Abstract:
The invention relates to a locator, in particular a handheld locator for detecting inclusions in walls, ceilings and/or floors, having a capacitive sensor device disposed in a housing, having means for generating a detection sensor of the at least one capacitive sensor device, having a control and evaluation unit, communicating with the sensor device, for ascertaining measurement values from the detection sensor, and having an output unit for reproducing measurement values of the capacitive sensor device. 
     According to the invention, it is proposed that a measuring capacitor ( 16 ) of the capacitive sensor device ( 10 ) has a first electrode ( 21 ), which includes one face of the housing ( 14 ) of the sensor device ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a locator, in particular a handheld locator, for detecting inclusions in walls, ceilings and/or floors with the aid of a capacitive sensor device that makes it possible to detect differences in impedance of a measurement signal and draw conclusions about the hidden objects that generate the differences in impedance. 
     For locating inclusions in wall material, essentially two different measuring methods are used at present. The inductive methods, which are the basis for a first family of locators, utilize the fact that introducing metal objects into magnetic alternating fields affects the course of the magnetic field lines. This influence of the metal objects is expressed for instance in the amount of the impedance of a coil that generates a magnetic alternating field of this kind. Inductive methods are especially well suited for detecting ferromagnetic materials. However, the search for nonmagnetic materials, such as copper or plastic, presents difficulties. Plastic lines, especially, which are increasingly used in the field of installation work, cannot in principle be found by this method. 
     The three-dimensional sensitivity of a sensor that functions inductively is directly associated with the three-dimensional distribution of the magnetic fields generated by the measuring coils. It is decisive in designing a sensor to take a directional characteristic into account. When the locator is placed on an object to be investigated, such as wall material, the sensor should as much as possible detect only hidden objects inside the wall, and thus the locator should respond only to objects that are located in front of the transmitter. Objects behind and next to the sensor must not alter the outcome of measurement. 
     In sensors that function inductively, this problem is typically solved by using ferrite bodies onto which the coils of the sensor of the locator are wound. These ferrite bodies have the property of focusing the electromagnetic field generated by the coils and thus of guiding it in a certain way. Focusing the field can be expressed for instance in the course of the field lines and can also be detected. The parameter that is decisive for focusing the field lines and thus for generating the directional characteristic of such a sensor is the amount of magnetic susceptibility of the core material (ferrite body). With ferromagnetic materials, magnetic susceptibility values on the order of magnitude of 100 are technically not a problem and can be attained economically. If a suitable core geometry is selected, the desired directional characteristic can therefore be attained by simple means and at low cost, for inductive locating methods. 
     A second class of location sensors or locators utilizes capacitive methods for detecting enclosed objects. Such capacitive methods are currently used in the building trade to search for instance for substructures, studs, and comparable wall inclusions in lightweight buildings. The key element of a capacitive sensor or locator of this kind is a capacitor element. The measurement principle fundamental to this method is based on the variation in the impedance of the measuring capacitor by the dielectric medium surrounding it. The presence of an object with a deviant dielectric constant in the surroundings of the measurement sensor results in a variation in the capacitance of the sensor element and thus in an electrically measurable effect. 
     Unlike inductive locators, in capacitive sensors it is markedly more difficult to achieve a directional characteristic. Although here as well, analogous to the methods in inductive sensors described above, it is conceivable in principle to use materials that focus the electrical field, nevertheless at feasible costs for such a detection system to be used commercially, it is realistically possible to use only such materials as have low values of the dielectric constant ∈ and thus a low capability of focusing the electrical field, or of focusing the electric field lines described by the electrical field. Typical values of the dielectric constant E for usable materials are on the order of magnitude of 5, so that an adequate directional characteristic requires the use of more-complicated and thus more-cost-intensive focusing mechanisms and shielding geometries. 
     From U.S. Pat. No. 5,726,581, a capacitive proximity sensor is known, in which the current through a sensor element is increased by the presence of an object, so that this increase in current can be detected from the altered voltage drop at a resistor. To generate a certain directional characteristic for the measurement field, an additional shielding electrode is applied to the side of the sensor electrode remote from the object. Both electrodes are connected to a common ground potential. 
