Method for operating a multi-frequency metal detector and multi-frequency metal detector

Abstract

To provide an improved method for operating a multi-frequency metal detector and an improved multi-frequency metal detector to be operated according to this method.SOLUTION: A metal detector (1) comprises: a drive coil (L61) for producing an electromagnetic field in a product; at least one detection coil (L62, L63) arranged to detect fluctuations in the magnetic field caused by metallic particles present in the product; and a multifrequency transmitter unit (10) comprising a converter (4) with a plurality of drive switches (S41, S42; S43, S44). The plurality of drive switches (S41, S42; S43, S44) is driven by a drive controller (2) according to operating instructions such that the drive switches (S41, S42; S43, S44) alternately conduct a drive current (iD) through the drive coil (L61) so that the generated electromagnetic field exhibits two or more different frequency components (fD1, fD2).SELECTED DRAWING: Figure 1a

Description

[Technical Field]

[0001]

[0001] The present invention relates to a method for operating a multi-frequency metal detector, and a multi-frequency metal detector operating according to this method. [Background technology]

[0002]

[0002] As described in U.S. Patent Application Publication No. 20120206138(A1), metal detectors are used to detect and remove unwanted metal contamination. When properly installed and operated, metal detectors help reduce metal contamination and improve food safety. Modern metal detectors utilize a searching head that comprises a coil system having a drive coil that receives a drive signal and generates an electromagnetic field within the product, and at least one sensing coil positioned to detect fluctuations in the magnetic field caused by the presence of metal particles in the product, such as ferrous, non-ferrous, and stainless steel in a wide variety of products, including fresh and frozen foods.

[0003]

[0003] A metal detection system operating according to the principle of "balancing coils" typically comprises three coils: a drive coil and two identical detection coils wound around a non-metallic frame, each precisely parallel to the other. The detection coils typically surround the drive coil at the center between them, and because these detection coils are identical, the same voltage is induced in each of them. To receive an output signal that is zero when the system is in equilibrium, a first receiving coil is connected in series with a second receiving coil having a reverse winding. Thus, the voltages induced in the receiving coils, having the same amplitude and opposite polarity, cancel each other out when the system is in equilibrium and there is no contamination in the product being observed.

[0004]

[0004] However, as soon as the metal particles pass through the coil array, the electromagnetic field is disrupted, first near one sensing coil and then near the other sensing coil. As the metal particles are transported through the sensing coils, the voltage induced in each sensing coil changes (by only nanovolts). This change in equilibrium results in a signal at the output of the sensing coils, which can be processed and amplified in a receiving device and then used to detect the presence of metal contamination in the product being observed.

[0005]

[0005] In a typical metal detector, a signal processing channel provided within the receiving device splits the received signal into two distinct components separated by 90° from each other. The combined vector has magnitude and phase angle, which is typical for products and contaminants transmitted through the coil system. To identify metal contaminants, the "product effect" needs to be eliminated or reduced. If the phase of the product is known, the corresponding signal vector can be reduced. Removing undesirable signals from the signal spectrum in this way results in greater sensitivity to signals originating from metal contaminants.

[0006]

[0006] Therefore, the method applied to eliminate undesirable signals from the signal spectrum takes advantage of the fact that metal contaminants, products, and other interferences have different effects on the magnetic field, resulting in signals with different phases. Signals caused by metals or products can be divided into two components, specifically a resistive component and a reactant component, when passing through a coil system, according to the conductivity and permeability of the object being measured. Signals caused by ferrite are primarily reactant, while signals from stainless steel are primarily resistive. Conductive products typically produce signals with a strong resistive component. By distinguishing the phases of signal components of different origins using a phase detector, it becomes possible to obtain information about products and contaminants. The signal components, or phase and amplitude, change depending on the frequency of the applied drive signal, which is selected such that the signal components of the metal contaminants are out of phase with the signal components of the product signal from which they are observed.

[0007]

[0007] U.S. Patent No. 8,473,235 discloses a metal detector having a drive circuit comprising a plurality of switches connected to a drive coil and driven by a drive control device, the plurality of switches alternately connecting the drive coil across a potential difference to drive the drive coil at a predetermined operating frequency. The drive control device can be programmed to operate the plurality of switches to obtain any single operating frequency that may be selectable in the range of 40 to 900 kHz in 1 Hz increments. However, driving a coil system with a square wave (or a trapezoidal wave due to the inductance of the coil) generates a large amount of relatively high-energy harmonics compared to a conventional sinusoidal signal generated by a tuning circuit. To avoid the adverse effects of these harmonics, the device comprises a detection circuit for obtaining a signal from the coil system, the detection circuit comprising a phase-sensitive detector coupled to a low-pass filter that removes the aforementioned interfering harmonics, which are generally considered the most undesirable.

[0008]

[0008] One operating frequency may be suitable for one particular metal contaminant, but the same frequency may not yield the desired results for other metal contaminants. By using two or more transmission frequencies selected according to the product and potential contaminants simultaneously, it becomes possible to obtain more accurate information about two or more different metal contaminants without switching operating frequencies.

[0009]

[0009] U.S. Patent No. 8,159,225 discloses a multi-frequency metal detector having a multi-frequency transmitter, and a method for generating a multi-frequency drive signal by generating at least two square wave signals, each having a different fundamental frequency, and mixing the selected square wave signals to produce a switching signal containing different frequency components having a relatively strong magnitude at frequencies corresponding to the convolution of the fundamental frequencies of the two selected square wave signals. Here again, in addition to the desired frequency components, there are other frequency components that need to be removed or suppressed.

[0010]

[0010] U.S. Patent No. 8,159,225 further discloses that a digital drive switching signal is applied to a full-bridge switching power stage connected to the drive coil of a metal detector. The full-bridge switching power stage consists of two half-bridges, each comprising two half-bridge switches: one half-bridge driven by a digital switching signal and the other half-bridge driven by an inverting digital switching signal. The current in the half-bridge switches of the full-bridge switching power stage corresponds to the current flowing through the drive coil. Therefore, with high currents in the drive coil, the half-bridge switches are required to be able to deliver this high coil current. Consequently, multi-frequency transmitters must be sized and constructed accordingly, which incurs considerable costs. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] U.S. Patent Application Publication No. 20120206138(A1) [Patent Document 2] U.S. Patent No. 8473235 [Patent Document 3] U.S. Patent No. 8159225 [Non-patent literature]

[0012] [Non-Patent Document 1] Sarbari Das and Manish Bharat, Implementation of IGBT series resonant inverters using pulse-density modulation, International Journal of Industrial Electronics and Electrical Engineering, Vol. 3, No. 2, February 2015. [Non-Patent Document 2] MJGrimble, MAJohnson, Jian Sun, Advances in industrial Control, Springer-Verlag London Limited2012, Chapter 2 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013]

[0011] Accordingly, the present invention is based on the objective of providing an improved method for operating a multi-frequency metal detector, and an improved multi-frequency metal detector that operates according to this method. [Means for solving the problem]

[0014]

[0012] The method and multi-frequency metal detector of the present invention are advantageous in that they enable the production of a multi-frequency drive signal having at least two different frequency components. Filter circuits are avoided or at least reduced.

