CN104101785B - A kind of four-end method high level condensance measurement apparatus and its measuring method - Google Patents
A kind of four-end method high level condensance measurement apparatus and its measuring method Download PDFInfo
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Abstract
The present invention is a kind of four ends high level capacitance measuring device and its measuring method, and the measurement apparatus include inductive shunt, capacitive, calibration resistor, resistance box, testing capacitor, digital voltmeter and power supply；Inductive shunt includes that turn ratio is 1:1 a pair of windings；Capacitive and calibration resistor are composed in series measuring loop A；Resistance box and testing capacitor are composed in series measuring loop B；A pair of windings of inductive shunt are reversely accessed in two measuring loops；Calibration resistor and testing capacitor are respectively adopted four-end method connection；The measuring method makes the current value in two measuring loops equal by adjusting impedance balance, and then the series equivalent capacitance value and loss factor of testing capacitor are obtained by discrete Fourier transform method and synchronous sampling technique；The present invention realizes isolation, floating ground measurement, can eliminate interference of the power supply to measurement apparatus, be avoided that electric current is impacted to calibration result again, the significant increase accuracy of capacitance measurement.
Description
Technical Field
The invention relates to a measuring device in the field of electromagnetic measurement, in particular to a four-terminal high-value capacitance impedance measuring device and a measuring method thereof.
Background
In recent years, manufacturers at home and abroad produce various real objects and equivalent high-value standard capacitors, the accuracy is between 0.05 and 2 percent, the capacity reaches the mF level, and the standard capacitors are urgently needed to be verified or calibrated; commonly used impedance measuring instruments, such as GR7600, Agilent4284A, etc., also need to be certified or calibrated in a high value capacity range. However, a high-value capacitance traceability system is not established in China, and when some manufacturers and metering departments measure high-value capacitance devices, the high-value capacitance devices are measured by using an uncalibrated impedance measuring instrument, so that the reliability and accuracy of the high-value capacitance values in China cannot be guaranteed.
The existing high-value capacitance standard device usually adopts a four-terminal connection mode, and common measurement methods include a constant current circuit method, an alternating current bridge method, a current comparator method and the like. Several high value capacitance measurement methods are described below.
1) Ac bridge method
As shown in FIG. 1, the capacitor to be measured and the reference capacitor are connected in parallel with the power supply by ZAAnd ZBForming a ratio to form a classical bridge. Wherein each lead and contact resistance is Z12、Z35、Z46And Z78Measurement errors may be introduced. And is measured by a capacitance CXIn fact, the connection mode is two-end connection mode, and connection measurement is not carried out according to the definition of four ends.
2) Current comparator method
As shown in FIG. 2, the measuring system comprises a current comparator, a standard device and a power supplyThe device comprises a source, an instruction instrument, a capacitor to be detected and an operational amplifier. Wherein T is1Is a two-stage current transformer, T2Is a current comparator, T3Is a five-disk voltage divider, A1And A2An amplifier. Standard device CSThe capacitor is a capacitor with a nominal value of 1 muF, the ratio part is composed of an operational amplifier, a two-stage current transformer and a current comparator, and the capacitance value of 1 muF-1F can be measured. However, the current comparator has residual inductance and resistance, which are the main causes of measurement errors; if other methods are used for compensation, the complexity of the circuit is increased.
In summary, the conventional capacitive impedance measuring devices all have the problem of large measuring errors.
Disclosure of Invention
In order to solve the problem of larger measurement error in the prior art, the invention provides a four-terminal high-value capacitance impedance measurement device and a measurement method, which utilize a new method of four-terminal high-value capacitance measurement combining an inductive current divider technology and a sampling technology to realize the capacitance measurement of a capacitor with the capacitance range of 10 mu F-1 mF and the frequency range of 100 Hz-1 kHz.
