CN202886483U - Low-frequency large-capacitance measuring device - Google Patents
Low-frequency large-capacitance measuring device Download PDFInfo
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- CN202886483U CN202886483U CN 201220628492 CN201220628492U CN202886483U CN 202886483 U CN202886483 U CN 202886483U CN 201220628492 CN201220628492 CN 201220628492 CN 201220628492 U CN201220628492 U CN 201220628492U CN 202886483 U CN202886483 U CN 202886483U
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Abstract
The utility model relates to a low-frequency large-capacitance measuring device, wherein the measuring device comprises a current source, an insulation diverter, a standard current diverter, a current comparator, a standard capacitor, an in-phase amplifying circuit and a measured element, wherein the current source sequentially bypasses the insulation diverter, the standard current diverter, the current comparator, the standard capacitor to the in-phase amplifying circuit; the insulation diverter and the standard current diverter are connected with a current input end of the measured element; the in-phase amplifying circuit is connected with a voltage input end of the measured element; and the current comparator is also connected with a null indicator for indicating magnetomotive force balance in an iron core of the current comparator and a difference stream testing instrument for comparing currents at two ends of the current comparator. The measuring device can provide wide-range driving current through regulating the current source according to characteristics of a large measured capacitor, and the normal operation of the measured capacitor is ensured.
Description
Technical field
The utility model relates to capacitance measuring device, particularly relates to the large capacitance measuring device of a kind of low frequency.
Background technology
At present, electric capacity greater than 10 μ F does not also have stable material standard device, it is very expensive and unpractical making stable high value electric capacity substantive standard, now many by current transformer and voltage transformer (VT) in conjunction with 1 a stable μ F electric capacity, adopt impedance transformer network to substitute entity capacitance.Yet these analoglike four ends are subjected to the impact of mutual inductor performance larger on large electric capacity, can only provide stable value under fixing operating voltage or electric current.Simultaneously, the error that causes in order to eliminate lead resistance and terminal place contact resistance is made four ends to form with large electric capacity usually.
Alternating current bridge is the instrument of measuring specially capacitance parameter, the electric bridge of measuring in the market electric capacity mainly comprises the series of products such as GR1693,4284A, 4294A, 4287A, E4980A, the method of this class bridge measurement impedance mainly contains following four kinds: bridge method, resonance method, voltammetry and automatic bridge balancing method.Bridge method has higher measuring accuracy, but need to repeatedly regulate, and Measuring Time is long, should not automatically measure fast.Resonance method requires to have the pumping signal of upper frequency, generally is not easy to satisfy the requirement of high-acruracy survey.Because test frequency is unfixing, test speed is difficult to improve.Voltammetry is subject to the impact that probe uses mutual inductor, is mainly used in the measurement of device.Free bridge balance method measurement range is wider, and frequency range is present most widely used measuring method for also wider, and its principle of work is to make tested impedance and normal impedance flow through identical electric current, measures its voltage ratio.
Mainly there are following two problems in employing based on the large capacity of method measure analog of above-mentioned measurement impedance, one, and electric bridge all is for capacitor design in kind in the market, the impact that electric bridge itself is introduced for the simulation class standard during measurement is larger.Simultaneously, the induced signal of simulating the inner mutual inductor coil of large electric capacity also can disturb the performance of electric bridge, affects the accuracy of measurement result.
They are two years old, in large capacitance measurement, particularly during the above value of 10mF, because the large equiva lent impedance of electric capacity own is less, be subjected to the impact of the working current of electric bridge own or voltage capability, can't provide enough large driving signal to electric capacity, make its coil normal operation, therefore can not carry out the measurement of the above value of 10mF.Summary of the invention
For above the deficiencies in the prior art, the utility model proposes the large capacitance measuring device of a kind of low frequency.Can by regulating current source, provide the drive current of wide-range according to the characteristic of tested large electric capacity, guarantee the normal operation of measured capacitance.Adopt the in-phase amplifier of high input impedance, can effectively isolate the driving signal of large electric capacity and the carrying out of sampled signal, avoid device to have influence on the performance of bulk container itself, measurement range that again can expanded capacitor.
