Patent Publication Number: US-2021164766-A1

Title: Electronic appliance with inductive sensor

Description:
FIELD OF THE INVENTION 
     The invention relates to an electronic device having a housing and an actuating element movable relative to the housing. 
     STATE OF THE ART 
     Such devices are well known and can be provided, for example, in the form of hand-held measuring devices in which the actuating element can be actuated, in particular moved, by a user of the device. The actuating elements of known devices often act directly on an electric circuit or form a part of a circuit, respectively, which results in a complex structure and a susceptibility to soiling. Therefore, good electric contacting of electric contact elements which can be actuated by the actuating element is often not ensured over a long period of time. 
     DE 41 37 485 A1 describes a switching device having an inductive proximity switch. DE 296 20 044 U1 describes a layer thickness measuring device. DE 33 18 900 A1 describes a proximity switch. 
     DISCLOSURE OF THE INVENTION 
     Preferred exemplary embodiments relate to an electronic device according to claim  1 . 
     An electronic device is proposed, comprising a housing and an actuating element movable relative to the housing, wherein the actuating element comprises at least one metallic component, wherein the device comprises an inductive sensor for detecting a position and/or movement of the actuating element, wherein the inductive sensor comprises: a first measuring resonant circuit comprising a sensor coil, in which a first measuring oscillation can be generated, and an oscillation generator configured to generate an excitation oscillation and to at least temporarily apply the excitation oscillation to the first measuring resonant circuit, wherein the device comprises an evaluation device configured to determine, dependent on the first measuring oscillation, movement information characterizing the position and/or movement of the actuating element. 
     The device comprises at least one functional component, wherein the device is configured to control an operating state and/or a change of an operating state of the at least one functional component depending on the movement information. 
     The provision of an inductive sensor according to the invention advantageously allows a reliable operation of the device, wherein at the same time a particularly low electric energy consumption is required for its operation due to the construction of the inductive sensor according to the invention. By means of the measuring oscillation, an interaction of the metallic component of the actuating element with the sensor coil can be detected, and from this, a position and/or movement of the actuating element can be determined by the evaluation device. The excitation oscillation can advantageously be generated in a very energy-efficient manner and does not require any electric energy supply during a decay. 
     The measuring oscillation can be generated by applying the excitation oscillation, in the case of particularly advantageous embodiments in particular by resonance with the excitation oscillation, and therefore does not require a separate energy supply. 
     According to studies carried out by the applicant, this allows a current consumption for the inductive sensor of approximately 200 nA (nanoamperes) at an operating voltage of approximately 3 V (volts). 
     With preferred embodiments, the measuring oscillation has a swelling and subsequently decaying signal course, which can be evaluated very easily by the evaluation device, for example, always between the swelling and the decay, in particular when a signal maximum of the envelope of the measuring oscillation appears. The swelling signal course results, for example, from the fact that energy provided in the form of the excitation oscillation is transferred to the first measuring resonant circuit, whereby the latter can be excited to the swelling oscillation, and the decaying signal course results, for example, from the fact that the excitation oscillation itself decays, whereby—in contrast to the swelling oscillation—less energy per time or no energy at all, respectively, is transferred to the first measuring resonant circuit, and the latter therefore also dies away. 
     In general, an oscillation of the first measuring resonant circuit can be characterized, for example, by a time-varying electric voltage appearing at the sensor coil and/or by a time-varying electric current flowing through the sensor coil. In some embodiments, the evaluation device can, for example, evaluate said electric voltage and/or said electric current in order to determine movement information characterizing a position and/or movement of the actuating element. 
     Furthermore, a particular advantage of the present embodiments, which involve a swelling and then decaying oscillation in the measuring resonant circuit, is that a signal maximum (e.g. maximum voltage) of the swelling and then decaying oscillation in comparison to a merely decaying oscillation, for example, is much more strongly depending on an interaction of the sensor coil with the actuating element or its at least one metallic component, which results in a greater sensitivity of the proposed measuring principle than with conventional inductive methods, and which enables a more precise detection of the position and/or movement of the actuating element which is more independent of disturbances. 
     In some embodiments, the actuating element itself may, for example, be electrically non-conductive, but may have at least one metallic or electrically conductive component whose electrically conductive material may interact with the measuring oscillation of the first sensor coil and may thus be evaluated. In other embodiments, the actuating element itself can also be made at least partially or regionally electrically conductive, and may also have an additional electrically conductive component. 
     With preferred embodiments, an interaction of the actuating element (or its metallic or electrically conductive component, respectively) with the sensor coil, which can be evaluated by the evaluation device, is such that an alternating magnetic field in the region of the sensor coil caused by the measuring oscillation induces eddy currents in the actuating element or its metallic or electrically conductive component. This can, for example, cause an attenuation of the first measuring oscillation. Depending on the arrangement of the actuating element in relation to the sensor coil, this interaction can be stronger or weaker, which can be evaluated. In particular, both a position of the actuating element and movements of the actuating element can be detected. 
     With other embodiments, it is conceivable that an approach of the actuating element or its metallic component to the sensor coil or a withdrawal of the same from the sensor coil, respectively, affects the resonant frequency of the first measuring resonant circuit, so that instead of the above-mentioned attenuation, also an amplification of the first measuring oscillation may result when the actuating element approaches the first sensor coil. 
     In other embodiments, the oscillation generator is configured to generate a plurality of temporally consecutive excitation oscillations and to apply the plurality of excitation oscillations to the first measuring resonant circuit, resulting in particular in a plurality of measuring oscillations corresponding to the number of the plurality of temporally consecutive excitation oscillations. 
     With other embodiments, it may also be intended to apply a single excitation oscillation to the first measuring resonant circuit, resulting in a single measuring oscillation. 
     According to studies carried out by the applicant, the evaluation of a single measuring oscillation may be sufficient to determine movement information with sufficient accuracy for some applications. In contrast, in other embodiments, if a plurality of excitation oscillations and a plurality of measuring oscillations are applied, a comparable evaluation can be carried out repeatedly, for example, which in some cases increases the accuracy and/or improves detectability of movements. 
     With other embodiments, the oscillation generator is configured to periodically generate the plurality of excitation oscillations with a first clock frequency and to apply the periodically generated excitation oscillations to the first measuring resonant circuit. With other embodiments, the first clock frequency is between about 0.5 Hertz and about 800 Hertz, preferably between about 2 Hertz and about 100 Hertz, and more preferably between about 5 Hertz and about 20 Hertz. 
     With other embodiments, the oscillation generator is configured to apply the excitation oscillation to the first measuring circuit such that the first measuring oscillation is a swelling and subsequently decaying oscillation. This results in a particularly sensitive evaluation, as already mentioned above. 
     With other embodiments, the first measuring resonant circuit can be brought into resonance with the excitation oscillation, in particular for generating a swelling and subsequently decaying measuring oscillation. 
     With other embodiments, the first measuring resonant circuit is a first LC oscillator with a first resonant frequency, wherein the sensor coil is an inductive element of the first LC oscillator, and wherein a capacitive element of the first LC oscillator is connected in parallel with the sensor coil. In this case, in a manner known per se, the first resonant frequency, which is the natural resonant frequency of the first LC oscillator, results from the inductance of the sensor coil and the capacitance of the capacitive element. 
     With other embodiments, the oscillation generator is configured to generate the excitation oscillation at a second frequency, wherein the second frequency is between about 60 percent and about 140 percent of the first resonant frequency of the first LC oscillator. Preferably, the second frequency is between about 80 percent and about 120 percent of the first resonant frequency of the first LC oscillator, and more preferably between about 95 percent and about 105 percent of the first resonant frequency. 
     With other embodiments, the oscillation generator has a second LC oscillator and a clock generator which is configured to apply to the second LC oscillator a first clock signal or a signal derived from the first clock signal (for example an amplified first clock signal) which has the first clock frequency and a pre-determinable duty cycle. 
     With other embodiments, the pre-determinable duty cycle is between about 100 nanoseconds and about 1000 milliseconds, in particular between about 500 nanoseconds and about 10 microseconds, and more preferably about one microsecond. 
