JPH07229801A - Signal processing circuit for magnetostrictive strain gauge - Google Patents

Abstract

PURPOSE:To achieve the high accuracy by providing a differential amplifier for compensation which amplifies the difference between output signals from a differential amplifier for detection and a BPF thereby removing the fluctuation in a distortion signal caused by disturbance noise or the like. CONSTITUTION:When a sensor shaft 102 is subjected to strain, the permeability of a magnetostrictive film 103 varies to cause variation in the voltage amplitude of a detection coil 104. Since the magnetostrictive film 103 is not present on the detection coil 105 side, the voltage amplitude does not vary. The AC detection voltages are amplified by amplifiers 106, 107 and converted through full-wave rectifying circuits 108, 109 into DC voltages. The difference thereof is amplified through a differential amplifier 110 for detection and the difference from an output signal from a BPF 112 is then determined by a first differential amplifier 11 for compensation. The differential output signal is rectified, along with the output signal from the BPF 112, through a rectifier circuit 113 and the difference between signals processed through a zero adjusting circuit 114 and a gain adjusting circuit 115 is determined by a second differential amplifier 116 for compensation. This circuitry removes fluctuation due to disturbance noise perfectly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for improving the accuracy of a magnetostrictive strain sensor.

[0002]

2. Description of the Related Art The structure of a general magnetostrictive strain sensor is shown in FIG. In FIG. 7, 102 is a sensor shaft, 103 is a magnetostrictive film, 101a and 101b are excitation coils, and 104 and 105 are detection coils. FIG. 8 shows a signal processing circuit of a magnetostrictive strain sensor as a conventional example. In FIG. 8, 119 is an oscillator and 118 is a power amplifier.
The excitation circuit is composed of 8, 106 and 107 are the first stage amplifier, and 108 and
Reference numeral 109 is a full-wave rectifier circuit, 110 is a detection differential amplifier, and 117 is a low-pass filter, and a signal processing circuit for detection from the first-stage amplifiers 106 and 107 to the low-pass filter 117 is configured. When strain is applied to the sensor shaft 102, the magnetic permeability of the magnetostrictive film 103 changes and the sensor shaft 102
The voltage amplitude of the detection coil 104 changes according to the increase or decrease in the amount of magnetic flux. Since the magnetostrictive film 103 is not provided on the detection coil side 105, the detection voltage amplitude basically does not change. These AC detection voltages are first-stage amplified by first-stage amplifiers 106 and 107, and then converted into DC voltages by full-wave rectifier circuits 108 and 109. These DC voltages are differentially amplified by the detection differential amplifier 110 and then passed through the low-pass filter 117 to be used as the distortion output signal of the sensor output. Incidentally, although there is no other precedent to be seen, if one dare to mention it, as a method for correcting the offset drift potential of the magnetoresistive effect sensor, for example, Japanese Patent Laid-Open No. 63-91580.
You can see the issue. This is because Joule heat is generated in these elements when a current is passed from the power supply to the magnetoresistive effect element to measure the strain, and the heat dissipation state is bad, and the temperature differs between the internal side and the external side. Since it includes a temperature drift, it is only a means for making the surface temperature distribution uniform and correcting the offset drift voltage.

[0003]

However, in the conventional example, for example, when a sensor is attached to a distribution line, an electric train line, etc., when a current flows through the sensor [so-called sensor shaft] or other disturbance noise, However, there is a problem that the distortion output signal varies. If this fluctuation is superimposed on the original distortion output signal with equal positive and negative amplitudes, it can be removed by a low-pass filter or the like provided in the conventional output stage. Since the fluctuation appears only on one side of the original distorted signal, DC [DC] fluctuation occurs even through the low-pass filter of the conventional example, and the influence of the current completely flowing through the sensor and other disturbance noises. Could not be removed. Therefore, an object of the present invention is to completely eliminate the distortion signal fluctuation of the sensor output due to the current flowing in the sensor and other disturbance noises, and to improve the accuracy of the sensor.