[0015]

[0013] Furthermore, the frequency of the multi-frequency drive signal is preferably selectable as needed so that the metal detector can be used flexibly for a wide range of products and potential contaminants.

[0016]

[0014] The metal detector shall be equipped with an improved multi-frequency transmitter which has improved efficiency, is structurally simple, can be constructed at reduced cost, and allows for maximizing the coil current delivered to the drive coil.

[0017]

[0015] The method and metal detector of the present invention enable the creation of a high drive current in the drive coil while maintaining a relatively low current in the transmitter device, and as a result the transmitter circuit can be sized accordingly, for example, with reduced power performance and cost.

[0018]

[0016] In a first broad embodiment of the present invention, a method for operating a metal detector is provided, the metal detector comprising a drive coil for generating an electromagnetic field within a product, at least one sensing coil arranged to detect fluctuations in the magnetic field caused by metal particles present in the product, and a multi-frequency transmitter device comprising a transducer 4 having a plurality of drive switches, the plurality of drive switches being driven by a drive control device according to an operating command such that the drive switches alternately conduct drive currents to the drive coils, resulting in the generated electromagnetic field exhibiting two or more different frequency components.

[0019]

[0017] An electromagnetic field having two or more different frequency components is - A step of determining the waveform of the drive current for at least two different frequency components; - A step of determining at least one pulse sequence signal (hereinafter referred to as the PXM signal) corresponding to the defined waveform of the drive current; - A step of selecting at least one determined PXM signal, which is determined online or stored in a memory module, according to a provided operating instruction. - This is achieved by the steps of generating and applying a determined PXM signal to control the drive switch of the transmitter device, thereby generating a drive current having a defined waveform.

[0020]

[0018] At least one PXM signal, preferably a pulse-width modulated or pulse-density modulated signal, may be determined and then stored in memory for later use. However, preferably the PXM signal is determined and generated online so that the metal detector can be tuned online to products and contaminants or adapted online to changes in products and contaminants. Thus, the user can adjust the metal detector according to their personal requirements.

[0021]

[0019] Sarbari Das and Manish Bharat, Implementation of IGBT series resonant inverters The article "using pulse-density modulation," in the International Journal of Industrial Electronics and Electrical Engineering, Vol. 3, No. 2, February 2015, explains that pulse-density modulation is a form of modulation used to represent analog signals as digital data. In PDM, instead of a specific amplitude value, the relative density of pulses corresponds to the amplitude of the analog signal.

[0022]

[0020] Pulse width modulation techniques are described in Chapter 2 of MJ Grimble, MA Johnson, and Jian Sun, Advances in Industrial Control, Springer-Verlag London Limited, 2012. In principle, a PWM signal can be produced by comparing a reference signal with a carrier signal, such as a sawtooth carrier, an inverted sawtooth carrier, or a triangular carrier. Thus, a preferably mathematically determined waveform of the drive current can be used as a reference signal compared with a carrier signal, such as a sawtooth or triangular carrier.

[0023]

[0021] The drive switch of the converter, preferably a power FET device, may be arranged as, for example, a bridge circuit or a half-bridge circuit. In a first embodiment, the drive switch is arranged as a full-wave bridge or H-bridge, comprising first and second branches, each having a first or second center tap connected to a first or second end of a drive coil that functions as a load, with one end connected to a first voltage potential, e.g., a drive voltage and the other end connected to a second voltage potential, e.g., a ground potential. A first pair of drive switches are arranged in the first branch and connected to each other at the first center tap, and a second pair of drive switches are arranged in the second branch and connected to each other at the second center tap. The drive switch is then controlled so that the first and second ends of the drive coil are alternately connected to the first and second voltage potentials. That is, the upper part of the first branch and the lower part of the second branch on one side, and the lower part of the first branch and the upper part of the second branch on the opposite side, are alternately activated, thus driving an alternating current through the drive coil in a predetermined shape or waveform.

[0024]

[0022] In a second embodiment, the first and second drive switches form a half-bridge circuit connected on one side to a first voltage potential, e.g., a first drive voltage, and on the other side to a second voltage potential, e.g., a second drive voltage. The first and second drive switches are connected at the center tap of the half-bridge circuit and are controllable so that the first end of a drive coil connected to the center tap can alternately connect to the first voltage potential and the second voltage potential.

[0025]

[0023] The drive switches are operated using a default PXM signal or by two or more PXM signals. If only one PXM signal is provided, this PXM signal is applied to the drive switches directly or via an inverter so that each individual drive switch is operated correctly. If two PXM signals are provided, the drive circuit, preferably with an amplifier, can be simplified.

[0026]

[0024] In a preferred embodiment, the step of determining the shape or waveform of the drive current for two or more different frequency components includes superimposing current components individually with respect to at least one of the two different frequency components. Such frequency components may be sinusoidal and may be odd and / or even harmonics. Thus, a function of the drive current in the time domain may be determined mathematically, for example, by a corresponding program module. The PXM signal may be determined in advance or whenever the user selects that the new operating frequency is a frequency component.

[0027]

[0025] Thus, the user of the metal detector can determine which frequency or frequency component is suitable for detecting potential contaminants or metal particles. The signal function or drive current for each frequency component is then determined by the superposition of each frequency component in the time domain. The fundamental angular frequency, i.e., the first frequency component, is ω. In the following equation, the remaining angular frequencies are selected as the 3rd, 7th, and 17th harmonics. The weights of each of the four frequency components are inversely proportional with respect to frequency. i(ωt)=Isin(ωt)+I / 3sin(3ωt)+I / 7sin(7ωt)+I / 17sin(17ωt)

[0026] The user of the metal detector can preferably determine any number of drive current waveforms for different sets of two or more different frequency components. Thus, for different products and / or different potential contaminants, the user can select a drive current waveform having a suitable set of frequency components. In other words, the user can continuously optimize the detection process.

[0028]

[0027] The PXM signal corresponding to the preferably mathematically determined waveform of the drive current can be determined in various ways with desired precision so that only the desired frequency components appear in the frequency domain. If interfering frequency components remain, such interfering frequency components can be suppressed by filters located before or after the phase detector that receives the signal from the sensing coil and the reference signal from the transmitter device.

[0029]

[0028] In a preferred embodiment, the pulse sequence or PXM signal is obtained by approximating the triangular or trapezoidal signal to the waveform of the drive current, preferably mathematically determined, such that the maximum and minimum values ​​of the determined waveform of the drive current and the maximum and minimum values ​​of the triangular or trapezoidal signal correspond to and / or coincide with each other. The switching angles of the falling and rising edges of the PXM signal are then sequentially defined at the maximum and minimum values ​​of the triangular or trapezoidal signal. The approximation of the triangular or trapezoidal signal is preferably made in such a way that the minimum or maximum value of the determined waveform of the drive current and the maximum or minimum value of the triangular or trapezoidal signal overlap at the same location. The basic concept of this morphological approximation is that if two signals have similar time-domain waveforms, they share similar amplitude spectra. Alternatively, one of the PWM or PDM methods may be used to obtain the pulse sequence signal.

