JP5069997B2 - Geomagnetic sensor device - Google Patents

Description

  The present invention relates to a fluxgate type geomagnetic sensor device used in an environment having a large range of environmental temperature change.

  The operation principle of a fluxgate type geomagnetic sensor device conventionally used will be briefly described with reference to the drawings. FIG. 6 is a diagram showing a schematic configuration of the sensor unit 10 of the fluxgate type geomagnetic sensor device. An exciting coil 2 is wound around a part of an annular magnetic core 1 made of a high permeability material such as permalloy. Moreover, the detection coil 3A and the detection coil 3B are wound around the magnetic core 1 with the same number of turns in opposite directions. The detection coil 3 includes detection coils 3A and 3B.

The exciting coil 2 is supplied with, for example, a rectangular wave exciting current I _H having a frequency f ₀ from an exciting unit (not shown). Excitation current I _H magnetomotive force is generated in the excitation coil 2 by the generated magnetic flux φ is interlinks the detection coil 3A and 3B. By setting the value of the excitation current _{IH to} a value sufficient to magnetically saturate the magnetic core 1, the magnetic core 1 periodically repeats magnetic saturation.

FIG. 7 schematically shows the BH characteristics of the magnetic core 1. The horizontal axis represents the magnetic field strength H, and the vertical axis represents the magnetic flux density B. The magnetic flux density of the magnetic core 1 changes between two values of the magnetic flux densities B _B and B _A by the excitation current I _H whose current value changes from I _B to I _A.
A waveform of the sensor unit 10 when there is no geomagnetism Δφ is schematically shown in FIG. The magnetic flux density of the magnetic core 1, in the course of the magnetic flux density is changed from B _B to B _A, in a non-saturation state where the excitation current and the magnetic flux density is proportional, due to the magnetic flux density changes in the detection coil 3A and 3B An induced voltage is generated.

Since the detection coils 3A and 3B are wound in opposite directions, the induced voltages thereof have opposite polarities. Accordingly, the voltage across the detection coil 3 is zero because the induced voltages cancel each other.
FIG. 9 schematically shows the waveform of the sensor unit 10 when there is geomagnetism Δφ. As shown in FIG. 6, the direction of the geomagnetism Δφ is parallel to the detection coils 3A and 3B. If the exciting current is changed to I _A from I _B, the detection coil 3A, since the direction of the magnetic flux φ and geomagnetic Δφ by the exciting current I _A is the same, the change in B _A from the magnetic flux density B _B than when there is no terrestrial magnetism Δφ It begins early and becomes saturated quickly. A change in magnetic flux density when there is no geomagnetism is indicated by a one-dot chain line.

On the other hand, in the detection coil 3B, since the direction of the magnetic flux φ and the geomagnetism Δφ due to the excitation current is opposite, the magnetic flux density changes from B _A to B _B after canceling the geomagnetism. Therefore, the change of the magnetic flux density B _A to B _B starts and delays later than the case where there is no geomagnetism Δφ, and becomes magnetically saturated. A change in magnetic flux density when there is no geomagnetism is indicated by a one-dot chain line.

Thus, a difference is generated in the induced voltage generated in the detection coils 3A and 3B due to the influence of the geomagnetism Δφ. Looking at this in voltage across the detection coil 3, the two pulse waveform negative per from I _B of the exciting current as shown in FIG. 9 for one change to I _A is obtained. By a similar operation also changes to I _B from the opposite direction of the I _A of the exciting current, the two pulse waveforms of positive and negative occurs.
Therefore, the frequency of this pulse waveform is a frequency 2f _{0 that} is twice the frequency f ₀ of the excitation current. The pulse width and amplitude of this pulse waveform vary with the magnitude of the geomagnetism. By converting this pulse waveform (hereinafter referred to as a sensor output signal) into a voltage value, geomagnetism can be detected.