The design scheme of the invention is as follows,
a four-terminal method high-value capacitance impedance measuring device comprises an induction shunt 1, a measuring loop A2, a measuring loop B3, a digital voltmeter 5 and a power supply 7;
the induction shunt 1 comprises a winding A1-1 and a winding B1-2;
the turn ratio of the winding A1-1 to the winding B is 1: 1;
the measurement loop A2 comprises a capacitance box 2-1 and a standard resistor 2-2 which are connected in series in sequence;
the measurement loop B3 comprises a resistance box 3-1 and a capacitor to be measured 3-1 which are sequentially connected in series;
the standard resistor 2-2 is connected into the measurement loop A2 by adopting a four-terminal method, namely, the current measurement end of the standard resistor 2-2 is arranged outside the voltage measurement end;
the capacitor 3-2 to be measured is connected to the measurement loop B3 by adopting a four-end method; namely, the current measuring end of the capacitor to be measured 3-2 is arranged outside the voltage measuring end;
the number of the digital voltmeters 5 is one pair, and the digital voltmeters are respectively connected with voltage measuring ends of the standard resistor 2-2 and the capacitor 3-2 to be measured;
the inductive shunt 1 distributes the power supply 7 voltage to the measurement loop a2 and measurement loop B3 in proportion to the number of turns of a pair of windings.
The head end of the winding A1-1 is connected to the current input end of the measuring loop A2, and the tail end of the winding A1-1 is connected to the current output end of the measuring loop A2;
the head end of the winding B1-2 is connected to the current output end of the measuring loop B3, and the tail end is connected to the current input end of the measuring loop B3.
The induction shunt 1 is formed by uniformly winding two mutually insulated wires which are uniformly twisted on a ring-shaped iron core, the leakage inductance is small, the excitation impedance is very high, and the current ratio between two loops is determined by the excitation impedance of the induction shunt.
When the loads carried by the two measurement loops are equal, the currents flowing through the two windings of the induction shunt 1 are opposite, and the self-inductance voltage and the mutual-inductance voltage generated in each measurement loop are mutually offset, so that the induction shunt 1 only has a shunting function, namely, two paths of equal working currents are provided for the circuit, and no voltage drop is generated in the circuit.
In order to avoid that when the inductive shunt 1 is calibrated, a loop current exists between the ground of the lock-in amplifier 6 and the ground of the measuring device, which brings additional current error to the inductive shunt 1, the measuring device further comprises an isolation transformer 4;
the isolation transformer 4 comprises an input end and two output ends;
the input end of the isolation transformer 4 is connected in series with the power supply 7;
the turn ratio of the two output ends of the isolation transformer 4 is 1:1, and the two output ends are respectively arranged in the measurement loop A2 and the measurement loop B3 in series.
The measuring device further comprises a calibration module comprising a lock-in amplifier 6;
the lock-in amplifier 6 comprises a signal input end A, a signal input end B and a reference input end;
the signal input end A is connected with a voltage measuring end of the standard resistor 2-2, and the signal input end B is connected with a voltage measuring end of the capacitor to be measured 3-2;
the reference input is connected to the reference winding of the isolation transformer 4.
The measuring device further comprises a sampling module;
the sampling module comprises a sampling trigger 8, a computer 9 and a pair of digital voltmeters 5;
the sampling trigger 8 is respectively connected with the external trigger ends of the pair of digital voltmeters 5;
the computer 9 is connected to the pair of digital voltmeters 5 and the sampling trigger 8, respectively.
In a specific embodiment, the first and second electrodes are,
the capacitance value range of the capacitor 3-2 to be measured is 10 muF-1 mF;
the frequency range of the capacitor to be measured 3-2 is 100 Hz-1 kHz.
The digital voltmeter 5 is Agilent 3458A;
the sampling trigger 8 is Agilent 33220A.
The computer 9 is connected to the pair of digital voltmeters 5 and the sampling trigger 8 through a GPIB-USB interface, respectively.
