068]     If other sensor arrangements are used, for example, an optical sensor arrangement as described at the outset, comparable assembly conditions to those shown in  FIG. 1  can be selected. In this case, greater freedoms result in the selection of the materials, from which the individual components of the load cell are formed, since optical sensor arrangements cannot be influenced as such by electromagnetic radiations occurring in the surrounding environment. However, it is often advantageous to design evaluation electronics together with a sensor element, whether this be a Hall sensor element or an optical detection element, and to arrange them in the interior of the load cell such that signals already processed can be transferred to the outside via the connection lines  58 . In such a case, it is also preferable in the case of an optical sensor arrangement to use an electromagnetic, screening material for the production of the cover part  14  and the base part  16  in order to ensure a reliable functioning of the sensor arrangement electronics even in the case of rough, electromagnetic surroundings.  
         [0069]     The characteristics of a sensor arrangement with Hall sensor and permanent magnet are not exactly linear but a linearization of the sensor signal need not occur when a precision of 1 % is adequate.  
         [0070]     A particularly high temperature stability may be achieved with this sensor arrangement as a result of the fact that two Hall sensor elements are arranged opposite a monopole on the part of the permanent magnet and the signal is received as a differential signal. Alternatively thereto, the arrangement of a dipole opposite a Hall sensor element could be considered.  
         [0071]     At the same time, it is possible with the differential measurement for a maximum effective signal to be obtained via the amplifier arrangement and for this to be obtainable essentially unloaded from a zero point level.  
         [0072]     The Hall sensor may often be integrated with an analog-to-digital converter on a chip so that digitalized signals are obtained from the load cell and these signals are not susceptible to interference even in rough electromagnetic surroundings.  
         [0073]      FIG. 2  shows a second embodiment of a load cell  60  according to the invention with a housing  62  which is formed by a cover part  64  and a base part  66 . In the interior of the housing  62 , a disc-shaped interior space  68  is created between the cover part  64  and the base part  66  and a membrane force transducer  70  is accommodated in this space.  
         [0074]     The force transducer  70  is essentially of the same construction as the force transducer  44  of  FIG. 1  and has a force introduction member  74  in its center next to a membrane  72  as well as an annular collar  76  projecting beyond a surface of the membrane  72  at the circumferential edge. In the assembled state, the annular collar  76  engages without clearance in an annular groove  78  formed complementarily in the cover part  64  and is held in this position by the base part  66 . For this purpose, the base part  66 , in contrast to the base part  16  of  FIG. 1 , has at its external circumference a projection  80  which extends all the way around and abuts against the annular collar  76 . The inwardly located surface of the base part  66  is at a distance in relation to the membrane  72 .  
         [0075]     In the central area of the internal space  68 , recesses are again provided in the respective inner surfaces of the cover part  64  and the base part  66  and these offer, with a corresponding annular flange on the part of the force introduction member  74 , a mechanical overload protection against tensile and pressure forces which are too large.  
         [0076]     In contrast to the force introduction member  44 , the force introduction member  74  does not protrude beyond the outer surface of the cover part  64  but ends approximately level with the outer surface. In order to be able to connect the force introduction member  74  to the surroundings, in order to be able to determine tensile and/or pressure forces with the load cell  60  in a reliable manner, the force introduction member  74  has a blind-end bore  82  with an internal thread at its free end pointing towards the outer surface of the cover part. On the opposite side, the base part  66  has a screw bolt  84  which extends away from the outer surface of the base part  66  in axial direction of the force introduction member. A blind-end bore could, of course, also be machined into the base part  66  instead of the screw bolt  84  and this would then preferably have an internal thread.  
         [0077]     The arrangement and the construction of the sensor arrangement in  FIG. 2  is similar to that in  FIG. 1  and will not be discussed here in greater detail for this reason. In comparison with  FIG. 1 , the connection of the sensor arrangement to the surroundings is, however, accomplished differently. In this case, a socket connector  86  is provided in the base part  66 , at which signal and supply lines  88  of the sensor arrangement end, so that the load cell  60  can be connected, for example, to an associated electronic evaluation circuit or be disconnected from it in a simple manner.  
         [0078]      FIG. 3  shows an additional, alternative embodiment of a load cell  90  with a housing  92  with a cover part  94  and a base part  96  which are, again, designed in a similar way to the corresponding parts in  FIG. 1 .  
         [0079]     Cover part  94  and base part  96  define between them an interior space  98  which serves to accommodate a membrane force transducer  100 . The force transducer  100  consists of a membrane  102  which bears a circumferential annular collar  104  at its outer circumference and has a force introduction member  106  in the form of a bolt passing through it centrally. The design of the force introduction member  106  is comparable to that shown in  FIG. 1  and described and so further details will not be given here. In order to bring about an additional sealing of the housing  92 , the force introduction member with its screw bolt section projecting outwards is surrounded by a rubber sleeve  108 . As a result, the interior space  98  may be shielded from the surroundings more or less dust-tight.  
