Inductive analysis of metal objects

Abstract

A measuring device and a method for inductively analyzing a metal object, comprising: a coil arrangement having an excitation coil (1.1) which can be excited by means of an excitation current and at least one receiving coil (1.2), the excitation coil and the receiving coil being inductively coupled to each other. An output signal (5.4) of the measuring device is evaluated by means of an evaluation unit. A component is provided for generating a ramp-shaped voltage signal of an excitation voltage (2.5) in order to preset a ramp-shaped current through the excitation coil. The regulating unit regulates the current at the base point of the excitation coil (1.1) so that a ramp-shaped excitation current is formed, which is modulated by the metal object (1.6) and influences the change of the excitation voltage. This results in an inductive analysis or detection method, in which temperature influences do not act on the coil system at all and the method also enables a spectral analysis of the inductive properties of the metal to be analyzed in a wide frequency range.

Description

[0001] Cross-references to related applications

[0002] This application is related to and claims the benefit of priority from German patent application 10 2018118 408.5 filed on July 30, 2018 and German patent application 10 2018 120 912.6 filed on August 27, 2018, the corresponding disclosure contents of which are expressly incorporated in their entirety into the subject matter of the present application by reference. Technical Field

[0003] The invention relates to a measuring device and a method for analyzing metal objects.

[0004] definition

[0005] If, within the context of the present application, reference is made to the “inductive property” of a coil, this refers to the influence on the energy emission, in particular on the phase and / or amplitude of a signal received at a receiving coil.

[0006] In the context of the present application, “high impedance” means that the output signal of the receiving coil is tapped with high impedance, so that temperature-induced changes in the line resistance have no effect on the output signal to be evaluated, or at most have a negligible effect. Background Art

[0007] Inductive sensors for analyzing metal objects use coils to generate an alternating magnetic field, which is immersed in the metal to be inspected. Based on the influence of the magnetic field, for example, the type of metal or the distance of the coil from the metal can be inferred. The latter is used, for example, in "layer thickness measurement", in which the thickness of the paint layer between the metal and the coil is determined without being influenced by the induction.

[0008] The coil for generating an alternating magnetic field can be driven with a rectangular or sinusoidal signal of any frequency and can be designed in various types. Therefore, typical metal detectors often use "decoupled coils". Here, the coil (excitation coil) is driven with an alternating current and an alternating magnetic field is provided. The second coil (receiving coil) is mechanically arranged so that the rising and falling field lines of the excitation coil cancel each other out in the receiving coil, and thus the coil (in the absence of metal influence) does not provide an output signal. In the case of metal influence, the symmetry of the field lines is shifted, and the corresponding electrical signal can be received at the receiving coil. This is known, for example, from DE 4339419C2 as the "double D" method. Of course, the disadvantage of this measuring method is that the excitation coil and the receiving coil do not have a common axis of symmetry.

[0009] A metal detector of the pulse induction type is known from US 2008 / 0150537 A1, which is able to distinguish between metal objects and minerals that imitate metals by absorbing and releasing energy. During a first measurement interval, the object to be measured is influenced by a magnetic field that rises in a ramp shape, which magnetic field can also act in the object to be measured during a subsequent second measurement and thus influence the measured value of the second measurement. The remaining energy in the object is measured by comparing the signals generated during specific intervals of a coil excitation pulse sequence, which comprises a bipolar current ramp that induces the same signal in a metal target, but a different signal in a magnetic mineral. However, the metal detector is not used for the precise analysis of metal objects. The output signal is adjusted to zero via a microcontroller and a DAC according to a predetermined standard and voltage amplitude control. No adjustment occurs at the base point of the excitation coil.

[0010] DE 10 2012 001 202 A1 discloses a sensor for locating metal objects using coils that are inductively coupled to one another, which are arranged partially overlapping to decouple the interaction. In this case, the excitation coil and the receiving coil have essentially the same coil shape and are arranged twisted and / or offset relative to one another, wherein a plurality of symmetrically arranged overlapping regions are formed. Furthermore, meandering sections are provided that overlap one another. Although the excitation coil is completely decoupled from the receiving coil, the method works using a common axis of symmetry of the two coil systems.

[0011] Other methods use two coils, preferably connected in series, one of which is the measuring coil that is affected by the presence of metal, while the other represents a reference coil and is preferably arranged remote from the measuring coil. If the two coils are fed with two sinusoidal or rectangular signals that are offset by 180 degrees from one another, then in the case of exactly identical coil parameters, the fed signals cancel out at the center tap of the two coils. Only when metal approaches the measuring coil does the inductive properties of the measuring coil change and a corresponding signal can be tapped at the center tap.

