CN111308401A - Detection circuit based on impedance sensitive type magnetic sensor and magnetic sensor - Google Patents
Detection circuit based on impedance sensitive type magnetic sensor and magnetic sensor Download PDFInfo
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Abstract
A detection circuit based on an impedance sensitive magnetic sensor and the magnetic sensor comprise an orthogonal signal generator, a phase detection PSD, a band-pass filter BPF, a low-pass filter LPF, an analog-to-digital conversion ADC, a microprocessor and the magnetic sensor; the orthogonal signal generator outputs two paths, each path is sequentially connected with the phase detection PSD, the low pass filter LPF and the analog-to-digital conversion ADC, and the analog-to-digital conversion ADC of each path is connected with the microprocessor; the magnetic sensor is connected with the orthogonal signal generator and the band-pass filter BPF, and the band-pass filter BPF is divided into two paths and respectively connected to the two phase detection PSDs. Compared with the self-resonance state of the magnetic core winding inductor, the series capacitance is far larger than the distributed capacitance of the inductor, so that the series resonance frequency of the LC series device is smaller than the self-resonance frequency of the LC series device. By using the LC series state, the frequency of the excitation signal of the impedance-sensitive magnetic sensor is effectively reduced.
Description
Technical Field
The invention belongs to the technical field of magnetic sensors, and particularly relates to a detection circuit based on an impedance sensitive magnetic sensor and the magnetic sensor.
Background
The magnetic sensor is an application and a universal sensor, has excellent performance and strong anti-interference capability, plays an important role in modern technology, and is widely applied to engineering technology and industrial fields, such as automatic control, geomagnetic navigation, biological detection and the like. Giant magneto-impedance (GMI) type magnetic sensors are highly spotlighted by researchers and engineers because of their extremely high sensitivity, as compared to other types of magnetic sensors. In the research on GMI, researchers successively find GMI effect in materials such as amorphous wires, amorphous ribbons, thin films, sandwiches/multilayer films and the like. Most of the existing commercial GMI sensors adopt soft magnetic amorphous wire materials as sensitive units. The processing technology is complicated, so that the whole sensor is high in cost and is not beneficial to large-area application. Meanwhile, a scheme of a koppez oscillator and a diode peak detection is commonly adopted in a general GMI drive detection circuit, and the scheme has a simple structure, but has many defects: poor anti-interference ability, insufficient sampling precision, low signal frequency and the like. Such a defect inevitably causes insufficient performance of the GMI sensor in practical application, cannot well meet the application scene requirements, and seriously hinders the improvement of the performance of the GMI sensor and the popularization of the application. With the development of modern technology, the number of GMI sensors is increasing dramatically and there are higher demands on performance. The existing GMI sensor can not meet the requirements of future development and application due to the problems of complex process, high cost, insufficient performance and the like.
Disclosure of Invention
The present invention is directed to a detection circuit based on an impedance-sensitive magnetic sensor and a magnetic sensor, so as to solve the above problems.
In order to achieve the purpose, the invention adopts the following technical scheme:
a detection circuit based on an impedance sensitive magnetic sensor comprises an orthogonal signal generator, a phase detection PSD, a band-pass filter BPF, a low-pass filter LPF, an analog-to-digital conversion ADC, a microprocessor and a magnetic sensor; the orthogonal signal generator outputs two paths, each path is sequentially connected with the phase detection PSD, the low pass filter LPF and the analog-to-digital conversion ADC, and the analog-to-digital conversion ADC of each path is connected with the microprocessor; the magnetic sensor is connected with the orthogonal signal generator and the band-pass filter BPF, and the band-pass filter BPF is divided into two paths and respectively connected to the two phase detection PSDs.
Further, the quadrature signal generator is used for generating two paths of quadrature alternating current signals, namely, a signal S1, sin (ω t + α) and a signal S2, cos (ω t + α), wherein the signal amplitude is set to be 1V, and the signal S1 and the signal S2 are respectively used as input reference signals of the two phase detection PSDs.
Further, a resistor R is connected in series between the magnetic sensor and the orthogonal signal generator; the magnetic sensor is used for changing the signal amplitude at two ends of the magnetic sensor according to the change of an external magnetic field.
Furthermore, the band-pass filter BPF filters and reduces noise of the signal S6 at both ends of the magnetic sensor, so as to improve the quality of the signal input to the PSD, where the output signal S5 is Asin (ω t + β) and a is the signal amplitude.
Furthermore, the phase detection PSD multiplies the reference input signal S2/S1 and the detected signal S5, the low pass filter LPF filters the output signal of the PSD to remove the high frequency part in the signal S3/S4 and only leave the direct current component V1/V2, and the signal amplitude is continuously solved according to the output formulas of V1 and V2 by theoretical analysis of V1-0.5 Asin (β - α) and V2-0.5 Acos (β - α)
Further, the analog-to-digital conversion chip ADC converts the signals V1 and V2 into digital signals, and the digital signals are input into the microprocessor for further analysis and operation; the microprocessor is used for carrying out an evolution operation, and solving the amplitude A of the signal S5 according to the voltage values of V1 and V2.
