INDUCTIVE MEASURING APPARATUS AND CALIBRATION DEVICE AND METHOD

Abstract

The invention relates to a 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), the measuring device having a calibration device for reducing an interference influence on the measurement result, characterized in that the calibration device is configured such that a current pulse can be introduced into the coil (3; 4; 16) from a current source (DC) and the signal processing device (7, 8, 9; 18) can perform a measurement value correction using the calibration signal generated by the current pulse and can determine a measurement result from the response and the measurement value correction.

The invention further relates to a measuring method.

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), the measuring device having a calibration device for reducing an interference influence on the measurement result, characterized in that the calibration device is configured such that a current pulse can be introduced into the coil (3; 4; 16) from a current source (DC) and the signal processing device (7, 8, 9; 18) can perform a measurement value correction using the calibration signal generated by the current pulse and can determine a 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 (R.sub.dr) and the first electrical resistor (R.sub.dr) is connected to a second electrical resistor (R.sub.d) and the second electrical resistor (R.sub.d) is connected to the coil (3; 4; 16) and the electrical connection between the first and second electrical resistors (R.sub.dr, R.sub.d) 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 (R.sub.dr) 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 (R.sub.d) is greater than the first resistor (R.sub.dr).

8. Measuring device according to one of the three preceding claims, characterized in that the first electrical resistor (R.sub.dr) is 10 kΩ to 30 kΩ and/or the second electrical resistor (R.sub.d) 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.

Description

[0035] The figures show:

[0036] FIG. 1: Block diagram of a measuring device;

[0037] FIG. 2: current pulses and resulting calibration signals;

[0038] FIG. 3: calibration device

[0039] As shown in FIG. 1, the measuring device may comprise an AC power source with an AC generator 1 and an electronic amplifier 2. The transmitter may have a transmitter coil 3. The receiver may have a receiver coil 4. The transmitter coil 3 and receiver coil 4 may be spatially separated from each other. Transmitter coil 3 and receiver coil 4 may be located in air 5 above a ground 6 to allow examination of the ground 6.

[0040] A signal processing device connected to the transmitter 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 control 10, a component assembly or circuit 11, and an electrical switch 12 to enable an electrical pulse to be applied to the receiver coil 4.

[0041] For a measurement, an alternating current can be introduced into the transmitter coil 3 by the alternating current source 1, 2. The transmitter coil 3 thereby generates an electromagnetic wave. A part 13 of the electromagnetic wave passes through the ground 6 and thus reaches the receiver coil 4. A part 14 of the electromagnetic wave reaches the receiver coil 4 exclusively through the air 5. The ground 6 causes a phase shift of the part 13 relative to the part 14. This phase shift provides a measure for characterizing the ground 6. A response is induced in the receiver coil 4 by the electromagnetic wave 13, 14. The response is passed to the signal processing device 7, 8, 9, which determines a measured value from the response.

[0042] For example controlled by a control, the AC source 1, 2 can be temporarily switched off. Within a measurement pause thus created, a current pulse can be introduced into the receiver coil 4 controlled by the control 10. The control 10 can, for example, open and close the switch 12 so as to introduce a current pulse into the receiver coil 4. This may be done periodically. For example, FIG. 2 shows rectangular current pulses TF(IN) periodically introduced into the receiver coil 4 during measurement pauses. This causes the receiver coil 4 to generate a response TF(OUT) shown in FIG. 2. The portion 15 of the response TF(OUT) can now be used as a calibration signal. The calibration signal 15 temporally follows the end of a current pulse. Temporally after the end of a calibration signal, a measurement can be continued, i.e. the AC source 1, 2 can be switched on again, for example. The calibration signal 15 can be a damped oscillation as shown in FIG. 2.

[0043] 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 to determine a measurement value therefrom.

[0044] A calibration device may also be provided for a transmitter coil 3, as is shown in FIG. 1. If a transmitter or a receiver comprises a plurality of coils, a further calibration device may be provided for each additional coil. The measuring device is scalable in this sense.

[0045] For example, the following oscillation function TFA(t), which depends on the time t, can be adapted to the calibration signal 15 by the signal processing devices 7, 8, 9.

TFA(t)=Ae.sup.−+tRe(e.sup.j(ω.sup.d.sup.t+ϕ))+B.

[0046] The parameters determined in this way can be inserted into the following frequency function:

[00001]$G_{\mathrm{TFA}}\left(j\omega \right)=\frac{j\omega +\alpha }{{\left(j\omega +\alpha \right)}^2+{\omega }_d^2}.$

[0047] The value G.sub.TFA(jω) determined in this way is a measure of the phase shift caused by the coil and can therefore be a correction value. This measure can be taken into account when the measured value is determined by the signal processing device 7, 8, 9.

[0048] FIG. 3 shows further possible details. Shown is an equivalent circuit diagram 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 DC. The DC voltage source DC is connected to a first electrical resistor R.sub.dr through an electrical conductor. The first electrical resistor R.sub.dr is connected to a second electrical resistor R.sub.d through an electrical conductor. The first electrical resistor R.sub.dr may be 20 kΩ. The second electrical resistor R.sub.d may be 200 kΩ. The electrical conductor between the first electrical resistor R.sub.dr and the second electrical resistor R.sub.d is connected to an electrical switch 19, which can be opened and closed controlled by a microcontroller MC. When the electrical switch 19 is closed, an electrical current flows from the DC voltage source DC to ground 20. When the electrical switch 19 is opened and closed again under the control of the microcontroller MC, an electrical pulse is applied to the coil Rx coil as shown in FIG. 2.

LIST OF REFERENCE SIGNS

[0049] 1: AC generator [0050] 2: Amplifier/electronics [0051] 3: Transmitter coil [0052] 4: Receiver coil [0053] 5: Air [0054] 6: Ground [0055] 7: Amplifier/electronics [0056] 8: ADC, analog-to-digital converter [0057] 9: Signal processor [0058] 10: Control [0059] 11: TFA [0060] 12: Switch [0061] 13: Electromagnetic wave [0062] 14: Electromagnetic wave [0063] 15: Calibration signal [0064] 16: Equivalent circuit diagram for a coil “Rx coil” [0065] 17: Switching device [0066] 18: Signal processing device [0067] 19: Switch [0068] 20: Ground [0069] Dc: DC voltage source [0070] R.sub.dr: First electrical resistor [0071] R.sub.d: Second electrical resistor