CN103885006B - There is the AC magnetic field sensor measuring frequency scanning function - Google Patents

Abstract

The invention provides an AC magnetic field sensor with the function of measuring frequency scanning, including a frequency adjustable multi-channel signal generator (1), a first frequency converter (4), a crystal filter (5), a second frequency converter (6 ), a low-pass filter (7), a low-noise amplifier (8), and a probe, and the frequency-adjustable multi-channel signal generator (1) is connected to the probe, the first frequency converter (4), and the second frequency converter respectively device (6), the probe, the first frequency converter (4), the crystal filter (5), the second frequency converter (6), the low-pass filter (7), the The above-mentioned low noise amplifiers (8) are connected in sequence. The beneficial effect of the invention is that the AC frequency magnetic field can be scanned and measured and noise and interference can be effectively filtered out.

Description

AC Magnetic Field Sensor with Measurement Frequency Sweep

technical field

The invention relates to the technical field of weak magnetic field measurement and an AC magnetic field measurement device, in particular to an AC magnetic field sensor with a measurement frequency scanning function.

Background technique

AC magnetic field sensors are widely used in the fields of industry, measurement, and medicine. There are many magnetic field measurement methods and measurement technologies in current applications. Commonly used are Hall effect, giant magnetoresistance effect, giant magnetoimpedance effect, and superconducting quantum interference effect. Various types of technologies have resulted in related products such as search coil sensors, giant magnetoresistance sensors, giant magnetoresistance sensors, Hall sensors, fluxgate sensors, and superconducting quantum interferometers.

Compared with other sensing technologies such as fluxgate sensors and giant magnetoresistance sensors, sensors using giant magnetoresistance effects have obvious advantages in mechanical, mechanical, chemical and electromagnetic properties, and have higher sensitivity, especially with miniature Based on the advantages of size and fast response, a large number of new sensors based on magnetic field measurement have been developed on the basis of this technology.

The magnetic field sensor made by the giant magneto-impedance effect, its main working principle is that when the high-frequency excitation current signal is applied to the amorphous wire (ribbon), the measured magnetic field signal in the axial direction of the amorphous wire (ribbon) makes the amorphous wire (ribbon) The impedance at both ends of the band) changes with the change of the measured magnetic field signal. Using the corresponding circuit form to convert this impedance change into other signal forms can realize the measurement of the magnetic field.

At present, there are two main methods of making sensors based on the principle that the complex impedance of amorphous wire (ribbon) changes with the measured magnetic field signal: (1) Convert the change of impedance of amorphous wire (ribbon) into the change of frequency, that is, the change of amorphous wire (ribbon) As a variable reactance component, wire (ribbon) is applied to an oscillating circuit, and its impedance change is converted into a frequency change. By processing the frequency signal, the detection of the magnetic field signal is realized. The circuit generally includes an oscillating circuit and a rectifying circuit (detection circuit) and amplifier circuit. (2) Directly measure the complex impedance at both ends of the amorphous wire (ribbon), for example, using a bridge, apply the amorphous wire (ribbon) to a bridge arm of the bridge circuit, and the output of the bridge is a Frequency, a signal with a fixed phase difference, its amplitude-frequency characteristics reflect the change of impedance, realize the measurement of the magnetic field signal, and use the vector impedance test method to measure the voltage, current amplitude and phase at both ends of the amorphous wire (ribbon), Realize complex impedance measurement.

There are various types of noise and interference in the AC magnetic field measurement environment, and the measured AC magnetic field signal is very weak, and the methods currently used cannot effectively filter out the noise and interference.

Contents of the invention

In order to solve the problems in the prior art, the invention provides an AC magnetic field sensor with measurement frequency scanning function.

The invention provides an AC magnetic field sensor with the function of measuring frequency scanning, including a frequency adjustable multi-channel signal generator, a first frequency converter, a crystal filter, a second frequency converter, a low-pass filter, a low-noise amplifier, and a probe , the frequency adjustable multi-channel signal generator is respectively connected with the probe, the first frequency converter, and the second frequency converter, the probe, the first frequency converter, the crystal filter, the second frequency converter The frequency converter, the low-pass filter, and the low-noise amplifier are connected in sequence.