A measuring method of a four-terminal method high-value capacitance impedance measuring device is utilized, the method comprises the following operation steps,
step 1, building the measuring device:
step 1-1, reversely connecting two windings in the induction shunt 1 into a pair of measuring loops, namely using the head end of one winding and the tail end of the other winding as the input ends of two paths of current;
step 1-2, connecting the input end of the isolation transformer 2 to the power supply 7, and respectively connecting a pair of output ends in series in a pair of measurement loops;
step 2, calibration step: calibrating the inductive shunt 1 with the lock-in amplifier 6; if the calibration result is less than or equal to 10-6If the level is not equal to the preset value, continuing to execute the step 3; if the calibration result is greater than 10-6If the current is in the magnitude range, adjusting the turn ratio of the winding A1-1 to the winding B1-2 in the induction shunt 1, and then returning to the step 1-1 to execute in sequence;
step 3, impedance balance adjustment: connecting a signal input end A of the phase-locked amplifier 6 with a winding A1-1 of the induction shunt 1, and connecting a signal input end B with a winding B1-2 of the shunt 1 to be induced; manually adjusting the capacitance box 2-1 and the resistance box 3-1, and observing the reading of the phase-locked amplifier 6;
when the reading is zero, stopping adjusting; the impedances of the measurement loop A2 and the measurement loop B3 reach an equilibrium state, that is, the inductive shunt 1 supplies equal and opposite currents to the measurement loop A2 and the measurement loop B3 respectively;
if the reading is not zero, continuing to adjust the resistance box 3-1 and the capacitance box 2-1 until the reading is zero;
step 4, sampling:
step 4-1, the lock-in amplifier 6 is taken down, the measuring ends of the pair of digital voltmeters 5 are respectively connected to the voltage measuring ends of the standard resistor 2-2 and the capacitor to be measured 3-2, the external trigger ends of the pair of digital voltmeters 5 are respectively connected to the signal output end of the sampling trigger 8, and the sampling trigger 8 is connected with the computer 9;
4-2, respectively measuring the instantaneous voltage values at the two ends of the standard resistor 2-2 and the capacitor 3-2 to be measured by using a pair of digital voltmeters 5, and respectively recording the instantaneous voltage values asAnd
andsatisfying the relationship of formula (1) and formula (2):
wherein,andthe current in the measurement loop A2 and the measurement loop B2, respectively, andRNis the resistance value of the standard resistor 2-2; cXIs the series equivalent capacitance value, R, of the capacitor 3-2 to be measuredXThe series equivalent resistance value of the capacitor 3-2 to be tested is obtained; omega is angular frequency, and omega is calculated by omega =2 pi f according to the power supply frequency f;
step 4-3, controlling the digital voltmeter 5 by using a sampling trigger 8 to synchronously sample the voltage signals at the two ends of the standard resistor 2-2 and the capacitor 3-2 to be tested at equal intervals;
step 4-4, transmitting the acquisition results of the digital voltmeter 5 and the sampling trigger 8 to the computer 9;
and 5, data processing: obtaining the series equivalent capacitance C of the capacitor 3-2 to be tested by the computer 9XAnd loss factor DX；
Comparing the formula (1) in the step 5 with the formula (2) to obtain a formula (3):
is provided withAnd
wherein A is the instantaneous value of the voltage across the standard resistor 2-2 obtained by the digital voltmeter 5, B is the instantaneous value of the voltage across the capacitor under test 3-2 obtained by the digital voltmeter 5, the phase angles of voltage signals at two ends of the standard resistor 2-2 and the capacitor 3-2 to be tested are respectively;
will be provided with Substituting into the formula (3) to obtain a formula (4):
according to the principle that the real part and the virtual step in the formula (4) are correspondingly equal, the following can be obtained:
obtaining the series equivalent capacitance C of the capacitor 3-2 to be measured according to the formula (7) and the formula (8)XAnd loss factor DX；
Wherein,andthe capacitance value of the capacitor 3-2 to be tested is traced to the resistance and the loss factor is traced to the phase angle by the discrete Fourier transform algorithm.
In the step 2, the phase-locked amplifier 6 is used to calibrate the inductive shunt 1, and the calibration comprises the specific steps of,
step 2-1, EliminationAAndBinfluence of (2)
Step 2-1-1, voltage at two ends of the mode measuring resistors R1 and R2 of the phase-locked amplifier A-B is used to obtain a formula (9)
The reading of the lock-in amplifier is the value of the subtraction of the two equations of equation (9), i.e.
Step 2-1-2, exchanging the channels of the phase-locked amplifier, and then using the voltages at the two ends of the mode measuring resistors R2 and R1 of the phase-locked amplifier A-B to obtain a formula (11);
the reading of the lock-in amplifier is the subtracted value of equation (11), i.e.