     With other embodiments, the first measuring resonant circuit is, especially at least temporarily, inductively coupled to the oscillation generator. With other embodiments, the first measuring resonant circuit is capacitively coupled to the oscillation generator, preferably via a coupling element comprising an electric serial connection of a coupling resistor and a coupling capacitor. This allows precise adjustment of the coupling impedance. 
     With other embodiments, the evaluation device is configured to compare at least two maximum or minimum amplitude values of different oscillation periods of the (same) measuring oscillation with each other. 
     With other embodiments, the evaluation device is configured to compare a maximum or minimum amplitude value of a first measuring oscillation of the plurality of measuring oscillations with a corresponding maximum or minimum amplitude value of a second measuring oscillation of the plurality of measuring oscillations, wherein preferably the second measuring oscillation follows the first measuring oscillation, in particular directly follows the first measuring oscillation (without a further measuring oscillation occurring between the first and second measuring oscillations). 
     With other embodiments, the evaluation device is configured to compare a first amplitude value of the measuring oscillation of a first clock cycle with an amplitude value of the measuring oscillation of a second clock cycle, wherein the comparing in particular comprises forming a difference. A clock cycle can be understood as the sequence of a clock pulse and the subsequent clock pause or as a clock period, respectively. 
     For example, with some embodiments, it is possible to determine whether or not a position of the actuating element has changed between two clock cycles on the basis of an exceeding or falling below a pre-defined threshold value for the difference. Thus, for example, changes of the position can be detected. Depending on the design, with some embodiments (only) a withdrawal or (only) an approach of the actuating element or both can be detected. For example, with preferred embodiments, if the actuating element remains in one (same) position, the threshold value is not passed upwardly or downwardly. 
     With other embodiments, at least one second measuring resonant circuit is provided which has a second sensor coil and in which a secondary measuring oscillation can be generated, wherein the oscillation generator is configured to at least temporarily apply the excitation oscillation also to the second measuring resonant circuit, wherein the evaluation device is configured to determine, depending on the first measuring oscillation and the secondary measuring oscillation, the movement information which characterizes the position and/or movement of the actuating element. 
     With other embodiments, the evaluation device comprises a comparator which is configured to compare an amplitude value of the measuring oscillation with a preset value. 
     With other embodiments, a preset value generating device is provided which is configured to generate the preset value, wherein the preset value generating device is in particular configured to generate the preset value at least temporarily a) as a static value and/or at least temporarily b) depending on an amplitude value of the measuring oscillation. 
     With other embodiments, a flip-flop element is provided, a set input of which is connected or can be connected to an output of the comparator and a reset input of which can be supplied with a clock signal, in particular the first clock signal. 
     With other embodiments, a low-pass filter is provided and an output of the flip-flop element is connected to an input of the low-pass filter. 
     With other embodiments, the device is configured to carry out the following steps: periodically generating a plurality of excitation oscillations, in particular decaying excitation oscillations, by means of the oscillation generator, and applying the plurality of excitation oscillations to the first measuring resonant circuit, wherein in particular the plurality of excitation oscillations can be applied to the first measuring resonant circuit such that a) the first measuring resonant circuit is brought, preferably at least approximately, into resonance with a respective excitation oscillation and/or b) the measuring oscillation is obtained as a swelling and subsequently decaying oscillation. 
     With other embodiments, the at least one functional component is a measuring device which is configured to measure layer thicknesses, wherein the measuring device is configured in particular to measure layer thicknesses of layers of lacquer and/or paint and/or rubber and/or or plastic on steel and/or iron and/or cast iron, and/or layers of lacquer and/or paint and/or rubber and/or or plastic on non-magnetic base materials such as, for example, aluminum, and/or copper and/or brass. 
     With other embodiments, the device is configured to carry out at least one layer thickness measurement by or by means of the measuring device depending on the movement information. 
     With other embodiments, the device is configured to at least temporarily deactivate the oscillation generator, wherein in particular the device is configured to at least temporarily deactivate the oscillation generator depending on the movement information. 
     With other embodiments, the housing has a substantially circular cylindrical basic shape, wherein the actuating element has a substantially hollow cylindrical basic shape and is coaxially surrounding a first axial end region of the housing. 
     With other embodiments, the sensor coil is arranged inside the housing and at least partially in the first axial end region. 
     With other embodiments, a compression spring is provided radially between the housing and the hollow cylindrical actuating element. 
     With other embodiments, the housing is hermetically sealed, at least in the first axial end region. 
     Further embodiments are directed to the use of an electronic device according to the embodiments for measuring at least one physical quantity, in particular a layer thickness of at least one lacquer layer. 
     Further features, possible applications and advantages of the invention can be derived from the following description of exemplary embodiments of the invention, which are shown in the figures of the drawings. All described or depicted features, either individually or in any combination, form the subject-matter of the invention, irrespective of their combination in the claims or the references of the claims, and irrespective of their formulation or representation in the description or in the drawings, respectively. 
    
    
     
       In the drawings: 
         FIG. 1  shows schematically a block diagram of an electronic device according to a first embodiment, 
         FIG. 2  shows schematically a block diagram of an electronic device according to another embodiment, 
         FIG. 3  shows schematically a block diagram of an electronic device according to another embodiment, 
         FIG. 4  shows schematically a block diagram of an inductive sensor according to an embodiment, 
         FIG. 5A  shows schematically a simplified flow chart of a method according to an embodiment, 
         FIG. 5B  shows schematically a simplified flow chart of a method according to a further embodiment, 
         FIG. 6  shows schematically a circuit diagram of an inductive sensor according to an embodiment, 
         FIGS. 7A, 7B  show schematically signal courses of an excitation oscillation and a measuring oscillation for a first clock cycle and a second clock cycle of the inductive sensor of  FIG. 6 , 
         FIGS. 8A to 8F  show schematically different time responses of different signals of the inductive sensor shown in  FIG. 6  in a first operating state; 
         FIGS. 9A to 9F  show schematically each of the signal courses shown in  FIGS. 8A to 8F  in a second operating state, 
         FIG. 10  shows schematically a circuit diagram of an inductive sensor according to a further embodiment, 
         FIG. 11  shows schematically a maximum value memory according to an embodiment, 
         FIGS. 12A to 12D  show schematically signal courses of an excitation oscillation and of a differential signal in different time windows, and 
         FIG. 13  shows a simplified block diagram of an electronic device according to another embodiment. 
     
    
    
       FIG. 1  schematically shows a block diagram of an electronic device  1000  according to a first embodiment. The device  1000  comprises a housing  1002  and an actuating element  1004  which is movable relative to the housing  1002 . For example, actuator  1004  can be moved back and forth relative to housing  1002  along a longitudinal axis of the housing  1002 , as indicated by the double arrow a 1 . A first (in  FIG. 1  the right) axial end position of actuator  1004  is denoted with reference sign  1004 , and a second (in  FIG. 1  the left) axial end position is denoted with reference sign  1004 ′. Actuating element  1004  has at least one metallic component in which eddy currents can be induced, in particular when applied with an alternating magnetic field. In some embodiments, actuating element  1004  can be made entirely of metal. In other embodiments, actuating element  1004  can also have a non-metallic base body and, for example, a metallic layer, in particular a metallization of a surface of the base body. Alternatively or in addition, a metallic body can be arranged on the base body of actuating element  1004 . With other embodiments, it is also conceivable to design the actuating element non-metallic, but electrically conductive. With other preferred embodiments, actuating element  1004  is movably attached to housing  1002  in the manner described above, e.g. detachably connectable or (non-destructively) non-detachably connectable to the same. 
     With other embodiments, it is also conceivable not to attach or at least not to permanently attach actuating element  1004  to housing  1002 , but to provide it as a separate component and, if necessary, to approach it to housing  1002  in order to enable the evaluation described below. 
     Device  1000  also comprises an inductive sensor  1100  having a sensor coil  1112  for detecting a position and/or movement of actuating element  1004 , which—like sensor coil  1112 —is preferably located inside housing  1002 . In contrast, actuating element  1004  is usually arranged outside housing  1002 , regardless of whether it is attached to housing  1002  or not. 