As a further improvement of the present invention, the probe includes an amorphous material component, a preamplifier, and a DC bias coil, the amorphous material component is connected to the input end of the preamplifier, and the frequency adjustable multi-channel signal is generated The device is connected to the amorphous material part, the DC bias coil is wound on the outer surface of the amorphous material part, and the output terminal of the preamplifier is connected to the first frequency converter;

The frequency adjustable multi-channel signal generator: used to respectively provide the high-frequency excitation frequency signal of the amorphous material component, the modulation frequency signal of the first frequency converter, and the demodulation frequency signal of the second frequency converter;

The DC bias coil: used to generate a bias magnetic field;

The amorphous material part: under the action of the high-frequency excitation frequency signal and the DC bias magnetic field, the complex impedance at both ends of the amorphous material part changes with the change of the detected AC magnetic field signal passing through its axial component change, an AC voltage signal reflecting the amplitude change of the detected AC magnetic field signal is generated at both ends of the amorphous material component in the circuit;

The preamplifier: used for preliminary amplification of the AC voltage signal output by the amorphous material component;

The first frequency converter: used to mix or convert the modulation frequency signal output by the frequency adjustable multi-channel signal generator and the AC voltage signal output by the amorphous material component, the signal output by the first frequency converter contains a signal equal to the center frequency of said crystal filter;

The center frequency of the crystal filter is one of the excitation frequency of the amorphous material component, the frequency of the measured AC magnetic field signal, and the combined frequency of the modulation signal frequency. After passing through the crystal filter, output signals of other frequencies are filtered out;

The second frequency converter is used to mix or convert the output frequency signal of the crystal filter and the demodulated frequency signal, and the output signal of the second frequency converter contains the measured AC magnetic field signal after frequency mixing or frequency conversion and other combined frequency signals;

In the low-pass filter, other combined frequency signals in the signal output by the second frequency converter are much higher than the frequency of the measured AC magnetic field signal, and the low-pass filter is used to filter out the combined frequency;

The low noise amplifier is used to amplify the output signal of the low pass filter.

As a further improvement of the present invention, the amorphous material component is a Co-based or Fe-based amorphous alloy material with a giant magnetoresistance effect.

As a further improvement of the present invention, the amorphous material part is an amorphous wire or an amorphous ribbon.

As a further improvement of the present invention, the crystal filter is a narrow-band crystal filter.

As a further improvement of the present invention, the narrowband crystal filter is a fixed frequency narrowband crystal filter.

As a further improvement of the present invention, the first frequency converter is a nonlinear device with frequency conversion function.

The nonlinear devices include analog multipliers and mixers.

The beneficial effect of the invention is that the AC magnetic field sensor with the measurement frequency scanning function of the invention can effectively filter out noise and interference.

Description of drawings

Fig. 1 is a functional block diagram of the present invention.

detailed description

As shown in Figure 1, the present invention discloses an AC magnetic field sensor with the function of measuring frequency scanning, including a frequency adjustable multi-channel signal generator 1, a first frequency converter 4, a crystal filter 5, a second frequency converter 6, Low-pass filter 7, low noise amplifier 8, probe, described frequency adjustable multi-channel signal generator 1 is connected with described probe, first frequency converter 4, and second frequency converter 6 respectively, described probe, described The first frequency converter 4 , the crystal filter 5 , the second frequency converter 6 , the low-pass filter 7 , and the low-noise amplifier 8 are connected in sequence.

The probe includes an amorphous material part 2, a preamplifier 3, and a DC bias coil 9, the amorphous material part 2 is connected to the input end of the preamplifier 3, and the frequency adjustable multi-channel signal generator 1 Connected to the amorphous material part 2, the DC bias coil 9 is wound on the outer surface of the amorphous material part 2, and the output end of the preamplifier 3 is connected to the first frequency converter 4;

The frequency adjustable multi-channel signal generator 1: used to provide the high-frequency excitation frequency signal of the amorphous material component 2, the modulation frequency signal of the first frequency converter 4, and the demodulation frequency signal of the second frequency converter 6;

The DC bias coil 9: used to generate a bias magnetic field;