Obtaining a formula (13) through the formula (10) and the formula (12);
step 2-2, replacing resistance and eliminatingR1AndR2the influence of (a);
step 2-2-1, exchange resistance R1And R2；
After the resistor is switched, the mode measuring resistor R of the phase-locked amplifier A-B is used1And R2The voltage across the terminals can be given by the formula (14);
subtracting the two formulas in the formula (14) to obtain a formula (15);
step 2-2-2, exchanging channels of the phase-locked amplifier to obtain a formula (16);
subtracting the two formulas in the formulas (1 and 6) to obtain a formula (17);
obtaining a formula (18) through the formula (15) and the formula (17);
obtaining a formula (19) through the formula (13) and the formula (18);
Δu1-Δu2=IRI
in the step 5, the step of processing the image,andthe acquisition process of (a) is as follows,
for the periodic signal y (x), as long as the dirichlet condition is satisfied, that is, there are a finite number of extreme points in a period and there are connections, or there are a finite number of class i discontinuities, all of which can be decomposed into a fourier series form, as shown in equation (9);
wherein, a0Is the direct current component of the signal; a iskAnd bkIs the sine and cosine amplitude of the kth harmonic of the signal; obtaining a by equation (10)0、akAnd bkA value of (d);
（10）；
in actual calculation, the signal y (x) is sampled and the sample sequence is accumulated to find the area, instead of the above-mentioned integration process of the signal, and the calculation formula (11) is shown as follows:
（11）；
the trapezoidal compensation formula is adopted to calculate the sine and cosine amplitudes of the 5 th harmonic, and the adopted trapezoidal compensation formula (12) is shown as follows:
where Δ is the complement of the sample, which is obtained by sampling data calculation, as shown in equation (13):
Δ=（y0+y1-yn-yn+1)/(-y0+y1-yn+yn+1) （13）；
according to akAnd bkThen the amplitude and phase angle of the k-th harmonic are calculated as shown in equation (14):
the series equivalent capacitance value C of the capacitor 3-2 to be measured by adopting the methodXSum loss factor value DXThe indexes are shown in Table 1;
TABLE 1
The invention has the following beneficial effects:
1) the inductive shunt is used for providing two paths of equal working currents for the standard resistor and the capacitor to be measured, and the virtual ground problem in impedance measurement is avoided.
2) The high-value capacitance measuring device composed of the induction shunt and the isolation transformer is utilized to realize isolation and floating measurement, so that the interference of a power supply to the measuring device can be eliminated, the influence of the circulation current between the ground of the measuring device and the ground of the phase-locked amplifier on a calibration result when the induction shunt is calibrated can be avoided, and the accuracy of the capacitance measuring device is greatly improved.
Drawings
FIG. 1 is a schematic diagram of a measurement apparatus of the prior art 1;
FIG. 2 is a schematic diagram of a measurement apparatus of prior art 2;
FIG. 3 is a schematic structural diagram of a four-terminal high-valued capacitive impedance measurement apparatus according to the present invention;
FIG. 4 is a schematic diagram of the connection between the lock-in amplifier and the four-terminal capacitance impedance measuring device;
FIG. 5 is a schematic diagram of the connection of a sampling module to a four-terminal capacitance impedance measuring device;
description of the figure numbering:
1-an inductive shunt; 1-1 winding A; 1-2 winding B; 2-measurement loop a;
2-1 a capacitor box; 2-2 standard resistors; 3-measurement loop B; 3-1 resistance box;
3-2 capacitor to be tested; 4-an isolation transformer; 5-digital voltmeter; 6-a phase-locked amplifier;
7-a power supply; 8-a sampling trigger; 9-a computer;
the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments, and the scope of the present invention is not limited to the specific embodiments described below.
Detailed Description
According to the illustrations of figures 3, 4 and 5,
a four-terminal method high-value capacitance impedance measuring device comprises an induction shunt 1, an isolation transformer 4, a measuring loop A2, a measuring loop B3, a digital voltmeter 5 and a power supply 7;
the induction shunt 1 comprises a winding A1-1 and a winding B1-2;
the head end of the winding A1-1 is connected to the current input end of the measuring loop A2, and the tail end of the winding A1-1 is connected to the current output end of the measuring loop A2;
the head end of the winding B1-2 is connected to the current output end of the measuring loop B3, and the tail end of the winding B1-2 is connected to the current input end of the measuring loop B3;
the turn ratio of the winding A1-1 to the winding B is 1: 1;
the measurement loop A2 comprises a capacitance box 2-1, a standard resistor 2-2 and a winding A1-1 which are connected in series in sequence;
the measurement loop B3 comprises a resistance box 3-1, a capacitor to be measured 3-1 and the winding B1-2 which are sequentially connected in series;
the standard resistor 2-2 is connected into the measurement loop A2 by adopting a four-terminal method, namely, the current measurement end of the standard resistor 2-2 is arranged outside the voltage measurement end;
the capacitor 3-2 to be measured is connected to the measurement loop B3 by adopting a four-end method; namely, the current measuring end of the capacitor to be measured 3-2 is arranged outside the voltage measuring end.