[0012] Another measuring method is to use three coils which are mechanically arranged one behind the other in a row with axis symmetry. If the middle coil is energized with alternating current, a signal is generated at each of the other two coils which cancel each other out again when the coils are connected accordingly. The proximity of a metal to one of the two outer coils changes the inductive properties of the coil so that no complete cancellation occurs and the presence or type of metal can be inferred from the signal thus generated. The reverse configuration is also used, i.e. two transmitting coils on the outside and one receiving coil on the inside.

[0013] The systems described above usually work with sinusoidal oscillations or with waveform resonant characteristics in order to increase the sensitivity to metallic influences. This is disadvantageous if the excitation frequency and the resonant frequency of the receiving circuit do not exactly coincide, since then phase or amplitude errors can occur.

[0014] Temperature influences on the measuring system can also have a negative effect, since the internal resistance of the coil wire can change under temperature influences, which in turn causes a shift in the phase or amplitude of the resonant circuit. In order to compensate for temperature influences on the transmitting or measuring coil, some measuring systems use a timed measurement of the current through the coil system and determine the temperature-dependent internal resistance from this. The resistance measurement value obtained in this way is then used to perform a correction factor for the actual metal type determination.

[0015] If an unknown metal is to be analyzed inductively, the measuring frequency must be selected accordingly beforehand. More complex methods operate with multiple, usually switchable frequencies, where effective temperature compensation is particularly difficult.

[0016] With the induction system described above, it is also possible to measure the paint thickness on a known metal. The paint thickness means that the distance between the metal surface and the coil system changes the amplitude and phase of the excitation signal measured in the receiving circuit. For this purpose, good temperature compensation of the measuring system must also be achieved.

[0017] Other methods (CA2 951 848 A1) transmit rectangular pulses into a transmitting coil and, after the pulses have been switched off, measure the inductive reaction of the metal to be detected or analyzed with the transmitting coil or another coil.

[0018] Therefore, typically in inductive measuring systems, one or more coils are excited with a sinusoidal or rectangular signal of a specific frequency or with a single rectangular pulse so that the amplitude and / or phase changes at one of the excitation coils or at a separate detection coil arranged specifically for detecting the transmitted alternating magnetic field can be measured through the inductive effect of the metal on these excited coil systems.

[0019] In all of these inductive analysis or detection systems, temperature changes can have undesirable effects on the inductive properties of the transmitting or receiving coil system, so that a large number of systems are equipped with temperature compensation methods. Summary of the invention

[0020] The object of the present invention is to provide an inductive analysis or detection method in which temperature influences do not act at all on the coil system and which furthermore allows a spectral analysis of the inductive properties of the metal to be analyzed over a wide frequency range.

[0021] In addition, these measuring systems for analyzing metallic materials, material compositions (multi-layer arrangements / multi-layer plates), material thicknesses (plate thickness measurement), paint thickness determination (distance of coil system from the metal), detection of metal objects, for example behind metal walls (e.g. the position of a clutch chain in a closed clutch housing in a motor vehicle) should be used as proximity sensors, etc.

[0022] In the context of spectral analysis of the inductive properties, the spectrum of individual frequencies is displayed in the output signal of the measuring system, which frequencies influence and change the output signal to a greater or lesser extent depending on the metal type and metal properties. This information about the object to be inspected can preferably be obtained by Fourier transformation of the output signal.

[0023] For this purpose, in a measuring device for inductive analysis of metal objects, an excitation coil is excited by means of an excitation voltage. The excitation coil is inductively coupled to a receiving coil. The output signal is tapped off at the receiving coil for evaluation. The excitation voltage is supplied as a ramp-shaped voltage signal to a control device provided with a comparator stage, which changes the effective self-inductance of the coil at the beginning of the measurement, i.e. at the moment of ramp-up, at the coil input, so that the predetermined ramp-shaped shape of the excitation voltage is applied again at the resistor at the base point of the coil, wherein the self-inductance of the coil actually counteracts the formation of the magnetic field. Therefore, a means for generating a ramp-shaped voltage signal for the excitation voltage is provided in order to predetermine a ramp-shaped current through the excitation coil, wherein the control device regulates the current at the base point of the excitation coil so that a ramp-shaped excitation current is generated, wherein the current flowing into the coil is modulated by the metal object and influences the change of the excitation voltage. In practice, it has already been shown that a ramp-like rising magnetic field, ie preferably a nonlinear magnetic field, is built up in the excitation coil in such a way that it penetrates into the object to be examined and is modulated over time by the metallic object.

