JP3353533B2 - Magnetometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetometer, and more particularly to a highly sensitive fluxgate magnetometer.

[0002]

2. Description of the Related Art Conventionally, fluxgate type magnetometers are:
As shown in FIG. 16, in the detection unit 1, an excitation coil 4 and a detection coil 5 are wound around a core 3, while a signal of a frequency 2f ₀ is generated by an oscillator 6 of the control unit 2, and this signal is /
The frequency is divided by the frequency divider 2 to f _0, and is applied from the exciter 8 to the excitation coil 4. On the other hand, a magnetic signal detected by the detection coil 5 is input to a band-pass LCR filter 10 through a DC cut capacitor 9 to remove frequency components other than 2f ₀ , and further an AC amplifier 11 and a synchronous rectifier 12
Then, the output V ₀ is derived through the DC amplifier 13. The gate signal of the synchronous rectifier 12 is added with a rectangular wave signal having a frequency of 2f ₀ from the oscillator 6. 14 is a feedback resistor.

[0003]

In the conventional fluxgate magnetometer described above, a rectangular wave signal generated from an excitation oscillator is used as an excitation current. Originally, a triangular wave current having the same gradient of increase and decrease is ideal as the excitation current, but it is very difficult to divide the frequency by 1/2, and a rectangular wave has been used unavoidably. In addition, temporarily
Even if the 周 frequency division can be performed, there is a problem that the original signal and the 分 frequency divided signal are not necessarily similar.

The present invention has been made in view of the above problems, and has as its object to provide a magnetometer which can be excited by a triangular wave current with a simple circuit configuration.

[0005]

According to a first aspect of the present invention, there is provided a magnetometer in which an excitation coil and a detection coil are wound around a core, and the excitation coil of a fluxgate is excited by an oscillator. A first circuit for generating a triangular wave current as an exciting current from the oscillator and detecting a peak point of the triangular wave exciting current, wherein the first circuit detects the peak point of the triangular wave exciting current. A second circuit for detecting a zero crossing point of the triangular wave excitation signal, and a flip-flop that is set and reset by the output of the first circuit and the second circuit. The output of the flip-flop circuit is a gate for synchronous rectification. It is used as a signal.

In this magnetometer, every time the triangular wave excitation current reaches a peak, for example, this is detected by the first circuit, and the flip-flop is set. When the zero-crossing of the excitation current passing through the peak is detected in the second circuit, for example, the flip-flop is reset in response to this, and this flip-flop is added to the synchronous rectifier circuit as a gate signal for synchronous rectification. Can be Therefore, a gate signal for synchronous rectification can be created with a simple circuit configuration.

According to a second aspect of the present invention, there is provided a magnetometer in which an excitation current is applied from an oscillator to the excitation coil of a flux gate formed by winding an excitation coil and a detection coil around a core, and an output from the detection coil is output by a synchronous rectifier circuit. In a synchronous rectification output, a triangular wave current is generated as an exciting current from the oscillator, a rectangular wave signal having the same cycle as the triangular wave current is generated, and the triangular wave current and the rectangular wave signal are received and logically processed. A synchronous signal generating circuit for generating a synchronous rectifying gate signal, and adding the generated synchronous rectifying gate signal to the synchronous rectifying circuit.

In this magnetometer, a rectangular wave signal having the same cycle as the triangular wave current is also output from the oscillation circuit that generates the triangular wave current, and the triangular current and the rectangular wave signal are logically processed to generate a gate signal for synchronous rectification. Therefore, a gate signal for synchronous rectification can be obtained with a simple circuit configuration.

[0009]

The present invention will be described in more detail with reference to the following examples. FIG. 1 is a block diagram showing the configuration of a fluxgate magnetometer according to one embodiment of the present invention. This magnetometer includes a flux gate (detection unit) 20 and an electronic circuit unit (control unit) 21. Although the flux gate 20 and the electronic circuit unit 21 are actually connected by a cable, the cable is not shown here. As the flux gate 20, the thin film type flux gate shown in FIG. 2 is used. This thin film flux gate is provided on a substrate with two thin film cores 28, parallel to each other.
An excitation coil 23 and a detection coil 24 formed to be wound around 29 are provided.

The electronic circuit section 21 includes a transmission circuit 30 for outputting a triangular wave signal as an excitation signal, a constant current circuit 31 for supplying the excitation signal to the excitation coil 23, and an AC for amplifying the output of the detection coil 24. Amplifying circuit 32, synchronous rectifying circuit 33 for synchronously rectifying the detection signal input from differential circuit 32, and integrating circuit 3 for integrating the synchronously rectified signal
4 and a feedback circuit 3 for feeding back the integrated output to the detection coil 24
5 and a peak detection circuit 36 for detecting the peak of the excitation current
A zero-crossing detection circuit 37 for detecting a zero-crossing of the excitation current; and a flip-flop 38 which is set by the peak detection and reset by the zero-crossing detection and uses its output as a gate signal for synchronous rectification of the synchronous rectification circuit 33. ing.