[0004]

In order to solve the above problems, the present invention is suitable for a detection differential amplifier output signal and the detection differential amplifier output signal for a bandpass filter or an AC coupling device. The differential signal is taken, and this differential output signal is further passed through a bandpass filter or A
Distorted output signal in which fluctuations due to current flowing in the sensor and other disturbance noises are completely removed by full-wave rectifying the output signal of the C coupling device and taking the differential with the signal with zero adjustment and gain adjustment. Is obtained as the first means. As another solution, the output signal of the detection differential amplifier is subjected to full-wave rectification of a signal that has passed through a bandpass filter or an AC coupling device, and a signal for which zero point adjustment and gain adjustment have been performed and a detection difference signal. The second means is to obtain a distorted output signal in which fluctuations due to the current flowing in the sensor and other disturbance noises are completely removed by taking the differential of the output signal of the dynamic amplifier from the signal passed through the notch filter. . Furthermore, as another solution, from the signal after full-wave rectification of each detection signal, only the AC fluctuation signal due to the current flowing through the sensor is extracted by a bandpass filter, and these are filtered with the same gain as the detection differential amplifier. The third means is to obtain a distorted output signal that is not affected by the current flowing in the sensor by taking the differential between the dynamically amplified signal and the detection differential amplifier output. Furthermore, as another solution, only an AC fluctuation signal due to the current flowing through the sensor from the output of the detection differential amplifier is taken out by a bandpass filter, and the differential signal between this signal and the output signal of the detection differential amplifier is extracted. The fourth means is to obtain a distorted output signal that is not affected by the current flowing through the sensor.

[0005]

With the above means, the present invention can remove only the noise fluctuation component appearing in the distortion output signal even if a current flows through the sensor or other disturbance noise occurs, so that it is not affected by the current or other disturbance noise. An accurate distortion signal can be obtained.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the circuit configuration of the first embodiment of the present invention. In all the drawings, the same reference numerals indicate the same or corresponding members. In FIG. 1, the excitation circuit of the sensor and the differential amplifier 110 in the detection circuit are the same as those in FIG. 4, but the detection signal passed through the detection differential amplifier 110 is the first compensation differential amplifier 111, band. Pass filter or AC coupling device 112, full-wave rectification circuit 113
, The zero adjustment circuit 114, the gain adjustment circuit 115, and the second compensation differential amplifier 116 are output via the low-pass filter 117.

Further, FIG. 5 is a waveform chart of each part for explaining the first principle of the present invention. For example, sensor shaft
In the case of normal operation in which no current flows through 102, the output of the detection differential amplifier 110 is a distortion-free output signal as shown in FIG. 5 (a). Here, for example, when an alternating current of 60 Hz flows through the sensor shaft 102, a fluctuation signal of 120 Hz having a doubled frequency is mainly converted into a DC voltage signal as shown in FIG. 5B, and the original distortion output signal [FIG. It has been confirmed by an experiment that it appears superimposed on one side of)]. Therefore, in the present invention, the output of the detection differential amplifier 110 is passed through a bandpass filter [passband center frequency 120 Hz in this case] or an AC coupling device 112, and AC fluctuation due to noise as shown in FIG. By picking up only that portion and taking the differential with the output of the detection differential amplifier 110 by the first compensation differential amplifier 111, a DC signal as shown in FIG. 5D is obtained.

For example, assuming that the fluctuation amplitude due to noise is A, this DC signal is output by superimposing the DC signal due to noise having a size of A / 2. In order to eliminate the DC signal component due to this noise, first, the detection differential amplifier 110
The AC output signal of is converted into a DC signal by the full-wave rectification circuit 113. Assuming that the AC output signal of the detection differential amplifier 110 is a sine wave and the amplitude is A, a full-wave rectifier circuit as shown in Fig. 5 (e).
The DC output signal of 113 has a magnitude of A / π. Therefore,
The second compensating differential amplifier 116 takes a differential between the first compensating differential amplifier 111 and a signal obtained by multiplying the DC output signal of the full-wave rectifying circuit 113 by a gain √2, so that
It is possible to obtain a signal that is not affected by the current flowing in the sensor as in (f).

