INDUCTIVE MEASURING DEVICE WITH CALIBRATION DEVICE AND METHOD

Description

[0001] The invention relates to a measuring device comprising a transmitter for transmitting a measurement signal, a receiver for receiving a response to the transmitted measurement signal, and a signal processing device for determining a measurement result from the response. The transmitter and / or the receiver have at least one coil. The measuring device comprises a calibration device for reducing interference with the measurement result. The invention further relates to a method for operating the measuring device.

[0002] From the publication DE 197 31 560 A1, a measuring device with a transmitter for transmitting a measurement signal and a receiver for receiving a response to the transmitted measurement signal is known for locating and identifying metallic munitions below the earth's surface. A transmitter coil of the transmitter generates a time-varying magnetic field as a measurement signal. This can generate an eddy current in a ferromagnetic munition and, with it, a secondary field as a response. This induces a location signal in the receiver's receiving coils, which is then evaluated.

[0003] According to EP 1 289 147 A1, in a measuring device of the type mentioned above, an excitation signal is generated as a measurement signal by an oscillating circuit. The excitation signal can be influenced by the approach or presence of an object. This influence is detected by a receiver of the measuring device. The determined response is evaluated by the measuring device.

[0004] Document DE 10 2009 026 403 A1 also discloses a measuring device with a transmitter for transmitting a measurement signal and a receiver for receiving a response to the transmitted measurement signal. The transmitter comprises a primary circuit containing a transmitting coil. The receiver comprises a secondary circuit with a receiving coil. There is a short-circuit path through which the transmitting coil can be inductively coupled to the receiving coil for diagnostic purposes.

[0005] The publication WO 2018 / 014891 A1 describes a calibration method for electromagnetic induction measuring systems and a suitable device for this purpose. A calibration method is provided which, when measuring apparent electrical conductivity in the ground, takes into account influences that are attributable to the measuring device itself or originate from the environment and affect the measurement. This method enables the individual calibration of an electrical induction system, taking environmental influences into account. For calibration, an induction measuring device with at least one transmitter and at least one receiver is set up at least two heights above the ground to be measured. The apparent electrical conductivities are calculated using a forward model and then optimized using an inversion method.

[0006] EP 2 657 726 A2 discloses a method for electromagnetically measuring the electrical conductivity of a medium. A transmitting coil applies an alternating magnetic field (primary field) to the medium, inducing currents in the medium and forming another alternating magnetic field (secondary field). The secondary field is measured with a receiving coil, and the conductivity of the medium is evaluated from this. According to the invention, the primary field at the location of the transmitting coil is measured directly or indirectly, and the contribution of the primary field to the field at the location of the receiving coil is evaluated from this. Due to the superposition principle, the contributions of the primary field and the secondary field to the overall field at the location of the secondary coil overlap without interference. The voltage induced in the secondary coil, which serves as the measurement signal, is linearly dependent on this overall field.Therefore, the contribution of the primary field and thus also its temperature-dependent drift can be corrected if the primary field at the location of the transmitting coil and the spatial arrangement of the transmitting and receiving coils relative to each other are known.

[0007] A method and a device for MRI imaging are known from DE 10 2012 203 111 A1. A system and a method related to MRI excitation are known from US 2010 / 0241389 A1. A wireless sensor is disclosed in US 2011 / 0115497 A1. The invention disclosed in US 2005 / 0190100 A1 relates to weather radar calibration. A method for controlling a magnetic resonance system is known from DE 10 2011 083 959 A1. US 2012 / 0139776 A1 discloses a method for obtaining calibration parameters for antennas.

[0008] The present invention is intended to enable particularly precise measurements to be carried out with little technical effort using a measuring device of the aforementioned type.

[0009] The problem is solved by a measuring device having the features of the first claim. A method for solving the problem comprises the features of the secondary claim. Advantageous embodiments emerge from the subclaims.

