JP3580035B2 - Magnetometer - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetometer using a fluxgate.
[0002]
[Prior art]
As shown in FIG. 5, the conventional fluxgate magnetometer includes a detection unit 1 and a control unit 2, and the excitation coil 4 and the detection coil 5 are wound around a core 3 as the detection unit 1. The oscillator 6 of the control unit 2 oscillates a signal of frequency 2f ₀ , divides this into a signal of frequency f _{0 by} a 分 frequency divider 7, and supplies the signal to the excitation coil 4 via an exciter 8. In the control unit 2, a capacitor 15 is connected to the detection coil 5 in parallel. Also, this parallel circuit is connected to the capacitor 9 of the DC component cutting further includes a buffer amplifier 16 of high input impedance between the AC amplifier 11 and the capacitor 9, 2f ₀ bandpass active filter 17 is connected . 2f ₀ bandpass active filter 17 includes an operational amplifier, and a capacitor and a resistor. In this magnetometer, the resonance circuit constituted by the detection coil 5 and the capacitor 15 resonates with the frequency of 2f _0, where the harmonic component other than f ₀ and 2f ₀ is attenuated, only the component of 2f ₀ is derived Is done. Signal of 2f ₀ is passed through an AC amplifier 11, are synchronous rectification with synchronous rectifiers 12 and is output through a DC amplifier 13 (see actual fair No. 6-23980).
[0003]
[Problems to be solved by the invention]
In the above-mentioned conventional magnetometer, a crystal oscillator is used as an oscillator, but its oscillation frequency is fixed, and it cannot cope with a shift in a natural resonance frequency due to, for example, a variation in parts used in an LCR filter. However, there has been a problem that it is complicated and expensive. In particular, the crystal oscillator requires special attention in assembly (for example, soldering, cleaning, etc.), and also has a problem that a power supply also requires three power supplies of +5 V and other circuits ± 15 V in the oscillator section. Was.
[0004]
The present invention has been made in view of the above problems, and has as its object to provide a magnetometer which can be manufactured with high sensitivity at low cost and which can be easily assembled.
[0005]
[Means for Solving the Problems]
The magnetometer of the present invention includes an excitation coil and a detection coil wound around a core, a comparator, a limiter, and an integration circuit. The comparator compares a reference voltage with an output of the integration circuit, and outputs the output via the limiter. A triangular wave generating circuit that generates a triangular wave by inputting to an integrating circuit, a double frequency generating circuit that doubles the frequency of the triangular wave, and an excitation circuit that supplies a triangular wave output from the triangular wave generating circuit to the excitation coil A detection circuit that derives a voltage corresponding to an external magnetic field with the detection coil, a resonance circuit that receives a detection signal from the detection circuit, and sets a unique resonance frequency to twice the frequency of the excitation signal, the signal from the frequency doubler circuit, fees and synchronous rectifier circuit for synchronous rectification of the output of the resonant circuit, in the oN state, the output of the synchronous rectifier circuit to the detection circuit And a switch circuit for back, the switch circuit off, in order to match the excitation frequency to the natural resonant frequency of the resonant circuit, and a constant adjusting means when adjusting the time constant of the integrating circuit.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a circuit block diagram showing a fluxgate magnetometer according to one embodiment of the present invention. The fluxgate magnetometer according to this embodiment includes a detection unit 1 and a control unit 2 as in the conventional case. In the detection unit 1, an excitation coil 22 and a detection (reception) coil 23 are wound around a core 21.
[0007]
The control circuit 2 includes a comparator 24, a limiter 25 that receives the output of the comparator 24 and outputs a constant level, a time-constant variable-type integration circuit 26 that receives and integrates the output of the limiter 25, A current amplifier (excitation circuit) 27 that receives the triangular wave signal of frequency f output from the circuit 26 and excites the excitation coil 22, and a double frequency that receives the outputs of the comparator 24 and the integration circuit 26 and outputs a signal of frequency 2f A generation circuit 28, a preamplifier (detection circuit) 29 for amplifying a reception signal of the detection coil 23, a resonance circuit 30 whose unique resonance frequency is set to 2f, a buffer circuit 31, and input from the buffer circuit 31 There is provided a synchronous rectifier circuit 32 for synchronously rectifying the detection signal with a signal having a frequency of 2f from the frequency doubler 28. The integration circuit 26 includes changing the time constant by changing the resistance value, the variable resistor VR ₁ for adjusting the frequency of the output triangle wave.
[0008]
The resistance value of the variable resistor VR _1, for example, manually change the time constant of the integrating circuit 26 is varied, the frequency of the triangular wave output will change.