Here, when the fluctuation component is not a perfect sine wave but includes a harmonic component, the full-wave rectifier circuit 11
The DC output signal of 3 does not have a magnitude of A / π. Further, due to the characteristics of the circuit and the like, even when the current flowing through the sensor is zero, an offset may occur in the output of the full-wave rectification circuit 113. Therefore, in the present embodiment, a zero point adjusting circuit 114 and a gain adjusting circuit 115 for adjusting the zero point and the gain of the output signal of the full-wave rectifying circuit 113 are provided. Further, the output signal of the second compensating differential amplifier 116 is passed through a low-pass filter 117 at the final stage to remove the harmonic noise and produce a distorted output signal.

The present embodiment effectively operates against disturbance noise other than the current flowing through the sensor. However, when the noise frequency cannot be determined, the AC coupling device 112 is used instead of the bandpass filter. The AC coupling device 112 is a so-called high-frequency pass filter connected to the signal line in which a capacitor is connected in series to the signal line with the capacitor interposed and the output end of the capacitor is grounded via a resistor.

Next, a second embodiment of the present invention will be described based on the block diagram showing the circuit configuration of FIG. The circuit configuration of FIG. 2 is different from the circuit configuration of FIG. 1 except that the first compensating differential amplifier 111 is removed and a notch [band stop] filter is used instead.
120 are provided. In this embodiment, the detection differential amplifier 11
The AC output signal of 0 is passed through a notch filter 120 having the fluctuation frequency as the center frequency of the stop band, and the AC fluctuation due to noise is removed. However, this signal contains a DC fluctuation component like the output signal of the first compensation differential amplifier 111 of the previous embodiment [FIG. 1]. Therefore, as in the previous embodiment [FIG. 1], the AC output signal of the detection differential amplifier 110 is
Bandpass filter or AC coupling device 112
The full-wave rectifier circuit 113 full-wave rectifies this signal to convert it into a direct current signal, and the zero adjustment circuit 114 and the gain adjustment circuit
The zero point adjustment and the gain adjustment are performed by 115 (the gain is π / 2, and the gain adjustment circuit 115 performs the fine adjustment). By taking the differential between the output signal of the second compensating differential amplifier 116 and the output signal of the gain adjusting circuit 115, a signal that is not influenced by the sensor is obtained as in the previous embodiment [FIG. 1]. be able to. This signal is passed through a low-pass filter 117 at the final stage to remove harmonic noise and produce a distorted output signal. In this embodiment, if the frequency of the noise can be determined, the AC fluctuation can be removed as the notch filter frequency characteristic corresponding to the frequency noise established as described above. Even works effectively.

Further, FIG. 3 shows a block diagram of a circuit configuration of a third embodiment of the present invention. In FIG. 3, 112a is a first bandpass filter and 112b is a second bandpass filter. The frequency characteristics of the first and second bandpass filters are the same. FIG. 6 is a waveform chart of each part for explaining the second principle of the present invention. Sensor shaft 102
In the normal operation with no current flowing in the full-wave rectifier circuit 108,
The output signal of 109 is a distorted output signal without fluctuation as shown in FIG. 5 (a). Now, on the sensor shaft 102, for example, 60 Hz
It has been confirmed by experiments that the output signals of the full-wave rectification circuits 108 and 109 appear mainly when a fluctuation signal of 120 Hz with a doubled frequency is superimposed on the DC voltage signal when an AC current flows. ing.

In the output signals of the full-wave rectification circuits 108 and 109 of the respective phases, if the fluctuation waveforms have the same magnitude and the same phase, the differential amplifier for detection 110 cancels them.
It does not affect the output. However, due to the presence or absence of the magnetostrictive film 103 on the sensor shaft 102, the imbalance of the excitation coils 101a and 101b and the impedances of the detection coils 104 and 105, and the imbalance of each phase circuit element (first stage amplifier 106 and 107, full wave rectification circuit 108 and 109), This 120
The magnitude and phase of the fluctuation waveform of Hz are different, and a large fluctuation waveform appears in the distortion output signal [Fig. 6 (c)].