The peak detecting circuit 36, that is, a circuit for detecting a point where the signal gradient changes rapidly, is, for example, a differentiating circuit 4 comprising a capacitor C ₁ and a resistor R _{1 as} shown in FIG.
1 and a comparator 42 are used. FIG. 3 shows the detection in the case where the slope suddenly changes from the + slope to the minus slope.
What is necessary is just to reverse the polarity of the battery connected to the comparator 42 and the (-) input terminal. The battery is provided for quick response, and the (-) input terminal of the comparator 42 may have a zero potential in principle. The zero-crossing detection circuit 37 may use a comparator 43 which receives a zero potential and a detection input as inputs, for example, as shown in FIG. In this case as well, zero crossing is performed at a positive slope, and detection of zero crossing at a negative slope may be performed by reversing the polarity of the comparator 43.

FIG. 5 is a waveform diagram showing the relationship between the waveform of the excitation current of the flux gate, the output waveform, and the gate signal for synchronous rectification. Since an excitation current of a triangular wave is output from the oscillation circuit 30, A-1 in FIG. 5 is an excitation waveform when the input magnetic field H _i = 0 and the field-back magnetic field H _f = 0. Is a form in which the A surface is mapped to the B surface using the BH function as a function, that is, B-1. Here, the core 28 is indicated by a solid line, and the core 29 is indicated by a broken line. The output of the waveform B-1 is added in such a manner that the solid line and the broken line portion cancel each other in both coils of the detection coil 24, and the AC amplification circuit 32
Is 0.

On the other hand, the flip-flop 38 is set in response to the change point from the positive to the negative slope detected by the peak detection circuit 36, and then set by the zero-cross detection circuit 37 at the negative slope. When a zero cross is detected, the flip-flop 38 is reset and the flip-flop 3
The set output of No. 8 has a B-4 waveform indicated by oblique lines in FIG. The output of the flip-flop 38 is applied to the synchronous rectification circuit 33 as a synchronous rectification gate signal. However, even if the gate signal for synchronous rectification is given to the synchronous rectifier circuit 33, the input to the synchronous rectifier circuit 33 is the input magnetic field H.
_{Since i} is 0 when 0, no output is derived.

Next, the input magnetic field H is applied to the flux gate 20.
_{Suppose i} is entered. This excitation waveform is represented by A-2 in FIG.
As shown in, it is assumed that the triangular wave component is superimposed on a DC component H _i, the waveform outputted from the detection coil 24 B-
The result is shown in FIG. According to B-2, the solid line, that is, the output of the detection coil 24 on the core 28 side, and the broken line, that is, the output of the detection coil 24 on the core 29 side, have the input magnetic field _Hi =
It is shifted right and left around the center line at 0. That is, the phases are shifted. This phase shift increases as the input magnetic field _Hi increases. The waveform signal of the solid line and the waveform signal of the dashed line are added to the AC amplifier circuit 32 in an additive manner, and since the polarities are reversed, the two are subtracted, resulting in a signal having a waveform indicated by B-3. The pulse width of the waveform B-3 is, the larger the input field H _i, becomes larger.

On the other hand, a triangular wave input to the excitation coil 23
The gate signal for synchronous rectification formed based on the current is
Since the waveform B-4 is indicated by oblique lines, the synchronous rectification circuit
The output of the path 33 is the shaded portion of the waveform B-3.
You. This signal is integrated by an integration circuit 34 and a feedback circuit 35
And returns to the feedback magnetic field H_fAnd create H
_f= H_iAnd The integrated current output at this time finally enters
Force magnetic field H_iThe output signal is proportional to.

In order to detect the peak and the zero level of the solid-line triangular wave signal and the broken-line triangular wave signal of the waveform A-1 in FIG. 5, respectively, to obtain a gate signal for synchronous rectification, as shown in FIG. And two flip-flops 38
a, 38b, one of which is a SET by a solid triangular wave signal
Signal and a RESET signal, and to the other, a SET signal and a RESET signal based on a dashed triangular wave signal.
In this case, the output of the flip-flop 38a changes between 0 and + B, the amplifier 55 changes the output between 0 and -B, and turns on / off the switching MOSFET 56 for synchronous rectification.

FIG. 7 is a circuit diagram specifically showing the peak detection circuit 36, the zero-cross detection circuit 37, and the like in the case where one flip-flop is provided as in FIG. Here, the peak detecting circuit 36 includes a differentiating circuit 41, a peak detecting comparator 42a for the positive electrode, and a comparator 42b for the negative electrode. Also, a zero-cross detection circuit 3
Reference numeral 7 includes a comparator 43a for a positive electrode that compares a positive input signal with a zero level, and a comparator 43b for a negative electrode that compares a negative input signal with a zero level.