[0010] A measuring device comprises a transmitter for transmitting a measurement signal, a receiver for receiving a response to the transmitted measurement signal, and a signal processing device. The signal processing device is set up such that it can be used to determine a desired measurement result from the response. The transmitter and / or the receiver have a coil. A calibration device is provided in order to be able to reduce any interference with the measurement result. The calibration device is set up such that a current pulse is introduced into the coil of the receiver from a current source. Alternatively or additionally, the calibration device is set up so that a current pulse can be introduced into the coil of the transmitter from a current source. A calibration signal is generated by introducing a current pulse. The signal processing device orA signal processing device connected to the receiver coil performs a measurement correction using the calibration signal generated by the current pulse. The respective signal processing device can determine a measurement result from the response and the measurement correction. The calibration signal contains information about an interference effect from the coil. "Measurement correction" means that this interference effect is determined by the signal processing device and a result is output as the measurement result that no longer includes this determined interference effect. With minimal technical effort, a measurement result is obtained in which distorting interference is reduced. Measurement results can therefore be determined with particularly high accuracy.

[0011] The calibration device is advantageously configured so that a measurement is interrupted and the current pulse is applied to the coil during the interruption. "Interrupting" means that a measurement pause is inserted. After the measurement pause has expired, the measurement is resumed. This allows interference during a measurement to be identified. This further improves the ability to determine measurement results with greater accuracy. A measurement can be interrupted by temporarily switching off the transmitter, thus preventing the transmission of a measurement signal.

[0012] In one embodiment, the calibration device comprises a switching device configured so that the current pulse can be introduced into the coil by switching the switching device on and then off. The current pulse can be generated using technically simple means. It is also possible to introduce a current pulse into the coil during a measurement pause using technically simple means.

[0013] Advantageously, the signal processing device is configured to use a signal generated by the coil after the switching device is switched off and before a measurement is performed or continued as a calibration signal. In this embodiment, the calibration signal is thus a response following the current pulse introduced into the coil. This further contributes to the ability to determine a measurement signal with greater precision.

[0014] The switching device preferably comprises a DC voltage source and a first electrical resistor. The DC voltage source is connected to the first electrical resistor. This means that there is an electrical conductor that is electrically connected to the DC voltage source on the one hand and to the first electrical resistor on the other, so that a current can flow from the DC voltage source to the first electrical resistor. The electrical conductor can be a metal wire or comprise such a wire. The electrical conductor can be a conductor track of a circuit board. The electrical conductor can be made of copper.

[0015] The first electrical resistor is connected to a second electrical resistor by an electrical conductor, allowing a current to flow from the DC voltage source through the first resistor to the second electrical resistor. The second electrical resistor is connected to the coil by an electrical conductor, allowing current to flow from the first electrical resistor through the second electrical resistor into the coil.

[0016] The electrical connection or conductor between the first and second electrical resistors is electrically connected to ground via a switch. When the switch is closed, current flows from the DC power source to ground. When the switch is open, current cannot flow from the DC power source to ground. This current then flows to the coil. When the switch is opened and then closed again, a current pulse is introduced into the coil.

[0017] The switching device comprises a microcontroller which is configured so that the microcontroller can control the opening and closing of the switch.

[0018] Overall, this switching device is capable of introducing a current pulse into the coil in a suitable manner within a short measurement pause in order to generate a calibration signal.

[0019] The first electrical resistance is advantageously at least 1,000,000 times greater than the short-circuit resistance of the switch, allowing the current to be diverted almost entirely through the closed switch, preventing it from flowing through the second resistor. The short-circuit resistance is advantageously less than 10 mΩ. The first electrical resistance can be between 10 kΩ and 30 kΩ.

[0020] The second electrical resistance is advantageously larger than the first. The second electrical resistance can be between 100 kΩ and 300 kΩ.

[0021] The signal processing device is advantageously configured to adapt a predefined oscillation equation to the calibration signal during operation. Parameters of the oscillation equation are determined through this adaptation. A correction value is determined from the parameters using a frequency equation. In this way, the signal processing device can determine a measurement signal adjusted for a correction value.