[0024] Information about the type and properties of the object and also the layer thickness and the layer is obtained from the output signal. Temperature influences on the excitation coil and thus on the resulting magnetic field are also eliminated by means of the regulation of the current at the measuring point or the point resistor.

[0025] Preferably, the regulating device regulates the current at the base point of the excitation coil so that a continuously rising excitation current is generated, wherein during the ramp-shaped voltage signal for generating the excitation current, the effect of the metal object as a result of the regulation of the current at the base point of the excitation coil influences the current so that a corresponding measured value about the influencing metal can be derived from the voltage change. This information can be tapped via the receiving coil for thermal decoupling. The output signal influenced in this way allows the desired, in-depth analysis of the metal object.

[0026] It has proven to be advantageous that the metal type of the metal object is an effect which changes the intensity of the excitation current in a temporally dependent manner with respect to the immersion depth during the time of the magnetic field rise. From this, the composition of the alloy and the layer structure of the metal object can also be inferred.

[0027] Preferably, the component for generating the ramp-shaped voltage signal of the excitation voltage first generates a steep rise relative to the ramp-shaped rise of the excitation voltage at the beginning of the ramp-shaped rise. This ensures that when the excitation coil is energized, a ramp-shaped excitation current is actually reached, which causes a non-linear magnetic field buildup due to the metal influence.

[0028] Preferably, the receiving coil is arranged adjacent to and / or parallel to the excitation coil. The receiving coil and the excitation coil are likewise wound bifilarly. This allows a space-saving design of the coil arrangement without impairing the analysis.

[0029] In order to also ensure the temperature stability of the excitation coil, the output signal is preferably tapped off at the receiving coil in a high-resistance manner.

[0030] The best results are achieved if the regulating device preferably comprises a comparator, at a first input of which the excitation voltage is present and at a second input of which the voltage at the base resistance of the excitation coil is present.

[0031] According to the method, the same advantages also occur if, for the inductive analysis of the metal object, at least one excitation coil which can be excited by means of an excitation voltage is energized and the output signal of the measuring device is evaluated for the analysis of the metal object. By supplying the regulated excitation voltage as a substantially ramp-shaped voltage signal of the excitation voltage to the excitation coil and by regulating the current at the base point or base point resistance of the excitation coil so that a ramp-shaped excitation current is actually formed, a ramp-shaped magnetic field can be immersed in the object, wherein, however, the excitation current is modulated by the energy absorption of the metal object and thus causes a deviation of the regulated excitation voltage from a predefined ideal ramp shape, the object can be analyzed in the receiving coil for the analysis of the object.

[0032] Preferably, the current at the base point of the excitation coil is regulated by comparing the voltage at the base point with a preset ramp voltage due to the deviation of the excitation voltage from an ideal ramp shape, so that a continuously rising excitation current is generated. During the ramp-shaped voltage signal for generating the excitation current, the effect of the metal object influences the current as a result of the regulation of the current at the base point of the excitation coil, so that a corresponding measured value about the influencing metal can be derived from the voltage change. For thermal decoupling, this information can be intercepted via the receiving coil. The output signal of the receiving coil influenced in this way allows the desired, in-depth analysis of the metal object.

[0033] Preferably, the regulating device regulates the current at the base point of the excitation coil in such a way that a continuously rising excitation current is generated. The output signal influenced in this way allows the desired analysis of the metal object in-depth into the metal object.

[0034] Advantageously, the intensity of the excitation current varies by the metal type of the metal object. From this, it is also possible to draw significant conclusions about the composition of the alloy and the layer structure of the metal object.

[0035] Preferably, at the beginning of the ramp-shaped voltage signal of the excitation voltage, a rise of the excitation voltage that is steeper than the ramp-shaped rise is first supplied to the excitation coil in a controlled manner. This ensures that a ramp-shaped excitation current actually occurs when the excitation coil is energized, which causes a nonlinear magnetic field to be built up.

[0036] Preferably, the receiving coil is arranged adjacent to and / or parallel to the excitation coil. The receiving coil and the excitation coil can also be wound bifilarly. This allows a space-saving design of the coil arrangement without impairing the analysis.

