CN110244105B - All-digital vector demodulation method of magnetic modulator - Google Patents
All-digital vector demodulation method of magnetic modulator Download PDFInfo
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- CN110244105B CN110244105B CN201910539746.2A CN201910539746A CN110244105B CN 110244105 B CN110244105 B CN 110244105B CN 201910539746 A CN201910539746 A CN 201910539746A CN 110244105 B CN110244105 B CN 110244105B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention discloses a full digital vector demodulation method of a magnetic modulator, which comprises the steps of introducing a first current with known magnitude into the magnetic modulator; converting analog signals generated on an excitation winding and a detection winding of the magnetic modulator into digital signals to obtain an excitation signal and a detection signal; constructing a second harmonic reference signal, removing a direct-current component of a detection signal to obtain a signal to be detected, and performing correlation operation on the second harmonic reference signal and the signal to be detected to obtain a signal output amplitude; introducing current to be detected into the magnetic modulator, and repeating the steps to obtain a signal output amplitude of the current to be detected; and obtaining the magnitude of the current to be measured according to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals. The invention improves the measurement resolution by simultaneously utilizing the second harmonic amplitude and the phase of the detection winding signal, reduces the noise interference brought by demodulation by using a full digital method, and reduces the error introduced by the change of the measurement sensitivity caused by the change of the excitation power supply frequency by using a proportionality coefficient self-calibration method.
Description
Technical Field
The invention belongs to the technical field of electricity, and particularly relates to a full-digital vector demodulation method of a magnetic modulator.
Background
The magnetic modulator is a high-precision current sensor based on the magnetic modulation principle and mainly comprises an iron core, an excitation winding, a detection winding and a demodulation loop. The magnetic modulator has the working principle that the iron core is in deep saturation through the exciting winding, and when no current flows, namely no bias magnetic field exists in the iron core, the magnetic flux in the iron core only contains odd harmonic components; when current flows, namely a bias magnetic field appears in the iron core, even harmonic components which are in direct proportion to direct current to be measured appear in the magnetic flux in the iron core.
The detection winding can induce harmonic waves in the iron core, and the characteristic value of even harmonic component on the detection winding is measured through the demodulation circuit, so that direct current to be detected can be measured. The traditional demodulation method mainly comprises peak demodulation and phase-sensitive demodulation, and has the common points that the demodulation algorithm is realized by adopting an analog circuit and only one characteristic value in even harmonics is measured.
The measurement resolution of existing magnetic modulators is typically only in the milliamp range. The reasons for limiting the resolution of demodulation are mainly: only single eigenvalues such as amplitude in even harmonic waves are measured, so that the interference of same-frequency noise of different phases is easily caused, and the demodulation resolution is reduced; by adopting an analog circuit, due to the influence of factors such as temperature drift of analog elements, deviation of measurement signals can occur, measurement noise is introduced, and the demodulation resolution can be reduced; the frequency of the excitation source is difficult to be constant, and measurement errors can be introduced due to the fact that the measurement sensitivity linearly changes along with the frequency of the excitation source, and sensitivity is reduced. There is therefore a need for a new method of demodulating a magnetic modulator that improves the measurement resolution of the magnetic modulator.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a full-digital vector demodulation method of a magnetic modulator, aiming at solving the problems that the demodulation method of the prior magnetic modulator can introduce errors and reduce the measurement resolution.
In order to achieve the above object, the present invention provides a method for fully digital vector demodulation of a magnetic modulator, comprising the steps of:
(1) passing a first current of a milliamp level with a known magnitude to the magnetic modulator;
(2) converting analog signals generated on an excitation winding and a detection winding of the magnetic modulator into digital signals to obtain an excitation signal and a detection signal;
(3) constructing a second harmonic reference signal according to the frequency of the excitation signal, removing the direct current component of the detection signal to obtain a signal to be detected, and performing correlation operation on the second harmonic reference signal and the signal to be detected to obtain a signal output amplitude;
(4) introducing the current to be detected into the magnetic modulator, and repeating the steps (2) to (3) to obtain a signal output amplitude of the current to be detected;
(5) and obtaining the magnitude of the current to be measured according to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals.
Preferably, the analog signals on the excitation winding and the detection winding of the magnetic modulator are converted into digital signals using a digital acquisition card.