Utilize poor current test instrument to adopt the poor method of direct measuring current, need not the adjustment criteria impedance, just can finish the measurement to electric capacity, introduce simultaneously software and revise and compensate, Effective Raise the accuracy of measurement result.
The large capacitance measuring device of a kind of low frequency is on current equivalence transformation of scale basis, utilizes current comparator and engages high-precision in-phase amplification circuit and the normalized current shunt is realized the measurement of the large electric capacity of low frequency.This measurement mechanism is according to the bridge arm equilibrium principle, drive current is added on the once end and measured capacitance of normalized current shunt, adopt in-phase amplification circuit that the sampled voltage on the measured capacitance is amplified, then this voltage is added to the branch road I of generation current on the standard capacitance
1Simultaneously, with normalized current shunt (using in order to range extension) secondary terminals generation current I
2And I
1Be added to simultaneously current comparator, measure the difference of two-way electric current by differing from the current test instrument, calculate its proportionate relationship.Schematic diagram as shown in the figure.
If tested impedance is Z
x, normal impedance is Z
s, then have according to schematic diagram 1
I
2=I×K
1（2）
Then have:
Because K
1, K
3Be respectively the diverting coefficient of standard shunt and the gain amplifier of amplifying circuit, known.So can be by I
2And I
1Proportionate relationship to obtain tested impedance be Z
xIt is the proportionate relationship of electric current on the diverting coefficient of gain amplifier, normalized current shunt of operational amplification circuit and the current comparator with the impedance ratio relationship conversion of measured capacitance and standard capacitance.
Wherein, current source provides can provide 500 μ A～10A according to the size of measured capacitance, and frequency is the drive current of 100Hz～1kHz, satisfies the measurement demand of different values.
Because the sampled voltage on the measured capacitance is very little, the small interference that outer signals is introduced all may produce larger mushing error to the sampled voltage on the measured capacitance.So adopt the isolation shunt that the ground of drive current and the ground of measured capacitance and in-phase amplification circuit are isolated, avoid introducing common mode interference, have influence on measured result.
The normalized current shunt is in order to enlarge the range of measured capacitance, generation current I
2, the homophase amplification appliance amplifies the voltage on the measured capacitance, and is added to generation current I on the standard capacitance
1, be used for equally enlarging the measured capacitance range.Tested impedance range can be enlarged 10 by standard shunt and in-phase amplification circuit
4Doubly.
Current comparator is the core of measurement mechanism, plays a part expanded range, and it once holds the electric current I on the connection standard electric capacity simultaneously
1With the electric current I on the secondary terminals normalized current shunt
2, inject poor stream by regulating external poor current test instrument to comparator, make the zero indicator balance.Poor stream by the two-way electric current calculates the two-way electric current I
1And I
2Proportionate relationship.
The purpose of this utility model is achieved through the following technical solutions:
The large capacitance measuring device of a kind of low frequency, this measurement mechanism comprises current source, isolation shunt, normalized current shunt, current comparator, standard capacitance, in-phase amplification circuit and detected element, described current source successively through, isolation shunt, normalized current shunt, current comparator, standard capacitance be to in-phase amplification circuit, described isolation shunt links to each other with the current input terminal of detected element respectively with the normalized current shunt, and described in-phase amplification circuit is connected with the voltage input end of detected element; Described current comparator also is connected with the zero indicator that is used to indicate magnetic potential balance in the current comparator iron core and is used for the relatively poor current test instrument of current comparator two ends electric current.
Described in-phase amplification circuit comprises sampling amplifier, Hi-pass filter, low-pass filter and voltage follower, described sampling amplifier successively through Hi-pass filter, low-pass filter to voltage follower.
Described detected element links to each other with a test fixture, and this test fixture links to each other with voltage output end with the current input terminal of detected element with the protected type twisted-pair feeder of banana head.