[0037] In order to also ensure the temperature stability of the receiving coil, according to the method the output signal is preferably tapped off at the receiving coil in a high-resistance manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be described in more detail below based on the embodiments shown in the accompanying drawings. It shows:

[0039] Figure 1 A coil arrangement of a measuring system according to the invention is shown,

[0040] Figure 2 A circuit for feeding the field voltage into the field coil is shown.

[0041] Figure 3 An alternative circuit for generating a ramp-shaped current is shown,

[0042] Figure 4 shows the voltage profile of the ramp over time,

[0043] Figure 5 shows a circuit with an integrated coil arrangement according to the invention,

[0044] Figure 6 The voltage curve at the excitation coil and the current curve at the base resistor are shown over time.

[0045] Figure 7 shows the different time profiles of the voltage of the output signal of the measuring system for different metal types and compositions,

[0046] Figure 8shows the alternating rise and fall of the ramp-shaped excitation signal and the associated output signal,

[0047] Fig. 9 An alternative embodiment of a measuring system using a microcontroller is shown. DETAILED DESCRIPTION

[0048] The present invention is now described in more detail with reference to the accompanying drawings. However, the embodiments are only examples, which should not limit the concept of the invention to a specific device. Before describing the present invention in detail, it should be noted that the present invention is not limited to the corresponding components of the equipment and the corresponding method steps, because these components and methods can be changed. The terms used herein are intended only to describe specific embodiments, rather than to be used restrictively. In addition, if a singular or indefinite article is used in the specification, this also refers to the plural number of these elements unless the overall context clearly indicates otherwise.

[0049] A practical inductive measuring system consists of a very simple coil arrangement, wherein the electronics consists of only a few components in comparison with known measuring methods.

[0050] according to Figure 1 The coil arrangement of the measuring system 1.3 is composed of at least two coils, which are preferably oriented in parallel. Here, one of the two coils acts as an excitation coil 1.1 and the other acts as a receiving coil 1.2. In this embodiment, each coil arrangement 1.3 is composed of an excitation coil 1.1 and a receiving coil 1.2, but it is also possible to use a plurality of excitation coils and receiving coils.

[0051] In the simplest case, the coil system consists of a winding body with two bifilar-wound coils. This means that no spacing is required between the excitation coil 1.1 and the receiving coil 1.2. Coil arrangements are also possible in which the receiving coil 1.2 and the excitation coil 1.1 are arranged directly next to each other or inside each other. The number of turns of the excitation coil 1.1 and the receiving coil 1.2 can also be different. Preferably, the excitation coil has fewer turns than the receiving coil with a greater wire thickness.

[0052] In contrast to typical inductive measuring systems, the excitation coil 1.1 is not excited with a sinusoidal or rectangular signal or rectangular pulse, but rather with a DC current which preferably rises uniformly and in a ramp-shaped manner starting from zero, which is excited by Figure 2 The curve of the excitation voltage 2.5 is shown. In principle, a single measurement can be sufficient for the analysis of a metal object. If continuous measurement is desired, the measurement can be repeated periodically.

[0053] Coil arrangement 1 . 3 thus exerts a magnetically inductive interaction on metal object 1 . 6 .

[0054] If a ramp-shaped excitation voltage 2.5 is applied directly to the feed terminal 2.2 of the excitation coil 1.1, the current through the excitation coil does not directly follow the voltage curve of the excitation voltage 2.5, but rather with a time delay, due to the self-induction. This is visible when a base resistor 2.3 is used at the base of the excitation coil 1.1, at which the excitation coil current is measured due to the voltage 2.4 generated. Figure 4 This is explained. The curve of the excitation voltage 2.5 corresponds to the ramp-shaped voltage rise at the feed terminal 2.2, and the curve 4.1 shows the current resulting therefrom, which is measured as the voltage value at the base resistor 2.3. (For the sake of better illustration, the voltages at the excitation coil and the receiving coil are not shown to scale.)

[0055] Therefore, the excitation current follows exactly the preset curve of the excitation voltage 2.5, as shown in FIG. Figure 3 The circuit is supplemented as shown: the excitation voltage 2.5 is supplied to the non-inverting input 3.3 of the operational amplifier (comparator) 3.1. The output of the operational amplifier feeds the feed terminal 2.2 of the excitation coil 1.1. In addition, the inverting input is connected to the base resistor 2.3 and the voltage 2.4 of the base resistor 2.3 is obtained. By this measure, the excitation current is actively regulated and now corresponds exactly to the curve of the excitation voltage 2.5.

