Metal detection apparatus

Abstract

A metal detection device is provided, comprising a balanced coil system (2) having a transmitter coil (21) connected to a transmitter unit (1) via a first coil terminal (211) and a second coil terminal (212), and first and second receiver coils (22A, 22B) connected to the input of a receiver unit (3). The output of the receiver unit (3) is connected to a signal processing unit (45). The transmitter unit (1) includes a controllable frequency generator (11) that provides an input signal with a selectable operating frequency to the input of an amplifier stage (12). The output of the amplifier stage (12) is connected to an adapter unit (14), the adapter unit (14) including a... A coupling transformer (143) comprising at least one primary coil and at least one secondary coil, the secondary coil having transformer coil terminals (143T) and a plurality of transformer taps (143A, 143B, 143C), and the adapter unit (14) comprising a plurality of tuning capacitors (144A, 144B, 144C) having first and second capacitor terminals, and the adapter unit (14) comprising switching devices (141A, 142A; 141B, 142B; 141C, 142C) by means of which at least one of the tuning capacitors (144A, 144B, 144C) and the secondary coil of the coupling transformer (143) can be connected to the transmitter coil (21). According to the present invention, a plurality of individually selectable resonator channels are provided, each resonator channel, when selected, includes one of the transmitter coil (21), a tapped winding of the secondary coil of the coupling transformer (143), and a tuning capacitor (144A, 144B, 144C) interconnected by a first semiconductor switching device (141A, 141B, 141C) and a second semiconductor switching device (142A, 142B, 141C), wherein the first semiconductor switching device (141A, 141B, 141C) and the second semiconductor switching device (142A, 142B, 141C) can be controlled by a channel selector (140) such that one of the resonator channels is always selectable.

Description

Technical Field

[0001] This invention relates to a metal detection device that uses multiple operating frequencies. Background Technology

[0002] For example, the industrial metal detection equipment described in US8587301B2 is used to detect metal contamination in products. When properly installed and operated, it helps reduce metal contamination and improve food safety. Most modern metal detectors utilize a probe head that includes a "balanced coil system." Detectors designed in this way can detect all types of metal contaminants, including ferrous, non-ferrous, and stainless steel, in a wide variety of products, such as fresh and frozen products.

[0003] Metal detection devices operating on the principle of "balanced coils" consist of three coils: a transmitter coil and two identical receiver coils. These three coils are wound around a non-metallic frame, with each coil typically parallel to the others. The receiver coils usually center the transmitter coil between them. Because the receiver coils are identical, the same voltage is induced in each of them. To receive a zero output signal when the system is balanced, the first receiver coil is connected in series with a second receiver coil having a reverse winding. Therefore, when the system is balanced and there are no contaminants in the observed product, the voltages induced in the receiver coils, with the same amplitude but opposite polarity, cancel each other out.

[0004] However, once the metal particle passes through the coil arrangement and is exposed to the magnetic field, eddy currents are forced to flow within it. These eddy currents generate a secondary magnetic field that first interferes with the primary electromagnetic field near one receiver coil, and then near the other. As the metal particle is conveyed through the receiver coils, the voltage induced in each coil changes (in nanovolts). This change in balance results in a signal at the output of the detection coil, which can be processed, amplified, and possibly filtered in the receiver unit, and subsequently used to detect the presence of metal contaminants in the observed product passing through the metal detection equipment on the conveyor system.

[0005] In the receiver unit, the input signal is typically split into in-phase and quadrature components. The vector synthesized from these components has amplitude and phase angle, which are typical for products and contaminants conveyed through the coil system. To identify metallic contaminants, it is necessary to remove or reduce the "product effect." If the phase of the product is known, the corresponding signal vector can be reduced, thereby achieving higher sensitivity for detecting signals originating from metallic contaminants.

[0006] Methods for eliminating unwanted signals from the signal spectrum utilize the fact that metallic contaminants, products, and other interferences have different effects on magnetic fields, causing the detected signals to differ in phase. Materials with high electrical conductivity induce signals with a high negative reactance signal component and a low resistance signal component. Materials with high magnetic permeability induce signals with a low resistance signal component and a high positive reactance signal component. Signals induced by ferrites are primarily reactive, while signals induced by stainless steel are primarily resistive. Conductive products typically induce signals with a strong resistance component. When products or contaminants are conveyed through metal detection equipment, the phase angle between the resistance and reactance signal components of the signal vector typically remains constant.