[0022] Advantageously, a calibration device controls a measurement in such a way that the measurement is repeatedly interrupted, and during each interruption, the calibration device introduces a current pulse into the coil. Temporal changes in interference can thus be continuously taken into account. This makes it possible to further improve the measurement result.

[0023] The transmitter may comprise an electrical voltage source with which a voltage can be applied to a coil of the transmitter or to an electrical resonant circuit of the transmitter to generate a magnetic or electromagnetic measurement signal. The transmitter and / or the receiver may comprise one or more coils. The signal processing device may comprise an amplifier with which the response is amplified.

[0024] The signal processing device may comprise an analog-to-digital converter with which the response can be digitized. The signal processing device may comprise a processor with which the response is evaluated. The signal processing device may comprise an output device with which a processed response, i.e., a measured value, is output.

[0025] The measuring device can be configured to determine a phase difference between the measurement signal and the response, and then evaluate the determined phase difference. The measuring device can be configured to be used for the analysis of a subsurface. The measuring device can be configured to determine a measure of the electrical conductivity of a subsurface.

[0026] The output device may comprise a monitor and / or a speaker for outputting the processed response. The output device may comprise a data interface via which the processed response can be transmitted to another device.

[0027] The measuring device can be configured to measure the apparent electrical conductivity of soils. The measuring device can be configured to allow the examination of near-surface soil down to a depth of, for example, 40 or 50 meters.

[0028] A suitable measuring device typically comprises a transmitter with a coil, also called a "transmitting coil," and a receiver with one or more coils, also called "receiving coil(s)." There is a predetermined distance between the transmitting coil and the one or more receiving coils. By exciting the transmitting coil with an alternating current in the frequency range typically between 100 Hz and 100 kHz, a magnetic field can be generated, also known as the primary field. Due to the electrical conductivity of the soil, the primary field induces induced currents, which in turn generate a magnetic field, the so-called secondary field. The secondary field is usually several orders of magnitude smaller than the primary field. The receiver can measure both fields together to determine the apparent electrical conductivity (ECa) of a soil.

[0029] Interference can affect the accuracy of a measurement result. Such interference can be caused, for example, by temperature influences or noise. The present invention can reduce such interference, thus improving measurement results.

[0030] Every coil can cause interference. The present invention makes it possible to at least reduce any interference from each coil. A measuring device according to the invention is accordingly scalable.

[0031] Other components such as analog-to-digital converters can also lead to temperature-dependent interference. To reduce such interference, temperature sensors are preferably used for the corresponding components. These sensors measure the temperature of the respective component. For example, calibration measurements can be used to determine the interference as a function of temperature. The respective interference can then be determined using measured temperatures. On this basis, further correction values ​​can be created for the respective components. These correction values ​​are also preferably used to obtain a measured value that is as unaffected by such interference as possible.

[0032] The invention also relates to a method for operating a measuring device, in which a measurement is interrupted at least once, preferably several times, within one second. A calibration signal is generated during each measurement pause to determine measurement results by incorporating the calibration signals. Thus, interference is continuously detected. Measurement results are obtained that are not influenced by these interferences. Therefore, particularly precise measurements can be performed without requiring excessive effort.

[0033] They show: Figure 1: Block diagram of a measuring device; Figure 2: Current pulses and resulting calibration signals; Figure 3: Calibration device

[0034] As in the Figure 1As shown, the measuring device may comprise an alternating current source with an alternating current generator 1 and an electronic amplifier 2. The transmitter may have a transmitting coil 3. The receiver may have a receiving coil 4. The transmitting coil 3 and the receiving coil 4 may be spatially separated from each other. The transmitting coil 3 and the receiving coil 4 may be arranged in the air 5 above a soil 6 in order to be able to examine the soil 6.

[0035] A signal processing device connected to the transmitting coil 3 may comprise an electronic amplifier 7, an analog-to-digital converter 8, and a signal processor 9. The signal processor 9 may comprise a microcontroller. A calibration device may comprise a controller 10, a component group or circuit 11, and an electrical switch 12 for introducing an electrical pulse into the receiving coil 4.