The amorphous material part 2: under the action of the high-frequency excitation frequency signal and the DC bias magnetic field, the complex impedance at both ends of the amorphous material part 2 changes with the detected AC magnetic field signal passing through its axial component change, the two ends of the amorphous material part 2 in the circuit generate an AC voltage signal that reflects the amplitude change of the detected AC magnetic field signal;

The preamplifier 3: used to initially amplify the AC voltage signal output by the amorphous material component 2;

The first frequency converter 4: used to mix or convert the modulation frequency signal output by the frequency adjustable multi-channel signal generator 1 and the AC voltage signal output by the amorphous material component 2, the first frequency converter 4 The output signal contains a signal equal to the center frequency of the crystal filter 5;

The center frequency of the crystal filter 5 is one of the excitation frequency of the amorphous material part 2, the frequency of the measured AC magnetic field signal, and the combined frequency of the modulation signal frequency. After passing through the crystal filter 5, the output signals of other frequencies are filter out;

The second frequency converter 6 is used to mix or convert the output frequency signal of the crystal filter 5 and the demodulated frequency signal, and the output signal of the second frequency converter 6 contains the measured AC magnetic field signals and other combined frequency signals;

The low-pass filter 7, other combined frequency signals in the signal output by the second frequency converter 6 are much higher than the frequency of the measured AC magnetic field signal, and the combined frequency is filtered out using the low-pass filter 7;

The low noise amplifier 8 amplifies the output signal of the low pass filter 7 .

The amorphous material component 2 is Co-based or Fe-based amorphous alloy material with giant magnetoresistance effect.

The amorphous material component 2 is an amorphous wire or an amorphous ribbon.

The crystal filter 5 is a narrowband crystal filter, and the narrowband crystal filter is a fixed frequency narrowband crystal filter.

The first frequency converter 4 is a nonlinear device with frequency conversion function, and the nonlinear device includes an analog multiplier and a mixer.

After frequency mixing or frequency conversion by the first frequency converter 4, a combined frequency of the output signals at both ends of the amorphous material component 2 is modulated to the center frequency of the narrow-band crystal filter.

When the frequency of the detected AC magnetic field signal changes, the modulation frequency of the first frequency converter 4 can be changed accordingly to keep the frequency of the modulated signal at the center frequency of the narrow-band crystal filter, so a fixed-frequency narrow-band crystal filter can be used device as a filter component.

During the scanning process of the measurement frequency, the system uses a general-purpose, low-cost and high-performance fixed-frequency narrow-band crystal filter to filter the signal output by the first frequency converter 4, which has good frequency selection performance and simple system structure.

The second frequency converter 6 mixes (converts) the signal output by the narrow-band crystal filter and the demodulated signal provided by the frequency-adjustable multi-channel signal generator 1 to obtain the combined frequency signal of the detected AC magnetic field signal and other higher frequencies .

When the frequency of the detected AC magnetic field signal changes, the demodulation frequency of the second frequency converter 6 can be correspondingly changed so that the demodulated signal frequency includes the combined frequency signal of the detected AC magnetic field signal and other higher frequencies.

The frequency of the combined signal of higher frequency output by the second frequency converter 6 is more than ten times the frequency of the measured AC magnetic field signal. When the frequency of the detected AC magnetic field signal changes, the parameters of the narrow-band crystal filter, low-pass filter 7 and other components that need to be set remain unchanged within the selected scanning frequency range.

The amorphous material part 2 has the GMI effect. Applying a high-frequency excitation current and a DC bias magnetic field to the amorphous material part 2 will change its complex impedance when the axial component of the AC magnetic field signal of the measured signal passes through the amorphous material part 2. , so that the amplitude of the AC voltage output from both ends of the amorphous material component 2 in the circuit also changes accordingly, and the present invention can realize the measurement of the measured AC magnetic field signal with variable frequency through frequency selection components such as frequency converters and filters. The high-frequency excitation signal of the amorphous material component 2 is provided by the frequency-adjustable multi-channel signal generator 1, and a current-limiting resistor is connected in series in the line to ensure an appropriate driving current.