[0007] Information about products and contaminants can be obtained by distinguishing the phases of signal components from different sources using a phase detector. The phase detector, such as a mixer or analog multiplier circuit, generates a voltage signal representing the phase difference between the signal input (e.g., the output signal of the receiver coil) and a reference signal provided to the receiver unit by the transmitter unit. Therefore, by selecting the phase of the reference signal to coincide with the phase of the product signal component, a zero phase difference and the corresponding product signal are obtained at the output of the phase detector. If the phase of the signal originating from the contaminant differs from the phase of the product signal, the product signal can be suppressed, while the contaminant signal can be further processed. However, if the phase of the contaminant signal is close to the phase of the product signal, contaminant detection fails because the contaminant signal is suppressed along with the product signal. To separate the phase angle of the product signal from the phase angle of the contaminant, an appropriate operating frequency is determined and applied.

[0008] US8841903B2 discloses a metal detection device comprising a transmitter unit that provides a transmitter signal to a transmitter coil inductively coupled to first and second receiver coils connected to a receiver unit, which is connected to a signal processor. The transmitter unit includes a frequency generator that provides an operating frequency to the input of an amplifier stage, the output of which is connected to the transmitter coil via a coupling transformer. The output of the amplifier stage is connected to a first tap via a first set of switches, and the transmitter coil is connected to a second tap of the same transformer winding via a second set of switches. With this arrangement, a resonant circuit consisting of the transmitter coil and a selectable capacitor can be tuned to a selected operating frequency independently of other parts of the transmitter unit. The amplifier stage includes Class A circuitry, which amplifies the signal with minimal distortion but is inefficient because the power transistors continuously consume current even in quiescent mode.

[0009] US10184908B2 discloses a metal detection device with a coupling transformer, the coupling transformer including a primary coil having a first winding and a second winding, and a secondary coil connected to a transmitter coil, the first winding and the second winding being connected to the output of an amplifier stage. The first winding and the second winding are connected to a power supply voltage via a first terminal and each has at least one tap at the same number of turns counted from the first terminal. The amplifier stage includes a first amplifying wing with at least one tap of a first power transistor connected to the first winding and a second amplifying wing with at least one tap of a second power transistor connected to the second winding. The first amplifying wing amplifies a first half-wave of the input signal, and the second amplifying wing amplifies a second half-wave of the input signal. The secondary coil of the coupling transformer includes multiple taps. A first terminal of the transmitter coil is connected to one of these taps, and a second terminal of the transmitter coil can be selectively connected to another of these taps via a switch. With this arrangement, the transmitter coil can be adapted to the amplifier stage over a wider range. By connecting with a tuning capacitor, the transmitter coil forms a resonant circuit that can be tuned. The first end of the transmitter coil can be selectively connected to one side of one of the tuning capacitors via a switch, and the second end of the transmitter coil is connected directly or via multiple turns of the secondary winding to the other side of the tuning capacitor. The connection between the transmitter coil and the taps of the secondary coil, as well as the connection to the tuning capacitor, is established by means of a suitable power relay, such as Power Relays, Catalogue 202, or Panasonic Industry.

[0010] The problem with this metal detection equipment is that it takes a considerable amount of time to change the system from the first tuning state to the second tuning state, making it almost impossible to change the operating frequency back and forth and maintain optimal tuning while detecting contaminants in the transported products.

[0011] US20150234075A1 discloses a method for compensating for imbalances in a coil system and for suppressing the effects of vibration and noise. The metal detection device is calibrated to suppress signals caused by ferrite, which are similar to signals originating from noise. Therefore, by eliminating signals originating from the ferrite, signals caused by vibration and noise are also automatically suppressed. According to this method, the output signal of the metal detection device is measured in the presence of ferrite in the coil system and digitally adjusted so that the resistive signal component of the ferrite is eliminated. While the described method for compensating for imbalances and suppressing vibration and noise is highly efficient, random interference caused by the transmitter unit itself can still cause problems. Summary of the Invention

[0012] Therefore, the object of the present invention is to provide an improved metal detection device that can be tuned to multiple operating frequencies.

[0013] The metal detection device should be able to be tuned to different operating frequencies in the shortest possible time.

[0014] Furthermore, the metal detection equipment should be redesigned so that random interference caused by the transmitter unit, which is difficult for the electronic compensation system to handle, is reduced or avoided. Moreover, potential heat losses that could cause imbalances should be reduced.

[0015] In a first broad aspect of the invention, a metal detection device is provided, the metal detection device comprising a balanced coil system having a transmitter coil connected to a transmitter unit via first coil terminals and second coil terminals, and first and second receiver coils connected to an input terminal of a receiver unit, the output terminal of the receiver unit being connected to a signal processing unit, the transmitter unit including a controllable frequency generator providing an input signal having a selectable operating frequency to an input terminal of an amplifier stage, the output terminal of the amplifier stage being connected to an adapter unit including a coupling transformer having at least one primary coil and at least one secondary coil, the secondary coil having transformer coil terminals and a plurality of transformer taps, and the adapter unit including a plurality of tuning capacitors having first and second capacitor terminals, and the adapter unit including a switching device by means of which at least one of the tuning capacitors and the secondary coil of the coupling transformer can be connected to the transmitter coil.