[0030]

[0029] In a more preferred embodiment, the described process for preferably mathematically determining the waveform of the drive current for selected frequency components and for determining the corresponding PXM signal is performed automatically by a processor and corresponding program provided within the metal detector. Thus, a user of the metal detector can freely select two or more preferred frequency components, after which the processor and program determine the PXM signal or the associated switching angle of the PXM signal. Alternatively, the switching angles of a set of standard operating frequencies may be selected according to an industrial or non-industrial process that is tightly programmed and stored within the drive control unit and performed.

[0031]

[0030] The waveform of the embossed frequency component of the drive current is preferably determined over the duration of one cycle of the frequency component having the lowest frequency present in the waveform of the drive current. This time segment of the drive current contains all the information of the continuous drive current. Thus, the actual drive current can be generated by the repeated application of the corresponding sequence of PXM signals, which sequentially repeats the preferably mathematically determined waveform of the drive current over the period of the lowest frequency present in the drive current.

[0032]

[0031] The drive current can be supplied directly to the drive coil such that the drive current provided by the transducer and the coil current delivered to the drive coil are identical. However, in a preferred embodiment, the drive current is supplied to the drive coil via an admittance device, which together with the drive coil forms a resonant circuit active in two or more different frequency components of the drive current. By tuning the resonant circuit of the admittance device and the drive coil to the frequency components of the drive current, or vice versa, the current appearing in the drive coil is significantly larger than the drive current flowing through the drive switch or power FET. A multi-frequency transmitter device with a power FET can be sized for a current smaller than the current actually required in the drive coil. Furthermore, when the output impedance of the transducer is high by properly tuning the resonant circuit, the level of the frequency components desirable for detecting contaminants in the product is increased, while other undesirable frequency components are neither increased nor even decreased, thus improving the signal-to-noise ratio and metal detector sensitivity of the resulting signal.

[0033]

[0032] In a preferred embodiment, the admittance device comprises at least a first branch having a first capacitor and a first inductor that together with the drive coil form a first resonant circuit, and a second branch having a second capacitor and a second inductor that together with the drive coil form a second resonant circuit. Preferably, the branches and / or individual capacitors and inductors may be connected to the drive coil individually or in groups to establish individual resonant circuits corresponding to frequency components embossed in the drive current.

[0034]

[0033] Most preferably, one of the stored PXM signals having a specific set of frequency components and the corresponding resonant circuit in the admittance device can be jointly selected by the user of the metal detector. In this way, the metal detector can be instantly optimized for any combination of product and contamination.

[0035]

[0034] The methods and device implementations for generating a multi-frequency drive current on one side and using an admittance device on the other side are particularly advantageous when implemented in combination, but also provide significant improvements when implemented independently of each other. That is, the admittance device of the present invention, which forms two or more individually tuned resonant circuits together with the drive coil, can also be advantageously applied in metal detectors in which the multi-frequency drive current is obtained according to another method.

[0036]

[0035] Detailed aspects and examples of the present invention are described below with reference to the drawings. [Brief explanation of the drawing]

[0037] [Figure 1a] This figure shows a metal detector 1 of the present invention, comprising a converter 4 having four drive switches S41, S42, S43, S44, which are for bridging and are controlled using a selectable pulse width or pulse density modulated signal sPXM, hereafter referred to as a PXM signal, provided by a drive control device 2, and which provide a drive current iD to a drive coil L61 via an admittance device 5. [Figure 1b] Figure 1a shows a metal detector 1 comprising a converter 4 having two drive switches S41 and S42 that form a half-bridge and are controlled using a selectable PXM signal sPXM provided by a drive control device 2, and that supply a drive current iD to a drive coil L61 via an admittance device 5. [Figure 2] Figure 1a shows a metal detector 1 equipped with a drive control device 2 that provides a first PXM signal sPXM1 used to control drive switches S41 and S42 and a corresponding second PXM signal sPXM2 used to control drive switches S43 and S44. [Figure 3] Figure 1a shows a metal detector 1 equipped with a drive control device 2 that allows selection of one of several stored PXM signals sPXM, each having a specific set of frequency components, and an admittance device 5 that allows selective connection of at least one of several branches, each having at least one capacitor C51, C52, C5n and at least one inductor L51, L52, L5n, to a drive coil L61 to create a resonant circuit tuned to the frequency components of the selected PXM signal sPXM. [Figure 4] This figure shows the mathematically determined waveform of the drive current iD or i(ωt) which includes four frequency components ω, 3ω, 7ω, and 17ω, as well as the associated PXM signal sPXM which is determined by approximating the triangular signal iDA to the determined waveform of the drive current i(ωt). [Figure 5] Figures 1a, 1b, 2, and 3 show the complete frequency spectra of the metal detector, illustrating the coil current iL61 in the drive coil L61, the currents iL51 and iL52 in the branches of the admittance device 5, and the drive current iD delivered by the drive switches S41, S42, S43, and S44 in the transducer device 4. The figures show that when the frequency components fD1 and fD2 of the drive current iD are set to the resonance frequencies fRES1 and fRES2 of the admittance circuit 5, the drive current iD is significantly lower than the coil current iL61. [Modes for carrying out the invention]

[0038]

[0036] Figure 1a shows a first embodiment of the metal detector 1 of the invention, comprising a transmitter 10, a receiver 11, a drive coil L61 connected to the output of the transmitter 10, and a balanced coil system 6 having two sensing coils L62 and L63, one end of which is at ground potential and the other end of which is connected to the input stage of the receiver 11. At the input stage 7, the input signal is typically amplified and filtered and then transferred to a phase detector 8. The phase detector 8 enables the distinction of phases of signal components of different origins, as well as obtaining information about the product being observed and, if present, contaminants. A typical phase detector, for example, a frequency mixer or analog multiplier circuit, generates two independent voltage signals representing the in-phase and right-angle components provided by the input stage 7, as well as a reference signal fm provided by the transmitter 10. The output signal of the phase detector 8 is further processed, preferably in a control unit 9 equipped with a signal processor, input / output devices, a keyboard, and a display. Using the control unit 9, the user can control the operation of the metal detector 1. In particular, the user can select the operating conditions of the metal detector, specifically the applied drive current and operating frequency, as described below. The receiver device 11 may further include features commonly known from conventional metal detectors.

[0039]

[0037] The transmitter device 10 is a multi-frequency transmitter designed to provide a drive signal having multiple frequencies, for example, 2 to 8 frequencies, and provides good sensitivity to a wide range of products and contaminants. The transmitter device 10 includes a drive control device 2, a drive device 3, a converter 4, and preferably a drive current i provided by the converter 4. D The system includes an admittance device 5 that transfers the signal to the drive coil L61.