Furthermore, the impedance sensitive type magnetic sensor comprises an inductor L and a capacitor C which are connected in series to form an LC series magnetic sensor, and an LC series circuit generates resonance with resonance frequency
The impedance value at the resonance frequency is minimum | Zmin |; the AC drive current and signal readout circuit is connected to the LC series magnetic sensor through an interface A.
Furthermore, the inductor L is a magnetic core winding inductor, and the capacitor C is a ceramic capacitor.
Compared with the prior art, the invention has the following technical effects:
the invention relates to an impedance sensitive magnetic sensor under LC series resonance. The impedance value of the LC series circuit is a magnetic field sensitive quantity. When a magnetic field is applied outside the device, the impedance value of the LC series circuit changes monotonously with the applied magnetic field. The sensing scheme provided by the invention utilizes the magnetic core winding inductor and the ceramic capacitor which are mature in technology, has simple process and low cost, and has very high magnetic field detection sensitivity based on the giant magneto-impedance effect of the magnetic core winding inductor.
Compared with the self-resonance state of the magnetic core winding inductor, the series capacitance is far larger than the distributed capacitance of the inductor, so that the series resonance frequency of the LC series device is smaller than the self-resonance frequency of the LC series device. By using the LC series state, the frequency of the excitation signal of the impedance-sensitive magnetic sensor is effectively reduced.
The invention provides a hardware detection circuit based on an impedance type magnetic sensor, which can realize rapid and efficient magnetic field detection.
Drawings
FIG. 1 is a schematic diagram of an LC series circuit of the present invention;
FIG. 2 is a series resonance and self-resonance curve of an LC series circuit of the present invention;
FIG. 3 is a graph of the impedance of the LC series circuit of the present invention as a function of magnetic field and frequency;
fig. 4 is a graph of the rate of change of impedance versus magnetic field for different excitation frequencies for the LC series circuit of the present invention.
FIG. 5 is a graph of the relationship between the sensitivity of the impedance change rate to the magnetic field and the magnetic field of the LC series circuit of the present invention at different excitation frequencies;
FIG. 6 is a graph showing the variation of impedance with applied magnetic field of the LC series circuit of the present invention.
FIG. 7 is a schematic diagram of a hardware detection circuit of the impedance-sensitive magnetic sensor.
Detailed Description
The invention is further described below with reference to the accompanying drawings:
referring to fig. 1 to 7, a detection circuit based on an impedance-sensitive magnetic sensor includes a quadrature signal generator, a phase detection PSD, a band pass filter BPF, a low pass filter LPF, an analog-to-digital conversion ADC, a microprocessor, and a magnetic sensor; the orthogonal signal generator outputs two paths, each path is sequentially connected with the phase detection PSD, the low pass filter LPF and the analog-to-digital conversion ADC, and the analog-to-digital conversion ADC of each path is connected with the microprocessor; the magnetic sensor is connected with the orthogonal signal generator and the band-pass filter BPF, and the band-pass filter BPF is divided into two paths and respectively connected to the two phase detection PSDs.
The orthogonal signal generator is used for generating two paths of orthogonal alternating current signals S1 sin (ω t + α) and S2 cos (ω t + α), the signal amplitude is set to be 1V, and the signal S1 and the signal S2 are respectively used as input reference signals of the two phase detection PSDs.
A resistor R is connected in series between the magnetic sensor and the orthogonal signal generator; the magnetic sensor is used for changing the signal amplitude at two ends of the magnetic sensor according to the change of an external magnetic field.
The band-pass filter BPF filters and reduces noise of the signal S6 at both ends of the magnetic sensor, so as to improve the quality of the signal input to the PSD, where the output signal S5 is Asin (ω t + β) and a is a signal amplitude.
A phase detection PSD for multiplying a reference input signal S2/S1 and a signal to be detected S5, a low-pass filter LPF for filtering the output signal of the PSD to remove the high-frequency part in the signal S3/S4 and only leave a direct-current component V1/V2, and the amplitude of the signal is continuously solved according to the output formulas of V1 and V2 by theoretical analysis of V1-0.5 Asin (β - α) and V2-0.5 Acos (β - α)
The analog-to-digital conversion chip ADC converts the signals V1 and V2 into digital signals, and the digital signals are input into the microprocessor for further analysis and operation; the microprocessor is used for carrying out an evolution operation, and solving the amplitude A of the signal S5 according to the voltage values of V1 and V2.