[0016] According to the present invention, a plurality of (preferably two, three or more) individually selectable resonator channels are provided, each resonator channel including, when selected, one of the transmitter coil, the tap winding of the secondary coil of the coupling transformer, and a tuning capacitor interconnected by a first semiconductor switching device and a second semiconductor switching device, the first semiconductor switching device and the second semiconductor switching device being controllable by a channel selector such that one of the resonator channels is always selectable.

[0017] The individual selectable resonator channels are arranged in parallel so that they do not interfere with each other. Therefore, the selected resonator channel is not affected by the circuitry of other selectable resonator channels. Consequently, the precise tuning of the selected resonator channel is not compromised by the remaining circuitry.

[0018] In a preferred embodiment, for each resonator channel, when selected, the associated tap winding of the secondary coil of the coupling transformer is connected in series or parallel to the transmitter coil via an associated first semiconductor switching device. The transmitter coil is switchably or securely connected to a transformer coil terminal via one of its coil terminals. Generally, the transformer winding between the transformer coil terminal and the selected transformer tap is defined as the "tap winding". Preferably, for each resonator channel, when selected, the associated tuning capacitor is connected in series or parallel to the transmitter coil via an associated second semiconductor switching device. By connecting the tap winding and tuning capacitor in series or parallel, resonator channels with different characteristics can be created.

[0019] Most preferably, for each resonator channel, when selected, the associated tap winding of the secondary coil of the coupling transformer and the associated tuning capacitor are connected in parallel to the transmitter coil via associated first and second semiconductor switching devices.

[0020] The semiconductor switching device allows switching within nanoseconds, enabling the metal detection device according to the invention not only to switch operating frequencies but also to maintain optimal tuning for each selected operating frequency while switching back and forth at short intervals. Therefore, the metal detection device according to the invention can be equipped with an operating procedure that allows switching and tuning within short time intervals without substantially interrupting the measurement process. Thus, the operating procedure can be designed to perform a change in operating frequency while measuring an object to detect contaminants. Changing the operating frequency allows for the detection of signals from a variety of contaminants and products. Maintaining optimal tuning allows for the measurement of signals with the highest signal-to-noise ratio.

[0021] Semiconductor switching devices, preferably comprising at least one MOS-FET, allow switching between intervals of approximately 20 ns and have a small channel resistance typically below 0.010 ohms. This avoids contact heating and corresponding losses that have undesirable effects on the circuit, as experienced by power relays. Furthermore, suitable semiconductor switching devices can block voltages up to 150V and support currents up to 10A or greater.

[0022] However, power relays are considered more robust to high-voltage oscillations, and therefore such power relays are integrated into the transmitter circuit. Accordingly, the transmitter of the present invention is designed. In a preferred embodiment, for each of the first and second semiconductor switching devices, the channel selector includes at least one isolation driver, such as a photovoltaic driver, whose input and output lines are current-separated from each other. Therefore, the control circuitry is isolated from the power stage.

[0023] Preferably, the first semiconductor switching device and the second semiconductor switching device are bidirectional MOS-FET units. Each bidirectional MOS-FET unit preferably includes a first MOS-FET and a second MOS-FET, both of which have a source terminal, a drain terminal, and a gate terminal. The two matched MOS-FETs preferably have source terminals, which are connected to each other on one hand and to the same first terminal of two diodes on the other hand. Each of the two diodes is connected to the drain terminal of the first MOS-FET or the second MOS-FET through its second terminal, respectively.

[0024] Two MOSFETs connected in series and pointing in opposite directions have four possible states: ON-ON, ON-OFF, OFF-ON, and OFF-OFF. To activate the resonator channel, both MOSFETs of the associated first and second semiconductor switching devices are turned on, and to deactivate the resonator channel, both MOSFETs of the associated first and second semiconductor switching devices are turned off. When on, current can flow through the circuit in both directions. In one direction, current flows through the first MOSFET and its associated first diode, and in the other direction, it flows through the second MOSFET and its associated second diode. When off, current cannot flow in either direction because, with both MOSFETs off, the two diodes impede current flow in either direction.

[0025] The input lines of the isolation drivers, respectively assigned to the first and second semiconductor switching devices of the associated selectable resonator channels, are preferably connected in series, and the input lines of the isolation drivers are all connected to light-emitting diodes. The output lines of the isolation drivers are respectively connected to the input terminals of the first and second semiconductor switching devices of the associated selectable resonator channels. A control voltage is applied to the gate terminals of the interconnected MOS-FETs and is typically applied to the source terminals. Therefore, the isolation drivers and the connected first and second semiconductor switching devices, together with the integrated MOS-FETs, always switch simultaneously without delay or time shift.