     The change in capacitance of the sensor electrode that is due to the object is maximized by providing that the capacitance between the sensor element and ground is minimized. This is attained by providing that the electrical field lines originating at the measuring electrode are deformed, over a wide three-dimensional range, by the larger shielding electrode in such a way that a direct connection with the ground potential is not possible. In this way, a certain directional effect of the electrical field of the measuring electrode is also generated. 
     A further problem in constructing capacitive sensors is undesired crosstalk between the conductor faces of the measuring capacitor on one side and the electronic components of the evaluation circuit on the other. If even small objects are to be detected, even the slightest signals must be filtered out of the background noise in the measurement signal. Crosstalk of the electrical fields of the measurement signal, for instance to the electronic components of the evaluation device of a locator of this kind, can alter the measurement outcomes and thus can make precision measurements impossible. For this reason, these two component parts, that is, the actual capacitive sensor element and the electronic evaluation circuits of the capacitive locator, are often disposed spatially separately from one another and are connected to one another by cables. 
     It is the object of the invention to disclose a capacitive locator of the type defined at the outset that has a compact structure, low cost, and easy technical feasibility along with adequate directional precision. It is also the object of the invention, in a locator of the type described at the outset, to realize parasitic crosstalk phenomena between the capacitive sensor device and electronic components for generating and evaluating the measurement signal of such a device, by means that are as simple as possible from a production standpoint yet are mechanically stable. 
     SUMMARY OF THE INVENTION 
     The locator of the invention for detecting inclusions in walls, ceilings and/or floors uses a capacitive sensor in the form of a capacitor, whose first electrode includes a housing face of the sensor device. Because of the design according to the invention of the capacitive sensor, it is possible to realize a directional characteristic for the sensor without having to integrate complicated additional components into the housing of the sensor device for the sake of shielding the electrical field of the capacitor. 
     According to the invention, the capacitive sensor device has a housing which on the one hand is intended to provide the mechanical protection of the sensor device but on the other is simultaneously intended to be part of a first electrode of a capacitor of the capacitive sensor device. With the aid of this housing, a defined directional characteristic of the capacitive sensor device of the locator can then be made possible in a simple, advantageous way. 
     The actual sensor device with its housing can then be integrated with a locator housing that is permeable to the electrical field of the sensor, which has various operator control elements and also has an output device for measurement values, for instance in the form of a display. 
     By means of the characteristics recited in the other claims, advantageous refinements of an improvements to the locator defined by claim  1  are possible. 
     In one advantageous feature of the locator of the invention, the second electrode of the measuring capacitor of the sensor device is mechanically connected to a printed circuit board of the sensor device. The printed circuit board itself is in turn connected to the housing of the sensor device. In this way, a mechanically stable construction for the measuring capacitor and simultaneous electrical separation of the two capacitor electrodes can be achieved, since by definition the electronic components for generating a detection sensor already have a printed circuit board or the like. 
     Advantageously, the printed circuit board can be joined mechanically to a housing face, such as a shoulder of the housing of the sensor device, by being screwed or riveted, welded, or soldered to the housing. Other joining techniques known to one skilled in the art are also possible. 
     Advantageously, the electronic components, for instance for generating a detection sensor for the capacitive sensor device, can also be mounted on this printed circuit board. It is especially advantageous for these electronic components to be mounted on the second side of the printed circuit board, that is, the side remote from the second electrode of the measuring capacitor. In this way, shielding of the electronic components for generating and evaluating the detection sensor from the electrical field of the second electrode of the measuring capacitor is possible by simple means. 
     To improve the shielding, the printed circuit board can be provided with a metal layer. It is especially advantageous if such a printed circuit board together with the housing of the capacitive sensor device forms an enclosed chamber, in which the electronic components are disposed. 
     The electrically conductive layer in or on the printed circuit board, together with a housing face of the sensor device of the locator, thus creates a Faraday cage, so that the chamber in which the electronic components are disposed are effectively shielded against electromagnetic radiation. This is especially necessary for precision measurements with the locator of the invention, since they require good shielding of the electronic components that are required for generating and evaluating the measurement signal. 