The isolation transformer 4 comprises an input end and two output ends;
the input end of the isolation transformer 4 is connected in series with the power supply 7;
the turn ratio of the two output ends of the isolation transformer 4 is 1:1, and the two output ends are respectively arranged in the measurement loop A2 and the measurement loop B3 in series.
The measuring device further comprises a calibration module comprising a lock-in amplifier 6;
the lock-in amplifier 6 comprises a signal input end A, a signal input end B and a reference input end;
the signal input end A is connected with a voltage measuring end of the standard resistor 2-2, and the signal input end B is connected with a voltage measuring end of the capacitor to be measured 3-2;
the rightmost winding labeled Ref in fig. 4 is the reference winding of the isolation transformer 4; the reference winding of the isolation transformer 4 is double-ended, and the input end thereof is connected with the power supply 7, and the output end thereof is connected with the reference input end of the phase-locked amplifier 6.
The measuring device further comprises a sampling module;
the sampling module comprises a digital voltmeter 5, a sampling trigger 8 and a computer 9;
the number of the digital voltmeters 5 is one pair, and the digital voltmeters are respectively connected with voltage measuring ends of the standard resistor 2-2 and the capacitor 3-2 to be measured;
the sampling trigger 8 is respectively connected with the external trigger ends of the pair of digital voltmeters 5;
the computer 9 is connected with the pair of digital voltmeters 5 and the sampling trigger 8 through GPIB-USB interfaces respectively.
The capacitance value range of the capacitor 3-2 to be measured is 10 muF-1 mF;
the frequency range of the capacitor to be measured 3-2 is 100 Hz-1 kHz.
The digital voltmeter 5 is Agilent 3458A;
the sampling trigger 8 is Agilent 33220A.
A measuring method of a four-terminal method high-value capacitance impedance measuring device is utilized, the method comprises the following operation steps,
step 1, building the measuring device:
step 1-1, reversely connecting two windings in the induction shunt 1 into a pair of measuring loops, namely connecting the head end of the winding A1-1 into the current input end of the measuring loop A2, and connecting the tail end of the winding A1-1 into the current output end of the measuring loop A2; the tail end of the winding B1-2 is connected to the current input end of the measuring loop B3, and the head end of the winding B1-2 is connected to the current output end of the measuring loop B3;
step 1-2, connecting the input end of the isolation transformer 2 to the power supply 7, and respectively connecting a pair of output ends in series in a pair of measurement loops;
step 2, calibration step: calibrating the inductive shunt 1 with the lock-in amplifier 6; if the calibration result is less than or equal to 10-6If the level is not equal to the preset value, continuing to execute the step 3; if the calibration result is greater than 10-6If the current is in the magnitude range, adjusting the turn ratio of the winding A1-1 to the winding B1-2 in the induction shunt 1, and then returning to the step 1-1 to execute in sequence;
step 3, impedance balance adjustment: connecting a signal input end A of the phase-locked amplifier 6 with a winding A1-1 of the induction shunt 1, and connecting a signal input end B with a winding B1-2 of the shunt 1 to be induced; manually adjusting the capacitance box 2-1 and the resistance box 3-1, and observing the reading of the phase-locked amplifier 6;
when the reading is zero, stopping adjusting; the impedances of the measurement loop A2 and the measurement loop B3 reach an equilibrium state, that is, the inductive shunt 1 supplies equal and opposite currents to the measurement loop A2 and the measurement loop B3 respectively;
if the reading is not zero, continuing to adjust the resistance box 3-1 and the capacitance box 2-1 until the reading is zero;
step 4, sampling:
step 4-1, the lock-in amplifier 6 is taken down, the measuring ends of the pair of digital voltmeters 5 are respectively connected to the voltage measuring ends of the standard resistor 2-2 and the capacitor to be measured 3-2, the external trigger ends of the pair of digital voltmeters 5 are respectively connected to the signal output end of the sampling trigger 8, and the sampling trigger 8 is connected with the computer 9;
4-2, respectively measuring the instantaneous voltage values at the two ends of the standard resistor 2-2 and the capacitor 3-2 to be measured by using a pair of digital voltmeters 5, and respectively recording the instantaneous voltage values asAnd
