CN101819234B - Device and method for measuring AC mutual inductance by compensation method - Google Patents

Abstract

The invention relates to a new method for precisely measuring alternating current mutual inductance by adopting a compensator technology. Tracing the mutual inductance value to the measurement of the resistance value and the frequency, wherein the uncertainty of the measurement of the resistance value and the frequency can reach 10^-9Of even higher order, so that the uncertainty in measuring the mutual inductance can be at least 10^-8Magnitude. The most precise method for obtaining the standard mutual inductance disclosed in the present foreign literature is the "mutual inductance calculation method", that is, the mutual inductance is calculated according to the measurement result of the geometric dimension of the mutual inductance coil. Due to the limitation of geometric dimension measurement accuracy, the uncertainty of foreign methods can only reach 10^-6Magnitude. The invention adopts direct digital synthesis technology to generate multi-path alternating current signals,the right angle of the signal is ensured. The constant current source is adopted to provide excitation for mutual inductance, so that the mutual inductance and the current flowing in the sampling resistor are always the same. The variation of the excitation signal voltage has no influence on the measurement process. The phase-locked amplifier based on phase-sensitive detection technique is used as an instruction instrument, only acts on signals with the same working frequency, eliminates the influence of noise and harmonic waves, and has the resolution of a nulling instrument of 1 multiplied by 10^-8. Compared with the existing foreign methods, the new method provided by the invention is improved by ten times.

Description

Device and method for measuring AC mutual inductance by compensation method

technical field

The invention relates to a new technology for establishing a measurement standard instrument, in particular to a device and method for measuring AC mutual inductance through a compensation method.

Background technique

my country is rich in rare earth metal resources, which can be used to produce high-quality magnetic materials. In the past, most of my country's rare earth metals were exported cheaply in the form of raw materials. Foreign countries used these materials to make high-end instruments (such as medical human magnetic resonance imagers, etc.) and then sold them to my country, making a lot of profits. To change this situation, it is necessary to make high-accuracy magnetic measuring instruments to precisely measure the characteristics of magnetic materials, so that my country can also use its own rare earth resources to produce high-quality magnetic materials. The accuracy of magnetic measuring instruments needs to be traced to the magnetic flux standard to ensure, so the magnetic flux standard is the most important basic standard in the field of magnetic measurement. In electrotechnics, a precision magnetic flux standard is derived from the mutual inductance of two coils.

Mutual inductance is an important quantity in electromagnetic measurement technology. In AC measurement, mutual inductance is often used as a right-angle component provider in AC compensators due to its excellent 90-degree angle characteristics. In DC measurement, it is often used to provide standard magnetic flux. In addition, the improvement of the measurement uncertainty of mutual inductance is also of great value to other electrical and magnetic measurement problems.

The most precise method of establishing the standard mutual inductance published in foreign literature is to calculate the mutual inductance according to the results of measuring the geometric dimensions of the mutual induction coil. Due to the limitation of the measurement accuracy of geometric dimensions, the mutual inductance measurement technology at home and abroad is still at the level of the 1970s, and the uncertainty remains at the order of 2×10 ^-6 , and there has been no new progress in recent decades. The invention proposes a new scheme for precise measurement of mutual inductance, combining compensator technology and phase-sensitive wave detection technology, to trace the mutual inductance value to the measurement of frequency and resistance. The uncertainty of the frequency measurement is in the order of 10 ^-14 , and the uncertainty of the quantized Hall resistance reference can also reach the order of 10 ^-9 . Therefore the new scheme that the present invention proposes is just superior to existing scheme both at home and abroad in principle.