In order to ensure that the subsequent signal processing circuit does not affect the working state of the amorphous material component 2, and initially amplify the output voltage signal at both ends of the amorphous material component 2, the output voltage at both ends of the amorphous material component 2 is first sent to the preamplifier 3 . The preamplifier 3 has a very high input impedance and a very low output impedance, and at the same time preliminarily amplifies the input signal. The differential input of the preamplifier 3 is the voltage signal at both ends of the amorphous material component 2 , and the output end of the preamplifier 3 is connected to the input end of the first frequency converter 4 .

The output voltage signal of the preamplifier 3 contains the combined frequency signal of the frequency of the measured AC magnetic field signal and the frequency of the high-frequency excitation signal of the amorphous material part 2. In order to filter the signal with a fixed-frequency narrow-band crystal filter, the signal needs to be frequency-converted (Frequency mixing), the present invention calls it modulation, and the frequency of the modulated signal is equal to the center frequency of the narrowband crystal filter.

One input signal of the first frequency converter 4 is the output signal of the preamplifier 3 , and the other input signal is the modulation signal provided by the frequency-adjustable multi-channel signal generator 1 . The modulated signal includes multiple combined frequency signals of the frequency of the detected AC magnetic field signal, the frequency of the high-frequency AC excitation signal of the amorphous material part 2 and the frequency of the modulation signal. The frequency of the modulated signal can be adjusted according to the frequency of the measured AC magnetic field signal, so that a combined frequency including the frequency of the detected AC signal in the modulated signal is always equal to the center frequency of the narrow-band crystal filter with a fixed frequency.

Narrowband crystal filters have good frequency selection characteristics and extremely small relative bandwidth, and can be used as narrowband bandpass filters. For applications such as eddy current metal flaw detection and medical tumor detection, the frequency of the measured AC magnetic field signal is between a few KHz and several hundred KHz, and the frequency range of the general frequency band, small size and low cost monolithic crystal filter Between 1 MHz and tens of MHz, in order to use a common narrow-band crystal filter, it is necessary to convert (mix) the signal output by the amorphous material part 2 containing the component of the detected AC magnetic field. The input end of the narrowband crystal filter is connected to the output end of the first frequency converter 4 , and the output end of the narrowband crystal filter is connected to the input end of the second frequency converter 6 .

The output signal of the narrow-band crystal filter includes a plurality of combined frequencies, and the second frequency converter 6 performs frequency conversion (mixing) on the output signal of the narrow-band crystal filter. The present invention refers to it as demodulation. By adjusting the frequency of the demodulation signal, The demodulated signal contains the frequency of the detected AC signal and other higher combined signal frequencies. Since the frequency difference between the frequency of the measured AC magnetic field signal and other combined frequency signals is large, the low-pass filter 7 can be used to filter out unnecessary frequency signals. One input signal of the second frequency converter 6 is the output signal of the crystal filter 5 , and the other input signal is the modulation signal provided by the frequency-adjustable multi-channel signal generator 1 .

The frequency of the output signal of the second frequency converter 6 includes the combined frequency of the measured AC magnetic field signal frequency with a lower frequency and the higher frequency amorphous wire AC excitation frequency, modulation signal frequency and demodulation signal frequency, and low-pass filtering can be used Filter 7 filters out the higher frequency part. The input end of the low-pass filter 7 is connected to the output end of the second frequency converter 6 , and the output end of the low-pass filter 7 is connected to the input end of the low-noise amplifier 8 .

The output signal of the low-pass filter 7 only contains the detected AC magnetic field signal, which can be amplified to meet the voltage required by the detection transposition.

The working principle of the present invention is: the probe composed of the amorphous material part 2 and the bias circuit is placed in the detected AC magnetic field space, and the frequency adjustable multi-channel signal generator 1 provides the high-frequency AC excitation signal of the amorphous material part 2 to the The amorphous material part 2 provides the drive. Appropriate DC bias magnetic field is applied to make the amorphous material component 2 in a higher sensitivity working state. When the axial component of the measured AC magnetic field signal acts on the amorphous material part 2, the impedance of the amorphous material part 2 changes, and then the AC voltage amplitude at both ends of the amorphous material part 2 changes with the change of the external AC magnetic field signal , to achieve the purpose of detecting the AC magnetic field signal.