An impedance sensitive magnetic sensor comprises an inductor L and a capacitor C which are connected in series to form an LC series magnetic sensor, wherein the LC series circuit generates resonance with resonant frequency
Minimum value of impedance value | Z at resonance frequencymin |; the AC drive current and signal readout circuit is connected to the LC series magnetic sensor through an interface A.
The inductor L is a magnetic core winding inductor, and the capacitor C is a ceramic capacitor.
(1) As shown in fig. 1, the LC series impedance sensitive magnetic sensor proposed by the present invention is composed of a core wire wound inductor L1 and a ceramic capacitor C1 connected in series. The AC drive current and signal readout circuit is connected to the LC series magnetic sensor through an interface A.
(2) The LC series magnetic sensor provided by the invention realizes magnetic field detection through the sensitivity of a magnetic core winding inductance magnetic core to a magnetic field. When the inductance magnetic core receives the action of an external magnetic field, the magnetic permeability of the inductance magnetic core changes, and the performance reflected in the LC series circuit is the change of the resonant frequency f0 and the change of the impedance value. The core winding inductance, due to its distributed capacitance, produces an LC parallel resonance peak, as shown in curve a of fig. 2, which illustrates the self-resonance phenomenon of the core winding inductance.
The impedance of the LC series resonant mode proposed by the present invention varies with frequency, as shown by curve B in fig. 2. Through the series capacitor C1, the impedance versus frequency curve shows a trough at low frequencies, i.e. the LC series resonance point. By means of the series capacitance C1, it is achieved that the impedance at the resonance frequency takes a minimum value.
Since the magnetic core wire wound inductor has a self-resonant characteristic, a ceramic capacitor of an appropriate size needs to be selected to form an LC series resonance at a low frequency far from the self-resonant frequency. The inductance distribution capacitance of a common magnetic core winding is below 20pF, so the series ceramic capacitance is selected to be far larger than the inductance distribution capacitance. The capacitor selected in the present example was a 100pF ceramic capacitor.
(3) Due to the action of an external magnetic field on the inductance magnetic core, the series resonance frequency of the LC series resonance circuit is changed, and meanwhile, the impedance value is changed. As shown in fig. 3, in the series resonance state, the resonance frequency f0 increases as the applied magnetic field increases. Meanwhile, the impedance value corresponding to the excitation signal with the same frequency also changes obviously, and the phenomenon shows that the impedance value is related to the magnetic field under the same excitation signal frequency.
(4) According to the characteristics of the LC series magnetic sensor shown in FIG. 3, the variation of the impedance value Z with the magnetic field H of the device at different excitation signal frequencies f is further tested. According to the impedance change rate R calculation formula of the general magnetic impedance device:
the relationship between the impedance change rate R of the LC series magnetic sensor and the applied magnetic field H can be obtained, as shown in fig. 4. Within a certain magnetic field range, about 7-10Oe, the impedance change rate R has a change similar to a step with the increase of the magnetic field, and the step is an available effective working area of the sensor. Further obtaining the sensitivity of the resistance change rate R to the change of the magnetic field: s ═ dR/dH, the results shown in fig. 5 can be obtained.
From the results shown in fig. 4 and 5, it can be seen that the LC tandem type sensor has a high sensitivity S, a high sensitivity operation region is around 8Oe, and a bias magnetic field Hbias needs to be applied when it operates.
(5) According to the results shown in fig. 2, 3, 4 and 5, the response characteristics of the LC series magnetic sensor to the applied magnetic field H are tested by selecting the proper excitation signal frequency f and the bias magnetic field Hbias. A1 Hz sinusoidal magnetic field signal is applied to the LC series magnetic sensor, the amplitude of the external magnetic field H is changed, the impedance variation delta Z of the sensor is measured, the test result is shown in FIG. 6, the impedance variation delta Z is reduced along with the gradual reduction of the external magnetic field H, and the external magnetic field H and the impedance variation delta Z basically change linearly within the range of 800nT-3 nT. When the value of the applied magnetic field is lower than 3nT, the impedance change amount does not change along a linear fitting curve.
(6) According to the characteristic of the impedance-sensitive magnetic sensor proposed by the present invention, the change in the impedance value is mapped to the change in the amplitude on the sensor drive signal. According to the signal amplitude variation characteristic, the invention provides a hardware detection principle circuit, as shown in fig. 7. The hardware circuit adopts the design of an orthogonal bidirectional lock-in amplifier, and eliminates the influence of the phase difference between a reference signal and a measured signal in a single lock-in amplifier. The hardware detection principle circuit provided by the invention comprises: the device comprises an orthogonal signal generator, a phase detection PSD, a band-pass filter BPF, a low-pass filter LPF, an analog-to-digital conversion ADC, a microprocessor and an RLC series network.
The orthogonal signal generator is used for generating two paths of orthogonal alternating current signals S1 sin (ω t + α) and S2 cos (ω t + α), the signal amplitude is set to be 1V, and the signal S1 and the signal S2 are respectively used as input reference signals of the two phase detection PSDs.