andsatisfying the relationship of formula (1) and formula (2):
wherein,andthe current in the measurement loop A2 and the measurement loop B2, respectively, andRNis the resistance value of the standard resistor 2-2; cXIs the series equivalent capacitance value, R, of the capacitor 3-2 to be measuredXThe series equivalent resistance value of the capacitor 3-2 to be tested is obtained; omega is angular frequency, and omega is calculated by omega =2 pi f according to the power supply frequency f;
step 4-3, controlling the digital voltmeter 5 by using a sampling trigger 8 to synchronously sample the voltage signals at the two ends of the standard resistor 2-2 and the capacitor 3-2 to be tested at equal intervals;
step 4-4, transmitting the acquisition results of the digital voltmeter 5 and the sampling trigger 8 to the computer 9;
and 5, data processing: obtaining the series equivalent capacitance C of the capacitor 3-2 to be tested by the computer 9XAnd loss factor DX；
Comparing the formula (1) with the formula (2) to obtain formula (3):
is provided withAnd
wherein A is the instantaneous value of the voltage across the standard resistor 2-2 obtained by the digital voltmeter 5, B is the instantaneous value of the voltage across the capacitor under test 3-2 obtained by the digital voltmeter 5, the phase angles of voltage signals at two ends of the standard resistor 2-2 and the capacitor 3-2 to be tested are respectively;
will be provided with Substituting into the formula (3) to obtain a formula (4):
according to the principle that the real part and the virtual step in the formula (4) are correspondingly equal, the following can be obtained:
according to said formula(7) And the formula (8) obtains the capacity value C of the capacitor 3-2 to be measuredXAnd loss factor DX；
Wherein,andand obtaining the result through a discrete Fourier transform algorithm.
Andthe acquisition process of (a) is as follows,
for the periodic signal y (x), as long as the dirichlet condition is satisfied, that is, there are a finite number of extreme points in a period and there are connections, or there are a finite number of class i discontinuities, all of which can be decomposed into a fourier series form, as shown in equation (9);
wherein, a0Is the direct current component of the signal; a iskAnd bkIs the sine and cosine amplitude of the kth harmonic of the signal; obtaining a by equation (10)0、akAnd bkA value of (d);
（10）；
in actual calculation, the signal y (x) is sampled and the sample sequence is accumulated to find the area, instead of the above-mentioned integration process of the signal, and the calculation formula (11) is shown as follows:
（11）；
the trapezoidal compensation formula is adopted to calculate the sine and cosine amplitudes of the 5 th harmonic, and the adopted trapezoidal compensation formula (12) is shown as follows:
where Δ is the complement of the sample, which is obtained by sampling data calculation, as shown in equation (13):
Δ=（y0+y1-yn-yn+1)/(-y0+y1-yn+yn+1) （13）；
according to akAnd bkThen the amplitude and phase angle of the k-th harmonic are calculated as shown in equation (14):
the above-described embodiments are intended to be illustrative only, and various modifications and alterations will readily occur to those skilled in the art based upon the teachings herein and the principles and applications of the present invention, which are to be considered in the foregoing detailed description of the invention.
Claims (8)
1. A four-terminal method high value capacitance impedance measuring device is characterized in that:
the measuring device comprises an induction shunt (1), a measuring loop A (2), a measuring loop B (3), a digital voltmeter (5) and a power supply (7);
the induction shunt (1) comprises a winding A (1-1) and a winding B (1-2);
the turn ratio of the winding A (1-1) to the winding B is 1: 1;
the measurement circuit A (2) comprises a capacitance box (2-1) and a standard resistor (2-2) which are connected in series;
the measurement loop B (3) comprises a resistance box (3-1) and a capacitor to be measured (3-1) which are connected in series;
the standard resistor (2-2) is connected in the measurement loop A (2) by adopting a four-end method, namely, the current measurement end of the standard resistor (2-2) is arranged outside the voltage measurement end;
the capacitor (3-2) to be measured is connected to the measurement loop B (3) by adopting a four-end method; namely, the current measuring end of the capacitor (3-2) to be measured is arranged outside the voltage measuring end;
the number of the digital voltmeters (5) is one pair, and the digital voltmeters are respectively connected with the voltage measuring ends of the standard resistor (2-2) and the capacitor (3-2) to be measured.