[0040]

[0038] In this embodiment of the present invention, the drive control device 2 receives data related to the state of the drive switches S41, S42, S43, S44 for all clock cycles over a long period of time at the lowest operating frequency, for example, pulse-width modulated signals or PXM signals s PXM no Sui The system includes a memory device 23 having one memory module 231 in which the tuning angles α1, α2, ... are stored at associated addresses. PXM The determination is discussed below with respect to Figure 4. As outlined above, any pulse sequence PXM signal s corresponding to the drive current when applied to drive switches S41, S42, S43, S44 PXM These may be used. Preferably, a pulse-width modulated signal or sequence, or a pulse-density modulated signal or sequence, is applied. Therefore, instead of using the acronym PWM for pulse-width modulated signals and PDM for pulse-density modulated signals, the acronym PXM is used to represent a modulated pulse sequence corresponding to the drive current.

[0041]

[0039] After the system is reset by the reset signal rs issued by the control device 9, the memory module 231 receives the PXM signal s PXM The data is sequentially read from the memory module 231 and sequentially addressed by the address counter 22 using the address signal ad so that it is applied to the drive switches S41, S42, S43, and S44 via the drive device 3. PXM signal s PXMis routed to the input of drive switch S41 via drive elements 31 and 311, to the input of drive switch S42 via drive elements 32 and 321, to the input of drive switch S44 via drive elements 31' and 312, and to the input of drive switch S43 via drive elements 32' and 322. Drive elements 32 and 32' are inverters that ensure that drive switches S42 and S43 are always open when drive switches S41 and S44 are closed, and that drive switches S42 and S43 are always closed when drive switches S41 and S44 are open. In this way, an alternating current flows through drive coil L61 while short circuits are avoided. For the purpose of simplicity of the drawings, elements 31, 31' and 32, 32' are duplicated. However, the output of element 31 may be connected to the inputs of elements 311 and 312, and the output of element 32 may be connected to the inputs of elements 321 and 322 without requiring elements 31' and 32'.

[0042]

[0040] To obtain the phase synchronization operation of the metal detector, a clock device 21 is provided, which delivers a reference signal fm to an address counter 22, a memory device 23, and a phase detector 8.

[0043]

[0041] The data of the PXM signal s PXM is preferably stored over only one period of the minimum operating frequency, so the data is repeatedly read from the memory module 231. Therefore, the segments of the drive current i D shown in FIG. 4 are sequentially and repeatedly generated until the user terminates the operation or changes the settings. Therefore, the address counter 22 counts from the lowest address number to the highest address number and restarts at the lowest address number.

[0044]

[0042] Drive switches S41, S42; S43, S44 have a drive voltage V on one side DThe other end of the PXM signal s is located within a full-wave bridge circuit or H-bridge, comprising a first branch and a second branch, the opposite end of which is connected to ground potential. The first branch has a first center tap connected to the first end of the drive coil L61. The second branch has a second center tap connected to the second end of the drive coil L61. The first pair of drive switches S41, S42 are located within the first branch of the bridge and connected to each other at the first center tap. The second pair of drive switches S43, S44 are located within the second branch and connected to each other at the second center tap. As described above, the PXM signal s PXM By applying the drive voltage V to the drive switches S41, S42; S43, S44, the first and second ends of the drive coil L61 are turned on. D They are alternately connected to the ground potential.

[0045]

[0043] The converter 4, for example, receives PXM signals s PXM The formula used to determine: i(ωt)=Isin(ωt)+I / 3sin(3ωt)+I / 7sin(7ωt)+I / 17sin(17ωt) Accordingly, PXM signals s PXM A drive current i containing the desired frequency components, preferably the lowest frequency harmonics. D Convert to.

[0046] Refer to Figure 4 and explain below the PXM signals s PXM Preferably, after conversion in the converter 4, a drive current i having, for example, the four frequency components of this formula or an approximate value thereof is used. D It is created according to such an equation so that the following is generated. Other harmonics are preferably avoided or suppressed. To increase sensitivity, the desired harmonics are amplified. Furthermore, a relatively small drive current i D High coil current i L61 It is desirable to generate the drive current i. D This is achieved by inducing the drive coil L61 via the admittance device 5.

[0047]

[0044] In the embodiment shown, the admittance device 5 comprises several branches, each comprising capacitors C51, C52, C5n and inductors L51, L52, L5n. The number of branches n is the drive current i D Corresponds to the number of frequency components present within. Each of the branches C51, L51; C52, L52; C5n, L5n, together with the drive coil L61, drives the current i D A resonant circuit is formed that is tuned to the corresponding frequency components ω, 3ω, 7ω, and 17ω. The coil current i in the drive coil L61 is in resonance. L61 The drive current i D It is significantly larger than that. Therefore, on the one hand, the drive current i flowing through the drive switches S41, S42; S43, S44 D While this can be reduced, high coil current i L61 This is achieved. Therefore, the converter 4 can be sized for lower currents and can be constructed at reduced cost.

[0048]

[0045] The metal detector in Figure 1a receives PXM signals s stored in the drive control device 2. PXM It is tuned to a specific set of frequencies. Admittance device 5, having branches C51, L51; C52, L52; C5n, L5n, is fixed to resonate (harmonize) with drive coil L61 at this set of frequency components ω, 3ω, 7ω, 17ω.

[0049]

[0046] Figure 1b shows a half bridge and selectable PXM signals such as pulse width or pulse density modulated signals provided by the drive control device 2. PXM Figure 1a shows a metal detector 1 in an embodiment having a transducer 4 having two drive switches S41 and S42 controlled by a drive current i. D The first voltage potential V is supplied to the drive coil L61 via the admittance device 5. The drive switches S41 and S42 provide the first voltage potential V on one side. D For example, to the first driving voltage, and on the opposite side, to the second voltage potential V SFor example, a half-bridge circuit is formed that is connected to a second drive voltage. Drive switches S41 and S42 are connected at the center tap of the half-bridge circuit, and the first end of the drive coil L61 connected to the center tap is at the first voltage potential V D and the second voltage potential V S It is controlled to connect alternately to each other.

[0050]

[0047] Furthermore, as described above, in a preferred embodiment, the PXM signals s PXM These signals can be generated online and transferred to the converter 4. In Figure 1b, a selector switch S2 is provided, which is controlled by the control unit 9 using the control signal ctrl. The selector switch S2 receives PXM signals s provided by the memory module 23. PXM-STORED PXM signals s provided online by a processor device 25, such as a digital signal processor DSP, which is controlled by a control device 9 using a control signal ctrl, or to receive PXM signals s PXM-ONLINE It can be configured to receive. In the processor device 25, a program is executed, and this program can generate suitable pulse-width modulated signals and / or pulse-density modulated signals. The processor device 25, which is preferably integrated into the control unit 9 together with other circuits, is also for later use It can generate PXM signals that are stored in the memory device 23.