     Because of the design according to the invention of the housing faces of the sensor device, in conjunction with an advantageous disposition of the printed circuit board that carries both the electronic components and an electrode of the measuring capacitor, the problem of undesired crosstalk of electrical signals can thus be solved without additional effort or expense, or in other words without additional components, and so the proposed locator can be attained with a very compact design and can be used in versatile ways in the form of a lightweight handheld locator. 
     The housing of the sensor device of the locator of the invention is advantageously designed such that it three-dimensionally embraces the second electrode of the measuring capacitor in such a way that the field applied between the capacitor electrodes is given a pronounced directional characteristic. 
     To that end, the housing of the sensor device is for instance shaped from a metal, or is drawn from a metallized plastic. An electrically conductive coating of the housing of the sensor device can also be advantageously used for orienting the electrical field of the measuring capacitor. 
     Since the housing according to the invention of the sensor device serves not only to provide mechanical stability and electromagnetic shielding of the electronic components of the sensor device but simultaneously also forms one electrode of the sensor capacitor, it is possible for the housing according to the invention to be shaped in such a way that the electrical field created between the electrodes of the sensor capacitor is given a directional characteristic. This can advantageously be realized for instance by providing that the housing of the sensor device is open on one side and laterally embraces the second electrode of the capacitor. 
     The first electrode of the measuring capacitor of the capacitive sensor device can advantageously also be realized in such a way that this electrode is formed by one face of the housing of the capacitive sensor device and by an electrically conductive surface of the printed circuit board. This makes a further advantageous shaping of the electrical field of the measuring capacitor possible. 
     In particular, in this way, by simple mechanical means, a directional characteristic of the capacitive sensor can be realized that causes a strong measurement signal to penetrate the medium to be investigated underneath the sensor. The development of stray fields in directions that are not in the preferential direction of this directional characteristic can be effectively suppressed in this way, so that an intensive measurement signal without major stray fields can be used. 
     The capacitive sensor device with its housing open on one side is built into a housing of the locator that is transparent to the electrical measuring field of the sensor, so that the electrical measuring field can penetrate the measurement object to be investigated (wall, floor, or the like). 
     The housing of the locator therefore comprises a plastic, for instance, that also covers the opening of the housing of the sensor device, so that the sensor device is mechanically protected. The housing of the locator also receives the other operator control elements and also for instance a display for reproducing the outcomes of measurement. The housing of the locator is advantageous constructed in such a way that a compact, relatively lightweight and thus handheld measuring instrument is obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawing, one exemplary embodiment of a capacitive sensor device of a locator of the invention is shown, which will be explained in further detail in the ensuing description. The drawing figures, their description, and the claims directed to the locator of the invention include numerous characteristics in combination. One skilled in the art will also consider these characteristics individually and put them together to make other appropriate combinations. 
       Shown are: 
         FIG. 1 , a perspective view of the housing of the sensor device of the locator of the invention; 
         FIG. 2 , a section through the housing of the sensor device of the invention, shown schematically; 
         FIG. 3 , a view of the housing of the locator of the invention, shown schematically as in  FIG. 2 , in which a distribution of the electrical field lines of the sensor capacitor are drawn schematically, to illustrate a directional characteristic. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows the fundamental construction of the sensor device  10  of the locator  12  of the invention. The sensor device  10  has a housing  14  with a conductive surface. The housing  14  can be made for instance from a metal in the form of a one-piece die-cast part, or of metallized plastic by means of a shaping. Metallically conductive coatings are also possible for the housing  14  of the sensor device. 
     The housing  14  is open on one side, in the direction of an object to be measured, and includes essential components of the sensor device  10  and is itself an integral component part of this sensor device  10 . The sensor device  10  has essentially two groups of components. One group of components is electrical circuits for processing the measurement signals. The second component group of the sensor device includes the actual capacitive sensor, which in the locator of the invention is realized by means of an especially designed measuring capacitor  16 . 