Contents of the invention

补偿电压

和参考电压激励电压

是恒流源的参考电压，补偿电压与激励电压

的频率、幅值和初始相位相同，参考电压

是与激励电压

和补偿电压

同频的方波信号，所述恒流源包括激励电压运算放大器、缓冲器和采样电阻R_S，所述数字锁相放大器用作电桥指零仪，在测量交流互感的过程中，在调节激励电压的幅值和相位、所述多路信号发生器的频率ω和补偿电压

的相位

使所述电桥指零仪实现指零之后，通过对所述频率ω和所述参考电阻R_S进行测量，从而获得交流互感的测量值M。In order to achieve the purpose of the above invention, according to the first aspect of the present invention, a device for measuring AC mutual inductance by compensation method is provided, wherein the device includes a multi-channel signal generator, a constant current source, a digital lock-in amplifier and switch, the multiplexer generates the excitation voltage

compensation voltage

and reference voltage Excitation voltage

Is the reference voltage of the constant current source, the compensation voltage and excitation voltage

The frequency, amplitude and initial phase of the same, the reference voltage

is the excitation voltage

and compensation voltage

with a square wave signal of the same frequency, the constant current source consists of an excitation voltage Operational amplifier, buffer and sampling resistor R _S , the digital lock-in amplifier is used as a bridge reference zero instrument, in the process of measuring the AC mutual inductance, adjusting the excitation voltage The amplitude and phase of the multiplexer, the frequency ω and the compensation voltage

phase of

After the bridge zeroing instrument realizes zeroing, the measured value M of AC mutual inductance is obtained by measuring the frequency ω and the reference resistance R _S .

Preferably, said measured value M is equal to the ratio of said frequency ω to the value of said reference resistance R _S .

Preferably, in the above device according to the present invention, the same crystal oscillator provides the clock reference, and the same voltage reference provides the voltage reference.

Preferably, the multi-channel signal generator includes a waveform memory, and the waveform amplitude information is stored in the waveform memory.

Preferably, a low-frequency AC signal is used to provide excitation for the constant current source, and the constant current source is used to provide current for the mutual inductance.

补偿电压

和参考电压

激励电压

是恒流源的参考电压，补偿电压与激励电压

的频率、幅值和初始相位相同，参考电压是与激励电压

和补偿电压同频的方波信号；调节激励电压

的幅值和相位，使得用作电桥指零仪的所述数字锁相放大器指零；调节所述多路信号发生器的频率ω和补偿电压

的相位

使所述电桥指零仪实现指零；通过对所述频率ω和所述参考电阻R_S进行测量，获得交流互感的测量值M。According to a second aspect of the present invention, there is provided a method for measuring AC mutual inductance by means of a compensation method, wherein the method utilizes a multi-channel signal generator, a constant current source, a digital lock-in amplifier, a switch and a reference resistor R _S To realize the measurement of AC mutual inductance, the method includes the step: the multi-channel signal generator generates an excitation voltage

compensation voltage

and reference voltage

Excitation voltage

Is the reference voltage of the constant current source, the compensation voltage and excitation voltage

The frequency, amplitude and initial phase of the same, the reference voltage is the excitation voltage

and compensation voltage Square wave signal with the same frequency; adjust the excitation voltage

amplitude and phase, so that the digital lock-in amplifier used as a bridge zeroing instrument refers to zero; adjust the frequency ω and compensation voltage of the multi-channel signal generator

phase of

Making the bridge zeroing instrument realize zeroing; by measuring the frequency ω and the reference resistance R _S , the measured value M of the AC mutual inductance is obtained.

Preferably, said measured value M is equal to the ratio of said frequency ω to the value of said reference resistance R _S .

Preferably, in the above device according to the present invention, the same crystal oscillator provides the clock reference, and the same voltage reference provides the voltage reference.

Preferably, the multi-channel signal generator includes a waveform memory, and the waveform amplitude information is stored in the waveform memory.

Preferably, a low-frequency AC signal is used to provide excitation for the constant current source, and the constant current source is used to provide current for the mutual inductance.

In the device and method according to the present invention, the resolution of the bridge indexer can reach the order of 1×10 ^-8 by adopting the low-frequency AC measurement scheme and the digital lock-in amplifier based on the phase-sensitive detector technology. This method has the following advantages: it not only avoids problems such as thermoelectric potential in DC measurement, but also reduces error sources such as skin effect and eddy current effect in high frequency state.

Description of drawings

Fig. 1 is a schematic diagram of a device and a method for measuring AC mutual inductance by a compensation method.