[0056] Therefore, a ramp-shaped voltage signal for generating the excitation voltage 2.5 is provided to predetermine a ramp-shaped current component through the excitation coil 1.1. The described regulating device regulates the current at the base point of the excitation coil 1.1 so that a ramp-shaped excitation current is generated, which is modulated by the metal object 1.6 and affects the change of the excitation voltage.

[0057] Preferably, the regulating device regulates the current at the base point of the excitation coil 1.1 so that a continuously rising excitation current is generated in the base point resistor, wherein the effect of the metal object 1.6 changes the intensity of the excitation current during the ramp-shaped rise of the excitation current. In particular, this effect is based on the metal type of the metal object, which will be discussed in more detail below.

[0058] If you observe accurately Figure 4 The influence of the regulating device in , then, shows that: at the beginning of the ramp-shaped rise, the component for generating the ramp-shaped voltage signal of the excitation voltage 2.5 first generates a steep rise of the excitation voltage 4.2 relative to the ramp-shaped rise.

[0059] The voltage 3.2 generated at the feed terminal 2.2 preferably first rises sharply at the beginning of the ramp, so as to then transition into the linear region and follow the predetermined curve of the excitation voltage 2.5. Thus, in a preferred embodiment, the voltage at the base resistor 2.3 follows the predetermined curve of the excitation voltage 2.5 exactly. The voltage rise 4.2 reacts to the self-inductance of the excitation coil 1.1, thus causing a linear rise in the coil current. This leads to a gradual build-up of a magnetic field that is immersed in the metal object 1.6.

[0060] However, this measure also excludes temperature influences on the field coil 1.1, which are reflected in changes in the ohmic winding resistance and thus reduce the inductance or performance of the coil, since the field current actually directly follows the predefined voltage curve of the field voltage 2.5. This also applies when the curve of the field voltage 2.5 is selected non-linearly and / or when the curve is deliberately changed, for example to achieve metal shielding. Since the current through the field coil 1.1 determines the magnetic field, this magnetic field is no longer temperature-dependent due to the above-mentioned measures.

[0061] In contrast to typical inductive analysis systems, in which a decoupling between the transmitting and receiving coils is usually desired, the receiving coil 1.2 is arranged directly next to the excitation coil 1.1. Figure 1 The receiving coil 1.2 and the excitation coil 1.1 can also use a common ferrite core, preferably a pot-shaped core closed on one side.

[0062] If the excitation coil 1.1 is supplied with a ramp-shaped current 6.2 as is obtained at the base resistor 2.3 due to the predefined excitation voltage 2.5, a current according to Figure 6 Pure DC voltage 6.1. The DC voltage change during the time when metal approaches or the coil arrangement is arranged on the metal object can then be evaluated.

[0063] Complete temperature insensitivity is achieved when no current flows in the receiving coil 1 . 2 . This means that if one end of the receiving coil 1 . 2 is grounded, the resulting voltage is tapped off at the other end only with very high resistance.

[0064] The input resistance of the subsequent circuit should preferably be in the megohm range. This ensures that no significant current flows in the receiving coil 1.2 and that temperature-dependent resistance changes in the winding wire cannot have an influence. The input of such a circuit can be, for example, the FET input of an operational amplifier which only loads the receiving coil 1.2 with a few pA.

[0065] Figure 5A possible embodiment of the measuring method described here is shown. The clock generator 5.1 supplies a start clock pulse (starttakt), for example, every 100 ms, to the ramp generator 5.2. With each start clock pulse, the ramp generator 5.2 starts and supplies a ramp signal, for example, 20 ms long, as an excitation voltage to the comparator 3.1, which is used to ensure that a current corresponding to the excitation voltage flows through the excitation coil 1.1. The circuit for generating the ramp signal is known to the person skilled in the art, so it will not be discussed in detail here.

[0066] A power transistor can also be connected downstream of the comparator 3.1 to generate a high ramp-shaped current. In addition, the impedance transformer 5.3 can be connected as an amplifier. However, with a suitable ramp current and a matching number of turns, the voltage that can be evaluated at the receiving coil can be several Watts, so that no further amplification is required.

[0067] according to Figure 7 The curves discussed below were determined in practice using the following circuit variant: Coils 1.1 and 1.2 each have 100 turns, bifilar winding, coil body D=10 mm, ferrite pot core. The maximum ramp current is 200 mA. Without metal influence, voltage 6.1 at receiving coil 1.2 has a value of 1.8 Vpp.