Therefore, in the present invention, the full-wave rectifier circuit 10
The output signals of 8,109 are passed through band-pass filters 112a, 112b [passband center frequency 120 Hz in this case],
As in (d) and (e), only the fluctuation component is extracted, and these fluctuation signals are differentially amplified by the second compensation differential amplifier 116 [gain is the same as the detection differential amplifier 110]. As a result, the fluctuation amount of the signal appearing at the output of the detection differential amplifier 110 and the output signal of the compensation differential amplifier 113 have exactly the same waveform in magnitude and phase [FIG. 6 (f)]. By differentially amplifying the output of the detection differential amplifier 110 and the output of the compensation differential amplifier 113 with the differential amplifier 116, it is possible to obtain a signal that does not fluctuate and is not affected by the current flowing through the sensor shaft 102 [Fig. 6 (g)]. This signal is passed through the low-pass filter 11
Pass through 4 to remove high frequency noise and use as distortion output signal.

FIG. 4 is a block diagram showing the circuit configuration of the fourth embodiment of the present invention. In the above-mentioned another embodiment [FIG. 3], the signal fluctuation due to the current flowing in the sensor is taken out by the bandpass filters 112a and 112b after full-wave rectification of each phase, whereas in this embodiment, the detection differential amplifier 110 Only the fluctuations appearing in the output are taken out by the bandpass filter 112,
By differentially amplifying this signal and the output of the detection differential amplifier 110 by the second compensation differential amplifier 116, a signal that does not fluctuate and is not affected by the current flowing through the sensor shaft 102 can be obtained. This signal is passed through a low-pass filter 114 at the final stage to remove high frequency noise and output a distorted signal.

[0016]

As described above, according to the present invention, it is possible to obtain a highly accurate strain signal which is not affected by the current flowing through the sensor and other disturbance noises, so that the reliability of the magnetostrictive strain sensor is improved. There is a special effect that the improvement of the sex is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a circuit configuration according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a circuit configuration according to a fourth embodiment of the present invention.

FIG. 5 is a waveform chart of each part for explaining the first principle of the present invention.

FIG. 6 is a waveform chart of each part for explaining the second principle of the present invention.

FIG. 7 is an explanatory diagram of a configuration of a magnetostrictive strain sensor.

FIG. 8 is a block diagram showing a circuit configuration of a conventional example.

[Explanation of symbols]

 101a Excitation coil 101b Excitation coil 102 Sensor shaft 103 Magnetostrictive film 104 Detection coil 105 Detection coil 106 First stage amplifier 107 First stage amplifier 108 Full wave rectification circuit 109 Full wave rectification circuit 110 Detection differential amplifier 111 First compensation differential amplifier 112 Bandpass filter 112 AC coupling device [high-frequency pass filter] 112a Bandpass filter 112b Bandpass filter 113 Full-wave rectifier circuit 114 Zero adjustment circuit 115 Gain adjustment circuit 116 Second compensation differential amplifier 117 Lowpass filter 118 Power amplifier 119 Oscillator 120 Notch filter [Band stop filter]

Claims (6)