In this embodiment, the comparator 24 receives the output of the limiter 25 at a certain level at one input terminal, receives the output of the integration circuit 26 at the other input terminal, and compares the voltages of both inputs. While the output of the limiter 25 is larger, the comparator 24 supplies a high-level output to the limiter 25. Even if the high-level output of the comparator 24 fluctuates due to the fluctuation of the power supply voltage or the like, the limiter 25 always outputs a constant level output by the limit operation and supplies the output to the integration circuit 26. The integration circuit 26 charges the integration capacitor for a time corresponding to the time constant of the time constant circuit. As time elapses, the level of the output of the integration circuit 26 rises linearly. Since the output of the integrating circuit 26 is applied to one input terminal of the comparator 24, when the level reaches the other input terminal of the comparator 24, that is, the output level of the limiter 25, the output of the comparator 25 becomes low. Level. Therefore, the output of the limiter 25 also becomes low level, the integration circuit 26 discharges in response thereto, and the output of the integration circuit 26 gradually becomes low level. This low level signal is applied to one input terminal of the comparator 24. Therefore, the output of the comparator 24 goes high again soon. Then, the integration capacitor of the integration circuit 26 is charged via the limiter 25 in the same manner as described above. As described above, the triangular wave signal having the constant frequency f is output from the integration circuit 26. This triangular wave signal is supplied to the excitation coil 22 via the current amplifier 27, and the excitation coil 22 is energized.
[0009]
A voltage corresponding to the external magnetic field is induced in the detection coil 23 by the excitation by the excitation coil 22, and the induced voltage is amplified by the preamplifier 29, and is applied to the synchronous rectification circuit 32 via the resonance circuit 30 and the buffer circuit 31. Since the resonance frequency of the resonance circuit 30 is set to 2f, the resonance circuit 30 derives only the signal component of the frequency 2f among the excitation frequency f and its harmonic components. Therefore, the S / N ratio can be significantly increased. The detection signal input to the synchronous rectification circuit 32 is synchronously rectified by the gate signal of the frequency 2f from the 2f frequency generation circuit 28 and output. In this magnetometer, the switch 33 is always closed and the output of the synchronous rectifier circuit 32 is fed back to the detection coil 23.
[0010]
In this magnetometer, even if the natural resonance frequency deviates from the excitation frequency due to variation in the LCR constant of the resonance circuit 30 or due to aging, the switch 23 is turned off to form an open circuit and an appropriate external magnetic field (geomagnetic If the variable resistor of the integrating circuit 26 is changed so that the output of the buffer circuit 31 is maximized in a state in which the excitation frequency f is added to the resonance circuit 30, the excitation frequency f is adjusted to the inherent resonance frequency of the resonance circuit 30. And the gate signal to the synchronous rectifier circuit 32 automatically becomes twice the excitation frequency, so that the correlation is always maintained, so that the sensitivity can be adjusted to the highest sensitivity.
[0011]
Each circuit constituting the magnetometer of the embodiment shown in FIG. 1 may be designed as appropriate as to what circuit is to be used. As an example, FIG. 2 shows the comparator 24, the limiter 25, and the integrating circuit 26. FIG. 3 shows a specific example of the preamplifier 29, the resonance circuit 30 and the buffer circuit 31, and FIG. 4 shows a specific example of the 2f frequency generation circuit 28 and the synchronous rectification circuit 32.
[0012]
【The invention's effect】
According to the present invention, the switch circuit is turned off and the time constant of the integration circuit is adjusted, so that the maximum sensitivity is always obtained in order to match the excitation frequency with the natural resonance frequency of the resonance circuit. Also, unlike a crystal oscillator, a triangular wave oscillation circuit is composed of a comparator, a limiter, and an integration circuit, so that it can be produced at low cost, is easy to assemble, and has two power supplies.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing a magnetometer according to an embodiment of the present invention.
FIG. 2 is a circuit connection diagram showing a specific example of a comparator, a limiter, and an integration circuit that constitute the magnetometer of the embodiment.
FIG. 3 is a circuit connection diagram showing a specific example of a preamplifier, a resonance circuit, and a buffer circuit constituting the magnetometer of the embodiment.
FIG. 4 is a circuit connection diagram showing a specific example of a 2f frequency generation circuit and a synchronous rectification circuit constituting the magnetometer of the embodiment.
FIG. 5 is a circuit block diagram showing a conventional magnetometer.
[Explanation of symbols]
21 core 22 excitation coil 23 detection coil 24 comparator 25 limiter

Claims (1)

An excitation coil and a detection coil wound around the core,
A triangular wave generating circuit that includes a comparator, a limiter, and an integrating circuit, compares the reference voltage with the output of the integrating circuit, inputs the output to the integrating circuit via the limiter, and generates a triangular wave;
A double frequency generating circuit that doubles the frequency of the triangular wave,
An excitation circuit that energizes the excitation coil with a triangular wave output from the triangular wave generation circuit;
A detection circuit that derives a voltage corresponding to an external magnetic field with the detection coil,
A resonance circuit that receives a detection signal from the detection circuit and sets a unique resonance frequency to twice the frequency of the excitation signal;
A synchronous rectifier circuit for synchronously rectifying an output of the resonance circuit with a signal from the frequency doubler circuit;
In an ON state, a switch circuit that feeds back the output of the synchronous rectification circuit to the detection circuit,
Time constant adjusting means for adjusting the time constant of the integration circuit to turn off the switch circuit and adjust the excitation frequency to the natural resonance frequency of the resonance circuit ,
A magnetometer comprising:

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