[0051]

[0048] In all embodiments discussed, the PXM signals s PXM The inputs can be selected from the memory device 23 and / or the processor device 25, in the presence of any configuration of the drive switches S41, ..., S44, and, if present, in the presence of any configuration of the admittance device 5. Thus, the features of each embodiment can be freely combined. In particular, the processor device 25 can input PXM signals s having any set of operating frequencies. PXMIt can be most advantageously used to generate online. At the same time, admittance device 5 can be automatically tuned to the same set of operating frequencies. Processor device 25 can replace all memory devices 23 in the disclosed circuitry or PXM signals s PXM It is sometimes used as an alternative source.

[0052]

[0049] Figure 2 shows the first PXM signals used to control the drive switches S41 and S42. PXM1 and the corresponding second PXM signals used to control drive switches S43, S44 PXM2 Figure 1a shows a metal detector 1 equipped with a drive control device 2 that provides the first PXM signal s PXM1 This is stored in the memory module 23A, and the second PXM signal s PXM2 This is preferably stored in the memory module 23B at the corresponding address. Therefore, the address counter 22 receives the first PXM signal s PXM1 and the second PXM signal s PXM2 To read simultaneously, both memory modules 23A and 23B can be addressed synchronously. Memory modules 23A and 23B receive mutually inverted PXM signals s PXM1 and s PXM2 It can store the following. By having two PXM signals, when both PXM signals are at ground potential or both are at the drive voltage V D When at a potential of , the converter 4 is able to have a 0-volt differential at its output. This enables the generation of a trapezoidal wave and better current control.

[0053]

[0050] Figure 3 shows multiple stored PXM signals, each having a specific set of frequency components. PXM Equipped with a drive control device 2 that allows selection of one of the selected PXM signals s PXMFigure 1a shows a metal detector 1 having an admittance device 5 that allows selective connection to a drive coil L61 of at least one of a plurality of branches, each preferably comprising at least one capacitor C51, C52, C5n and at least one inductor L51, L52, L5n, in order to create a resonant circuit tuned to the frequency components of each PXM signal s PXM The data is stored individually in the corresponding memory modules 231, 232, and 23n. The branches of the admittance device 5 can be individually activated using switches S51, S52, and S5n, which are operated using the selector 50.

[0054]

[0051] A specific PXM signal having a desired set of operating frequencies ω1, ω2, ω3, ω4 PXM To select the corresponding resonant circuits or branches C51, L51; C52, L52; C5n, L5n within admittance device 5, the control device 9 provides a frequency selection signal sf to, for example, the address counter 22, optionally to the memory device 23, and to the selector 50. The address counter 22 then addresses the selected memory modules 231, 232, or 23n, and the selector 50, the corresponding switches S51, S52, S5n.

[0055]

[0052] Thus, the metal detector 1 in Figure 3 can be selectively tuned to any set of frequencies selected for specific products and potential contaminants. The resonant circuit can be tuned by adding capacitors and inductors, for example, using switches such as electronic switches. The values ​​of these items can also be changed electronically.

[0056]

[0053] Figure 4 shows four frequency components ω, 3ω, 7ω, and 17ω, but without interference. The mathematically determined waveform of the drive current i(ωt) is shown. i(ωt)=Isin(ωt)+I / 3sin(3ωt)+I / 7sin(7ωt)+I / 17sin(17ωt) Furthermore, the triangular signal i of the mathematically determined drive current i(ωt) to the determined waveform is shown. DA Related PXM signals determined by approximation PXM The drive current i D and coil current i L61 Since Figures 1 and 3 show only two potential gradients, and Figure 2 shows three potential gradients including zero, the mathematically determined waveform of the drive current i(ωt) is made to resemble or approximate it using a triangular or trapezoidal segment. The mathematically determined waveform of the drive current i(ωt) is shown by the dashed line. Approximated triangular signal i DA The waveform closely follows the waveform of the mathematically determined drive current i(ωt). In the first half of the period or positive half-wave, the triangular signal i DA The maximum value of is set to the maximum value of the mathematically determined drive current i(ωt). In the second half or negative half wave of the period, the triangular signal i DA The minimum value of is set to the minimum value of the mathematically determined drive current i(ωt). Approximate triangular signal i DA The actual drive current i D It is not exactly the same, but ideally it is its mirror image. Approximate triangular signal i DA , PXM signals s PXM This is then converted to the actual drive current i within the converter 4. D , approximated triangular signal i DA It is converted to a mirror image. In Figure 4, the actual drive current i is shown in parentheses. D Furthermore, at least approximately, the approximated triangular signal i DA It is shown that this corresponds to [the specified frequency]. However, if higher frequencies are suppressed, the virtual drive current i D This will be even more similar to the mathematically determined drive current i(ωt).

[0057]

[0054] Approximation by triangular or trapezoidal segments has the advantage that undesirable signals occur far from the selected frequency components ω1, ω2, ω3, ω4 and therefore do not significantly affect the measurement. Furthermore, typical locations of such interfering signals in the Fourier spectrum are known, and such interfering signals can be easily suppressed at the input stage 7 of the receiver device 11 by appropriately selected filters. U.S. Patent No. 8,473,235 mentioned above discloses a circuit in which a filter stage is placed following a phase detector. In the present invention, the filtering effort is less extensive. However, any known filtering technique can also be applied to the signal delivered by the sensing coils L62, L63 before or after demodulation, i.e., before and / or after the phase detector 8.

[0058]

[0055] Determined triangular signal i DA Using the PXM signal s PXM The switching angles α1, α2, ... can be determined, which are necessary to control the drive switches S41, S42, S43, S44 in the converter 4. These switching angles α1, α2, ... are determined by the triangle signal i DA It is positioned at the relative maximum and minimum values. As a result, the PXM signal s PXM The falling edge is determined by the triangular signal i DA It is set to occur at the maximum value of the PXM signal s PXM The rising edge is determined by the triangular signal i DA It is set to occur at the minimum value of the obtained PXM signals s PXM or PXM signals PXM1 , s PXM2 ... are then stored in the memory device 23, that is, in one of the memory modules 231, 232, 23n; 23A, 23B.

[0059]

[0056] Figure 4 shows the mathematically determined waveform i(ωt) of the drive current over the length of one period at the lowest frequency ω, and the approximated triangular signal i DA , and the determined PXM signalsPXM is shown. Thus, by repeatedly reading the data of the PXM signal s PXM from the associated memory modules 231, 232, 23n; 23A, 23B, it is possible to establish a continuous stream of the PXM signal s PXM .