  FIG. 10 is a diagram showing a schematic configuration of a fluxgate type geomagnetic sensor device 200. The configuration shown in FIG. 10 has feedback means for generating a feedback magnetic field having the absolute value equal to that of the geomagnetism Δφ and having the opposite polarity by using the output current of the integrator 68 in the detection coil 3. Each part constituting the fluxgate type geomagnetic sensor device 200 has temperature characteristics. In particular, the integration capacitor has a dominant influence on the temperature variation of the scale factor of the geomagnetic sensor device among the fluctuations of the value due to the temperature change of the integration capacitor and the integration resistor (not shown) in the integrator 68 constituting the detection function unit 60. The integrating capacitor is, for example, a multilayer ceramic capacitor. When the operating range of the geomagnetic sensor device is 0 ° C. to 175 ° C., the value of the integrating capacitor changes by about ± 10%. The change of the integration resistance is sufficiently smaller than that of the integration capacitor and is about + 0.4% (+25 ppm / ° C.), and the influence on the scale factor temperature characteristic of the geomagnetic sensor device is small.

  Since the integrator 68 constitutes the feedback means, the gain fluctuation of the integrator 68 causes the gain fluctuation of the feedback means, and the scale factor of the geomagnetism detection output of the geomagnetic sensor device 200 varies. When the geomagnetic input changes at, for example, about 1 Hz, a 10% change in the integrating capacitor of the integrator 68 becomes a magnitude of about 1% as a variation in the scale factor of the output signal of the geomagnetic sensor device.

A temperature compensation method for a conventional fluxgate type magnetic sensor device is disclosed in, for example, Japanese Patent Application Laid-Open No. H10-228707. The absolute value of the measured magnetic field is equal to the measured magnetic field using the output current, and the polarity is opposite to the measured magnetic field. A feedback means for generating a feedback magnetic field, connected in parallel to a load in the current path of the output current, and by dividing a part of the output current through a thermistor, due to temperature variation of the magnetic sensor device; Methods are known to compensate for the resulting magnetic output signal scale factor temperature variations.
The thermistor is a resistor having a large change in resistance value with respect to a change in temperature, and generally has a negative temperature coefficient. As is well known, the relationship between the resistance value R of the thermistor and the temperature T is approximated by equation (1).
R = R ₀ exp {B (1 / T−1 / T ₀ )} (1)

Here, R ₀ is the thermistor resistance at the temperature T ₀ , and B is the thermistor constant. As can be seen from Equation (1), the resistance value of the thermistor has a negative temperature coefficient and exhibits a characteristic that decreases exponentially as the temperature increases. The method of performing temperature compensation with a thermistor having such temperature characteristics is limited in the method of use, and it is difficult to accurately compensate over a wide temperature range. Therefore, the temperature compensation using the thermistor is limited to applications in which the temperature is within a relatively narrow temperature range or the accuracy improvement by the compensation may be slight.
Japanese Patent No. 3516644

A geomagnetic sensor to be mounted on an oilfield cutting machine is required to have a highly accurate geomagnetism detection performance under a high temperature environment of, for example, 175 ° C. deeply in the ground because of a deep excavation from the ground surface. However, conventionally, there has been no geomagnetic sensor suitable for applications requiring accurate geomagnetic detection in a wide temperature range from the ground surface temperature to the above-described underground temperature.
The present invention has been made in view of such a problem, and provides a geomagnetic sensor device capable of compensating for a scale factor variation in geomagnetic sensor output over a wide temperature range and capable of detecting geomagnetism with high accuracy. For the purpose.

  A geomagnetic sensor device according to the present invention includes a magnetic core, an excitation coil and a detection coil wound around the magnetic core, an excitation unit, a resonance circuit unit, a synchronous detection unit, a carrier signal generation unit, and an integration unit. It comprises. The excitation unit supplies an excitation current to the excitation coil. The resonance circuit unit is connected to the detection coil to form a resonance circuit. The synchronous detection unit synchronously detects the output signal of the resonance circuit unit with reference to the output signal from the excitation unit. The carrier signal generation unit generates a carrier signal of an AC signal. The integrator has an integrator that integrates the output signal of the synchronous detector and the carrier signal, and a feedback means that feeds back the output of the integrator to the control terminal of the integrator to compensate for changes in the integrator's gain. Suppresses the fluctuation of the scale factor of the geomagnetic sensor device output caused by.

  According to the geomagnetic sensor device of the present invention, it is possible to suppress the variation of the scale factor accompanying the temperature change of the geomagnetic sensor output, so that it is possible to improve the accuracy of geomagnetic detection in a wide temperature range.

Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are given to the same components in a plurality of drawings, and the description will not be repeated.
[Example]
A functional configuration example of the fluxgate type geomagnetic sensor device 100 of the present invention is shown in FIG. The fluxgate type geomagnetic sensor device 100 includes a sensor unit 10, an excitation unit 20 that applies an AC voltage to the excitation coil 2, and a detection function unit 30 that is connected to both ends of the detection coil 3.
Since the sensor unit 10 is the same as the sensor unit of the conventional fluxgate type geomagnetic sensor device described in the background art, the description thereof is omitted. Excitation portion 20 includes an oscillation circuit 22, the signal of the frequency _{f 0,} and supplies an excitation current _{I H} to the exciting coil 2. Further, the excitation unit 20 supplies an AC signal having a frequency of 2f ₀ to the synchronous detection unit 34 of the detection function unit 30.

The detection function unit 30 includes a resonance circuit unit 32, a synchronous detection unit 34, and an integration unit 36. The main part of the present invention is that the integrating unit 36 has a temperature compensation function.
The resonance circuit unit 32 includes a capacitor C. The resonance circuit 32 is connected to both ends of the detection coil 3 and forms a resonance circuit with the inductance component of the detection coil 3. The resonance circuit unit 32 detects a sensor output signal of the sensor unit 10. The frequency of the sensor output signal is twice the frequency f ₀ of the excitation signal.

The induced voltage output from the fluxgate type geomagnetic sensor unit 10 is shown as a rectangular waveform in the description with reference to FIG. 9, but is ideally twice the frequency f ₀ by the resonance circuit unit 32. Detected as a sine wave of frequency. The synchronous detection unit 34 performs synchronous detection on the sensor output signal of the resonance circuit unit 32. The output signal of the synchronous detection unit 34 is input to the integration unit 36. Since the magnitude of the geomagnetism is proportional to the magnitude of the waveform of the sensor output signal having the frequency 2f ₀ output from the resonance circuit unit 32, the magnitude of the geomagnetism is converted into a voltage value by synchronously detecting the sensor output signal. It becomes possible.

  The integrator 36 includes an integrator 38 having two systems of input terminals 38a and 38b, and a feedback means 40 that feeds back the output signal of the integrator 38 to the control terminal 38c of the variable impedance element 380. The input terminal 38 a of the integrator 38 is an input terminal for integrating via the variable impedance element 380. The input terminal 38b is an input terminal that integrates via a resistor not shown in FIG.

  The output signal of the synchronous detector 34 is input to one input terminal 38 a of the integrator 38. A carrier signal that is an AC signal generated by the carrier signal generator 50 is input to the other input terminal 38b. The carrier signal is a signal input to the integrator 38 in order to detect a change in the capacitance of the integrating capacitor of the integrator 38. For example, the carrier signal is a rectangular wave signal centered on a common potential (0 V) at 20 kHz. The integrator 38 integrates both the output signal of the synchronous detector 34 and the carrier signal.

  The feedback means 40 detects the temperature change of the integrating capacitor from the output signal of the integrator 38, and negatively feeds the detected result to the control terminal 38 c of the variable impedance element 380 as the output of the feedback means 40. As described above, the temperature variation of the gain of the integrator 38 can be suppressed. The output signal of the integrating unit 36 is connected to the detection coil 3. Supplying the output current of the integrating unit 36 to the detection coil 3 is a feedback means for generating a feedback magnetic field having an absolute value equal to the measured geomagnetism and having a reverse characteristic with respect to the measured geomagnetism. The scale factor linearity of the sensor device 100 is improved. This feedback means controls the output current of the integration unit 36 to be zero and the output of the synchronous detection unit 34 to be zero when geomagnetism is detected.