[0068] The ramp length is 15 milliseconds, which in the case of a sinusoidal oscillation corresponds to approximately 67 Hz as the "lowest" frequency. The maximum frequency calculated from the rate of rise of signal 6.1 corresponds to approximately 200 kHz. Thus, the entire frequency range from 67 Hz to 200 kHz is covered in a single measurement.

[0069] The distance between the coil arrangement and the metal surface is 1 mm. The coil arrangement is therefore placed almost exactly on the metal object 1.6, which is preferably also the usual case when using the measuring device.

[0070] When the metal influence changes the coil arrangement 1.3 of the measuring system, the amplitude curve of the output signal 5.4, i.e. Figure 6 The curve 6.1 shown in FIG. 6.1 changes. In the absence of metal influence, the amplitude curve is strictly linear and has the characteristics of a DC voltage, but the amplitude curve deviates from the curve shown at predetermined locations depending on the metal type or the composition of different metals.

[0071] Figure 7 This is explained. Figure 7The roughly drawn curve 6.1 in shows the output signal 5.4 without the influence of metal. The deviation of the value of 6.1 to a higher voltage indicates a ferromagnetic material, as shown in area 7.10. Paramagnetic and diamagnetic materials change the voltage of curve 6.1 to a lower value, as shown in area 7.11.

[0072] Therefore, the basic information about the ferromagnetic material is essentially the voltage magnitude of the output signal 5.4 at low frequencies, i.e. at the end of the curve, and is generally weaker during the signal rise and the further course of the curve. Curve 7.1 shows the course in the case of an iron plate with a thickness of 0.5 mm, curve 7.7 shows the course in the case of an iron plate with a thickness of 2 mm, and curve 7.12 shows the course in the case of an iron plate with a thickness of 20 mm.

[0073] Paramagnetic and diamagnetic materials show their magnetic interaction particularly in the high-frequency range, ie in the region of the signal rise, whereas in the low-frequency range they approach the values ​​of curve 6 . 1 (measured values ​​not influenced by the metal).

[0074] Below, a diagram of some curves resulting from different surface materials (metal sheets) is explained.

[0075] A 50 μm thick gold foil changes the signal rise only in the very high frequency range, which is shown in curve 7.8.

[0076] The same aluminum plate with a thickness of 1 mm, but provided with a 50 μm thick lacquer layer, produces a significantly different curve (7.15) in a specific frequency range.

[0077] A sandwich embodiment of different metal sheets can result, for example, in Figure 7 .2 curve direction.

[0078] Depending on the thickness of the metal sheet, the rise of the curve is "delayed", so that in the case of a thick sheet, the rise is later than in the case of a thin sheet. Curve 7.3 corresponds to 3 mm thick aluminum, curve 7.4 corresponds to 5 mm thick aluminum, and curve 7.5 and further curve 7.13 correspond to 10 mm thick aluminum.

[0079] This curve description also allows for a deeper discussion of the particularities of the present invention. Curve 7.5 and the continuation of the curve shown by dashed line 7.13 together correspond to the curve course in a 10 mm thick aluminum sheet. However, if there is a secondary ferromagnetic material behind this 10 mm thick primary aluminum sheet, the curve bends from the time point 7.9 determined by the thickness of the primary material, as shown in the changing curve 7.14. The thicker the non-ferromagnetic primary material, the later the curve changes. In addition, the output signal can be subjected to Fourier analysis to obtain further material-specific information.

[0080] In the absence of metal influences, during the ramp-up, the output signal 5.4 is substantially similar to a DC voltage. The change in the output signal contains information about the type, properties and thickness of the metal, which information can preferably be obtained by means of Fourier analysis.

[0081] The shape of the slope and thus also the slope shape modified by the surrounding metal can be modulated in order to mask the surrounding metal.

[0082] The curves formed in specific metals or metal mixtures can be stored, for example, in a database and the unknown material to be analyzed can then be identified or defined by comparison with the stored curves.

[0083] At the same time, using the measuring method it is of course also possible to examine the material for specific changes in its crystal structure due to stress (compression, elongation) or to detect hairline cracks or material defects.

[0084] In another embodiment, according to Figure 8 , the excitation current can also follow the continuous rising and falling ramp signal 8.1. Then, the output signal 5.4 is as follows Figure 8 In the embodiment, positive and negative values ​​are used as shown by curve 8.2, or in the case of metal influence, the curve trend 8.3 has the same change as in the single slope, but is additionally reflected in the negative range. This design is particularly suitable if rapid changes in metal type or rapid position changes need to be detected.