Preferably, the expression of the second harmonic reference signal is:
wherein f is the frequency of the excitation signal, t is the current time point,
to detect the phase difference between the signal and the excitation signal, the phase of the excitation signal is set to 0 °.
Preferably, the second harmonic reference signal and the signal to be measured are subjected to correlation operation, and the calculation method is that the amplitude of the second harmonic reference signal at a single time point is multiplied by the amplitude of the signal to be measured to obtain the amplitude U of the output signal at the single time pointiWherein i represents the serial number of the time point, and the signal amplitude U is output to each time point within the time T of the integral multiple of the period of the excitation signaliAnd summing to obtain the total output amplitude U.
Preferably, an average value of the detection signals within the excitation signal multiple times of the whole period time T is calculated to obtain a direct current component of the detection signals, and the detection signals are subtracted from the direct current component to obtain the signals to be detected so as to weaken the zero point error.
Preferably, the expression of the current to be measured is:
wherein U is the signal output amplitude of the current to be measured, K0The ratio of the signal output amplitude of the first current to the magnitude of the first current, f is the frequency of the excitation signal when the current to be measured is measured, f0To measure the frequency of the excitation signal at the first current.
Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:
1. the all-digital vector demodulation method of the magnetic modulator provided by the invention adopts a vector detection method, only measures the signal amplitude of a specific phase, avoids noise interference of different phases and improves the resolution of current measurement;
2. the all-digital vector demodulation method of the magnetic modulator converts the input analog signal into the digital signal, and uses the all-digital method to demodulate, thereby avoiding the introduction of the inherent microampere current of part of analog elements in the analog signal demodulation process, weakening noise interference and improving the resolution of measurement;
3. the all-digital vector demodulation method of the magnetic modulator provided by the invention adopts a proportionality coefficient self-calibration method, and real-time calibration is carried out by multiplying the measurement sensitivity by the frequency variation, so that the problem that the measurement sensitivity linearly changes along with the frequency is prevented, and errors caused by the change of the excitation power supply frequency and the change of the measurement sensitivity can be weakened.
Drawings
Fig. 1 is a schematic flow chart of a method for fully digital vector demodulation of a magnetic modulator according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention provides a full digital vector demodulation method of a magnetic modulator, which aims to improve the measurement resolution by improving the demodulation method of the magnetic modulator, and more particularly, mainly improves the demodulation method in three aspects, namely, the measurement resolution is improved by simultaneously utilizing the amplitude and the phase of the second harmonic of a detection winding signal, the noise interference brought by demodulation is weakened by using a full digital method, and the error introduced by the change of the measurement sensitivity caused by the change of the frequency of an excitation power supply is weakened by a proportionality coefficient self-calibration method.
In order to achieve the purpose, the method comprises the following steps:
(1) passing a first current of known magnitude to the magnetic modulator;
(2) converting analog signals generated on an excitation winding and a detection winding of the magnetic modulator into digital signals to obtain an excitation signal and a detection signal;
(3) constructing a second harmonic reference signal according to the frequency of the excitation signal, removing the direct current component of the detection signal to obtain a signal to be detected, and performing correlation operation on the second harmonic reference signal and the signal to be detected to obtain a signal output amplitude;
(4) introducing the current to be detected into the magnetic modulator, and repeating the steps (2) to (3) to obtain a signal output amplitude of the current to be detected;
(5) and obtaining the magnitude of the current to be measured according to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals.
Specifically, analog signals on the excitation winding and the detection winding of the magnetic modulator are converted into digital signals using a digital acquisition card.
Specifically, the expression for the second harmonic reference signal is:
wherein f is the frequency of the excitation signal, t is the current time point,
to detect the phase difference between the signal and the excitation signal, the phase of the excitation signal is set to 0 °.
Specifically, the second harmonic reference signal and the signal to be measured are subjected to correlation operation by a calculation method ofMultiplying the amplitude of the second harmonic reference signal at a single time point by the amplitude of the signal to be detected to obtain the amplitude U of the output signal at the single time pointiWherein i represents the serial number of the time point, and the signal amplitude U is output to each time point within the time T of the integral multiple of the period of the excitation signaliAnd summing to obtain the total output amplitude U.
Specifically, an average value of detection signals within a time T which is a multiple of the whole period of the excitation signal is calculated to obtain a direct current component of the detection signals, and the direct current component is subtracted from the detection signals to obtain signals to be detected so as to weaken zero point errors.