[0036] For a measurement, an alternating current can be introduced into the transmitting coil 3 via the alternating current source 1, 2. The transmitting coil 3 thereby generates an electromagnetic wave. A portion 13 of the electromagnetic wave passes through the ground 6 and thus reaches the receiving coil 4. A portion 14 of the electromagnetic wave reaches the receiving coil 4 exclusively through the air 5. The ground 6 causes a phase shift of portion 13 relative to portion 14. This phase shift provides a measure for characterizing the ground 6. A response is induced in the receiving coil 4 by the electromagnetic wave 13, 14. The response is forwarded to the signal processing device 7, 8, 9, which determines a measured value from the response.

[0037] For example, controlled by a controller, the alternating current source 1, 2 can be temporarily switched off. During a measurement pause thus created, a current pulse can be introduced into the receiver coil 4 under the control of the controller 10. The controller 10 can, for example, open and close the switch 12 in order to introduce a current pulse into the receiver coil 4. This can happen periodically. Figure 2 Rectangular current pulses TF(IN), which are periodically introduced into the receiver coil 4 during measurement pauses. As a result, the receiver coil 4 generates a Figure 2shown response TF(OUT). The portion 15 of the response TF(OUT) can now be used as the calibration signal. The calibration signal 15 follows the end of a current pulse. After the end of a calibration signal, a measurement can be continued, for example, the AC source 1, 2 can be switched on again. The calibration signal 15 can be used as shown in the Figure 2 shown to be a damped oscillation.

[0038] The signal processing device 7, 8, 9 processes both a measurement signal originating from the receiver coil 4 and a calibration signal 15 originating from the receiver coil 4 in order to determine a measured value therefrom.

[0039] A calibration device can also be provided for a transmitting coil 3, as shown in the Figure 1is shown. If a transmitter or receiver comprises multiple coils, a separate calibration device can be provided for each additional coil. The measuring device is scalable in this sense.

[0040] For example, the following oscillation function, which depends on time t, TFA ( t ) to the calibration signal 15 by the signal processing device 7, 8, 9. TFA t = Ae − αt Re e j ω d t + ϕ + B .

[0041] The parameters determined in this way can be used in the following frequency function: G TFA jω = jω + α jω + α 2 + ω d 2 .

[0042] The value G TFA (jω) thus determined is a measure of the phase shift caused by the coil and can therefore be used as a correction value. This measure can be taken into account when determining the measured value by the signal processing device 7, 8, 9.

[0043] The Figure 3shows further possible details. Shown is an equivalent circuit 16 for a coil "Rx coil," a switching device 17, and a signal processing device 18. The switching device 17 comprises a DC voltage source. The DC voltage source is connected by an electrical conductor to a first electrical resistor R dr. The first electrical resistor R dr is connected by an electrical conductor to a second electrical resistor R d. The first electrical resistor R dr can be 20 kΩ. The second electrical resistor R d can be 200 kΩ. The electrical conductor between the first electrical resistor R dr and the second electrical resistor R d is connected to an electrical switch 19, which can be opened and closed under the control of a microcontroller MC. When the electrical switch 19 is closed, an electrical current flows from the DC voltage source to ground 20.If the electrical switch 19 is opened and closed again under the control of the microcontroller MC, the process is as shown in the . Figure 2 As shown, an electrical impulse is introduced into the coil Rx coil. List of reference symbols

[0044] 1: Alternating current generator 2: Amplifier / Electronics 3: Transmitting coil 4: Receiving coil 5: Air 6: Ground 7: Amplifier / Electronics 8: ADC, Analog - Digital - Converter 9: Signal processing 10: Control 11: TFA 12: Switch 13: Electromagnetic wave 14: Electromagnetic wave 15: Calibration signal 16: Equivalent circuit for a coil "Rx coil" 17: Switching device 18: Signal processing device 19: Switch 20: Ground Dc: DC voltage source R dr : First electrical resistance R d : Second electrical resistance