[0085] With the help of Fig. 9 The excitation signal and the received signal are controlled and evaluated by a microcontroller 9.3, which makes the measuring system particularly simple to design, since essentially only one current driver 9.2 and one base resistor 2.3 are required, in order to be able to implement a temperature-stable, inexpensive evaluation method for various tasks, such as paint thickness measurement, bimetallic sheet recognition, multilayer analysis, material determination, etc. The microcontroller 9.3 can have a communication channel 9.1 to a display or evaluation unit, for example, in order to compare the measured values ​​with a database or to display them directly on a display, for example.

[0086] Thus, a system for measuring the inductive properties of any metallic object 1 . 6 is provided, wherein temperature influences have no influence on the coil system and the measurement. The system thus covers a wide spectral range from, for example, 50 Hz-200 kHz with measurements and requires only a low expenditure on electronics.

[0087] It should be emphasized that greater immersion depths, in particular increased immersion depths in the case of slowly rising ramp currents, for example with ramp lengths of more than 100 ms. By Fourier analysis of the output signal 5.4, for example, with a pot core coil arrangement with a diameter of 10 mm, three layers of different metal sheets (brass, aluminum, copper, bronze, etc.) arranged one above the other in any order and with respect to the thickness of the individual metal sheets can be determined, in terms of the sequence and the thickness of the individual metal sheets. It is clear from this that the measuring device and the method are also suitable for depth analysis or sheet thickness measurement. With a flat coil arrangement without a ferrite core with a diameter of 50 mm, for example, non-ferrous metals can be observed to a depth of more than 30 mm.

[0088] It goes without saying that the present specification is capable of various modifications, changes, and adjustments within the scope of equivalents of the description.

[0089] Reference numerals list

[0090] 1.1 Excitation coil

[0091] 1.2 Receiving coil

[0092] 1.3 Coil device

[0093] 1.4 Excitation current

[0094] 1.5 Receiving coil voltage

[0095] 1.6 Metal Objects

[0096] 1.7 Magnetic Induction Interaction

[0097] 2.2 Feed terminal

[0098] 2.3 Base point resistance

[0099] 2.4 Voltage at the base resistance

[0100] 2.5 Curve trend of preset excitation voltage

[0101] 3.1 Comparator (Operational Amplifier)

[0102] 3.2 Comparator Output

[0103] 3.3 Non-inverting input of the comparator

[0104] 4.1 Voltage value at base point resistance

[0105] 4.2 Voltage Rise

[0106] 5.1 Clock Generator

[0107] 5.2 Ramp Generator

[0108] 5.3 Impedance Inverter or Amplifier with High Impedance Input

[0109] 5.4 Output Signal

[0110] 6.1 Amplitude trend of 5.4

[0111] 6.2 Current flow at 2.3 due to 2.5

[0112] 7.1 Curved shape of 0.5 mm thick iron plate

[0113] 7.2 Curved shapes of sandwich structures with three metal plates

[0114] 7.3 3mm aluminum curve shape

[0115] 7.4 5mm aluminum curve shape

[0116] 7.5 10mm aluminum and 5mm iron plate in a curved shape

[0117] 7.6 Curved shapes of 5mm aluminum and 5mm iron plates

[0118] 7.7 Curved shape of 2 mm thick iron plate

[0119] 7.8 Curved shape of 50μm gold foil

[0120] 7.9 Bends in a curve

[0121] 7.10 Ferromagnetic Material Region

[0122] 7.11 Regions of Paramagnetic and Diamagnetic Materials

[0123] 7.12 Curved shape of 20 mm iron plate

[0124] 7.13 Continuation of curve 7.5

[0125] 7.14 Changes in the shape of the curve caused by the presence of another ferromagnetic metal

[0126] 7.15 Curved shape of the same metal sheet with 1 mm thickness but with 30 μ coating

[0127] 8.1 Rising and falling ramp signals

[0128] 8.2 Output Signals with Positive and Negative Values

[0129] 8.3 Curve trend of changes under metal influence

[0130] 9.1 Communication channels to display or evaluation unit

[0131] 9.2 Current Driver

[0132] 9.3 Microcontroller.