The flip-flop 38 is set when a peak of a positive or negative signal is detected from the peak detection circuit 36, and is used for zero cross detection from the positive to the negative direction or zero cross from the negative to the positive direction by the zero cross detection circuit 37. In response, the set output of the flip-flop 38 is applied to the switching MOSFET 56 via the amplifier 55 as a gate signal for synchronous rectification, turned on / off, and synchronously rectifies the input signal from the AC amplifier circuit 32. , To the integrating circuit 34.

Instead of the circuit shown in FIG.
6. As another circuit example of the zero-cross detection circuit 37, the circuit of FIG. In this circuit, the peak detection circuit 3
In each of the comparators 42a and 42b, differentiating circuits 41a and 41b are connected to the inverting input terminals, and a non-inverting input terminal is connected to a potential source having the same polarity. The comparators 43a and 43b of the zero-cross detection circuit 37 are also configured so that an input signal is supplied to a non-inverting input terminal and a zero-level potential is supplied to an inverting input terminal. However, the amplifier 57 is provided so that the triangular wave signal from the excitation coil 23 is inverted by the amplifier 57 and is added to the comparator 42b of the peak detection circuit 36 and the comparator 43b of the zero-cross detection circuit 37. Therefore, for each of the triangular wave signals having positive and negative polarities, a peak is detected, a SET signal is output, the flip-flop 38 is set, a zero level is detected, a RESET signal is output, and the flip-flop 38 is output. After resetting, the set output of the flip-flop 38 is used as a gate signal for synchronous rectification. This is the same as the circuit of FIG.

FIG. 9 is a block diagram showing a fluxgate type magnetometer according to another embodiment of the present invention. This magnetometer also includes a flux gate (detection unit) 20 and an electronic circuit unit (control unit) 21. Also, in fact,
Although the flux gate 20 and the electronic circuit unit 21 are connected by a cable, the cable is not shown here. As the flux gate 20, for example, a thin film type flux gate shown in FIG. 2 is used.

The electronic circuit section 21 outputs a triangular wave signal as an excitation signal, a constant current circuit 31 for supplying the excitation signal to the excitation coil 23, and differentially outputs the output of the detection coil 24. The derived AC amplifier circuit 32, a synchronous rectifier circuit 33 for synchronously rectifying the detection signal input from the AC amplifier circuit 32, an integration circuit 34 for integrating the synchronously rectified signal, and an integrated output fed back to the detection coil 24. A gate signal for synchronous rectification is created from the feedback circuit 35 and the triangular wave signal and the rectangular wave signal from the oscillation circuit 30, and the gate signal for synchronous rectification 5 is added to the synchronous rectification circuit 33.
8 is provided.

The magnetometer of this embodiment differs from the magnetometer shown in FIG. 1 only in the method of generating the gate signal for synchronous rectification.
Other circuit parts are the same. The oscillation circuit 30 of the magnetometer according to this embodiment is configured by a combination of a comparator and an integration circuit, and a triangular wave signal A and a rectangular wave signal B shown in FIG.
Is output. The synchronous rectification gate signal generation circuit 58 processes the triangular wave signal A and the rectangular wave signal B to generate a synchronous rectification gate signal.

As the gate signal for synchronous rectification, a signal that gates the section of the triangular wave signal A indicated by the solid bold line based on the waveform of FIG. Therefore, first, only the upper half of the rectangular wave signal B is derived (see FIG. 10B). The derivation of only the upper half of the rectangular wave signal B can be realized by the circuit shown in FIG. Next, the upper half of the triangular wave signal A is converted into a rectangular wave and derived (see FIG. 10C). The conversion of the lower half of the triangular wave signal into a rectangular wave can be realized by the circuit shown in FIG.

When the waveform of FIG. 10B is logically inverted in a binary manner, a signal shown in FIG. 10D is obtained. For this conversion, a NOT circuit may be used. Here, when the logical product of the signal of FIG. 10B and the signal of FIG. 10C is taken, FIG.
The signal of (f) of 0 is obtained. This signal is a signal that goes high in the descending gradient section of the upper half of the triangular wave signal A, that is, the section of the solid bold line.

The lower half of the triangular wave signal A is converted into a rectangular wave and derived (see FIG. 10 (e)), and the logical product of the signal of FIG. 10 (d) and the signal of FIG. 10 (e) is calculated. Then, the signal of FIG. 10 (g) is obtained. This signal is a signal that goes high in the rising gradient section of the lower half of the triangular wave signal A, that is, the section of the solid bold line. The conversion of the upper half of the triangular wave signal A into a rectangular wave to derive it can be realized by the circuit of FIG.
Finally, by taking the logical sum of the signal of FIG. 10 (f) and the signal of FIG. 10 (g), the intended gate signal for synchronous rectification can be obtained. This gate signal for synchronous rectification is used as the synchronous rectifier circuit 3
Added to 3.