Detailed ways

锁相放大器和参考信号

恒流源由激励信号

运放Amp，缓冲器Buffer和采样电阻R_S组成。为恒流源的参考电压；

为与

频率、幅值和初始相位均相等的补偿电压；为与

同频的方波信号，用作指零仪的参考信号。The invention adopts direct digital synthesis technology to provide stable and accurate right-angle ratio, and adopts perfect four-terminal definition to ensure accurate measurement of measured impedance. Fig. 1 shows a schematic diagram of a device for measuring AC mutual inductance through a compensation method according to the present invention. It mainly consists of six parts: constant current source, mutual inductance coil M, switch S, compensation voltage

Lock-in amplifier and reference signal

The constant current source is driven by the excitation signal

Composed of operational amplifier Amp, buffer Buffer and sampling resistor R _S. is the reference voltage of the constant current source;

for with

Compensation voltage with equal frequency, amplitude and initial phase; for with

The square wave signal with the same frequency is used as the reference signal of the zero indicator.

和

这两路电源提供准确稳定的直角比例。因此，电源的直角特性得以保证，同时可以看到，由于采用了恒流源电路，采样电阻R_S的电压引线和电流引线是独立的，保证了被比较阻抗的严格四端定义。These three signals are generated by a multiplexer based on direct digital frequency synthesis technology. And the clock reference is provided by the same crystal oscillator, and the voltage reference is provided by the same voltage reference. According to the principle of digital frequency synthesis technology, the amplitude information of the waveform is stored in the waveform memory, and the memory address corresponds to the phase of the waveform one by one. The amplitude is only related to the voltage reference of the DA, and the change of the phase does not affect the amplitude. By setting the memory address, you can make

and

These two power supplies provide accurate and stable right-angle ratios. Therefore, the right-angle characteristic of the power supply can be guaranteed. At the same time, it can be seen that due to the use of a constant current source circuit, the voltage lead and current lead of the sampling resistor R _S are independent, ensuring a strict four-terminal definition of the impedance being compared.

The mutual inductance is composed of two coils on the primary side and the secondary side. After the current is applied to the primary side, a voltage signal is induced on the secondary side, and the phase turns to 90 degrees.

The method according to the invention comprises two steps:

的幅值和相位，使指零仪指零，此时有1. Turn the switch S to the 1 position, Compare with the voltage across the reference resistor _RS . For an ideal op amp, there should be However, due to the fact that the actual open-loop gain of the device decreases as the frequency increases, Adjusting the excitation voltage source

Amplitude and phase, so that the zero indicator refers to zero, at this time there is

与互感副边的输出电压进行比较。由于互感副边的输出要移相90度左右，因此需要调节频率ω以及

的相位

约90度左右，使指零仪再次指零。从前面的介绍中知道，相位的变化不影响幅值。同时，补偿电压与产生电流的激励电压

是共用同一个D/A参考电压，两者的变化是同步的，因此此种变化对比较过程不产生影响。2. Turn the switch S to the 2 position,

Compare with the output voltage on the secondary side of the mutual inductance. Since the output of the secondary side of the mutual inductance needs to be shifted by about 90 degrees, it is necessary to adjust the frequency ω and

phase of

About 90 degrees, make the zero indicator point to zero again. We know from the previous introduction that changes in phase do not affect amplitude. At the same time, the compensation voltage The excitation voltage with the resulting current

They share the same D/A reference voltage, and the changes of the two are synchronous, so this change has no effect on the comparison process.

So there are:

Substituting (1) and (2) into (3), the balance equation of the new scheme is derived, which is also the calculation formula of mutual inductance

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; S</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

The frequency and the magnitude of the reference resistance can be accurately measured by means of real-time measurement, so the mutual inductance M is also accurately determined. At the same time, it can be noticed that the reference resistor R _S is completely connected according to the connection method of the four-terminal button resistor, which eliminates the error caused by the lead wire problem.

The new scheme that the present invention proposes has following advantage:

1) No need to use impedance phase-shifting network, and directly use digital technology to provide accurate and stable right-angle ratio;

2) Avoid the influence of thermoelectric potential and other phenomena during DC measurement;

3) Due to the low frequency measurement, problems such as skin effect and eddy current effect in high frequency state are reduced;

4) At the same time, as the phase-sensitive detection technology of the lock-in amplifier of the zero-pointing instrument, the relevant measurement method is realized, and it is also an important weapon to eliminate the influence of interference signals such as harmonics.