Claims

1. A measuring device, arranged to perform inductive analysis on a metal object (1.6), the measuring device comprising: - a coil arrangement comprising at least one excitation coil (1.1) which can be excited by means of an excitation voltage and at least one receiving coil (1.2), the excitation coil and the receiving coil being inductively coupled to one another, - electronic means for energizing the field coil (1.1), and - an evaluation unit for evaluating the output signal (5.4) of the measuring device which is tapped off by the receiving coil (1.2), - a ramp generator for generating a ramp-shaped voltage signal of the excitation voltage (2.5) in order to preset a ramp-shaped current through the excitation coil, - a control device, the control device comprising an operational amplifier (3.1) or a comparator, the excitation voltage (2.5) being applied to a first input (3.3) of the operational amplifier (3.1) or the comparator, and a voltage (2.4) being applied to a base resistance (2.3) of the excitation coil (1.1) at a second input of the operational amplifier (3.1) or the comparator, and the output of the operational amplifier (3.1) or the comparator directly feeding a feed terminal (2.2) of the excitation coil (1.1), - in, The regulating device is configured to regulate the current at the base point of the excitation coil (1.1) so as to generate a ramp-shaped excitation current, which can be modulated in time by the metal object (1.6) to change the excitation voltage. - wherein the evaluation unit is configured to evaluate an output signal of the measuring device in order to analyse the metal object.

2. The measuring device according to claim 1, characterized in that The regulating device is configured to regulate the current at the base point of the excitation coil (1.1) so as to generate a continuously rising excitation current, wherein during the ramp-shaped rise of the excitation current, the action of the metal object (1.6) can change the intensity of the excitation current.

3. The measuring device according to claim 2, characterized in that The intensity of the excitation current can be varied by the type of metal of the metal object (1.6).

4. The measuring device according to claim 1, characterized in that The ramp generator is configured to initially generate a steep rise (4.2) of the excitation voltage relative to the ramp-shaped rise at the beginning of the ramp-shaped rise in order to overcome the self-inductance of the excitation coil (1.1) which acts against the magnetic field.

5. The measuring device according to claim 1, characterized in that The receiving coil (1.2) is arranged adjacent to and / or in parallel with the excitation coil (1.1).

6. The measuring device according to claim 1, characterized in that The output signal (5.4) is tapped off at the receiving coil (1.1) with high impedance.

7. The measuring device according to any one of claims 1 to 6, wherein: The regulating device is a closed-loop controller.

8. A method for inductively analyzing a metal object (1.6) using a measuring device, the measuring device having a coil arrangement, the coil arrangement comprising at least one excitation coil (1.1) which can be excited by means of an excitation voltage (2.5) and at least one receiving coil (1.2), the excitation coil and the receiving coil being inductively coupled to each other, in, The excitation coil (1.1) is energized and the output signal (5.4) of the measuring device picked up by the receiving coil (1.2) is evaluated in order to analyze the metal object. The ramp-shaped voltage signal of the excitation voltage (2.5) is supplied to preset the ramp-shaped current passing through the excitation coil (1.1), The regulating device comprises an operational amplifier (3.1) or a comparator, the excitation voltage (2.5) is applied to the first input terminal (3.3) of the operational amplifier (3.1) or the comparator, and a voltage (2.4) is applied to the base point resistance (2.3) of the excitation coil (1.1) at the second input terminal of the operational amplifier (3.1) or the comparator, and the output terminal of the operational amplifier (3.1) or the comparator directly feeds the feed terminal (2.2) of the excitation coil (1.1), and the current passing through the excitation coil (1.1) is regulated at the base point of the excitation coil (1.1), thereby generating a ramp-shaped excitation current at the base point resistance (2.3), wherein the current flowing in the excitation coil can be modulated by the metal object (1.6) to change the excitation voltage, Therein, an output signal of the measuring device is evaluated in order to analyze the metal object.

9. The method according to claim 8, characterized in that The current is adjusted at the base point of the excitation coil (1.1) so that a continuously rising excitation current is generated, and the intensity of the excitation current can be changed during the ramp-shaped rise of the excitation current by the action of the metal object (1.6).

10. The method according to claim 9, characterized in that The intensity of the excitation current can be varied by the type of metal of the metal object (1.6).

11. The method according to claim 8, characterized in that At the beginning of the ramp-shaped voltage signal of the field voltage (2.5), a steep rise (4.2) in voltage relative to the ramp-shaped rise first occurs at the field coil (1.1).

12. The method according to claim 8, characterized in that The receiving coil (1.1) is arranged adjacent to and / or in parallel with the excitation coil (1.2).

13. The method according to claim 8, characterized in that The output signal (5.4) is tapped off at the receiving coil (1.1) with high impedance.

14. The method according to any one of claims 8 to 13, wherein: The regulating device is a closed-loop controller.

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