[0026] In a particularly preferred embodiment, the light-emitting diodes (LEDs) of the isolation driver are connected in series with a control resistor, individually or together. Thus, one or more LEDs connected in series with the control resistor form a control loop connected to the output of a constant voltage supply, preferably a low-dropout regulator. This circuit has a further advantage and allows for temperature stabilization of the MOS-FET. The voltage across the LEDs and control resistor of the isolation driver is constant. As the temperature increases, the voltage across the LEDs decreases, and the voltage across the control resistor and the current through the control resistor increase proportionally. The higher current causes the LEDs to emit more light toward the photodiode disposed in the isolation driver. Therefore, the control voltage applied to the MOS-FET increases, causing the channel resistance of the MOS-FET, which has already increased with temperature, to decrease again. Thus, the channel resistance of the MOS-FET remains constant when the temperature changes. Attached Figure Description

[0027] The following description, with reference to the accompanying drawings, details and examples of the invention, wherein:

[0028] Figure 1 A preferred embodiment of the metal detection device according to the present invention is shown. The metal detection device includes a transmitter unit 1, a coil system 2, a receiver unit 3, and a control unit 4. The control unit 4 has an operating program 40 and a signal processing unit 45. An adapter module 14 is also provided in the transmitter unit 1. The adapter module 14 includes a plurality of selectable resonator channels 14A, 14B, and 14C, which are tuned to a selected operating frequency.

[0029] Figure 2 A portion of the adapter unit 14 and a channel selector 140 are shown. The channel selector 140 includes control circuitry for controlling a first semiconductor switching device 141A and a second semiconductor switching device 142A. The first resonator channel 14A is selectable using the control circuitry. Detailed Implementation

[0030] Figure 1A preferred embodiment of a metal detection device according to the present invention is shown, the device comprising a transmitter unit 1, a balanced coil system 2 having a transmitter coil 21 and first and second receiver coils 22A, 22B, a receiver unit 3, and a control unit 4. The control unit 4 includes an operating program 40 implemented in a computing device, a signal processing device 45 (e.g., a digital signal processor), and input / output devices. Using the control unit 4, the metal detection device and the implemented measurement and calibration processes are monitored and controlled (i.e., via control signals 411, 414). A conveyor 6 is symbolically shown on which products can be transferred via the balanced coil system 2.

[0031] Transmitter unit 1 includes a controllable frequency generator 11, which provides an input signal r0° with a selectable operating frequency to the input of amplifier stage 12. The output of amplifier stage 12 is connected to adapter unit 14. Adapter unit 14 includes multiple tuning capacitors 144A, 144B, 144C and a coupling transformer 143. The coupling transformer 143 has at least one primary coil and at least one secondary coil, the secondary coil having transformer coil terminals 143T and multiple transformer taps 143A, 143B, 143C. The output lines of amplifier stage 12 are symmetrically connected to suitable taps M1, M1'; M2, M2'; M3, M3' of the primary coil of coupling transformer 143. The configuration of amplifier stage 12 can be designed to operate in any suitable mode (e.g., Class A or Class B mode). In this configuration, the amplifier operates in Class B mode, i.e., one half-wave is applied to tap M1 and the other half-wave is applied to the corresponding tap M1'.

[0032] Coil terminal 143T is connected to the first terminal 211 of transmitter coil 21, and the second terminal 212 of transmitter coil 21 can be connected to one of transformer taps 143A, 143B, and 143C. The winding of the secondary coil of coupling transformer 143 between transformer coil terminal 143T and isolation transformer taps 143A, 143B, and 143C is defined as the "tap winding".

[0033] During operation of the metal detection equipment, a transmitter signal is applied to the transmitter coil 21 of the balanced coil system 2. Furthermore, the transmitter unit 1 provides the receiver unit 3 with an in-phase reference signal r0° and a quadrature reference signal r90°. The transmitter signal induces signals in the same receiver coils 22A and 22B. As long as the system is balanced, i.e., as long as no product, especially not a product contaminated with metal, passes through the coil system 2, these signals have opposite polarities and the same amplitude. If a product, especially a product contaminated with a conductive object, passes through the coil system 2, the amplitude of the signals induced in the same receiver coils 22A and 22B will change, and the oppositely polarized signals will no longer compensate for each other. Thus, the transmitter signal induced in the receiver coils 22A and 22B is modulated by a baseband signal, the amplitude and frequency of which depend on the nature, size, and speed of the conductive object.