  Hereinafter, the operation of the integrator 38 and the feedback means 40 will be described in more detail with reference to the drawings for the integrator 36 which is the main part of the present invention. FIG. 2 shows a more specific functional configuration example of the integration unit 36. The integrator 38 is an integrating circuit that integrates the output signal of the synchronous detector 34 and the carrier signal, and includes an operational amplifier 382 having a non-inverting input terminal connected to a common potential, and an output terminal and an inverting input terminal of the operational amplifier 382. Between the integrating capacitor C1, a variable impedance element 380 connected to the inverting input terminal of the operational amplifier 382, and a resistor R5 connected to the inverting input terminal of the operational amplifier 382. The output signal of the synchronous detector 34 is input to the other end of the variable impedance element 380, and the carrier signal is input to the other end of the resistor R5. The variable impedance element 380 has a resistor R1 having one end connected to the inverting input terminal of the operational amplifier 382 and the other end connected to the output signal of the synchronous detector 34, and a P-type impedance change element in parallel with the resistor R1. A junction FET (hereinafter PJFET) 381 is connected. The output signal of the feedback means 40 is connected to the control terminal 38c (gate electrode) that controls the impedance of the PJFET 381. The variable impedance element 380 includes a control terminal 38c for controlling impedance and two terminals having impedance between the two terminals, and controls the magnitude of the impedance between the two terminals by a control voltage input to the control terminal 38c. can do. Hereinafter, the impedance will be described as a resistance value.

  The feedback unit 40 includes a carrier signal extraction unit 42 and a reference comparison unit 44. The output terminal of the integrator 38 is connected to the input terminal of the carrier signal extraction means 42 of the feedback means 40. The carrier signal extraction means 42 includes a synchronous detection circuit 421 that synchronously detects the output signal of the integrator 38 with reference to the carrier signal, and a smoothing circuit 422 that smoothes the synchronous detection output. As the extraction, the output signal of the integrator 38 is synchronously detected, and the synchronously detected signal is smoothed and output.

  Next, the operation of the carrier signal extraction means 42 will be described in more detail with reference to the drawings. First, the output waveform of the integrator 38 that integrates both the carrier signal and the output signal of the synchronous detector 34 is schematically shown in FIG. The horizontal direction in FIG. 3 is time, and the vertical direction is amplitude. FIG. 3A shows a carrier signal that swings around a common potential (0 V) input to the input terminal 38 b of the integrating unit 36, for example, a rectangular wave AC signal having a frequency of 20 kHz. The carrier signal is integrated by the integrator 38 to become a triangular wave as shown in FIG. The magnitude of this triangular wave changes following the temperature change of the integrating capacitor C1.

  On the other hand, the output signal of the synchronous detector 34 input to the input terminal 38 a is also integrated by the integrator 38. The feedback means for supplying the output current of the integrator 38 to the detection coil 3 is controlled so that the output voltage of the synchronous detector 34 becomes zero. As a result, as shown in FIG. The output is a voltage proportional to the magnitude of geomagnetism.

  Since the output signal of the integrator 38 is a signal in which a triangular wave obtained by integrating the carrier signal and a voltage proportional to the magnitude of geomagnetism are superimposed, a waveform obtained by offsetting the triangular wave by the amount of geomagnetism as shown in FIG. It becomes. The horizontal and vertical directions in FIGS. 4A and 4B are the same as those in FIG. The waveform of FIG. 4A becomes the waveform shown in FIG. 4B through the synchronous detection circuit 421 of the carrier signal extraction means 42. FIG. 4B, which is an output waveform of the synchronous detection circuit 421, shows a rectangular wave AC signal generated by synchronous detection of a triangular wave synchronous detection signal integrated with a carrier signal and a DC signal proportional to the geomagnetism. And are superimposed waveforms. The smoothing circuit 421 smoothes the waveform of FIG. By this smoothing, the signal component proportional to the geomagnetism is removed because it is an AC signal. In this way, the carrier signal extraction means 42 extracts a signal component obtained by integrating the carrier signal.

The output terminal of the carrier signal extraction means 42 is connected to the input terminal of the reference comparison means 44. The reference comparison unit 44 includes a reference voltage V _ref and an adder 441 that adds the reference voltage V _ref and the output voltage of the smoothing circuit 422. The reference signal V _ref and the reference voltage V _ref And a control signal for the variable impedance element 380 is generated. The reference voltage V _ref is a reference voltage to be compared in order to detect the temperature variation from the output signal of the carrier signal extraction means 42, and the temperature variation is extremely small. The polarity of the reference voltage V _ref is opposite to that of the output signal of the carrier signal extraction means 42.