Specifically, the expression of the current to be measured is:
wherein U is the signal output amplitude of the current to be measured, K0The ratio of the signal output amplitude of the first current to the magnitude of the first current, f is the frequency of the excitation signal when the current to be measured is measured, f0To measure the frequency of the excitation signal at the first current.
The present invention is further described with reference to the accompanying drawings and specific embodiments, as shown in fig. 1, the specific steps of demodulating to obtain the magnitude of the current value to be measured are as follows:
step 1, a first current I with a milliampere level and a known magnitude is introduced into a magnetic modulator0；
Step 2, converting analog signals generated on an excitation winding and a detection winding of the magnetic modulator into digital signals to obtain an initial excitation signal and an initial detection signal, and performing fast Fourier transform on the initial excitation signal to obtain the frequency f of the initial excitation signal0165Hz, the phase of the initial excitation signal is set to 0,
is the phase difference between the initial detection signal and the initial excitation signal;
step 3, according to the frequency f of the initial excitation signal0Constructing an initial second harmonic reference signal, and removing a direct current component of an initial detection signalObtaining an initial signal to be measured, and performing correlation operation on the initial second harmonic reference signal and the initial signal to be measured to obtain a signal output amplitude U of the first current0Thereby obtaining an initial proportionality coefficient K0＝U0/I0＝0.4257；
Step 4, current to be measured is introduced into the magnetic modulator, analog signals generated on an excitation winding and a detection winding of the magnetic modulator are converted into digital signals to obtain an excitation signal and a detection signal, the excitation signal is subjected to fast Fourier transform to obtain the frequency f of 161Hz, the phase of the excitation signal is set to be 0 degree,
the phase difference between the detection signal and the excitation signal is-1.26 rad;
step 5, constructing a second harmonic reference signal according to the frequency f of the excitation signal, in this embodiment, selecting a 1650-fold whole period of 10s of the excitation signal, removing a direct current component DC of the detection signal as 113.32mV to obtain a signal to be detected, performing correlation operation on the second harmonic reference signal and the signal to be detected, and obtaining a signal output amplitude U of the current to be detected as 48.14mV within 10 s;
step 6, obtaining the magnitude of the current to be measured according to the magnitude of the output amplitude of the two times of signals and the frequency of the two times of excitation signals,
the resolution of the measuring system reaches microampere level, and is greatly improved compared with the milliampere level resolution of the existing non-contact current measuring device.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. A method for fully digital vector demodulation of a magnetic modulator, comprising the steps of:
(1) passing a first current of known magnitude to the magnetic modulator;
(2) converting analog signals generated on an excitation winding and a detection winding of the magnetic modulator into digital signals to obtain an excitation signal and a detection signal;
(3) constructing a second harmonic reference signal according to the frequency of the excitation signal, removing the direct current component of the detection signal to obtain a signal to be detected, and multiplying the amplitude of the second harmonic reference signal at a single time point by the amplitude of the signal to be detected to obtain a signal output amplitude;
(4) introducing the current to be detected into the magnetic modulator, and repeating the steps (2) to (3) to obtain a signal output amplitude of the current to be detected;
(5) and obtaining the magnitude of the current to be measured according to the magnitude of the output amplitude of the two signals and the frequency of the two excitation signals.
2. The method of claim 1, wherein the conversion of the analog signal to a digital signal is performed by a digital acquisition card.
3. The method of claim 1, wherein the second harmonic reference signal is expressed by:
wherein f is the frequency of the excitation signal, t is the current time point,
to detect the phase difference between the signal and the excitation signal, the phase of the excitation signal is set to 0 °.
4. The method of claim 1, wherein the acquiring of the signal under test comprises: and calculating the average value of the detection signals in the excitation signal multiple times of the whole period to obtain the direct current component of the detection signals.
5. A method according to claim 3, wherein the signal output amplitude is the sum of the signal output amplitudes at each time point within a multiple of the full period of the excitation signal.
6. The method of claim 1, wherein the current to be measured is expressed by:
wherein U is the signal output amplitude of the current to be measured, K0The ratio of the signal output amplitude of the first current to the magnitude of the first current, f is the frequency of the excitation signal when the current to be measured is measured, f0To measure the frequency of the excitation signal at the first current.
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