     The two different component groups mentioned are disposed in two partial chambers  20  and  22  of the housing  14  that are separated from one another. The partial chambers  20  and  22  are separated from one another by a printed circuit board  18 , forming a first, open partial chamber  20  and a second, closed partial chamber  22 . The printed circuit board  18  is fixed in the housing  14  at its edges to the housing  14 . To that end, in the exemplary embodiment of  FIGS. 1-3 , the housing has a characteristic shoulder  42 , upon which the printed circuit board is placed and screwed to the housing. The housing  14  is shaped in such a way, and installed in a housing, not further shown, of the locator, in such a way that the two chambers  20  and  22  are disposed one above the other. 
     The electronic components for generating and evaluating the measurement signal are disposed in the second, closed partial chamber  22  of the housing  14  of the sensor device  10 . The second partial chamber  22  is formed by a bulge  28  in the housing  14  and by the printed circuit board  18  that is solidly joined to the housing. A metal layer  30  is advantageously integrated on or in the printed circuit board  18 , so that the partial chamber  22  of the housing  14  is enclosed by an electrically conductive surface. In this way, the partial chamber  22  forms a Faraday cage ( 23 ), which makes it possible for the electronic components disposed in the partial chamber  22  to be insulated against electromagnetic interference. 
     As can be seen from  FIG. 2 , the printed circuit board  18 , on one side, has electric circuits  48  for generating and evaluating the measurement signal, and an electrode  24  of the measuring capacitor  16  is secured to the other side. The printed circuit board  18  in turn is fixed to the housing  14 , for instance by means of screws  26 . Assembling the sensor device  10  of the locator  12  of the invention therefore requires merely introducing the printed circuit board  18 , on which the electric circuits and an electrode  24  of the measuring capacitor  16  have already been applied in a preassembly process, into the housing  14 . This advantageously leads to a simplification in terms of production technology, as well as economy of material, since the electric circuits and the capacitor arrangement are placed in a common housing. Separate housing arrangements for the electric circuits and for the measuring capacitor are unnecessary, in the locator of the invention. 
     The first partial chamber  20  of the housing  14  of the sensor device  10  is essentially formed by the surface  32  of the printed circuit board  18  and by side walls  34  of the housing  14 . Recesses  36  are integrated into the side walls  34  and make it possible to anchor the housing  14  and thus also the sensor device  10  in the housing of the locator. 
     The first partial chamber  20  of the housing  14  is open on one side by means of an opening  54  and essentially holds the measuring capacitor  16  of the sensor device  10  of the locator  12  of the invention. The measuring capacitor  16  is formed by the inside face  38  of the partial chamber  20  of the housing  14 , which face forms a first electrode  21  of the measuring capacitor, and by the second electrode  24  secured to the printed circuit board  18 . In this way, it is possible to realize the measuring capacitor  16  by means of merely one additional electrode  24 . The first electrode  21  of the measuring capacitor  16  is advantageously realized by the housing  14  itself. Also for this reason, the housing  14  has a conductive surface  40 , which is realized for instance by providing that the housing  14  of the sensor device  10  is shaped in one piece from a metal part. 
       FIG. 2  schematically shows a cross section through the sensor device  10  of the locator of the Invention. The housing  14  has a pronounced shoulder  42 , on which the printed circuit board  18  is secured. A metallized layer  30  is integrated with the printed circuit board  18  and is in conductive contact with the electrically conductive surface  46  of the housing  14  of the sensor device  10 . The electrical connection between the metallized layer  44  of the printed circuit board  18  and the housing  14  can be created for instance by means of the screws  26  for mechanically fixing the printed circuit board to the housing. 
     On the side of the printed circuit board  18  remote from the electrode  24 , various electronic components  48  are disposed, which serve to generate signals and in the present exemplary embodiment of  FIG. 2  also serve to evaluate the measurement signal. The partial chamber  22 , which is formed by the bulge  28  in the housing  14  and by the printed circuit board  18 , is surrounded in a closed way by an electrically conductive surface, so that this partial chamber  22  forms a Faraday cage  23 , which makes it possible for the electronic components  48  disposed in the partial chamber  22  to be shielded against electromagnetic radiation. 