[0034] The output signal of the receiver coil is applied to a matching unit 31, which includes, for example, a balancing transformer having a center-tapped primary winding mirrored by the receiver coil and two identical center-tapped secondary windings. The opposite ends of the two identical center-tapped secondary windings are connected to an amplifier 32. The output of the amplifier 32 is connected to a demodulation unit 33, which provides at its output the in-phase and quadrature components of the demodulated receiver signal, i.e., the in-phase and quadrature components of the baseband signal originating from the transported product. The in-phase and quadrature components of the baseband signal provided at the output of the demodulation unit 33 are converted from analog to digital form in analog-to-digital converters 34I and 34Q. The output signals of the analog-to-digital converters 34I and 34Q are forwarded to a signal processing unit 45, such as a known digital signal processor, located in the control unit 4. The signal processing unit 45 suppresses signal components originating from the product and processes signal components originating from contaminants. The receiver unit may also include a filter unit and a gain adjustment unit.

[0035] The measurement process is controlled by an operating program set in control unit 4. The operating frequency is selected according to the planned measurement process using control signal 411. The adapter unit is configured according to the selected operating frequency using control signal 414.

[0036] The adapter unit 14 is equipped with first semiconductor switching devices 141A, 141B, 141C and second semiconductor switching devices 142A, 142B, 142C. The first semiconductor switching devices 141A, 141B, 141C and the second semiconductor switching devices 142A, 142B, 142C can be controlled by a channel selector 140, such that one of the multiple resonator channels 14A, 14B, 14C is always selectable. The channel selector 140, which receives command 414 from the control unit 4, is designed to activate only one of the first semiconductor switching devices 141A, 141B, 141C and the second semiconductor switching devices 142A, 142B, 142C among the resonator channels 14A, 14B, 14C. For example, the uppermost resonator channel 14A is activated by actuating the first semiconductor switching device 141A and the second semiconductor switching device 142A, while the remaining first semiconductor switching devices 141B, 141C and second semiconductor switching devices 142B, 142C are turned off. If the first semiconductor switching devices 141B and 142B of the second resonator channel 14B are activated, then the first semiconductor switching devices 141A, 141C and second semiconductor switching devices 142A, 142C are turned off. If the first semiconductor switching devices 141C and 142C of the third resonator channel 14C are activated, then the first semiconductor switching devices 141A, 141B and second semiconductor switching devices 142A, 142B are turned off. Therefore, the metal detection device in the illustrated embodiment includes three resonator channels 14A, 14B, and 14C, each resonator channel including a pair of first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C. In other embodiments, the metal detection device may include two, four, or more resonator channels 14A, 14B, 14C, ... instead of three resonator channels 14A, 14B, and 14C.

[0037] Each of the resonator channels 14A, 14B, and 14C, when selected, includes a transmitter coil 21, one of the tuning capacitors 144A, 144B, and 144C, and a tapped winding of the secondary coil of the coupling transformer 143. In this embodiment, when the associated pairs of first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C are activated, the associated tuning capacitor 144A, 144B, or 144C and the tapped winding of the secondary coil of the coupling transformer 143 are connected in parallel to the transmitter coil 21.

[0038] The first coil terminal 211 of the transmitter coil 21 is fixedly connected to the coil terminal 143T of the secondary winding of the coupling transformer 143 and the first terminal of the tuning capacitors 144A, 144B, and 144C. The second coil terminal 212 of the transmitter coil 21 is fixedly connected to the common first terminal of each pair of first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C. The second terminal 212 of the transmitter coil 21 can be connected to one of the transformer taps 143A, 143B, and 143C via the first semiconductor switching devices 141A, 141B, and 141C. Therefore, the tap winding of the secondary winding of the coupling transformer 143 between the selected taps 143A, 143B, and 143C and the coil terminal 143T can be connected in parallel to the transmitter coil 21. The second terminal 212 of the transmitter coil 21 can be connected to the second terminals of the tuning capacitors 144A, 144B, and 144C via the second semiconductor switching devices 142A, 142B, and 142C. Therefore, the tuning capacitors 144A, 144B, and 144C can be connected in parallel to the transmitter coil 21. However, the channel selector 140 is preferably designed such that only one pair of the first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C is activated at a time. Using a control signal 414 applied from the control unit 4 to the channel selector 140, one of the resonator channels 14A, 14B, and 14C is selectable to tune the balanced coil system 2 to the operating frequency selected by the control unit 4.

[0039] Therefore, with each change of the operating frequency selected using control signal 411, the associated resonator channel 14A, 14B, or 14C is preferably also automatically selected. Thus, not only the change of operating frequency, but also the tuning of the balanced coil system 2 can be performed in the shortest possible time, which depends on the switching speed of the first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C, and is typically in the range of fractions of a microsecond. Therefore, the operating frequency and tuning of the balanced coil system can be changed back and forth at short intervals during the measurement process.

[0040] Resonator channels 14A, 14B, and 14C are individually selected and deselected, ensuring that the selected resonator channel 14A, 14B, or 14C is not affected by the components of the deselected resonator channel 14A, 14B, or 14C. Resonator channels 14A, 14B, and 14C are actually arranged in parallel and share only a portion of the secondary coil of the transmitter coil 21 and the coupling transformer 143. This design reliably suppresses interference between the components of the deactivated resonator channels 14A, 14B; 14A, 14C; 14B, 14C and the activated resonator channel 14A, 14B, or 14C.