Both the operational amplifier and the power amplifier in the measurement circuit need DC power supply, so they are placed together with the battery pack and charging device, and shielded with a brass box. The main measurement circuit is also included in the shielding box, and other devices and components are connected to the terminal board of the shielding box through coaxial lines or multi-core shielded wires to form the entire measurement circuit. A double-pole double-throw switch is set on the wiring board to switch the two balanced lines. The zeroing instrument used in the experiment is the SR830 lock-in amplifier, and the sensitivity of the minimum range is 2nV. The relative sensitivity is 1×10 ^-8 .

Adopt the AC mutual inductance measuring system developed by the present invention to the measurement result of a standard mutual inductance as shown in the following table:

serial number Mutual inductance measurement mH 1 9.9975695 2 9.9975681 3 9.9975691 4 9.9975762 5 9.9975754 6 9.9975736 7 9.9975746 Average 9.9975724 standard deviation 1.27E-07

Claims (6)

1. the device through penalty method measurement AC mutual induction is characterized in that said device comprises mutual inductor, multi-channel signals generator, constant current source, digital lock-in amplifier and switch, and said multi-channel signals generator produces driving voltage

Bucking voltage

And reference voltage

Driving voltage

Be the reference voltage of constant current source, bucking voltage

With driving voltage

Frequency, amplitude and initial phase identical, reference voltage

Be and driving voltage

And bucking voltage With square-wave signal frequently, said constant current source comprises driving voltage

Operational amplifier, impact damper and reference resistance R _S, said digital lock-in amplifier can be used as the electric bridge zero indicator, and in the process of the AC mutual induction of measuring said mutual inductor, using low-frequency ac signal is that said constant current source provides excitation, and uses said constant current source as mutual inductor electric current to be provided, and is regulating driving voltage

Amplitude and phase place, the frequencies omega and the bucking voltage of said multi-channel signals generator

Phase place

Said electric bridge zero indicator is realized after the nulling, through to said frequencies omega and said reference resistance R _SMeasure, thereby obtain the measured value M of the AC mutual induction of said mutual inductor, said measured value M equals said frequencies omega and said reference resistance R _SThe ratio of numerical value.

2. device according to claim 1 is characterized in that, in said device, by same crystal oscillator clock reference is provided, and by same voltage reference Voltage Reference is provided.

3. device according to claim 1 is characterized in that said multi-channel signals generator comprises wave memorizer, preserves the amplitude information of waveform in the said wave memorizer.

4. the method through penalty method measurement AC mutual induction is characterized in that said method is utilized multi-channel signals generator, constant current source, digital lock-in amplifier, switch and reference resistance R _SRealize that said method comprises step to the measurement of the AC mutual induction of mutual inductor:

Said multi-channel signals generator produces driving voltage

bucking voltage and reference voltage

driving voltage

is the reference voltage of constant current source; Bucking voltage is identical with frequency, amplitude and the initial phase of driving voltage

, and reference voltage

is and driving voltage

and the same square-wave signal frequently of bucking voltage

;

Using low-frequency ac signal is that said constant current source provides excitation, and uses said constant current source as mutual inductor electric current to be provided;

Regulate the amplitude and the phase place of driving voltage

, feasible said digital lock-in amplifier nulling as the electric bridge zero indicator;

Adjusting said multiplex signal generator frequency ω and the compensation voltage

phase

so that the bridge means the instrument to achieve zero means zero;

Through to said frequencies omega and said reference resistance R _SMeasure, obtain the measured value M of the AC mutual induction of said mutual inductor, said measured value M equals said frequencies omega and said reference resistance R _SThe ratio of numerical value.

5. method according to claim 4 is characterized in that, by same crystal oscillator clock reference is provided, and by same voltage reference Voltage Reference is provided.

6. method according to claim 4 is characterized in that said multi-channel signals generator comprises wave memorizer, preserves the amplitude information of waveform in the said wave memorizer.

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