The adder 441 is an inverting type adder circuit using an operational amplifier 441a. Since the reference voltage V _ref and the output voltage of the carrier signal extraction means 42 are opposite in polarity, the adder 441 can extract the difference compared to the reference voltage. The output terminal of the adder 441 is connected to the control terminal 38 c of the PJFET 381 as the output terminal of the feedback means 40.

  Since the gain of the integrator 38 with respect to the output signal of the synchronous detector 34 is determined by the resistance value of the variable impedance element 380 and the capacitance value of the integration capacitor C1, changing the voltage at the control terminal 38c of the variable impedance element 380 changes the variable impedance. The resistance value of the element 380 changes, and the gain of the integrator 38 can be controlled. The integrating unit 36 of the present invention detects the change in the capacitance of the integrating capacitor C1 using the carrier signal and the feedback means 40, and controls the resistance value of the variable impedance element 380 by the change, thereby gaining the integrator. Temperature compensation.

The resistance value of the PJFET 381 when the control voltage of the variable impedance element 380 is 0V is, for example, 10 KΩ. If the resistance value of the resistor R1 connected in parallel with the PJFET 381 is 10 KΩ, for example, the combined resistance of the variable impedance element 380 is 5 KΩ. Suppose that the reference voltage V _ref of the reference comparison unit 44 is set to −3 V at a predetermined temperature, the output voltage of the carrier signal extraction unit is 3 V, and the output voltage of the adder 441 is 0 V.

Next, it is assumed that the temperature has increased and the capacitance value of the integrating capacitor C1 has decreased. Note that the influence of temperature changes such as the resistor R5, the variable impedance element 380, and the reference voltage _{Vref on} the gain fluctuation of the integrator 38 is sufficiently small and can be ignored. For example, the temperature coefficient of the reference voltage V _ref is 5 ppm / ° C. or less. As the capacitance of the integrating capacitor C1 decreases, the gain of the integrator 38 increases. As the gain of the integrator 38 increases, the output voltage of the smoothing circuit 422 also increases from 3V. When the output voltage of the smoothing circuit 422 increases in the positive direction, the output voltage of the adder 441 changes from 0 V to a negative voltage. When the output voltage of the adder 441 becomes a negative voltage, the control voltage of the variable impedance element 380 becomes negative, and the resistance value of the variable impedance element 380 increases. As the resistance value of the variable impedance element 380 increases, the gain of the integrator 38 decreases. In other words, the gain of the integrator tries to increase by decreasing the capacitance value of the integrating capacitor C1, but by providing the feedback means 40, feedback control is performed in the direction of decreasing the gain of the integrator, so that the capacitance of the integrating capacitor C1 Even if the value decreases, the gain of the integrator 38 is held constant. Similarly, when the temperature decreases and the capacitance value of the integrating capacitor C1 increases, feedback control is performed and the gain of the integrator 38 is kept constant.

As described above, even if the capacitance value of the integrating capacitor C1 changes due to temperature change, the gain of the integrator 38 is kept constant, and temperature compensation of the gain of the integrator 38 can be performed.
In the present invention, the temperature change of the integrating capacitor of the integrating unit 36 is compensated for temperature by using feedback means, so that the scale factor temperature characteristic of the fluxgate type geomagnetic sensor device 100 is improved in a wide temperature range.

In the embodiment, the waveform of the carrier signal is described as a rectangular wave, but the waveform of the carrier signal may be a sine wave or a triangular wave. Although there is no special restriction on the frequency of the carrier signal, it is desirable to set the frequency outside the band of the geomagnetic sensor device from the viewpoint of preventing the carrier signal from entering the frequency band of the geomagnetic sensor device. In addition, the example in which the reference voltage V _ref is −3 V and the PJFET 381 is used as the variable impedance element 380 has been described. However, the same function can be realized even if these polarities are changed. Is the same as