       FIG. 4  shows a simplified block diagram of inductive sensor  1100 . Inductive sensor  1100  comprises: a first measuring resonant circuit  1110  comprising sensor coil  1112  ( FIG. 1 ), in which a first measuring oscillation MS can be generated, and an oscillation generator  1130 , which is configured to generate an excitation oscillation ES and to apply the excitation oscillation ES at least temporarily to first measuring resonant circuit  1110 . 
     Furthermore, the device comprises an evaluation device  1200  which is configured to determine, depending on the first measuring oscillation MS, movement information BI ( FIG. 4 ) characterizing the position and/or movement of actuating element  1004  ( FIG. 1 ). With preferred embodiments, the functionality of evaluation device  1200  can be integrated in inductive sensor  1100 . With other embodiments, it is also conceivable to implement the functionality of evaluation device  1200  at least partially outside inductive sensor  1100 . For example, in some embodiments, device  1000  ( FIG. 1 ) can comprise an optional control unit  1010  which controls the operation of device  1000  and of one or more optional functional units  1300 ,  1302 . With these embodiments, control unit  1010  can be configured to implement at least a part of the functionality of evaluation device  1200 . With preferred embodiments, the determined movement information BI can be used advantageously to control the operation of the device  1000  and/or at least one component, for example the functional unit  1300  ( FIG. 4 ). 
       FIG. 5A  shows a simplified flowchart of a method according to an embodiment. In a first step  100 , oscillation generator  1130  ( FIG. 4 ) generates an excitation oscillation ES. The excitation oscillation ES can be, for example, a decaying oscillation, as schematically indicated in  FIG. 7A  by reference sign  11 . 
     In step  110  ( FIG. 5A ), oscillation generator  1130  ( FIG. 4 ) applies the excitation oscillation ES to first measuring resonant circuit  1110  such that a swelling and then decaying first measuring oscillation  7 , see  FIG. 7B , is produced in first measuring resonant circuit  1110 . In step  120  ( FIG. 5A ), evaluation device  1200  ( FIG. 4 ) determines movement information BI characterizing the position and/or movement of actuating element  1004  ( FIG. 1 ) depending on the first measuring oscillation MS. 
     Optionally, in step  130 , an operation of device  1000  or of at least one of its functional components  1300 ,  1302 , for example, can advantageously be controlled depending on movement information BI. For example, it is conceivable that functional component  1300  is activated when actuating element  1004  approaches sensor coil  1112 , which can be determined according to the principle of the invention using inductive sensor  1100 . This can be done, for example, under the control of control unit  1010 . In order to achieve a particularly energy-efficient configuration, movement information BI provided by inductive sensor  1100  can be used, for example, to switch control unit  1010  from an energy-saving state to an operating state in which the activation of component  1300  can be carried out. 
     In general, the excitation oscillation ES and/or a measuring oscillation MS of first measuring resonant circuit  1110  can be characterized, for example, by a time-varying electric voltage and/or a time-varying electric current. In some embodiments, evaluation device  1200  can evaluate, for example, an electric voltage at sensor coil  1112  and/or an electric current through sensor coil  1112  to determine movement information BI. 
     A particular advantage of the embodiments that involve a swelling and then decaying measuring oscillation  7  ( FIG. 7B ) in measuring resonant circuit  1110  ( FIG. 4 ) is that a signal maximum (e.g. a maximum voltage) of the swelling and then decaying oscillation is, in comparison to a merely decaying oscillation, for example, considerably stronger dependent on an interaction of sensor coil  1112  ( FIG. 1 ) with actuating element  1004  or its at least one metallic component, which results in a greater sensitivity of the proposed measuring principle than with conventional inductive methods, and which enables a more precise determination of movement information BI. 
     With preferred embodiments, an interaction of actuating element  1004  ( FIG. 1 ) (or its metallic or electrically conductive component, respectively) with the sensor coil  1112 , which can be evaluated by evaluation device  1200 , is such that an alternating magnetic field caused by the measuring oscillation MS ( FIG. 4 ) in the region of sensor coil  1112  ( FIG. 1 ) induces eddy currents in actuating element  1004  (or its metallic or electrically conductive component). This can, for example, cause an attenuation of the first measuring oscillation. Depending on the arrangement of actuating element  1004  in relation to sensor coil  1112 , this interaction can be stronger or weaker, which can be evaluated by evaluation device  1200 . In particular, both a position of the actuating element and movements of the actuating element can be detected. For example, in some embodiments, a comparatively weak attenuation of the first measuring oscillation MS ( FIG. 4 ) by actuating element  1004  results when it is arranged in its right axial end position in  FIG. 1 , i.e. away from sensor coil  1112 , and a comparatively strong attenuation of the first measuring oscillation MS ( FIG. 4 ) by actuating element  1004  results when it is arranged in its left axial end position in  FIG. 1 , i.e. in the region of sensor coil  1112 , see reference sign  1004 ′. 
     With other embodiments, it is also conceivable that an approach of actuating element  1004  or of its metallic component to sensor coil  1112  or a withdrawal from sensor coil  1112  affects the resonant frequency of first measuring resonant circuit  1110 , so that instead of the above-mentioned attenuation, also an amplification of the first measuring oscillation MS can result when actuating element  1004  approaches first sensor coil  1112 . 
       FIG. 2  schematically shows a block diagram of an electronic device  1000   a  according to a second embodiment. In contrast to the configuration  1000  as shown in  FIG. 1 , configuration  1000   a  as shown in  FIG. 2  has actuator  1004   a  mounted rotatably around a fulcrum DP with respect to the housing  1002 , so that it can be moved, for example, between at least two different angular positions  1004   a ,  1004   a ′ in the sense of a rotation, see the double arrow a 2 . For the determination of movement information BI, the above with reference to  FIGS. 1, 4, 5A  applies accordingly. 
       FIG. 3  schematically shows a block diagram of an electronic device  1000   b  according to a third embodiment. Actuating element  1004   b  is essentially sleeve-shaped and is arranged coaxially around housing  1002  of device  1000   b  and is mounted on the same such that it can be moved axially back and forth, see double arrow a 3 . An axial end position of actuating element  1004   b  in the region of sensor coil  1112  is indicated by reference sign  1004   b ′. For the determination of movement information BI the above with reference to  FIGS. 1, 4, 5A  applies accordingly. 
     In other embodiments, oscillation generator  1130  ( FIG. 4 ) is configured to generate a plurality of temporally consecutive excitation oscillations ES and to apply the plurality of excitation oscillations to the first measuring resonant circuit, resulting in particular in a plurality of measuring oscillations corresponding to the number of the plurality of temporally consecutive excitation oscillations. This enables a non-vanishing “measuring rate”, i.e. the repeated determination of movement information BI. 
     In other embodiments, oscillation generator  1130  ( FIG. 4 ) is configured to periodically generate the plurality of excitation oscillations ES with a first clock frequency and to apply the periodically generated excitation oscillations to first measuring resonant circuit MS. In further embodiments, the first clock frequency is between about 0.5 Hertz and about 800 Hertz, preferably between about 2 Hertz and about 100 Hertz, and more preferably between about 5 Hertz and about 20 Hertz. The first clock frequency can, for example, define the above-mentioned measuring rate, provided that one movement information BI is determined for each measuring oscillation, for example. The first clock frequency must be distinguished from the natural frequency of the oscillation generator, which is usually much higher than the first clock frequency. For example, the excitation oscillation  11  shown in  FIG. 7A  comprises a large number of complete (e.g. sinusoidal) oscillation periods with the natural frequency of the oscillation generator. The entirety of this plurality of oscillation periods with the natural frequency of the oscillation generator shown in  FIG. 7A  is herein referred to as “one excitation oscillation” ES,  11  (the same applies to measuring oscillation  7  according to  FIG. 7B ). In contrast, the first clock frequency indicates how often per time unit such an excitation oscillation ES,  11  is generated. If, for example, the first clock frequency is selected to be 10 Hertz, then a total of 10 excitation oscillations  11  of the type shown in  FIG. 7A  are generated within one second. 