The magnetic field entering the axial direction of the amorphous material part contains not only the detected signal magnetic field but also the interference magnetic field and noise. Usually the detected magnetic field signal is very weak and submerged in the interference and noise, so the signal needs to be filtered and amplified. In the system, the frequency of the detected magnetic field signal is set by the system, and the frequency is a known parameter. Therefore, a crystal filter with a very narrow bandwidth can be used to filter the received signal. It is difficult to implement a crystal filter with a low operating frequency, and Larger size, so the system uses a crystal filter with a higher center frequency, while cost considerations can use a mass-produced narrow-band crystal filter for other purposes, such as a crystal filter for the frequency band of an FM receiver.

In order to make the amorphous material component 2 still use a fixed-frequency narrow-band crystal filter for filtering when the frequency of the measured AC magnetic field signal changes, it is necessary to use the first frequency converter 4 to convert the output signal of the amorphous material component 2, that is, to The signal is modulated, and by changing the modulation frequency of the first frequency converter 4, the frequency of the modulated signal is always kept at the center frequency of the narrow-band crystal filter.

After being filtered by a narrow-band crystal filter, the signal-to-noise ratio of the detected signal has been greatly improved. The output signal of the crystal filter includes the combined frequency of the measured AC magnetic field signal frequency, the excitation signal frequency of the amorphous material part 2, and the modulated signal frequency. One of the combined frequencies can be selected to extract the measured AC magnetic field signal through frequency conversion (mixing) Frequency No. Frequency, that is, to demodulate the signal. The frequency of other combined frequency signals in the demodulated signal is much higher than the frequency of the detected AC magnetic field signal, and the low-pass filter 7 can be used to filter out the rest.

The signal filtered by the narrowband filter only contains the frequency of the detected AC magnetic field signal, and is amplified by the low noise amplifier 8 to obtain an output signal of the detected AC magnetic field signal with sufficient amplitude.

The frequency-adjustable multi-channel signal generator 1 may also be called a frequency-adjustable multi-channel output AC signal generator.

Frequency adjustable multi-channel signal generator 1 output frequency calculation:

(1) The frequency of the high-frequency excitation signal of the amorphous material part 2 is f _amo , the frequency of the modulation signal of the first frequency converter 4 is f _mod , the frequency of the demodulation signal of the second frequency converter 6 is f _dem , and the frequency of the detected AC magnetic field signal is is f _ext , and the frequency f _amo is determined according to the characteristics of the amorphous wire material and the operating point of the circuit. (2) The output voltage signal at both ends of the amorphous material component 2 includes f _amo ±f _ext frequency signals. (3) The first frequency converter 4 converts (mixes) the modulation signal with the frequency f _mod and the AC signal with the output frequency f _amo ±f _ext of the amorphous material part 2, and generates a signal containing (f _amo ±f _ext )±f AC signal with _mod frequency components. (4) The center frequency of the narrowband crystal filter can be set to one of (f _amo ±f _ext )±f _mod , assuming that the selected center frequency is f _amo +f _ext +f _mod . (5) The second frequency converter 6 converts (mixes) the signal whose output frequency of the narrowband crystal filter is f _amo + f _ext + f _mod and the demodulation frequency signal f _dem , if the frequency of the demodulation signal is f _dem = f _amo +f _mod , the frequency components in the output signal of the second frequency converter 6 are f _ext and f _ext +2f _amo +2f _mod , as long as f _dem =f _amo +f _mod is guaranteed, the measured AC frequency of f _ext can be obtained magnetic field signal.

The beneficial effects of the present invention are:

1. Use a narrow-band crystal filter with good filtering performance to filter the detected AC magnetic field signal to obtain a very high signal-to-noise ratio.

2. By changing the frequency of the modulation signal and the demodulation signal, the frequency scanning of the measured AC magnetic field signal can be realized in the entire frequency band, and the accurate frequency response of the magnetic field signal can be obtained.

3. By modulating the frequency of the continuously variable detected signal to a fixed frequency, the common, low-cost, and good-performance crystal filter 5 on the market can be used to realize narrow-band filtering, which improves the cost performance of the system.

4. Since the crystal filter 5 has a fixed frequency, related circuits with fixed parameters can be used in the demodulation, low-pass filtering and low-noise amplification circuits, which reduces the complexity of system design and debugging. The frequency-adjustable multi-channel signal generator 1 provides precise and variable modulation and demodulation frequencies, which can ensure that the demodulated output signal only contains the frequency of the detected AC magnetic field signal.