Claims

1. Measuring device having a transmitter (1, 2, 3) for transmitting a measurement signal, a receiver (4) for receiving a response to the transmitted measurement signal and a signal processing device (7, 8, 9; 18) for determining a measurement result from the response, the transmitter and / or the receiver having a coil (3; 4; 16), characterized in that the measuring device comprises a calibration device for reducing an interference influence on the measurement result, wherein the calibration device is configured such that a current pulse can be introduced into the coil (3; 4; 16) of the receiver from a current source (DC) and the signal processing device (7, 8, 9; 18) can perform a measurement value correction using a calibration signal generated by the current pulse for determining the measurement result from the response and can determine a measurement result from the response and the measurement value correction, and / or a current pulse can be introduced into the coil (3; 16) of the transmitter from a current source (DC) and a signal processing device (7, 8, 9; 18) connected to the coil (3; 16) of the receiver can perform the measurement value correction using a calibration signal generated by the current pulse and determine the measurement result from the response and the measurement value correction.

2. Measuring device according to claim 1, characterized in that the calibration device is configured such that during the interruption of a measurement the current pulse is introduced into the coil (3; 4; 16).

3. Measuring device according to one of the preceding claims, characterized in that the calibration device comprises a switching device (17) configured such that the current pulse can be introduced into the coil (3; 4; 16) by switching on and subsequently switching off the switching device (17).

4. Measuring device according to the preceding claim, characterized in that the signal processing device (7, 8, 9; 18) is configured such that it processes as a calibration signal a signal generated by the coil (3; 4; 16) after the switching device (17) is switched off and before a measurement is performed.

5. Measuring device according to one of the two preceding claims, characterized in that the switching device (17) comprises a DC voltage source (DC) connected to a first electrical resistor (Rdr) and the first electrical resistor (Rdr) is connected to a second electrical resistor (Rd) and the second electrical resistor (Rd) is connected to the coil (3; 4; 16) and the electrical connection between the first and second electrical resistors (Rdr, Rd) is connected to ground (20) via a switch (19), so that, current flows from the direct current source (DC) to ground (20) when the switch (20) is closed and current flows from the direct current source (DC) to the coil (3; 4; 16) when the switch (19) is open, and the switching device (17) comprises a microcontroller (MC) which is configured such that the opening and closing of the switch (19) can be controlled by the microcontroller (MC).

6. Measuring device according to the preceding claim, characterized in that the first electrical resistor (Rdr) is advantageously 1000000 times greater than a short-circuit resistance of the switch (19).

7. Measuring device according to the preceding claim, characterized in that the second electrical resistor (Rd) is greater than the first resistor (Rdr).

8. Measuring device according to one of the three preceding claims, characterized in that the first electrical resistor (Rdr) is 10 kΩ to 30 kΩ and / or the second electrical resistor (Rd) is 100 kΩ to 300 kΩ.

9. Measuring device according to one of the four preceding claims, characterized in that the short-circuit resistance of the switch (19) is less than 10 mΩ.

10. Measuring device according to one of the preceding claims, characterized in that the signal processing device (7, 8, 9; 18) is configured such that during operation it adapts a predetermined oscillation equation to the calibration signal and thereby determines parameters of the oscillation equation and determines a correction value from the parameters using a frequency equation and determines a measurement signal corrected by the correction value.

11. Measuring device according to one of the preceding claims, characterized in that the calibration device controls a measurement in such a way that a measurement is recurrently interrupted and during each interruption the calibration device introduces a current pulse into the coil (3; 4; 16).

12. Measuring device according to one of the preceding claims, characterized in that one or more temperature sensors are present, by means of which the temperature of one or more components is measured and one or more correction values are determined on the basis of measured temperatures and by means of the signal processing device (7, 8, 9; 18) a measurement result can also be determined taking into account the one or more further correction values.

13. Method for operating a measuring device according to one of the preceding claims, characterized in that within one second a measurement is interrupted at least once, preferably several times, within each measurement pause a calibration signal is generated in order to determine measurement results involving the calibration signals.