     For manually operated devices, for example, a measuring rate of about 10 Hertz can be useful, because then, for example, a corresponding movement information BI can be determined ten times per second, which ensures a sufficiently fast response for many applications, e.g. for the detection of a change in position of actuating element  1004 ,  1004   a ,  1004   b.    
     With other embodiments, it is also conceivable to provide a device that is not or not only manually operable or operable by a person, but can be used, for example, within a (partially) automated system such as a manufacturing system with robots. With these embodiments, inductive sensor  1100  can also be used, for example, to detect the position and/or movement of a metallic and/or electrically conductive component of this system, e.g. to form an inductive proximity sensor. 
     In other embodiments, oscillation generator  1130  ( FIG. 4 ) is configured to apply the excitation oscillation ES to first measuring resonant circuit  1110  such that the first measuring oscillation MS is a swelling and subsequently decaying oscillation. This results in a particularly sensitive evaluation, as already mentioned above. 
     In other embodiments, first measuring resonant circuit  1110  can be brought into resonance with the excitation oscillation ES, in particular to generate a swelling and subsequently decaying measuring oscillation MS . 
       FIG. 5B  shows a simplified flowchart of a method according to another embodiment. Step  150  represents a periodic generation of a plurality of decaying excitation oscillations, e.g. with a waveform  11  according to  FIG. 7A . Step  160  represents the application of first measuring resonant circuit  1110  with a respective excitation oscillation, resulting in corresponding measuring oscillations, e.g. with a waveform  7  according to  FIG. 7B . Although steps  150 ,  160  are described herein as being carried out one after the other for reasons of clarity, it is clear that the generation of the plurality of excitation oscillations and the application of the respective excitation oscillations to the measuring resonant circuit is carried out such that after the generation of a respective excitation oscillation, this is first applied to the measuring resonant circuit in order to excite the corresponding measuring oscillation, and that only then the next excitation oscillation is generated. 
     In the optional step  170  in  FIG. 5B , evaluation device  1200  ( FIG. 4 ) determines movement information BI depending on one or more of the measuring oscillations previously generated by steps  150 ,  160 . In the further optional step  180 , a control of the operation of the device  1000  ( FIG. 1 ) or of at least one of its components  1010 ,  1300 ,  1302  can be performed depending on the previously determined movement information BI. 
     In further embodiments, first measuring resonant circuit  1110  ( FIG. 4 ) is a first LC oscillator having a first resonant frequency, wherein sensor coil  1112  ( FIG. 1 ) is an inductive element of the first LC oscillator, and wherein a capacitive element of the first LC oscillator is connected in parallel with sensor coil  1112 . In this case, in a manner known per se, the first resonant frequency, which is the natural resonant frequency of the first LC oscillator, results from the inductance of sensor coil  1112  and the capacitance of the capacitive element. 
     In other embodiments, oscillation generator  1130  is configured to generate the excitation oscillation ES with a second frequency, wherein the second frequency is between about 60 percent and about 140 percent of the first resonant frequency of the first LC oscillator, particularly preferably between about 80 percent and about 120 percent, and more preferably between about 95 percent and about 105 percent of the first resonant frequency. Thus, a preferred swelling and decaying signal shape for the measuring oscillation can be obtained in a particularly efficient manner. 
     In other embodiments, oscillation generator  1130  ( FIG. 4 ) comprises a second LC oscillator ( FIG. 4 ) and a clock generator which is configured to apply the second LC oscillator with a first clock signal or a signal derived from the first clock signal (for example an amplified first clock signal) which has the first clock frequency and a pre-determinable duty cycle. In further embodiments the pre-determinable duty cycle is between about 100 nanoseconds and about 1000 milliseconds, in particular between about 500 nanoseconds and about 10 microseconds, and more preferably about one microsecond. 
     In other embodiments, first measuring resonant circuit  1110  is inductively coupled with oscillation generator  1130 . In some embodiments, this can be achieved, for example, by an inductive element of the second LC oscillator being designed and arranged with respect to the sensor coil  1112  such that the magnetic flux generated by it at least partially passes also through sensor coil  1112  in accordance with the desired degree of coupling. For example, both the sensor coil  1112  and the inductive element of the second LC oscillator can be designed as cylindrical coils for this purpose. 
     With other embodiments, it is also conceivable that a magnetic or inductive coupling between oscillation generator  1130  and first measuring resonant circuit  1110  is undesirable. In this case, for example, the inductive element of the second LC oscillator can be designed such that the interaction of its magnetic field with sensor coil  1112  is as low as possible. In this case, for example, the inductive element of the second LC oscillator can be designed as a micro-inductance, e.g. in the form of an SMD component. 
     In other embodiments, first measuring resonant circuit  1110  is capacitively coupled to oscillation generator  1130 , e.g. via a coupling element which preferably consists of an electric serial connection of a coupling resistor and a coupling capacitor. This allows to precisely adjust the coupling impedance. 
     With reference to  FIG. 6 , a possible circuitry implementation  1  of the inductive sensor according to further embodiments is described below. 
     In a first region B 1  of the circuit diagram, an oscillation generator  13  is provided, which for example has the functionality of oscillation generator  1130  described above with reference to  FIG. 4 . In a second region B 2  of the circuit diagram, a first measuring resonant circuit  15 , for example comparable to first measuring resonant circuit  1110  described above with reference to  FIG. 4 , is provided, and in a third region B 3 , circuit components are provided which, for example, implement the functionality of evaluation device  1200  described above with reference to  FIG. 4 . 
     First measuring resonant circuit  15  as shown in  FIG. 6  comprises a parallel connection of a sensor coil  3 , corresponding for example to sensor coil  1112  described above with reference to  FIG. 1 , and a capacitor  53 , thus forming a first LC oscillator. Together with sensor coil  3 , capacitor  53  defines a natural resonant frequency of the first LC oscillator or measuring resonant circuit and can therefore also be described as a resonant capacitor. In the region of sensor coil  3 , a metallic (and/or electrically conductive) component  2  is schematically shown, the position and/or movement of which can be determined by applying the principle of the embodiments. Metallic component  2  is, for example, part of actuating element  1004 ,  1004   a ,  1004   b  according to  FIG. 1, 2, 3 , or forms this actuating element. 
     First measuring resonant circuit  15  is capacitively (or capacitively and resistively) coupled to oscillation generator  13  via a coupling impedance, presently formed by a serial connection of a resistor  55  and a capacitor  57 . Oscillation generator  13  is configured to apply, preferably periodically, excitation oscillations  11  to first measuring resonant circuit  15 , whereby corresponding measuring oscillations  7  are excited in first measuring resonant circuit  15 . For example, for this purpose, first measuring resonant circuit  15  can be periodically applied with current by the oscillation generator  13  via coupling impedance  55 ,  57 , wherein a coupling factor can be precisely adjusted by the selection of the resistance value of resistor  55  and/or the capacitance of capacitor  57 . 
     To generate the excitation oscillation(s)  11 , oscillation generator  13  comprises an excitation resonant circuit with an inductive element, in particular a coil  59 , and a capacitor  61 , which form a second LC oscillator. Oscillation generator  13  also comprises a clock generator  63 . By means of clock generator  63 , a first clock signal TS 1 , also indicated in  FIG. 6  by square pulse  65  (“clock”), can be generated. Clock  65 , for example, has a pulse duration or duty cycle of one microsecond (μs) at a first clock frequency of 10 Hertz. This corresponds to a period duration of 100 milliseconds (ms), whereby the duty cycle indicates that for a total of 1 microsecond the first clock signal TS 1  has a value of e.g. logic one (or another non-vanishing amplitude value, which also results e.g. from a value of the operating voltage V 1  in relation to the ground potential GND of e.g. 3 volts), and for the remaining period duration a value of zero. This comparatively small duty cycle of 1 μs/100 ms=1:100000 enables a particularly energy-efficient operation of sensor  1 . 