5. In the signal output by the second frequency converter 6, the frequency difference between the frequency of the detected AC magnetic field signal and other combined frequency signals is relatively large. After filtering by the subsequent low-pass filter 7, the frequencies other than the measured AC magnetic field signal are greatly reduced. Amplitude attenuation, the system obtains a good signal-to-noise ratio.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, some simple deduction or replacement can be made, which should be regarded as belonging to the protection scope of the present invention.

Claims (7)

1. one kind has the AC magnetic field sensor measuring frequency scanning function, it is characterized in that: include frequency-adjustable Multi-channel signal generator (1), first converter (4), crystal filter (5), second converter (6), low pass filter (7), low-noise amplifier (8), probe, described frequency-adjustable Multi-channel signal generator (1) respectively with described probe, first converter (4), and second converter (6) be connected, described probe, described first converter (4), described crystal filter (5), described second converter (6), described low pass filter (7), described low-noise amplifier (8) is sequentially connected；

Described probe includes non-crystalline material parts (2), preamplifier (3), direct current biasing coil (9), described non-crystalline material parts (2) are connected with described preamplifier (3) input, described frequency-adjustable Multi-channel signal generator (1) is connected with described non-crystalline material parts (2), described direct current biasing coil (9) is wound in described non-crystalline material parts (2) outer surface, and described preamplifier (3) outfan is connected with described first converter (4)；

Described frequency-adjustable Multi-channel signal generator (1): for providing described non-crystalline material parts (2) high frequency pumping frequency signal, the modulation frequency signal of the first converter (4), the frequency, demodulation frequency signal of the second converter (6) respectively；

Described direct current biasing coil (9): be used for producing bias magnetic field；

Described non-crystalline material parts (2): under the effect of high frequency pumping frequency signal and DC bias magnetic field, the complex impedance at described non-crystalline material parts (2) two ends changes along with the change by the detected AC magnetic field signal of its axial component, and the most described non-crystalline material parts (2) two ends produce the ac voltage signal of reflection detected AC magnetic field signal amplitude change；

Described preamplifier (3): the ac voltage signal for exporting non-crystalline material parts (2) tentatively amplifies；

Described first converter (4): the ac voltage signal that modulation frequency signal and the non-crystalline material parts (2) for described frequency-adjustable Multi-channel signal generator (1) being exported export is mixed or frequency conversion, contains the signal of the mid frequency equal to described crystal filter (5) in the signal that described first converter (4) exports；

Described crystal filter (5), its mid frequency be described non-crystalline material parts (2) driving frequency, tested AC magnetic field signal frequency, one of frequency modulating signal combination frequency, after this crystal filter (5), the output signal of remaining frequency is filtered out；

Described second converter (6), for carrying out being mixed or frequency conversion by described crystal filter (5) output frequency signal and frequency, demodulation frequency signal, containing tested AC magnetic field signal and other combination frequency signal in described second converter (6) output signal after mixing or frequency conversion；

Described low pass filter (7), in the signal that described second converter (6) exports, other combination frequency signal is far above tested AC magnetic field signal frequency, uses described low pass filter (7) combination frequency to be filtered；

Low-noise amplifier (8), is amplified described low pass filter (7) output signal.

AC magnetic field sensor the most according to claim 1, it is characterised in that: described non-crystalline material parts (2) are the amorphous alloy material that Co base or Fe base have giant magnetoresistance effect.

AC magnetic field sensor the most according to claim 2, it is characterised in that: described non-crystalline material parts (2) are amorphous wire or amorphous ribbon.

AC magnetic field sensor the most according to claim 1, it is characterised in that: described crystal filter (5) is narrow-band crystal filter.

AC magnetic field sensor the most according to claim 4, it is characterised in that: described narrow-band crystal filter is the narrow-band crystal filter of fixed frequency.

AC magnetic field sensor the most according to claim 1, it is characterised in that: described first converter (4) is the nonlinear device with frequency conversion function.

AC magnetic field sensor the most according to claim 6, it is characterised in that: described nonlinear device includes analog multiplier, frequency mixer.