2. The four-terminal high-value capacitance impedance measuring device according to claim 1, characterized in that:
the head end of the winding A (1-1) is connected to the current input end of the measurement loop A (2), and the tail end of the winding A is connected to the current output end of the measurement loop A (2);
the head end of the winding B (1-2) is connected to the current output end of the measuring loop B (3), and the tail end of the winding B (1-2) is connected to the current input end of the measuring loop B (3).
3. The four-terminal high-value capacitance impedance measuring device according to claim 1, characterized in that:
the measuring device further comprises an isolation transformer (4);
the isolation transformer (4) comprises an input end and two output ends;
the input end of the isolation transformer (4) is connected with the power supply (7) in series;
the turn ratio of two output ends of the isolation transformer (4) is 1:1, and the isolation transformer is respectively arranged in the measurement loop A (2) and the measurement loop B (3) in series.
4. The four-terminal high-value capacitance impedance measuring device according to claim 3, characterized in that:
the measuring device further comprises a calibration module comprising a lock-in amplifier (6);
the phase-locked amplifier (6) comprises a signal input end A, a signal input end B and a reference input end;
the signal input end A is connected with a voltage measuring end of the standard resistor (2-2), and the signal input end B is connected with a voltage measuring end of the capacitor to be measured (3-2);
the reference input end is connected with a reference winding of the isolation transformer (4).
5. The four-terminal high-value capacitance impedance measuring device according to claim 4, wherein:
the measuring device further comprises a sampling module;
the sampling module comprises a sampling trigger (8), a computer (9) and a pair of digital voltmeters (5);
the sampling trigger (8) is respectively connected with the external trigger ends of the pair of digital voltmeters (5);
the computer (9) is respectively connected with the pair of digital voltmeters (5) and the sampling trigger (8).
6. The four-terminal high-value capacitance impedance measuring device according to claim 1 or 4, characterized in that:
the capacitance value range of the capacitor (3-2) to be measured is 10 muF-1 mF;
the frequency range of the capacitor (3-2) to be tested is 100 Hz-1 kHz.
7. The method for measuring the high-value capacitance impedance measuring device by the four-terminal method according to claim 5, wherein:
the method comprises the following operation steps of,
step 1, building the measuring device:
step 1-1, reversely connecting two windings in the induction shunt (1) into a pair of measuring loops, namely, the head end of one winding and the tail end of the other winding are respectively used as input ends of two paths of current;
step 1-2, connecting the input end of the isolation transformer (4) to the power supply (7), and respectively connecting a pair of output ends in series in a pair of measurement loops;
step 2, calibration step: calibrating the inductive shunt (1) with the lock-in amplifier (6); if the calibration result is less than or equal to 10-6If the level is not equal to the preset value, continuing to execute the step 3; if the calibration result is greater than 10-6 orders, adjusting the turn ratio of the winding A (1-1) and the winding B (1-2) in the induction shunt (1), and then returning to the step 1-1 for sequential execution;
step 3, impedance balance adjustment: connecting a signal input end A of the phase-locked amplifier (6) with a winding A (1-1) of the induction shunt (1), and connecting a signal input end B with a winding B (1-2) of the induction shunt (1); manually adjusting the capacitance box (2-1) and the resistance box (3-1) and observing the reading of the phase-locked amplifier (6);
when the reading is zero, stopping adjusting; the impedance of the measurement loop A (2) and the impedance of the measurement loop B (3) reach an equilibrium state, namely the induction shunt (1) respectively provides currents with equal magnitude and opposite directions for the measurement loop A (2) and the measurement loop B (3);
if the reading is not zero, continuing to adjust the resistance box (3-1) and the capacitance box (2-1) until the reading is zero;
step 4, sampling:
step 4-1, the phase-locked amplifier (6) is taken down, the measuring ends of a pair of digital voltmeters (5) are respectively connected to the voltage measuring ends of the standard resistor (2-2) and the capacitor to be measured (3-2), the external trigger ends of the pair of digital voltmeters (5) are respectively connected to the signal output end of the sampling trigger (8), and the sampling trigger (8) is connected with the computer (9);
step 4-2, utilizing a pair of digital voltmeters (5) to respectively measure voltage instantaneous values at two ends of the standard resistor (2-2) and the capacitor to be measured (3-2), and respectively recording the voltage instantaneous values asAnd
andsatisfying the relationship of formula (1) and formula (2):
wherein,andrespectively the current in the measurement loop A and the measurement loop B, andRNis the resistance value of the standard resistor (2-2); cXIs the series equivalent capacitance value, R, of the capacitor (3-2) to be measuredXThe series equivalent resistance value of the capacitor (3-2) to be tested; omega is angular frequency, and omega is calculated by 2f pi according to the power frequency f;
step 4-3, controlling the digital voltmeter (5) to synchronously sample the voltage signals at the two ends of the standard resistor (2-2) and the capacitor to be tested (3-2) at equal intervals by using a sampling trigger (8);
4-4, transmitting the acquisition results of the digital voltmeter (5) and the sampling trigger (8) to the computer (9);
and 5, data processing: obtaining the series equivalent capacitance value C of the capacitor (3-2) to be measured through the computer (9)XAnd loss factor DX；
Comparing the formula (1) with the formula (2) to obtain formula (3):
is provided withAnd
wherein A is the instantaneous value of the voltage across the standard resistor (2-2) acquired by the digital voltmeter (5), B is the instantaneous value of the voltage across the capacitor to be tested (3-2) acquired by the digital voltmeter (5),the phase angles of voltage signals at two ends of the standard resistor (2-2) and the capacitor to be tested (3-2) are respectively;
will be provided withSubstituting into the formula (3) to obtain a formula (4):
according to the principle that the real part and the virtual step in the formula (4) are correspondingly equal, the following can be obtained:
obtaining the capacitance value C of the capacitor (3-2) to be measured according to the formula (7) and the formula (8)XAnd loss factor DX；
Wherein,andand obtaining the result through a discrete Fourier transform algorithm.
8. The measurement method according to claim 7, characterized in that:
in the step 5, the step of processing the image,andthe acquisition process of (a) is as follows,
for the periodic signal y (x), as long as the dirichlet condition is satisfied, that is, there are a finite number of extreme points in a period and continuous everywhere, or there are a finite number of class i discontinuities, all can be decomposed into a fourier series form, as shown in equation (9);
wherein, a0Is the direct current component of the signal; a iskAnd bkIs the sine and cosine amplitude of the kth harmonic of the signal; obtaining a by equation (10)0、akAnd bkA value of (d);
in actual calculation, the signal y (x) is sampled and the sample sequence is accumulated to find the area, instead of the above-mentioned integration process of the signal, and the calculation formula (11) is shown as follows:
the trapezoidal compensation formula is adopted to calculate the sine and cosine amplitudes of the 5 th harmonic, and the adopted trapezoidal compensation formula (12) is shown as follows:
where Δ is the complement of the sample, which is obtained by sampling data calculation, as shown in equation (13):
Δ＝(y0+y1-yn-yn+1)/(-y0+y1-yn+yn+1) (13)；
the amplitude and phase angle of the kth harmonic are then calculated from the values of ak and bk, as shown in equation (14):
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| CN106093642B (en) * | 2016-06-08 | 2019-02-01 | 福州大学 | Capacitance characteristic measuring circuit and its method under a kind of any AC carrier |
| CN106646029A (en) * | 2016-11-18 | 2017-05-10 | 武汉电联电力电气技术有限公司 | Capacitor measurement device and reactor characteristic testing method |
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| CN107315159B (en) * | 2017-07-11 | 2020-05-26 | 北京东方计量测试研究所 | Big-capacitance tracing circuit and method |
| CN108241129B (en) * | 2018-01-09 | 2020-09-29 | 中国电子产品可靠性与环境试验研究所（（工业和信息化部电子第五研究所）（中国赛宝实验室）） | Device and method for monitoring output filter capacitor of switching power supply |
| US11525881B1 (en) * | 2021-08-17 | 2022-12-13 | Fluke Corporation | Systems and methods for calibration using impedance simulation |
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