     Inductive sensor  1  shown in  FIG. 6  is applied with current by the first clock signal TS 1  during the duty cycle and is essentially currentless during the clock pauses. The preferred clock generator is an ultra-low power clock generator module having a current consumption of less than about 30 nanoamperes (nA) at an operating voltage of 3 V. This allows to provide a very energy-efficient inductive sensor. 
     With other embodiments, the values for the first clock frequency and/or the duty cycle itself can be selected as desired. If, for example, an industrial proximity sensor requires the fastest possible detection of metallic component  2  at sensor coil  3 , the generation of the next excitation oscillation  11  can be preferably started immediately after a first excitation oscillation  11  ( FIG. 7A ) has decayed below a pre-settable first threshold value, preferably about zero. 
     In a preferred embodiment, the first clock signal TS 1  controls an electric switching element  67 , for example a field effect transistor, which is connected in series with second LC oscillator  59 ,  61 . 
     With preferred embodiments, clock generator  63  or the entire sensor  1  can be supplied with operating voltage V 1  from an electric energy source not shown in  FIG. 6 , which is provided, for example, by a battery and/or a solar cell and/or a device for energy harvesting (taking energy from the environment and converting it into electric energy if necessary). Sensor  1  can preferably use an electric energy supply of its target system, here e.g. the device  1000  ( FIG. 1 ), for example a battery (not shown), which also supplies control unit  1010  and/or at least one functional unit  1300 ,  1302  with electric energy. 
     During a duty cycle of clock  65 , electric switching element  67  is switched on, e.g. a drain-source route of the field-effect transistor has low impedance, and as a result a DC voltage V 1  is applied to the second LC oscillator or excitation circuit  59 ,  61  of oscillation generator  13 . This causes a magnetic field to be built up in coil  59 . During the clock pauses, electric switching element  67  opens and the excitation resonant circuit of oscillation generator  13  gets into a decaying oscillation, the excitation oscillation  11 , see  FIG. 7A . In the clock pauses of clock  65 , first measuring resonant circuit  15  is thus energized via coupling impedance  55 ,  57  with the decaying excitation oscillation  11 . This excites it to a first measuring oscillation  7 , see  FIG. 7B , and in the case of preferred embodiments, it gets into resonance in particular with the excitation oscillation  11 , wherein the first measuring oscillation  7  preferably is obtained as a swelling and then decaying measuring oscillation  7 . 
     The measuring oscillation  7  depends via sensor coil  3  on the position and/or movement of metallic component  2 , for example on a presence or absence of component  2  in the region of sensor coil  3  and/or an approach or withdrawal of component  2 . To detect the position and/or movement of component  2  or to evaluate the first measuring oscillation  7 , a circuit group is assigned to first measuring resonant circuit  15  ( FIG. 7 ), which is shown mainly in the third region B 3  according to  FIG. 6 . 
     This circuit group has a maximum value memory  27  as well as a preset value generating device VG which is e.g. designed as a voltage divider with a first preset resistor  69  and a second preset resistor  71 . Maximum value memory  27  stores a maximum value of an amplitude value  17  of the first measuring oscillation  7  and provides it at its output as memory value  25 . Maximum value memory  27  is followed by a time delay element  73 . Time delay element  73  delays the memory value  25  present at the output of maximum value memory  27  preferably by a period PD ( FIG. 8 ) of the first clock signal TS 1 , whereby a delayed memory value  25 ′ is obtained. Alternatively, the delay is obtained by means of an integrating filter. In one configuration, time delay element  73  comprises a low-pass filter. 
     A preset output  75  of preset value generating device VG and an output of time delay element  73  are connected upstream of a comparator  77 . The delayed memory value  25 ′ (i.e. the first maximum amplitude value  17  delayed by one clock pulse) of a first clock cycle and a second amplitude value  21  of a second clock cycle being one clock pulse later are thus applied to comparator  77 . The delayed memory value  25 ′ is compared with the second amplitude value  21  by means of comparator  77 . In addition, the second amplitude value  21  is reduced by means of the voltage divider VG by a corresponding threshold  29  ( FIG. 7B ) before it acts on comparator  77 . 
     Maximum value memory  27 , time delay element  73  as well as comparator  77  can form a differentiating element in some embodiments, which differentiates the first measuring oscillation  7  over one period length of clock  65 . Comparator  77  generates a set signal  79  as an output signal if preset output  75  is greater than the delayed memory value  25 ′. 
     With preferred embodiments, the differential formed exemplarily by means of comparator  77 , time delay element  73  and maximum value memory  27  is thus compared with the threshold  29  via preset resistors  69  and  71 , wherein comparator  77  generates the positive set signal  79  when the differential of the first measuring oscillation  7  exceeds the threshold  29 . This can be the case with some embodiments if, for example, metallic component  2  is withdrawn from sensor coil  3  and thus causes no or only a lower attenuation of the signal in sensor coil  3 . 
     With other preferred embodiments, a flip-flop element  81  is connected downstream of comparator  77 , in particular a set input  81   a  for setting the flip-flop element  81 . 
     Moreover, a reset input  81   b  of flip-flop element  81  is connected downstream of clock generator  63 . In this way, flip-flop element  81  is reset at each clock  65 , i.e. when oscillation generator  13  is applied with current. This ensures that flip-flop element  81  is reset at the clock cycle of the disconnection of excitation resonant circuit  13  from the electric energy source not shown in detail (at the falling edge of the first clock signal TS 1  or of clock  65 ), i.e. when the excitation oscillation  11  begins. If the withdrawal and/or absence of metallic component  2  from sensor coil  3  is detected by comparator  77  and the latter generates the set signal  79 , as described above, flip-flop element  81  is being set. 
     With other embodiments, an optional low-pass filter  83  can be connected downstream of flip-flop element  81  to bridge time periods after resetting flip-flop element  81  by clock  65  and setting again by set signal  79 . A non-vanishing output signal  83 ′ of low-pass filter  83  is thus present, for example, when the withdrawal of component  2  has been detected. This output signal  83 ′ can be used with other preferred embodiments for switching and/or controlling at least one component of the target system of inductive sensor  1 , e.g. a device  1000  as shown in  FIG. 1 . For example, the output signal  83 ′ can be fed to control unit  1010  of device  1000 , which evaluates it, for example to determine movement information BI ( FIG. 4 ), and depending on this, to control an operating state and/or a change of an operating state of function component  1300  of device  1000 , for example. With other embodiments, the output signal  83 ′ can be used directly as movement information BI. 
     In order to achieve a particularly energy-efficient configuration, with other embodiments, the output signal  83 ′ can be used, for example, to switch control unit  1010  ( FIG. 1 ) of device  1000  from an energy-saving state to an operating state in which, for example, activation of component  1300  can be carried out. This can be done, for example, by connecting the output signal  83 ′ to an input of control unit  1010 , which may be a microcontroller or the like, such that the output signal  83 ′ triggers an interrupt request, which transfers the microcontroller from the energy-saving mode to an active operation mode. 
     With other preferred embodiments, depending on the design of the threshold values and/or resonant frequencies of first measuring resonant circuit  15  or its first LC oscillator and/or oscillation generator  13  or its second LC oscillator, the approach or withdrawal of metallic component  2  can be detected, for example. 
     With other preferred embodiments, maximum value memory  27  ( FIG. 6 ) is also connected downstream of clock generator  63 , so that an operating state of maximum value memory  27  can be controlled depending on the first clock signal TS 1 . For example, in each individual clock cycle  65 , maximum value memory  27  is preferably reduced in the whole or in part by a value. Alternatively, it is possible to dispense with maximum value memory  27 , preset resistors  69  and  71  as well as time delay element  73  and instead to provide a fixed threshold value, i.e. to check only the fixed or pre-settable threshold value and to switch depending on it. 