[0041] The first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C are preferably MOS-FET circuits, which are referred to below together with the channel selector 40. Figure 2 To describe in more detail.

[0042] Figure 2A portion of a channel selector 140 disposed within an adapter module 14 and a pair of first and second semiconductor switching devices 141A and 142A for a first resonator channel 14A are shown. The first and second semiconductor switching devices 141A and 142A are preferably configured as bidirectional MOS-FET cells in this embodiment. Each bidirectional MOS-FET cell 141A, 142A; 141B, 142B; 141C, 142C includes a first MOS-FET T1 and a second MOS-FET T2, both having a source terminal S, a drain terminal D, and a gate terminal G. The source terminals S of MOS-FETs T1 and T2 are connected to each other and to the same first terminal (anode) of two diodes D1 and D2, respectively. Both diodes D1 and D2 are connected to the drain terminal D of the first MOS-FET T1 or the second MOS-FET T2 through their second terminals (cathodes). Two MOS-FETs T1 and T2, connected in series and pointing in opposite directions, have four possible states: ON-ON, ON-OFF, OFF-ON, and OFF-OFF, but are always turned on and off in pairs. To activate the first resonator channel 14A, the MOS-FETs T1 and T2 of the associated first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C are both turned on, and to deactivate the first resonator channel 14A, 142A; 141B, 142B; 141C, 142C, the two associated MOS-FETs T1 and T2 of the associated first and second semiconductor switching devices 141A, 142A; 141B, 142B; 141C, 142C are both turned off. When on, current can flow through the MOS-FET circuit in two directions. In one direction, current flows, for example, through the first MOS-FET T1 and the associated first diode D1, and in the other direction, current flows through the second MOS-FET T2 and the associated second diode D2. When turned off, current cannot flow in either direction because, with both MOSFETs T1 and T2 off, the two diodes D1 and D2, with their cathodes facing opposite directions, impede current flow in either direction. The two MOSFETs T1 and T2, along with the two diodes D1 and D2, are matched to allow the desired current to flow in both directions; this desired current is typically in the range of 10A or higher.

[0043] For each of the selectable resonator channels 14A, 14B, and 14C, channel selector 140 includes the same channel selector module. The illustrated channel selector module 140A includes isolation drivers 145A and 146A for the first and second semiconductor switching devices 141A and 142A, using which the control lines of channel selector 140 are current-isolated from the control inputs of semiconductor switching devices 141A and 142A. The isolation drivers 145A and 146A are preferably optically isolated MOS-FET drivers, which include light-emitting diodes 1453A and 1463A and photodiodes 1454A and 1464A, and preferably also include internal or external shutdown circuitry 1455A and 1465A for improving overall switching speed by reducing turn-off time. The current required to drive the internal circuitry is preferably drawn from the low-voltage primary side of the isolation barrier or from the LED current on the input lines 1451A and 1461A of the isolation drivers 145A and 146A. The output lines 1452A and 1462A, located on the secondary side of the isolation barrier of the isolation drivers 145A and 146A, are connected to the input terminals G and S of the associated semiconductor switching devices 141A and 142A.

[0044] The first input terminal G is connected to the gate terminals of two MOS-FETs T1 and T2. The second input terminal S is connected to the source terminals of two MOS-FETs T1 and T2. Therefore, the MOS-FETs T1 and T2 of each semiconductor switching device 141A and 142A are simultaneously turned on and off.

[0045] The light-emitting diodes 1453A and 1463A of the isolation drivers 145A and 146A assigned to the first semiconductor switching device 141A and the second semiconductor switching device 142A are connected in series, so that they always carry the same current and are always turned on and off simultaneously.

[0046] The LEDs 1453A and 1463A of the isolation drivers 145A and 146A are further connected in series with the control resistor 147A, thereby forming a control loop 148A connected to the output of the constant voltage supply device 149A. This circuit allows for temperature stabilization of the MOS-FETs T1 and T2 of the semiconductor switching devices 141A and 142A. The voltage across the LEDs 1453A and 1463A and the control resistor 147A of the isolation drivers 145A and 146A is fixed by the constant voltage supply device 149A. As the temperature increases, the voltage across the LEDs 1453A and 1463A decreases, and the voltage across the control resistor 147A and the current through the control resistor 147A increase accordingly. The higher current causes the LEDs 1453A and 1463A to emit more light toward the photodiodes 1454A and 1464A disposed in the isolation drivers 145A and 146A. Therefore, the control voltages applied to the MOS-FETs T1 and T2 of the semiconductor switching devices 141A and 142A are increased accordingly, causing the channel resistances of MOS-FETs T1 and T2, which had already increased with temperature, to decrease again. Thus, the channel resistances of MOS-FETs T1 and T2 remain constant when the temperature changes. Therefore, temperature changes have no effect on the current flowing in the activated resonator channels 14A, 14B, and 14C. Because the channel resistances of MOS-FETs T1 and T2 are extremely low, the temperature loss and adverse effects of this circuit in the metal detection device are minimal when it is turned on, thereby reducing the calibration requirements.