[0060]

[0057] Figure 5 shows the coil current i L61 in the drive coil L61, the current i in the branch of the admittance device 5 L51 , i L52 (see Figure 3), and the drive current i D delivered by the drive switches S41, S42, S43, S44 in the converter device 4, for the complete frequency spectrum of the metal detectors of Figures 1a, 1b, 2, and 3. The gradient of the coil current i L61 extends approximately linearly, but the curve of the drive current i D shows strong attenuation at each resonance frequency frequency f RES1 , f RES2 . As a result, the drive current i D is much lower than the coil current i L61 at these spectral positions. Therefore, a large coil current i RES1 , f RES2 can be achieved with a relatively small drive current i D1 , f D2 set to the resonance frequencies f D of the admittance device 5 and the drive coil L61, or vice versa. The explanation of this advantageous attempt can be made with respect to the current i L61 appearing in the branch of the admittance device 5, the current i L51 , i L52 . The current i RES1 , f RES2 at the resonance frequencies f L51 , i L52 of the admittance device 5 is the coil current i L61The admittance device 5 includes passive elements within its branch, such as inductors L51; L52, L5n and capacitors C51, C52, C5n, which, when in a resonant state together with the drive coil L61, generate a current circulating between the drive coil L61 and the branch of the admittance device 5. Advantageously, the resonant frequency f RES1 ,f RES2 The default drive frequency f set to D1 ,f D2 Power circulation at is restricted within the loop formed by the admittance device 5 and the drive coil L61, resulting in zero drive point admittance on an ideal lossless system. As a result, the drive frequency f D1 ,f D2 Drive switches S41, S42, S43, S44, and typically drive current i flowing through the MOSFET. D This refers to the coil current i flowing through the drive coil L61 and the branch of the admittance device. L61 This is significantly lower. Among other advantages, it allows for extending the spectrum towards lower frequencies and enables the driving of the low-impedance drive coil L61.

[0061]

[0058] In the drawings, a preferred embodiment of the admittance device 5 is shown. However, the specified frequency f RES1 ,f RES2 Any other circuit that preferably selectively allows reaching a resonant circuit operating in that manner is also applicable, of course. <Note> [Form 1] A method for operating a metal detector (1), wherein the metal detector (1) comprises a multi-frequency transmitter device (10) having a converter (4) having a plurality of drive switches (S41, S42; S43, S44), wherein the plurality of drive switches (S41, S42; S43, S44) are driven by a drive current (i D ) is alternately conducted to the drive coil (L61), and as a result, the generated electromagnetic field has two or more different frequency components (f D1 ,f D2 The drive control device (2) is driven according to an operation command that exhibits the following behavior: - At least two different frequency components (f D1 ,f D2 ) Regarding the drive current (i D The steps include determining the waveform of ) and - A modulated pulse sequence, such as a pulse-width modulated or pulse-density modulated signal, and the drive current (i D At least one PXM signal (s) corresponding to the determined waveform of ) PXM ) and the step of determining - The at least one determined PXM signal (s) which is determined online or stored in the memory modules (231, 232) according to the provided operation command. PXM ) and the step of selecting, - The at least one determined PXM signal (s PXM The steps include generating and applying ) to control the drive switches (S41, S42; S43, S44) and A method for operating a metal detector (1), including the following. [Form 2] In a method for operating the metal detector (1) described in Embodiment 1, the drive current (i DThe step of determining the waveform of ) is that the sinusoidal frequency components (f) are odd and / or even harmonics. D1 ,f D2 ) and at least two different frequency components (f D1 ,f D2 A method for operating a metal detector (1), which includes superimposing a current component related to ). [Form 3] A method for operating a metal detector (1) according to Embodiment 1 or 2, wherein the drive current (i D The frequency component (f) having the lowest frequency within ) D1 For at least the cycle duration of ), the drive current (i D Determine the waveform of the drive current (i D The drive current (i D A method for operating a metal detector (1), including the step of generating a ). [Form 4] In a method for operating a metal detector (1) according to form 1, 2, or 3, the triangular or trapezoidal signal is used with the drive current (i D The drive current (i) is set such that the determined maximum and minimum values ​​of the waveform and the maximum and minimum values ​​of the triangular signal correspond to and / or coincide with each other. D By approximating the determined waveform of the PXM signal (s PXM The steps of determining the PXM signal (s) at the maximum and minimum values ​​of the triangular or trapezoidal signal PXM A method for operating a metal detector (1), comprising the step of sequentially defining switching angles (α1, α2, ...) for the falling and rising edges of ). [Form 5] A method for operating a metal detector (1) described in any one of Forms 1 to 4, wherein each of them has a frequency component (f D1 ,f D2 Two or more PXM signals (s) having different sets of ) PXM The steps include determining the two or more PXM signals (s PXM) the stored PXM signal (s PXM A method for operating a metal detector (1), comprising the steps of storing in a selectable memory module (231, 232) for generating and applying one of the following. [Form 6] A method for operating a metal detector (1) described in any one of the forms 1 to 5, wherein the PXM signal (s PXM )of, - One side has the first voltage potential (V D ) and the opposite side has a second voltage potential (V S A half-bridge circuit is formed that is connected to the center tap of the half-bridge circuit, and the first end of the drive coil (L61) connected to the center tap is at the first voltage potential (V D ) and the second voltage potential (V S The step of applying power to the first and second drive switches (S41, S42) of the drive switches (S41, S42; S43, S44), which are controlled to be alternately connected to the other, or - One side has the first voltage potential (V D The first and second branches are arranged as a bridge circuit, each having a first or second center tap, the first and second branches being connected to the first voltage potential (V) on the opposite side and to a second voltage potential such as ground potential, and the first or second center tap is connected to the first and second ends of the drive coil (L61) using a first pair of drive switches (S41, S42) located in the first branch and connected to each other at the first center tap, and a second pair of drive switches (S43, S44) located in the second branch and connected to each other at the second center tap, respectively, and the first and second ends of the drive coil (L61) are connected to the first voltage potential (V) on the opposite side. D Steps to apply to the drive switches (S41, S42; S43, S44) which are controlled to alternately connect to the second voltage potential and the first voltage potential. A method for operating a metal detector (1), including the following. [Form 7] A method for operating a metal detector (1) according to any one of embodiments 1 to 5, wherein the PXM signal (s PXM A method for operating a metal detector (1), comprising the step of applying ). [Form 8] A method for operating a metal detector (1) described in any one of Forms 1 to 7, wherein the drive current (i D The step of inducing the two or more different frequency components (f) directly or via the admittance device (5) to the drive coil (L61), wherein the admittance device (5) together with the drive coil (L61) D1 ,f D2 A resonant circuit is formed in an active state within the ) and within the resonant circuit, the coil current (i L61 ) is the drive current (i D A method for operating a metal detector (1), including an induction step that is larger than ). [Form 9] A method for operating a metal detector (1) according to Embodiment 8, comprising the steps of using at least a first branch having a first capacitor (C51) and a first inductor (L51) in the admittance device (5) that together form a first resonant circuit with the drive coil (L61), and a second branch having a second capacitor (C52) and a second inductor (L52) in the admittance device (5) that together form a second resonant circuit with the drive coil (L61). [Form 10] A method for operating a metal detector (1) according to form 8 or 9, wherein a set of frequency components (f D1 ,f D2 PXM signal (s PXM The steps include selecting the set of frequency components (f) of the selected PXM signal (sPXM). D1 ,fD2 A method for operating a metal detector (1), comprising the step of activating a resonant circuit in the admittance device (5) corresponding to the above. [Form 11] A metal detector (1) that operates in accordance with any one of the forms 1 to 10. [Form 12] In the metal detector (1) described in Embodiment 11, the metal detector (1) comprises a multi-frequency transmitter device (10) having a converter (4) having a drive coil (L61) for generating an electromagnetic field within the product, at least one detection coil (L62, L63) arranged to detect fluctuations in the magnetic field caused by metal particles present in the product, and a plurality of drive switches (S41, S42; S43, S44), wherein the plurality of drive switches (S41, S42; S43, S44) are driven by a drive current (i D ) is alternately conducted to the drive coil (L61), and as a result the generated electromagnetic field has two or more different frequency components (f D1 ,f D2 In accordance with an operation command that exhibits ) and the two or more frequency components (f D1 ,f D2 The drive current (i) determined for ) D At least one PXM signal (s) corresponding to the waveform of PXM The data of the at least one PXM signal (s PXM A metal detector (1) is driven by the drive control device (2) using a memory device (23) provided within the drive control device (2), which is selectable for controlling the plurality of drive switches (S41, S42; S43, S44). [Form 13] In the metal detector (1) described in Embodiment 11 or 12, the method for operating the metal detector (1) described in any one of Embodiments 1 to 5 is the PXM signal (s PXM )of, - One side has the first voltage potential (V D ) and the opposite side has a second voltage potential (V SA half-bridge circuit is formed that is connected to the center tap of the half-bridge circuit, and the first end of the drive coil (L61) connected to the center tap is at the first voltage potential (V D ) and the second voltage potential (V S The step of applying power to the first and second drive switches (S41, S42) of the drive switches (S41, S42; S43, S44), which are controllable to be alternately connected to the other, or - One side has the first voltage potential (V D The first and second branches are arranged as a bridge circuit, each having a first or second center tap, the first and second branches being connected to the first voltage potential (V) on the opposite side and to a second voltage potential such as ground potential, and the first or second center tap is connected to the first and second ends of the drive coil (L61) using a first pair of drive switches (S41, S42) located in the first branch and connected to each other at the first center tap, and a second pair of drive switches (S43, S44) located in the second branch and connected to each other at the second center tap, respectively, and the first and second ends of the drive coil (L61) are connected to the first voltage potential (V) on the opposite side. D Steps to apply to the drive switches (S41, S42; S43, S44), which are controllable to alternately connect to the second voltage potential and the first voltage potential, A metal detector (1), including a metal detector. [Form 14] In the metal detector (1) described in form 11, 12, or 13, the transducer (4) is connected to the drive coil (L61) either directly or via an admittance device (5), and the admittance device (5) together with the drive coil (L61) transmits the two or more different frequency components (f D1 ,f D2A metal detector (1) comprising two or more resonant circuits, each having a resonant frequency approximately tuned to one of the following, wherein the admittance device (5) preferably comprises at least a first branch having a first capacitor (C51) and a first inductor (L51) in the admittance device (5) that together with the drive coil (L61) form the first resonant circuit, and a second branch having a second capacitor (C52) and a second inductor (L52) in the admittance device (5) that together with the drive coil (L61) form the second resonant circuit. [Form 15] A metal detector (1) according to Embodiment 14 is provided, wherein switching means (50, S51, S52) are provided that enable the resonant circuits in the admittance device (5) to be individually activated and deactivated according to selection. [Explanation of Symbols]