     With other embodiments, it is conceivable that, for example, a single excitation oscillation  11  ( FIG. 7A ) is generated for a measuring process, which accordingly causes a single first measuring oscillation  7  or MS 1  ( FIG. 7B ) in first measuring resonant circuit  15 . When calibrating the inductive sensor  1 , e.g. by means of preceding reference measurements which involve an arrangement of metallic component  2  in various positions relative to sensor coil  3  and a corresponding evaluation of, for example, at least one amplitude value of the first measuring oscillation per position, already with the evaluation of a single measuring oscillation a movement information BI can advantageously be determined which describes a position of metallic component  2  relative to sensor coil  3 . With these embodiments, a comparison of several, for example directly consecutive, measuring oscillations of the first measuring resonant circuit is therefore not necessary. With other preferred embodiments, however, as described above with reference to  FIG. 6 , a plurality of measuring oscillations are excited by corresponding excitation oscillations and the movement information is determined depending on the plurality of measuring oscillations. 
       FIG. 7  shows different signal courses of the excitation oscillation  11  as well as the first measuring oscillation  7 . In a diagram A ( FIG. 7A ) of  FIG. 7 , the decay of the excitation oscillation  11  is clearly visible, which occurs after disconnecting excitation oscillation circuit  59 ,  61  ( FIG. 6 ) from the electric power supply V 1 , GND. 
     In a diagram B ( FIG. 7B ) of  FIG. 7 , two signal courses MS 1 , MS 2  of measuring oscillations  7  as a result of the energization of first measuring resonant circuit  15  ( FIG. 6 ) by means of the excitation oscillation  11  shown in  FIG. 7A  are each plotted in a comparison. A solid line MS 1  represents a first measuring oscillation of a first clock cycle (excited by an application with a first excitation oscillation  11  according to  FIG. 7A ), which has the first amplitude value  17 , which is symbolized in  FIG. 7  by a horizontal line. 
     A dotted line represents another one of the measuring oscillations  7  (excited by an application with a second excitation oscillation  11  as shown in  FIG. 7A ), which has the second amplitude value  21  at a second clock cycle, which is also symbolized in  FIG. 7B  by a horizontal line. The amplitude values  17  and  21  are each the maximum values of the measuring oscillations MS 1 , MS 2  which are swelling and then decaying with each clock cycle. 
     The situation MS 2  shown in  FIG. 7B  as a dotted line results, for example, when metallic component  2  ( FIG. 6 ) is withdrawn from sensor coil  3 , which is thus less attenuated. It can be seen that therefore, in a second clock cycle the second amplitude value  21  is higher than the first amplitude value  17  of the first clock cycle. If the second amplitude value  21  exceeds threshold  29  ( FIG. 7B ) specified by means of resistors  69  and  71  shown in  FIG. 6  and/or by the at least partial reduction of the memory value  25 , comparator  77  generates the set signal  79  for setting flip-flop element  81 . 
       FIG. 8  illustrates different signal courses A to F of different signals of inductive sensor  1  shown as an example in  FIG. 6 , when metallic component  2  is present in the region of sensor coil  3 .  FIG. 9  shows the signal courses of  FIG. 8 , but when metallic component  2  is withdrawn from sensor coil  3  and when metallic component  2  approaches sensor coil  3  again. 
     In a diagram A of  FIGS. 8 and 9 , a total of four periods of each of the first clock signal TS 1  ( FIG. 6 ) and the clock  65  are shown. In  FIG. 8A , a period duration is denoted with the reference sign PD and a duty cycle is denoted with the reference sign TL. The ratio between the duty cycle TL and the pauses P in between (corresponding to the period duration PD minus the duty cycle TL) or the period duration PD, respectively, is preferably chosen very small for a power-saving system according to preferred embodiments, see above, for example with values of about 1:10000 and smaller, preferably about 1:100000, and it is not shown to scale in  FIGS. 8, 9  for the sake of clarity. In a diagram B of  FIGS. 8 and 9 , the swelling and decay of the measuring oscillation  7  is shown, each schematized. In a diagram C of  FIGS. 8 and 9 , the set signal  79  provided at the output of comparator  77  and applied to the set input  81   a  of flip-flop element  81  is shown. In a diagram D of  FIGS. 8 and 9 , respectively, a signal is shown which is applied to the reset input  81   b  of flip-flop element  81  and which corresponds to the first clock signal TS 1  or clock  65 . In a diagram E of  FIGS. 8 and 9 , respectively, the memory state (output signal) of flip-flop element  81  is shown. In a diagram F of  FIGS. 8 and 9 , respectively, a temporal course of an output signal of time delay element  73  is shown, i.e. the temporally delayed memory value  25 ′ which is fed to comparator  77 . 
     As can be seen in  FIG. 8D , flip-flop element  81  is reset for each completed clock  65  and consistently shows the reset memory state, as shown in  FIG. 8E . As can be seen in  FIG. 8B , after each end (falling edge) of the respective clock  65 , one of the measuring oscillations  7  begins, which, due to the presence of metallic component  2 , each have identical maximum amplitude values, which is symbolized in  FIG. 8B  by a dashed horizontal line  21 ′. These maximum amplitude values  21 ′ preferably correspond to the respective first and second amplitude values  17 ,  21 , see also  FIG. 7B . Since the measuring oscillation  7  swells and then decays again, the respective maximum amplitude value only occurs after a certain number of oscillation periods of the respective measuring oscillation, in particular directly at the transition from the swelling to the decay. According to the principle of the present embodiments, the maximum of the respectively occurring amplitudes can be determined or stored with little effort and is already affected by the position or movement of metallic component  2  during the swelling oscillations. Since in some embodiments the influence is added up over time and is measured at a signal maximum occurring with a time delay, a sensitivity and a quality of the measurement can be further improved compared to conventional approaches (e.g. just considering a decaying oscillation). 
     In diagram F of  FIG. 8 , the temporal course of the output signal of time delay element  73 , the time-delayed memory value  25 ′, is shown as steady state. This is the case, for example, if metallic component  2  does not move relative to sensor coil  3  ( FIG. 6 ) for a time period exceeding the time delay of time delay element  73 . 
     In comparison to this,  FIG. 9  shows that an amplitude of the second measuring oscillation  7 ′ shown in  FIG. 9B  briefly exceeds threshold  29 , for example due to a movement of metallic component  2  relative to sensor coil  3  ( FIG. 6 ). This causes a non-vanishing output signal, namely the set signal  79 , at the output of comparator  77  and thus also at set input  81   a  of flip-flop element  81 , as shown in diagram C of  FIG. 9 . As can be seen in diagram E of  FIG. 9 , this sets flip-flop element  81 . Flip-flop element  81  remains set until the next clock  65 , which causes a reset. 
     After a third clock pulse shown in  FIG. 9 , there is another increase in the amplitude of the third measuring oscillation  7 ″, which, compared to the second measuring oscillation  7 ″ shown in  FIG. 9B , exceeds the threshold  29  even further. The set signal  79  is generated again, which sets flip-flop element  81  for another period of clock  65 . After a fourth period of clock  65 , metallic component  2  has again approached sensor coil  3   
     ( FIG. 6 ). It can be seen that as a result, the threshold  29  is not exceeded by the fourth measuring oscillation  7 ″&#39; and therefore flip-flop element  81  remains reset. It can also be seen that the time-delayed memory value  25 ′ slowly decreases again. 
     Generally, other methods of signal evaluation are also possible with other embodiments, for example using fixed or dynamically re-adjusted thresholds. 
     As can be seen in  FIGS. 8 and 9 , in the embodiment described, a measuring oscillation  7 ′ or the first amplitude value  17  of a first clock cycle  19  is compared with a subsequent measuring oscillation  7 ″ or a second amplitude value  21  of a second clock cycle  23 . This is preferably carried out cyclically once per clock cycle, wherein in particular the respective amplitude value of a current clock cycle is compared with the corresponding amplitude value (preferably the respective maximum or minimum amplitude value) of the clock cycle preceding this clock cycle. 
     The presence of metallic component  2  in the region of sensor coil  3  ( FIG. 6 ) causes in some embodiments an attenuation of the measuring oscillation  7  in sensor coil  3 , in particular due to eddy currents induced in component  2  by measuring oscillation  7  or the associated alternating magnetic field, and thus prevents a setting of flip-flop element  81 , as shown in  FIG. 8C . 