         [0080]     In the inserted state, the annular collar  104  engages in an annular groove  110  in the inner surface of the cover part  94  and is held in this position by the base part  96 . The base part  96  differs in its design from the base part  16  of  FIG. 1  in that no annular groove or no annular recess is provided in this case at the outer circumference but rather the surface of the base part  96  is of a flat design in this area. In order to have the inwardly pointing surface of the base part  96  spaced from the surface of the membrane  102 , a spacer ring  112  is inserted between the membrane force transducer  100  and the base part  96  in the area of the annular collar  104 .  
         [0081]     The side walls of the cover part  94  are dimensioned such that they project somewhat beyond the outwardly located surface of the base part  96  in the assembled state of the load cell  90  so that the base part  96  can be fixed in the cover part  94  by wedging it in. This is the simplest and, at the same time, reliable fixing of the base part  96  in the cover part  94  and, at the same time, this type of connection may be brought about in a manner which is just as sealed as, for example, the use of a screw thread or the like. Finally, the welding of base part and cover part also offers a suitable alternative.  
         [0082]     The sensor arrangement shown in  FIG. 3  is comparable, first of all, with that shown in  FIG. 1  and has a Hall sensor element  114  as well as a permanent magnet  116 . In this case, however, in contrast to  FIG. 1 , an additional Hall sensor  118  is used which is located opposite the Hall sensor  114 . As a result of such an arrangement of a first and an additional Hall sensor  114 ,  118 , the zero point error of the sensor arrangement may be eliminated in a first approximation.  
         [0083]     Finally,  FIG. 4  shows a variation of the embodiment of  FIG. 1  with respect to the design of the base part as well as the design of the screw connections on the part of the force introduction member and the base part. The fourth embodiment of a load cell  120  according to the invention, as illustrated in this case, has a housing  122  with a cover part  124  and a base part  126 . Cover part  124  and base part  126  define between them an interior space  128 , in which a membrane force transducer  130  is accommodated. The force transducer  130  consists of a membrane  132 , an annular collar  134  projecting beyond both membrane surfaces as well as a force introduction member  136 . The cover part  124  as well as the base part  126  have on their inwardly located surfaces respective recesses which extend all the way around, receive the annular collar projecting beyond both surfaces of the membrane  132  between them and clamp it free from clearance.  
         [0084]     In contrast to the design of the cover part  14  of  FIG. 1 , the side walls of the cover part  124  do not extend over the entire height of the load cell  120  while the base part  126  has at its lower end an annular flange  138  which protrudes all the way around and is aligned radially flush with the side walls of the cover part  124 . The sensor arrangement of the embodiment of  FIG. 4  will not be described in greater detail and it is merely emphasized that in this embodiment a continuous channel leads in radial direction from a recess for accommodating the Hall sensor as far as the outer circumference of the load cell  120  and ends in a socket connector for accommodating these signal lines.  
         [0085]     In this case, a screw connection provides a problem-free solution for connecting cover part and base part since the orientation between base part and cover part in the tightened state is irrelevant with a view to the cable guidance used in this case. Alternatively, a weld connection is also suitable.  
         [0086]     In order to connect the load cell  120  to the surroundings, the base part  126  has a blind-end bore  140  with an internal thread in the center and a blind-end bore  142  with an internal thread is likewise provided coaxially hereto in the force introduction member  136 .  
         [0087]     It is understood from the preceding description that the variations in the design of the membrane force transducer specified in FIGS.  1  to  4 , in particular, with respect to the annular collar as well as the design of the inner surfaces of the cover part or the base part corresponding hereto can be interchanged in the individual embodiments. The solutions which have been shown in order to provide screw connections to the load cells are likewise interchangeable. Finally, other types of connection are known to the person skilled in the art, such as, for example, welding or gluing, wedge connections etc., with which the base part and/or the force introduction member can be connected to the measurement environment. It is likewise clear that the special embodiment of the sensor arrangement of  FIG. 3  can also be transferred to the embodiments of the other Figures.  
         [0088]     In a further embodiment in accordance with the invention, the projecting edge of the membrane force transducer is fixed via the housing in force-locking manner. A recessed area is formed in the interior space of the housing. The projecting edge of the membrane force transducer is positioned in the recessed area and acted upon by at least one carrier. The carrier is supported by the housing and exerts a clamping force on the projecting edge to fix the projecting edge in the recessed area in a press-fit manner or force-locking manner.  
         [0089]     A corresponding embodiment is shown and described in the German application No. 10 2005 010 982.9 of Mar. 3, 2005, which is incorporated by reference.  
         [0090]     This listing of claims replaces all prior versions, and listings, of claims in the application.