[0062]

[0059] 1. Metal detector 10 Transmitter device 11 Receiver equipment 2. Drive control device S2 Selector Switch 21 Clock device 22 Address Counter 23 Memory device 23A, 23B memory modules 231, 232, 233 memory modules 3. Drive unit 31, 31' Driving element 32, 32' Inverting drive element 311, 312, 321, 322 amplifiers 4 Converters S41, S42, S43, S44 drive switches 5. Admittance device 50 Selector C51, C52, C53 Admittance Capacitors L51, L52, L53 Admittance Inductors S51, S52, S53 Admittance Switch 6 (Balanced) Coil System L61 drive coil L62, L63 detection coils 7 Input Stages 8 Phase detector 9. Control System / Computer System AD address signal FM clock signal f D1 ,f D2 Frequency components i D Drive current i(ωt) Mathematically calculated drive current i DA Approximated triangular signal i L51 Admittance current in inductor L51 i L52 Admittance current in inductor L52 i L61 Coil current RS reset signal sf frequency selection signal s PXM Pulse width or pulse density modulated signal V D First voltage potential, first drive voltage V S Second voltage potential, second drive voltage

Claims

1. A method for operating a metal detector (1), wherein the metal detector (1) comprises a multi-frequency transmitter device (10) having a converter (4) having a plurality of drive switches (S41, S42; S43, S44), wherein the plurality of drive switches (S41, S42; S43, S44) are driven by a drive current (i Ｄ ) is alternately conducted to the drive coil (L61), and as a result, the generated electromagnetic field has two or more different frequency components (f Ｄ１ , f Ｄ２ The drive control device (2) is driven according to an operation command that exhibits the following behavior: - At least two different frequency components (f Ｄ１ , f Ｄ２ The drive current (i Ｄ The steps include determining a mathematically determined waveform (i(ωt)) for the generation of ) - A modulated pulse sequence which is a pulse width modulated or pulse density modulated signal, and which corresponds to the mathematically determined waveform, and at least one PXM signal (s ＰＸＭ ) and - The at least one determined PXM signal (s) is determined online or stored in the memory modules (231, 232) in accordance with the provided operation command. ＰＸＭ ) the step of selecting, - generating and applying said at least one determined PXM signal(s ＰＸＭ ) to control said drive switches (S41, S42; S43, S44); Includes, The step of determining the at least one PXM signal (sPXM) is: The steps of approximating the triangular or trapezoidal signal (iDA) to the mathematically determined waveform such that the maximum and minimum values ​​of the mathematically determined waveform and the maximum and minimum values ​​of the triangular or trapezoidal signal (iDA) correspond to and / or coincide with each other, The PXM signal (s) at the maximum and minimum values ​​of the triangular or trapezoidal signal (i DA) ＰＸＭ The steps include sequentially defining switching angles (α1, α2, ...) for the falling and rising edges of ), The at least one PXM signal (s ＰＸＭ ) including determining A method for operating a metal detector (1).

2. A method for operating the metal detector (1) according to claim 1, wherein the step of determining the mathematically determined waveform comprises a sinusoidal frequency component (f) that is an odd and / or even harmonic. Ｄ１ , f Ｄ２ ) are at least two different frequency components (f Ｄ１ , f Ｄ２ A method for operating a metal detector (1), which includes superimposing a current component related to ).