[0047] The constant voltage supply device 149A has an input terminal for the power supply voltage VCC and a control input terminal EN. A control signal 414 is applied to the control input terminal EN, which varies, for example, between the potential of the power supply voltage VCC and the ground potential. When the ground potential is applied, current can flow through the control loop 148A to ground or to the ground potential applied to the control input terminal EN. The voltage applied to the control loop 148 by the constant voltage supply device 149A remains constant.

[0048] The constant voltage supply device 149A is preferably a low-dropout regulator that can regulate the output voltage supplied to the control loop 148A, even when the power supply voltage VCC is very close to the output voltage. Figure 2 In the diagram, the small figure shows that at time t1, the control input EN has been set to ground potential, causing current to flow through the control loop 148A, i.e., the control resistor 147A and the light-emitting diodes 1453A and 1463A. Therefore, the two semiconductor switching devices 141A and 142A, and thus the first resonator channel 14A, are precisely activated at time t1.

[0049] List of reference numerals

[0050] 1. Transmitter Unit

[0051] 11 Controllable frequency generator

[0052] 12 amplifier stages

[0053] 14 adapter units

[0054] 14A, 14B, 14C Selectable resonator channels

[0055] 140-channel selector

[0056] 140A Channel Selector Module for Resonator Channel 14A

[0057] 141A, 141B, 141C First Semiconductor Switching Device

[0058] 142A, 142B, 142C Second Semiconductor Switching Device

[0059] 143 coupling transformer

[0060] Transformer taps for secondary coils of 143A, 143B, and 143C

[0061] 143T secondary coil coil terminals

[0062] 144A, 144B, 144C tuning capacitors

[0063] 145A, 146A resonator channel 14A isolation driver

[0064] Input lines of 1451A and 1461A isolation drivers

[0065] Input lines of 145A and 146A isolation drivers

[0066] 1453A, 1463A isolation drivers and their LEDs (145A, 146A).

[0067] 1454A, 1464A isolation drivers; 145A, 146A photodiodes.

[0068] Shutdown circuits for 1455A and 1465A isolation drivers

[0069] 147A control resistor

[0070] 148A control loop

[0071] 149A Voltage Supply Unit / Low Dropout Regulator

[0072] 2. Coil System

[0073] 21. Transmitter Coil

[0074] Terminals 211 and 212 of the transmitter coil

[0075] Receiver coils for 22A and 22B

[0076] 3 Receiver Unit

[0077] 31 Matching Unit

[0078] 32 Amplifier

[0079] 33 Phase detector

[0080] 34I, 34Q Analog-to-Digital Converters

[0081] 4 Control Unit

[0082] 40 Operating Procedures

[0083] 411 Control signal applied to the frequency generator

[0084] 414 Control signals applied to the adapter module

[0085] 45 Signal Processing Unit / DSP

[0086] 6 Conveyors

[0087] MOS-FET of T1 and T2 semiconductor switching devices

[0088] D1 and D2 are diodes in the semiconductor switching device.

Claims

1. A metal detection device, comprising: The balanced coil system (2) has the following characteristics: Transmitter coil (21), which is connected to transmitter unit (1) via first coil terminal (211) and second coil terminal (212); and The first and second receiver coils (22A, 22B) are connected to the input terminal of the receiver unit (3), and the output terminal of the receiver unit (3) is connected to the signal processing unit (45). The transmitter unit (1) includes: A controllable frequency generator (11) provides an input signal with a selectable operating frequency to the input of an amplifier stage (12), the output of which is connected to an adapter unit (14), the adapter unit (14) comprising: A coupling transformer (143) having at least one primary coil and at least one secondary coil, the secondary coil having transformer coil terminals (143T) and multiple transformer taps (143A, 143B, 143C); and Multiple tuning capacitors (144A, 144B, 144C) having first and second capacitor terminals, and the adapter unit (14) includes semiconductor switching devices (141A, 142A; 141B, 142B; 141C, 142C), by means of which at least one of the multiple tuning capacitors (144A, 144B, 144C) and the secondary coil of the coupling transformer (143) can be connected to the transmitter coil (21). Its features are, Multiple individually selectable resonator channels (14A, 14B, 14C) are provided. Each resonator channel (14A, 14B, 14C), when selected, includes one of the transmitter coil (21), a tapped winding of the secondary coil of the coupling transformer (143), and one of multiple tuning capacitors (144A, 144B, 144C) interconnected by a first semiconductor switching device (141A, 141B, 141C) and a second semiconductor switching device (142A, 142B, 142C). The first semiconductor switching device (141A, 141B, 141C) and the second semiconductor switching device (142A, 142B, 142C) can be controlled by a channel selector (140) such that one of the multiple resonator channels (14A, 14B, 14C) is always selectable. The channel selector (140) includes at least one isolation driver (145A, 146A) for one of the first semiconductor switching devices (141A, 141B, 141C) and one of the second semiconductor switching devices (142A, 142B, 142C), respectively. With the isolation driver (145A, 146A), the control lines are all current-isolated from the control input terminals of the first semiconductor switching device (141A, 141B, 141C) and the second semiconductor switching device (142A, 142B, 142C).