     With other embodiments, it is also possible that metallic component  2  affects a natural resonant frequency of the first LC-oscillator or of the first measuring resonant circuit  15  such that it is closer to a frequency of the excitation oscillation  11 , and therefore a possible resonance of the first LC-oscillator of first measuring resonant circuit  15  with the second LC-oscillator of oscillation generator  13  is more amplified than attenuated by metallic component  2 . As a result, the presence of metallic component  2  can cause an increase in the amplitude values  17 ,  21  and thus sets flip-flop element  81 . 
       FIG. 10  shows schematically a circuit diagram of an inductive sensor  1   a  according to another embodiment, which also allows the detection of a position and/or movement of a metallic component  2 . Sensor  1   a  comprises a first sensor coil  3  as well as a further sensor coil  5 , wherein metallic component  2  for the above-mentioned detection is moved towards at least one of the two sensor coils  3  or  5 , for example. 
     In the following, only the differences to inductive sensor  1  shown in  FIG. 6  will be discussed, and apart from that, reference is made to  FIG. 6  and the corresponding description. In contrast to the illustration in  FIG. 6 , inductive sensor  1   a  in  FIG. 10  comprises the first measuring resonant circuit  15  as well as a further (second) measuring resonant circuit  16 . Both measuring resonant circuits  15 ,  16  are each formed by an LC oscillator with elements  3 ,  53  and  5 ,  53 ′ respectively. The measuring resonant circuits  15  and  16  are connected via a respective coupling impedance  55 ,  57  and  55 ′,  57  to excitation resonant circuit  59 ,  61  of oscillation generator  13 , so that both measuring resonant circuits  15  and  16  can be jointly applied with a corresponding excitation oscillation  11  by oscillation generator  13 . Accordingly, a first measuring oscillation  7  is formed in first measuring resonant circuit  15  and a secondary measuring oscillation  9  in second measuring resonant circuit  16 . 
     First measuring resonant circuit  15  generates a first output signal  33  which depends on the position and/or movement of metallic component  2 . In an analog manner, second measuring resonant circuit  16  generates a second output signal  35 . Both output signals  33 ,  35  are fed to a differential amplifier  43  which generates a differential signal  31  from them. Due to the forming of a difference, the differential signal  31  is basically robust against disturbances acting on sensor coil  3  as well as the other sensor coil  5  of second measuring resonant circuit  16 . 
     Both sensor coils  3  and  5  can preferably be oriented in the same way and in particular be arranged in front of or next to each other. A distance between the two sensor coils  3 ,  5  can preferably be selected for some embodiments such that, if applicable, metallic component  2  only acts on one of the two measuring resonant circuits  15 ,  16  without significantly affecting the other. 
     Since sensor coils  3  and  5  are at least a small distance apart due to their design, disturbances can, however, lead to a slightly changed differential signal  31  in some embodiments. In order to also eliminate this effect, with some embodiments, maximum value memory  27  and an evaluation circuit  39  connected downstream of it are designed such that differential signal  31  in a first time window  49 , which is shown in  FIG. 12 , is compared with differential signal  31  in a second time window  51 , which is also shown in  FIG. 12 . Maximum value memory  27  and evaluation circuit  39  are time-controlled for this purpose, for example by means of clock generator  63 . This allows to save electric energy. 
     The exact function and possible configurations of maximum value memory  27  shown in  FIG. 10  will be explained in more detail below with reference to  FIG. 11 . Maximum value memory  27  comprises a first partial memory  85 , which is connected during the first time window  49  by means of an electric switching element to the output of differential amplifier  43 , i.e. differential signal  31 . Analog to this, a second partial memory  87  is also connected during the second time window  51  by means of an electric switching element to the output of differential amplifier  43 , i.e. differential signal  31 . Comparator  77  compares the memory outputs of first partial memory  85  and second partial memory  87 , i.e. the respective differential signal  31  of the first time window  49  and the second time window  51  with each other. If a differential threshold merely indicated in  FIG. 11  by means of the reference sign  37  is exceeded, comparator  77  generates the set signal  79  to set the flip-flop element  81 . Partial memories  85  and  87  can preferably be supplied with electric energy by clock generator  63 , i.e. they are essentially currentless in the pauses of clock  65  or in measurement pauses specified by the same, respectively. This allows to further reduce the power consumption. 
       FIG. 12  shows in illustrations A to D different courses of the differential signal  31  of inductive sensor  1   a  depicted in  FIGS. 10 and 11 . 
     Clock  65  is shown in  FIG. 12A .  FIG. 12B  shows that during clock  65  there is no excitation oscillation  11  applied to measuring resonant circuits  15  and  16 . As soon as clock  65  ends, and thus, the excitation resonant circuit is no longer applied with current, the decaying excitation oscillation  11  occurs. According to the illustration in  FIG. 12C , the differential signal  31  from the measuring oscillation  7  and a further measuring oscillation  9  of the further measuring resonant circuit  16 , e.g. when metallic component  2  approaches, is shown as a result of the excitation by means of the excitation oscillation  11 . The approach of metallic component  2  leads to a detuning of at least one of the measuring resonant circuits  15  and/or  16 , and thus to a swelling and then decaying differential signal  31 , as shown with the course of  FIG. 12C . 
     In  FIG. 12D , it can be seen that without an approximation of metallic component  2 , the differential signal  31  has a substantially constant fundamental oscillation. This can be caused by an electromagnetic disturbance, for example, acting on inductive sensor  1   a.    
     In principle, the disturbance can be reduced by forming the differential signal  31 , but not completely due to a possibly different distance of sensor coils  3  and  5  from an disturbance signal source. In order to eliminate this remaining disturbance signal, with further embodiments, the differential signal  31  is considered in the first time window  49 , which is symbolized by two vertical lines in  FIG. 12 , in comparison to a course during the second time window  51 , which is also symbolized by two vertical lines in  FIG. 12 . As can be derived from  FIG. 12C , comparator  77  generates the set signal  79  only if a maximum value of an amplitude of the difference signal  31  of the second time window  51  exceeds a maximum value of the amplitude of the difference signal  31  of the first time window  49  by the difference threshold  37 . 
     With preferred embodiments, the first time window  49  corresponds in particular to the length of the clock  65 , i.e. a duty cycle TL, see also  FIG. 8 . The second time window  51  comprises at least a part of the measuring oscillations  7  and  9  generated in the measuring resonant circuits  15 ,  16  by coupling, in particular resonance, with the excitation oscillation  11  and the differential signal  31  formed therefrom. The second time window  51  preferably follows directly after the first time window  49  and begins, for example, as soon as clock  65  ends or the excitation oscillation  11  begins. 
     With preferred embodiments, the first time window  49  for the first determination of the amplitude of the differential signal  31  can be arranged within a period of time when inductive element  59  is energized, or can coincide with the same. With other preferred embodiments, the second time window  51  for the second determination of the amplitude of the differential signal  31  is arranged in a region of a maximum amplitude, in particular the highest resonant oscillation, of the differential signal  31  and/or the measuring oscillations  15 ,  16 , wherein the measurement takes place. If the first amplitude changes, for example due to a disturbance variable acting on sensor coil  3  and/or  5 , this is detected and, with preferred embodiments, the threshold value for the second amplitude, i.e. for the actual measurement to detect metallic component  2 , adjusts accordingly. 
     With other preferred embodiments, it is possible to transfer energy from oscillation generator  13  to measuring resonant circuit(s)  15  and/or  16  completely or at least partially via an inductive energy transfer path (not shown) instead of via capacitor  57  and/or resistor  55 . If applicable, coils  3  and/or  5  can receive the energy directly. 
     With other embodiments, evaluation device  1200  ( FIG. 4 ) is configured to compare at least two maximum or minimum amplitude values of different oscillation periods of (the same) measuring oscillation  7  ( FIG. 7B ) with each other. Thus, it is possible to determine, for example, a speed of the swelling and/or decay of the measuring oscillation  7 , from which movement information BI can be derived. 