3. A method for operating the metal detector (1) according to claim 1 or 2, wherein the frequency component (f) having the lowest frequency present in the mathematically determined waveform Ｄ１ The mathematically determined waveform is determined for at least the cycle duration of the ), and the drive current (i Ｄ A method for operating a metal detector (1), comprising the step of generating a )

4. A method for operating a metal detector (1) according to any one of claims 1 to 3, wherein each of them has a frequency component (f Ｄ１ , f Ｄ２ Two or more PXM signals (s) having different sets of ) ＰＸＭ The steps include determining the two or more PXM signals (s ＰＸＭ ) the stored PXM signal (s ＰＸＭ A method for operating a metal detector (1), comprising the steps of storing in a selectable memory module (231, 232) for generating and applying one of the following:

5. A method for operating a metal detector (1) according to any one of claims 1 to 4, wherein the PXM signal (s ＰＸＭ )of, - One side is the first voltage potential (V Ｄ ) and the opposite side to the second voltage potential (V Ｓ A half-bridge circuit is formed that is connected to the center tap of the half-bridge circuit, and the first end of the drive coil (L61) connected to the center tap is at the first voltage potential (V Ｄ ) and the second voltage potential (V Ｓ The step of applying power to the first and second drive switches (S41, S42) of the drive switches (S41, S42; S43, S44), which are controlled to be alternately connected to the other, or - One side is the first voltage potential (V Ｄ The first and second branches are arranged as a bridge circuit, each having a first or second center tap, the first and second branches being connected to a second voltage potential which is ground potential on the opposite side, and the first or second center tap being connected to the first and second ends of the drive coil (L61) using a first pair of drive switches (S41, S42) located in the first branch and connected to each other at the first center tap, and a second pair of drive switches (S43, S44) located in the second branch and connected to each other at the second center tap, respectively, and the first and second ends of the drive coil (L61) are connected to the first voltage potential (V Ｄ Steps to apply to the drive switches (S41, S42; S43, S44) which are controlled to alternately connect to the second voltage potential and the first voltage potential, A method for operating a metal detector (1), including the following.

6. A method for operating a metal detector (1) according to any one of claims 1 to 4, wherein the PXM signal (s ＰＸＭ A method for operating a metal detector (1), comprising the step of applying )

7. A method for operating a metal detector (1) according to any one of claims 1 to 6, wherein the drive current (i Ｄ The step of inducing the two or more different frequency components (f) directly or via the admittance device (5) to the drive coil (L61), wherein the admittance device (5) together with the drive coil (L61) Ｄ１ , f Ｄ２ A resonant circuit is formed in an active state within the ) and within the resonant circuit, the coil current (i Ｌ６１ ) is the drive current (i Ｄ A method for operating a metal detector (1), including an induction step that is larger than ).

8. A method for operating the metal detector (1) according to claim 7, comprising the steps of using at least a first branch having a first capacitor (C51) and a first inductor (L51) in the admittance device (5) that together form a first resonant circuit with the drive coil (L61), and a second branch having a second capacitor (C52) and a second inductor (L52) in the admittance device (5) that together form a second resonant circuit with the drive coil (L61).

9. A method for operating the metal detector (1) according to claim 7 or 8, wherein the set of frequency components (f Ｄ１ , f Ｄ２ ) PXM signal (s ＰＸＭ The steps include selecting the PXM signal (s ＰＸＭ The set of frequency components (f Ｄ１ , f Ｄ２ A method for operating a metal detector (1), comprising the step of activating a resonant circuit in the admittance device (5) corresponding to the above.

10. A metal detector (1), A drive coil (L61) for generating an electromagnetic field within the product, At least one detection coil (L62, L63) is arranged to detect fluctuations in the magnetic field caused by metal particles present in the product, A multi-frequency transmitter device (10), Equipped with, The multi-frequency transmitter device (10) is A converter (4) having a plurality of drive switches (S41, S42; S43, S44), wherein the plurality of drive switches (S41, S42; S43, S44) are driven by a drive current (i Ｄ ) is alternately conducted to the drive coil (L61), and as a result the generated electromagnetic field has two or more different frequency components (f Ｄ１ , f Ｄ２ A converter (4) is driven according to an operation command that exhibits the following characteristics: The two or more frequency components (f Ｄ１ , f Ｄ２ The determined drive current (i Ｄ At least one PXM signal (s) corresponding to a mathematically determined waveform (i(ωt)) for the generation of ) ＰＸＭ The data of the at least one PXM signal (s ＰＸＭ A memory device (23) provided within the drive control device (2) is selectable for controlling the plurality of drive switches (S41, S42; S43, S44), Equipped with, The aforementioned at least one PXM signal (sPXM) is The triangular or trapezoidal signal (iDA) is approximated to the mathematically determined waveform such that the maximum and minimum values ​​of the mathematically determined waveform and the maximum and minimum values ​​of the triangular or trapezoidal signal (iDA) correspond to and / or coincide with each other. This is determined by sequentially defining the switching angles (α1, α2, ...) for the falling and rising edges of the PXM signal (sPXM) at the maximum and minimum values ​​of the triangular or trapezoidal signal (iDA), The memory device (23) contains, Metal detector (1).

11. In the metal detector (1) according to claim 10, the PXM signal (s ＰＸＭ )but, - One side is the first voltage potential (V Ｄ ) and the opposite side to the second voltage potential (V Ｓ A half-bridge circuit is formed that is connected to the center tap of the half-bridge circuit, and the first end of the drive coil (L61) connected to the center tap is at the first voltage potential (V Ｄ ) and the second voltage potential (V Ｓ The first and second drive switches (S41, S42) of the drive switches (S41, S42; S43, S44) are controllable to be alternately connected to the following, or - One side is the first voltage potential (V Ｄ The first and second branches are arranged as a bridge circuit, each having a first or second center tap, the first and second branches being connected to a second voltage potential which is ground potential on the opposite side, and the first or second center tap being connected to the first and second ends of the drive coil (L61) using a first pair of drive switches (S41, S42) located in the first branch and connected to each other at the first center tap, and a second pair of drive switches (S43, S44) located in the second branch and connected to each other at the second center tap, respectively, and the first and second ends of the drive coil (L61) are connected to the first voltage potential (V Ｄ The drive switches (S41, S42; S43, S44), which can be controlled to alternately connect to the second voltage potential, are to be supplied with Metal detector (1).

12. In the metal detector (1) according to claim 10 or 11, the converter (4) is connected to the drive coil (L61) either directly or via an admittance device (5), and the admittance device (5) together with the drive coil (L61) the two or more different frequency components (f Ｄ１ , f Ｄ２ A metal detector (1) comprising two or more resonant circuits, each having a resonant frequency approximately tuned to one of the following, wherein the admittance device (5) comprises at least a first branch having a first capacitor (C51) and a first inductor (L51) within the admittance device (5) that together form a first resonant circuit with the drive coil (L61), and a second branch having a second capacitor (C52) and a second inductor (L52) within the admittance device (5) that together form a second resonant circuit with the drive coil (L61).

13. A metal detector (1) according to claim 12, wherein a switching means (50, S51, S52) is provided that enables the resonant circuits in the admittance device (5) to be individually activated and deactivated according to selection.

Images