     On the side of the printed circuit board  18  remote from the partial chamber  22 , the second electrode  24  of the measuring capacitor  16  is mechanically connected to the printed circuit board  18 . The first electrode  21  of the measuring capacitor  16  of the sensor device  10  of the locator is formed, in this exemplary embodiment, by the conductive surface  46  of the interior of the first partial chamber  20  of the housing  14 . The first partial chamber  20  can, as shown in the exemplary embodiment of  FIG. 2 , be closed by a wall  50 , as long as this wall presents no hindrance to the electrical field of the measuring capacitor  16 . 
     For this reason, the wall  50  can be embodied for instance by one side of a plastic housing of the locator of the invention. In that case, the locator of the invention would be passed with the housing wall  50  over the structure to be surveyed, such as a ceiling or a floor. The wall  50  serves to mechanically protect the electrode  24  of the measuring capacitor  16  and also any components  48  that may be disposed in the partial chamber  20  of the sensor device  10 . 
     In a simple way, the electrode  24  of the measuring capacitor  16  can be shaped for instance as a stamped and bent part. The electrode  24  advantageously has one face  25  disposed parallel to the printed circuit board  18 . The housing  14  can be in one piece as a die-cast metal part, or can be drawn from a metallized plastic. 
       FIG. 3  shows a cross section through the sensor device  10  of the locator  12  of the invention, in which the course of the field lines of the measuring capacitor upon operation of the locator are drawn in for the sake of illustration. The electrodes of the measuring capacitor are formed on the one hand by the electrode  24 , which is secured to the printed circuit board  18 , and on the other by the conductive inner surface  46  of the housing  14  in the region of the partial chamber  20 . 
     By means of the embodiment of the housing  14  according to the invention, a desired directional characteristic of the electrical field  52  of the measuring capacitor can be achieved. This is achieved for instance by providing that the side walls  34  of the housing  14  of the sensor device  10  laterally embrace the printed circuit board  18 , and thus the electrode  24  mounted thereon. Thus by the shape of the partial chamber  20 , the directional characteristic of the electrical fields  52 , which serves to detect the objects enclosed for instance in a wall, can be oriented in a desired way. The shape of the housing  14  is indicated only schematically in  FIGS. 1 ,  2  and  3 , so that the fundamental principle is clearly shown. Advantageously, still other housing shapes for the sensor device  10  with which the electrical field of a measuring capacitor  16  of such a sensor device can be optimized can be achieved. 
     For instance, as indicated in  FIG. 3 , the first capacitor electrode can also be formed by the conductive surface  46  of the interior of the first partial chamber  20  and by a conductive layer on the surface of the printed circuit board  18 . 
     The electrical field  52  emerges in oriented form from the housing  14  of the sensor device  10 , and thus also from the housing of the locator, and penetrates a wall, for instance, that is to be surveyed, when the locator is placed with its housing wall  50  against the wall. 
     The sensor device  10  described in  FIGS. 1-3  is integrated with a housing, not otherwise shown, of the locator. This housing of the locator has not only the sensor device  10  but at least also a display element, such as a display, on which location information about an object detected with the locator in a wall, ceiling or floor can be shown. On such a display, for instance, the precise location of an enclosed object can be displayed relative to the position of the locator. The display unit will not be described further here, because it is not the subject of the invention. The housing of the locator of the invention furthermore has switching means, for initiating appropriate measurement operations using the device. 
     It is equally possible for an interface to be integrated with the housing of the locator, for transmitting measurement data to a further device, such as a computer, or a second graphic display. 
     The locator of the invention is not limited to the embodiment shown in  FIGS. 1-3 . 
     In particular, the locator of the invention is not limited to the housing shape shown in the drawings. Advantageous refinements of the shape of the housing  14  of the sensor device  10  of the locator are possible. 
     The locator of the invention, with its sensor device  10 , is not limited to finding dielectric inclusions in wall materials, such as metal objects or plastic lines, but instead can also be used in all other applications in which a directional survey of the dielectric constant of a medium is desired. In this connection, reference may be made for instance to measuring the moisture content of walls. 
     The locator of the invention is not limited to detecting inclusions in walls, ceilings and/or floors, but instead can be used generally for detecting and demonstrating enclosed objects that are not visible to the human eye.