As the oscillation circuit 30, specific examples of a combination of a comparator and an integration circuit include a triangular wave / square wave oscillator shown in FIG. 14 and a voltage controlled oscillator shown in FIG. 14, a square wave signal is output from an output terminal 59, a triangular wave signal is output from an output terminal 60, and a triangular wave signal is output from an output terminal 61 and a square wave signal is output from an output terminal 62 in FIG. However, these triangular-wave / square-wave oscillators and voltage-controlled oscillators are generally well-known circuits.

[0027]

According to the first aspect of the present invention, the triangular wave signal applied to the excitation coil of the flux gate is used to
Since a gate signal for synchronous rectification is created, a triangular wave, which is an ideal excitation waveform, can be used without worrying about the phase of synchronous rectification. Also, when the detection unit and the control unit are relatively close, there is almost no phase shift of synchronous rectification,
No phase adjustment circuit is required. In addition, there is an effect that a synchronous rectification signal can be easily created from a triangular wave excitation signal.

According to the second aspect of the present invention, a triangular wave signal output for excitation from the oscillation circuit and a rectangular wave signal having the same period obtained when the triangular wave signal is generated are output. Is logically processed to generate a synchronous rectification gate signal, so that a synchronous rectification gate signal generation circuit having a simple configuration can be obtained by combining only a comparator and a logic circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a fluxgate magnetometer according to an embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of a thin film type flux gate used in the magnetometer of the embodiment.

FIG. 3 is a circuit diagram showing an example of a peak detection circuit used in the magnetometer of the embodiment.

FIG. 4 is a circuit diagram showing an example of a zero-cross detection circuit used in the magnetometer of the embodiment.

FIG. 5 is a waveform chart for explaining the operation of the magnetometer of the embodiment.

FIG. 6 is a circuit diagram showing a part of a circuit for generating a gate signal for synchronous rectification of the magnetometer of the embodiment.

FIG. 7 is a circuit diagram showing another example of a circuit for generating a gate signal for synchronous rectification of the magnetometer of the embodiment.

FIG. 8 is a circuit diagram showing still another circuit example for generating a gate signal for synchronous rectification of the magnetometer of the embodiment.

FIG. 9 is a block diagram showing a configuration of a fluxgate magnetometer according to another embodiment of the present invention.

FIG. 10 is a waveform chart for explaining creation of a gate signal for synchronous rectification of the magnetometer of the embodiment.

FIG. 11 is a circuit diagram of a circuit for deriving an upper half of a positive and negative rectangular wave for generating a gate signal for synchronous rectification of the magnetometer of the embodiment.

FIG. 12 is a circuit diagram of a circuit for converting only a lower half of a triangular wave signal into a rectangular wave for generating a gate signal for synchronous rectification of the magnetometer of the embodiment.

FIG. 13 is a circuit diagram of a circuit for converting only the upper half of the triangular wave signal to a rectangular wave for generating a gate signal for synchronous rectification of the magnetometer of the embodiment.

FIG. 14 is a circuit diagram showing an example of a specific circuit used as an oscillation circuit of the magnetometer of the embodiment.

FIG. 15 is a circuit diagram showing another example of the specific circuit used as the oscillation circuit of the magnetometer of the embodiment.

FIG. 16 is a circuit block diagram showing a conventional fluxgate magnetometer.

[Description of Signs] 20 flux gate 23 excitation coil 30 oscillation circuit 33 synchronous rectification circuit 36 peak detection circuit 37 zero cross detection circuit 38 flip-flop

Claims (2)

(57) [Claims] 1. A magnetometer in which an excitation current is applied from an oscillator to an excitation coil of a flux gate formed by winding an excitation coil and a detection coil around a core, and an output from the detection coil is synchronously rectified by a synchronous rectifier circuit and output. A first generator for generating a triangular wave signal as an exciting current from the oscillator and detecting a peak point of the triangular wave exciting current;
Circuit for detecting the zero-cross point of the triangular wave excitation current
A circuit and an output of the first and second circuits,
And a flip-flop to be reset, wherein an output of the flip-flop circuit is used as a gate signal for synchronous rectification. 2. A magnetometer in which an excitation current is applied from an oscillator to an excitation coil of a fluxgate formed by winding an excitation coil and a detection coil around a core, and an output from the detection coil is synchronously rectified by a synchronous rectifier circuit and output. A triangular wave signal is generated as an exciting current from the oscillator, a rectangular wave signal having the same cycle as the triangular wave current is generated, and the triangular wave current and the rectangular wave signal are logically processed to generate a gate signal for synchronous rectification. A magnetometer comprising a synchronizing signal generating circuit for performing the following.