[Claims] 1. A sensor shaft, a magnetostrictive film formed on the sensor shaft, a pair of exciting coils for exciting the sensor shaft, and a pair of detecting coils for detecting the amount of magnetic flux from the sensor shaft. A pair of first stage amplifiers for respectively amplifying the voltages of the pair of detection coils in the first stage, and a first and a first for converting an output signal of the first stage amplifiers into a DC voltage signal.
A magnetostrictive strain sensor provided with a second full-wave rectifier circuit, a detection differential amplifier that differentially amplifies the DC voltage signal, and a low-pass filter that removes high-frequency noise from the output of the detection differential amplifier. In a signal processing circuit to be applied, a bandpass filter for extracting only a variation from the detection differential amplifier, and a first amplification circuit for differentially amplifying an output signal of the detection differential amplifier and an output signal of the bandpass filter. Compensation differential amplifier, third full-wave rectifying circuit for full-wave rectifying the output of the bandpass filter, zero-point adjusting circuit for adjusting the zero point of the output of the third full-wave rectifying circuit, and the zero-point adjusting A gain adjustment circuit that adjusts the gain of the output signal of the third full-wave rectifier circuit in a subsequent stage of the circuit, and a second compensation that differentially amplifies the first compensation differential amplifier output and the gain adjustment circuit output. Difference A signal processing circuit for a magnetostrictive strain sensor, characterized in that the differential amplification output of the second compensation differential amplifier is used as an input of the low-pass filter. 2. A signal processing circuit applied to the magnetostrictive strain sensor, comprising: an AC coupling device for passing a high frequency component from the detection differential amplifier and extracting only a variation component; and a detection differential amplifier. A first compensating differential amplifier for differentially amplifying an output signal and an output signal of the AC coupling device;
A third full-wave rectifying circuit for full-wave rectifying the output of the C coupling device, a zero-point adjusting circuit for adjusting the zero point of the output of the third full-wave rectifying circuit, and the third stage after the zero-point adjusting circuit. A gain adjustment circuit that adjusts the gain of the output signal of the full-wave rectification circuit, and a second compensation differential amplifier that differentially amplifies the first compensation differential amplifier output and the gain adjustment circuit output. A signal processing circuit for a magnetostrictive strain sensor, wherein a differential amplification output of the second compensation differential amplifier is used as an input of the low pass filter. 3. A signal processing circuit applied to the magnetostrictive strain sensor, comprising: a bandpass filter for extracting only a fluctuation component from the detection differential amplifier; and a third-wave rectifying the output of the bandpass filter. A full-wave rectification circuit, a zero-point adjustment circuit that adjusts the zero point of the output of the third full-wave rectification circuit, and a gain that adjusts the gain of the output signal of the third full-wave rectification circuit after the zero-point adjustment circuit. An adjustment circuit, a notch filter that receives the output of the detection differential amplifier and has its fluctuation frequency in the center of the stop band, and a compensation differential amplifier that differentially amplifies the output signal of the notch filter and the output of the gain adjustment circuit. And a differential amplification output of the compensation differential amplifier as an input of the low-pass filter. 4. A signal processing circuit applied to the magnetostrictive strain sensor, wherein an AC coupling device for extracting a fluctuation component by passing a high frequency component from the detection differential amplifier, and an output of the AC coupling device. A full-wave rectifying circuit for full-wave rectifying, a zero-point adjusting circuit for adjusting the zero point of the output of the third full-wave rectifying circuit, and a third full-wave rectifying circuit at a stage subsequent to the zero-point adjusting circuit. A gain adjustment circuit that adjusts the gain of the output signal, a notch filter that receives the output of the detection differential amplifier and has its fluctuation frequency at the center of the stop band, and a difference between the output signal of the notch filter and the output of the gain adjustment circuit. A signal processing circuit for a magnetostrictive strain sensor, comprising: a compensation differential amplifier that dynamically amplifies, wherein a differential amplification output of the compensation differential amplifier is used as an input of the low-pass filter. 5. A signal processing circuit applied to the magnetostrictive strain sensor, wherein a pair of bandpass filters for extracting only fluctuations from both input terminals of the detection differential amplifier, and an output signal of the bandpass filter. A first differential amplifier for compensation, which differentially amplifies the output of the differential amplifier for detection and the output of the first differential amplifier for compensation to have the same gain as the differential amplifier for detection. A signal processing circuit for a magnetostrictive strain sensor, characterized in that a differential amplification output of the second compensation differential amplifier is used as an input of the low-pass filter. 6. A signal processing circuit applied to the magnetostrictive strain sensor, wherein a bandpass filter for extracting only a variation from the output of the detection differential amplifier, an output of the detection differential amplifier and the bandpass filter. A signal processing circuit for a magnetostrictive strain sensor, comprising: a compensation differential amplifier that differentially amplifies an output of the filter, wherein a differential amplification output of the compensation differential amplifier is used as an input of the low-pass filter.