     With other embodiments, evaluation device  1200  is configured to compare a maximum or minimum amplitude value of a first measuring oscillation  7 ′ ( FIG. 9B ) of a plurality of measuring oscillations  7 ′,  7 ″, . . . with a corresponding maximum or minimum amplitude value of at least one second measuring oscillation  7 ″ of the plurality of measuring oscillations, wherein preferably the second measuring oscillation follows the first measuring oscillation, in particular follows directly the first measuring oscillation (i.e. without a further measuring oscillation occurring between the first and second measuring oscillations). 
       FIG. 13  shows a simplified block diagram of an electronic device  1000   c  according to another embodiment. The device  1000   c  comprises a functional component  1300 , which in this case is a measuring device  1300 , which is configured to measure layer thicknesses, wherein measuring device  1300  is in particular configured to measure layer thicknesses of layers of lacquer and/or paint and/or rubber and/or or plastic on steel and/or iron and/or cast iron, and/or layers of lacquer and/or paint and/or rubber and/or or plastic on non-magnetic base materials such as aluminum, and/or copper and/or brass, for example. 
     Device  1000   c  is designed as a mobile device, in particular a hand-held device, and comprises a housing  1002  in which a control unit  1010  is provided for controlling an operation of device  1000   c  and in particular of measuring device  1300 . An inductive sensor  1100  according to at least one of the embodiments described above with reference to  FIGS. 1 to 12  or to a combination thereof is also arranged in housing  1002 . For example, inductive sensor  1100  can have the construction as shown in  FIG. 4 , wherein a circuitry implementation of at least some of the components  1130 ,  1110 ,  1200  of inductive sensor  1100  can be realized, for example, similar or comparable to the embodiments described with reference to  FIGS. 6 to 9  and/or comparable to the embodiments described with reference to  FIGS. 10 to 12 . 
     With preferred embodiments, device  1000   c  is configured to carry out or start at least one layer thickness measurement by measuring device  1300  depending on movement information BI which is determined by means of sensor  1100  and characterizes a position and/or movement of actuating element  1004   c.    
     With other embodiments, housing  1002  has a substantially circular-cylindrical basic shape, wherein actuator  1004   c  has a substantially hollow-cylindrical basic shape and is coaxially surrounding a first axial end region  1002   a  of housing  1002 . A compression spring is provided radially between housing  1002  and hollow-cylindrical actuating element  1004   c , which is indicated only schematically by double arrow  1005  in  FIG. 13 . Furthermore, a stop  1002   b  is provided on housing  1002 , which limits an axial movement of actuating element  1004   c  in  FIG. 13  to the left. A corresponding stop for limiting the axial movement of actuating element  1004   c  in an opposite direction, i.e. to the right in  FIG. 13 , can also be provided as an option, but is not shown in  FIG. 13  the sake of clarity. 
     To use the measuring device  1300 , device  1000   c  can be grasped by a user and actuating element  1004   c  can be moved from its rest position shown in  FIG. 13  against the spring force of compression spring  1005  in the direction of the first axial end region  1002   a  of housing  1002 , i.e. to the left in  FIG. 13 . As a result, actuating element  1004   c  approaches first sensor coil  1112  of inductive sensor  1100  arranged within housing  1002 , in particular in the first axial end region  1102   a , whereby the interaction between actuating element  1004   c  or its metallic component (not shown in  FIG. 13 ) and first sensor coil  1112 , which has already been described several times above, changes in a way that can be detected by means of inductive sensor  1100 . By means of evaluation device  1200  ( FIG. 4 ), which in this case is integrated in inductive sensor  1100 , for example, the movement information BI ( FIG. 4 ) characterizing the position and/or movement of actuating element  1004   c  is generated and output, for example, directly to control unit  1010 , which then activates measuring device  1300  to carry out one or more layer thickness measurements, for example by transferring it from an energy-saving state into an different operating state which allows coating thickness measurements. 
     With other embodiments, it may be provided that inductive sensor  1100  is used to determine when actuating element  1004   c  moves back into its rest position or when it is no longer positioned in the region of first sensor coil  1112 . In this case, in further embodiments, control unit  1010  can put measuring device  1300  back into an energy-saving state, for example. 
     With further embodiments, device  1000   c  is configured to at least temporarily deactivate oscillation generator  1130  ( FIG. 4 ), wherein in particular device  1000   c  is configured to at least temporarily deactivate oscillation generator  1130  depending on the movement information. This can be useful in those embodiments in which a signal  11 ,  7  generated by the inductive sensor according to the embodiments, in particular encompassing an alternating magnetic field, can possibly have a disturbing effect on the operation of measuring device  1300 . 
     Due to the low duty cycle of the first clock signal TS 1 , which is preferred in some embodiments, and the comparatively long clock pauses coming along with the same, it is also possible in other embodiments to synchronize the measuring operation of measuring system  1300  with the operation of inductive sensor  1100  such that layer thickness measurements are carried out by measuring device  1300  within the clock pauses of the first clock signal TS 1 , in particular during those phases of the clock pause(s) during which an excitation oscillation  11  and preferably also a measuring oscillation  7  generated as a result thereof has decayed again below a pre-determinable threshold value. This results in an operation of measuring system  1300  that is largely unaffected by inductive sensor  1100 . 
     With other embodiments, housing  1002  is hermetically sealed at least in the first axial end region  1002   a.    
     Inductive sensors  1100 ,  1 ,  1   a  in accordance with the above-described embodiments can be advantageously used to provide a man-machine interface, for example using the above-described actuating element  1004 ,  1004   a ,  1004   b ,  1004   c , wherein a metallic object or a metallic component or an at least partially metallic actuating element is arranged so as to be movable relative to the inductive sensor or at least the first sensor coil (translation and/or rotation or mixed forms thereof are possible). 
     The principle can also be used in particular for devices with partially or completely hermetically sealed (airtight) housings  1002 , because the magnetic alternating fields associated with the measuring oscillation  7  can usually penetrate the housing wall sufficiently well, so that the proposed principle can be used reliably. In particular, no electrical, especially galvanic, connection between the actuating element and the inductive sensor is required. 
     Furthermore, the actuator or a metallic component attached to it does not need to be magnetic in order for the proposed principle to be useful. Rather, it is sufficient if eddy currents can be induced in the actuating element or at least in its metallic component by the alternating magnetic field of the sensor coil, i.e. electrical conductivity is present in the actuating element or at least in the metallic component assigned to it. Generally, the proposed principle can thus also be used to detect a non-metallic medium with regard to its position and/or movement relative to the sensor coil, as long as it is electrically conductive. 
     Further fields of application for the principle of the present embodiments are devices with switches or other actuating elements for explosion-proof rooms, diving applications, and in particular all other fields where actuation, in particular switching and/or operating, e.g. by means of magnets and Hall sensors, is not possible due to the possible presence of magnetic particles. Also applications are conceivable where a manipulation with haptic feedback, encapsulation and/or extremely low power consumption is desired, for example energy-autonomous, battery-powered and/or mobile devices. 
     The principle of the present embodiments allows advantageously the provision of devices  1000  with a very energy-efficient detection of a position and/or movement of at least one actuating element. Furthermore, with other embodiments, a plurality of actuating elements on one (same) device are conceivable, whose position and/or movement can be determined by one or possibly a plurality of inductive sensors of the type described. 
     As an alternative or in addition to a “binary” detection of positions (“actuating element is in the region of the sensor coil”/“actuating element is not in the region of the sensor coil”) or movement states (movement of the actuating element towards/away from the sensor coil), a determination of positions with a finer spatial resolution can be advantageously obtained. For this purpose, a plurality of threshold values can be provided for the principle described above e.g. with reference to  FIG. 7B , the exceeding of which can be evaluated, e.g. by means of a plurality of comparators  77 . 
     The term detection of a movement is to be interpreted broadly, in particular it can be understood to mean whether a distance between the actuating element and the at least one sensor coil is static and/or increases and/or decreases, whether the actuating element moves towards the coil and/or is present there and/or is moved away from it and/or is not present there. Alternatively or additionally, other evaluations are also possible, for example by means of fixed or dynamically readjusted thresholds for an absolute value of the amplitude. The amplitude values are preferably determined as respective maximum amplitude values, i.e. between swelling and decay of the respective measuring oscillation, for example when a signal maximum of the respective measuring oscillation occurs.