2. The metal detection device according to claim 1, characterized in that, For each resonator channel (14A, 14B, 14C), when selected, the associated tap winding of the secondary coil of the coupling transformer (143) is connected in series or parallel to the transmitter coil (21) via the associated first semiconductor switching device (141A, 141B, 141C); and / or The isolation drivers (145A, 146A) are photovoltaic drivers.

3. The metal detection device according to claim 1 or 2, characterized in that, For each resonator channel (14A, 14B, 14C), when selected, the associated tuning capacitors (144A, 144B, 144C) are connected in series or in parallel to the transmitter coil (21) via associated second semiconductor switching devices (142A, 142B, 142C).

4. The metal detection device according to claim 1, characterized in that, For each resonator channel (14A, 14B, 14C), when selected, the associated tap windings of the secondary coil of the coupling transformer (143) are connected in parallel to the transmitter coil (21) via associated first semiconductor switching devices (141A, 141B, 141C), and the associated tuning capacitors (144A, 144B, 144C) are connected via associated second semiconductor switching devices (142A, 142B, 142C).

5. The metal detection device according to any one of claims 1, 2, and 4, characterized in that, The multiple individually selectable resonator channels (14A, 14B, 14C) are arranged in parallel.

6. The metal detection device according to any one of claims 1, 2, and 4, characterized in that, The first semiconductor switching device (141A, 141B, 141C) and the second semiconductor switching device (142A, 142B, 142C) are bidirectional MOS-FET units.

7. The metal detection device according to claim 6, characterized in that, Each bidirectional MOS-FET cell includes a first MOS-FET (T1) and a second MOS-FET (T2). The first MOS-FET (T1) and the second MOS-FET (T2) each have a source terminal (S), a drain terminal (D) and a gate terminal (G). The source terminals (S) are connected to each other on one side and connected to the same first terminal of two diodes (D1, D2) on the other side. The two diodes (D1, D2) are each connected to the drain terminal (D) of the first MOS-FET (T1) or the second MOS-FET (T2) respectively through their second terminals.

8. The metal detection device according to claim 6, characterized in that, The input lines (1451A, 1461A) of the isolation drivers (145A, 146A) of the first semiconductor switching device (141A, 141B, 141C) and the second semiconductor switching device (142A, 142B, 142C) respectively assigned to the relevant selectable resonator channels (14A, 14B, 14C) are connected in series. The input lines (1451A, 1461A) of the isolation drivers (145A, 146A) are all connected to light-emitting diodes (1453A, 1463A). The output lines (1452A, 1462A) of the isolation drivers (145A, 146A) are respectively connected to the input terminals (G, S) of the first semiconductor switching device (141A, 141B, 141C) and the second semiconductor switching device (142A, 142B, 142C) of the relevant selectable resonator channels (14A, 14B, 14C).

9. The metal detection device according to claim 8, characterized in that, The LEDs (1453A, 1463A) of the isolation drivers (145A, 146A) are connected in series with the control resistor (147A) to form a control loop (148A), which is connected to the output of the constant voltage supply device (149A).

10. The metal detection device according to claim 9, characterized in that, The constant voltage supply device (149A) is a low differential voltage regulator.

11. The metal detection device according to any one of claims 1, 2, 4, 7-10, characterized in that, The frequency generator (11) and channel selector (140) of the transmitter (1) can be controlled by a control program (40) implemented in the computer system (4), using which the operating frequency and associated resonator channels (14A, 14B, 14C) are selectable.

12. The metal detection device according to claim 11, characterized in that, The control program (40) is designed such that, during the measurement of the transported goods, the operating frequency and the associated resonator channels (14A, 14B, 14C) are alternately changed or keyed between at least two settings or operating frequencies.

13. The metal detection device according to any one of claims 1, 2, 4, 7-10, and 12, characterized in that, The adapter unit (14) includes at least three selectable resonator channels (14A, 14B, 14C).

Images