Further, the carrier signal is described as an example supplied from the carrier signal generation unit 50 different from the excitation unit 20, but the reference signal (2f ₀ ) to the synchronous detection unit 34 may be used as the carrier signal. . In this case, as shown in FIG. 5, the carrier signal generation unit 50 is provided in the excitation unit 20. By doing so, the signal source is shared and the circuit scale can be reduced. The output of the integrating unit 38 is the output of the geomagnetic sensor device 100 as shown in FIG. The output signal of the integration unit 36 includes a signal obtained by integrating the carrier signal in addition to the integration output of the signal obtained by synchronous detection of the sensor output signal by the synchronous detection unit 34. Although the amplitude of this signal is small, it may be difficult to use as output noise of the geomagnetic sensor device 100. In such a case, a smoothing circuit 52 may be provided at the output terminal of the integrating unit 36 as indicated by a broken line in FIGS.

The figure which shows the function structural example of the fluxgate type geomagnetic sensor apparatus 100 of this invention. The figure which shows the more specific structural example of the integration part. It is a figure which shows an integrated waveform typically, (a) is a figure which shows an example of a carrier signal, (b) is a figure which shows the waveform which integrated the carrier signal, (c) is an output signal of the synchronous detection part 34 integrated. FIG. FIG. 4 is a diagram schematically showing output waveforms of an integrator and a synchronous detection circuit 421, (a) is a diagram showing an output waveform of the integrator 38, and (b) is a diagram showing an output waveform of the synchronous detection circuit 421. . The figure which shows the functional structural example in which the carrier signal production | generation part 50 is provided in the excitation part 20 in the fluxgate type geomagnetic sensor apparatus 100 of this invention. The figure which shows schematic structure of the conventional fluxgate type | mold sensor part 10. FIG. The figure which shows the BH characteristic of the magnetic body core 1 typically. The figure which shows typically the waveform of each part of the fluxgate type | mold sensor part 10 in case there is no geomagnetism. The figure which shows typically the waveform of each part of the fluxgate type | mold sensor part 10 in case there exists geomagnetism (DELTA) phi. The figure which shows schematic structure of the conventional fluxgate type | mold geomagnetic sensor apparatus 200. FIG.

Claims (6)

A magnetic core;
An excitation coil and a detection coil wound around the magnetic core;
An excitation unit for supplying an excitation current to the excitation coil;
A resonance circuit unit connected to the detection coil to form a resonance circuit;
Referring to the output signal from the excitation unit,
A synchronous detector for synchronously detecting the output signal of the resonant circuit;
An integrator for feeding back an output current to the detection coil;
A carrier signal generation unit for generating a carrier signal of an AC signal,
The integrator unit integrates the output signal of the synchronous detector unit and the carrier signal;
A geomagnetic sensor device comprising feedback means for feeding back an output of the integrator to a control terminal of the integrator to compensate for a gain change of the integrator. The geomagnetic sensor device according to claim 1,
The feedback means is
Carrier signal extraction means for extracting an integrated value of the carrier signal from the output signal of the integrator;
Comprising reference comparison means for adding the output signal of the carrier signal extraction means and a reference voltage;
The integrator is
An operational amplifier with a non-inverting input terminal grounded;
A capacitor connected between the inverting input terminal and the output terminal of the operational amplifier;
A resistor connected between an inverting input terminal of the operational amplifier and a terminal to which the carrier signal is input ;
Is connected between the terminal to which the output signal from the inverting input terminal and the synchronous detector of the operational amplifier is input, comprising a variable impedance element output signal of the reference comparison means are entered to the control terminal <br A geomagnetic sensor device characterized by the above. The geomagnetic sensor device according to claim 2 ,
The carrier signal extraction means refers to the carrier signal, and a synchronous detection circuit for synchronously detecting the output signal of the integrator;
A geomagnetic sensor device comprising a smoothing circuit for smoothing an output signal of the synchronous detection circuit. The geomagnetic sensor device according to claim 2 or 3 ,
The variable impedance element has an internal resistance that varies depending on a voltage value input to the control terminal. The geomagnetic sensor device according to any one of claims 2 to 4,
The variable impedance element is a geomagnetic sensor device in which a second resistor and a field effect transistor are connected in parallel. The geomagnetic sensor device according to any one of claims 1 to 5,
A geomagnetic sensor device, wherein the carrier signal generation unit is provided in the excitation unit.

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