The RLC tandem network: based on the LC series resonance impedance sensitive magnetic sensor provided by the invention, voltage division is carried out through the series resistor R, the impedance value of the LC series network can change along with an external magnetic field, and therefore the amplitude of a signal S6 at two ends of the LC series network can also change along with the magnetic field.
And the BPF is a band-pass filter BPF which filters and reduces noise of signals at two ends of the LC to improve the quality of the signals input to the PSD, an output signal S5 is Asin (omega t + β), and A is a signal amplitude and is related to an external magnetic field signal.
The PSD is as follows: the PSD is a phase sensitive detector, and the PSD multiplies the reference input signal S2/S1 and the signal to be detected S5.
The LPF is a low pass filter LPF which carries out filtering processing on the output signals of the PSD, removes high frequency parts in signals S3/S4, only remains direct current components V1/V2, and can continuously solve signal amplitude values according to output formulas of V1 and V2 according to theoretical analysis that V1 is 0.5Asin (β - α) and V2 is 0.5Acos (β - α)
The ADC: the analog-to-digital conversion chip ADC can convert the signal V1V 2 into a digital signal and input the digital signal into the microprocessor for further analysis operation.
The microprocessor: the microprocessor is mainly used for carrying out an evolution operation, and solving the signal S5 amplitude A according to the voltage value of V1V 2.
According to the hardware detection circuit principle provided by the invention, the detection of the drive of the LC series resonance impedance sensitive type magnetic sensor can be realized, the detection of the magnetic field by the LC series resonance impedance sensitive type magnetic sensor can be realized through the circuit scheme, the final output voltage Vout is the S5 signal amplitude A after the evolution operation, and the output signal is related to the external magnetic field: vout ═ f (h).
Claims (8)
1. A detection circuit based on an impedance sensitive magnetic sensor is characterized by comprising an orthogonal signal generator, a phase detection PSD, a band-pass filter BPF, a low-pass filter LPF, an analog-to-digital conversion ADC, a microprocessor and a magnetic sensor; the orthogonal signal generator outputs two paths, each path is sequentially connected with the phase detection PSD, the low pass filter LPF and the analog-to-digital conversion ADC, and the analog-to-digital conversion ADC of each path is connected with the microprocessor; the magnetic sensor is connected with the orthogonal signal generator and the band-pass filter BPF, and the band-pass filter BPF is divided into two paths and respectively connected to the two phase detection PSDs.
2. The detection circuit based on the impedance-sensitive magnetic sensor as claimed in claim 1, wherein the quadrature signal generator is configured to generate two orthogonal ac signals S1 sin (ω t + α) and S2 cos (ω t + α), the amplitude of the signals is set to 1V, and the signals S1 and S2 are used as input reference signals of the two phase detection PSDs, respectively.
3. The detection circuit based on the impedance-sensitive magnetic sensor according to claim 1, wherein a resistor R is connected in series between the magnetic sensor and the quadrature signal generator; the magnetic sensor is used for changing the signal amplitude at two ends of the magnetic sensor according to the change of an external magnetic field.
4. The detection circuit based on the impedance-sensitive magnetic sensor as claimed in claim 1, wherein the band-pass filter BPF filters and de-noizes the signal S6 at both ends of the magnetic sensor to improve the quality of the signal input to the PSD, and the output signal S5 is Asin (ω t + β), where a is the signal amplitude.
5. The detection circuit based on the impedance-sensitive magnetic sensor as claimed in claim 1, wherein the phase detection PSD multiplies the reference input signal S2/S1 by the signal under test S5; low pass filter LPF, pairThe PSD output signal is filtered to remove the high frequency part in the signal S3/S4 and only leave the DC component V1/V2, and the signal amplitude is solved according to the output formulas of V1 and V2 by theoretical analysis that V1 is 0.5Asin (β - α) and V2 is 0.5Acos (β - α)
6. The detection circuit based on the impedance-sensitive magnetic sensor as recited in claim 1, wherein the analog-to-digital conversion chip ADC converts the signals V1, V2 into digital signals and inputs the digital signals into the microprocessor for further analysis; the microprocessor is used for carrying out an evolution operation, and solving the amplitude A of the signal S5 according to the voltage values of V1 and V2.
7. The impedance sensitive magnetic sensor is characterized by comprising an inductor L and a capacitor C which are connected in series to form an LC series magnetic sensor, wherein an LC series circuit generates resonance with resonance frequency
The impedance value at the resonance frequency is minimum | Zmin |; the AC drive current and signal readout circuit is connected to the LC series magnetic sensor through an interface A.
8. An impedance-sensitive magnetic sensor according to claim 7, wherein the inductor L is a core-wound inductor and the capacitor C is a ceramic capacitor.
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