Described current comparator adopts the connected mode of compensation winding and ratio winding parallel, and the ratio winding of current comparator, compensation winding, detection winding all adopt omnidirectional coiling and magnetic shielding line to draw, and detects simultaneously the magnetic shielding ground connection of winding.
Limit screen, interior screen, three layers of shielding construction of outer screen are adopted in described magnetic shielding.
An internal resistance of described comparator is less than 1 Ω, and the secondary internal resistance is less than 32m Ω.
The utility model has the advantage of:
This measurement mechanism is based on the bridge arm equilibrium principle and designs, with prior art be not both independently large driven with current sources measured piece of employing, adopt simultaneously high-precision current diverter and in-phase amplification circuit to enlarge the range of measured capacitance.The proportional precision of shunt and in-phase amplification circuit can independently be traced to the source respectively, adopts simultaneously error correcting technology to guarantee the accuracy of measuring system.
Proportional balancing method is regulated part, adopts poor current test instrument directly test the poor of comparator two-way electric current and flows, and need not the balance that the adjustment criteria resistance value just can reach bridge arm, system architecture simply, be easy to realization.
The mode that adopts current diverter, in-phase amplification circuit, three grades of ratios of current comparator to amplify is come expanded range, failure rate is low, and reliability is high, can be with the expanded range 10 of measured capacitance
6Doubly, by changing the diverting coefficient of shunt, the gain amplifier of in-phase amplifier and the no-load voltage ratio of comparator can realize the measurement to the large electric capacity of 1 μ F～1F.
Description of drawings
Fig. 1: the large capacitance measuring device schematic diagram of low frequency;
Fig. 2: in-phase amplification circuit theory diagram;
Fig. 3: current comparator structure principle chart.
Embodiment
Be illustrated in figure 1 as the utility model system architecture schematic diagram, the measurement mechanism of the large electric capacity of low frequency comprises: current source 1, isolation shunt 2, normalized current shunt 3, current comparator part 4, in-phase amplification circuit 5, standard capacitor 6, detected element 7.Wherein detected element links to each other with a test fixture, and the Rubber end cable of this test fixture links to each other with the current input terminal of measured piece, and test fixture is connected with the measured piece voltage output end with the protected type pair cable of BNC connector.Reduce common-mode noise, increase the vulnerability to jamming of system.
Below each assembly of the present utility model is introduced respectively.
Working current is added on the normalized current shunt 3, and then partly is added on the detected element electric capacity by test fixture with the form of series connection after isolating through isolation shunt 2.Wherein isolate shunt the ground of signal source and the ground of measured capacitance are kept apart, make it not form the loop, suppress to greatest extent the error that common mode interference is introduced.
The effect of normalized current shunt 3 is shunting drive currents, expands tested range.As seen from Figure 1, the electric current I after the shunting
2=K
1I.Current diverter adopts the mode of two-stage current transformer design to go design, and wherein secondary coil is made tappedly according to the ratio difference of shunting, and the tap of primary winding and secondary coil all is connected on the binding post of fixed panel, demarcates different ratios.Because operating frequency range is 100Hz～1kHz, use far above common power frequency, in order to reduce core loss, particularly eddy current loss selects the iron-nickel alloy material to make the iron core that thickness is 0.2mm.For fear of kelvin effect and so that conductor resistance increases, secondary coil is selected the multiply twisted-pair feeder.In order to reduce to greatest extent the drain capacitance electric current, coil interlayer is selected the insulating material of low-k simultaneously, adopts suitable electrostatic screening in the coil, and adopts the segmentation winding method.
Detected element 7, this detected element 7 is measured capacitance herein, described measured capacitance is connected with a test fixture, and test fixture links to each other with voltage output end with the current input terminal of measured capacitance with the protected type twisted-pair feeder of banana head, partly links to each other with in-phase amplification circuit in the BNC connector mode.Electric current line and pressure-wire as far as possible away from, to reduce the Mutual Inductance Coupling of current return and voltage circuit.Simultaneously, twisted-pair feeder can make the induced potential of each minor loop be mutually reverse counteracting.
The effect of in-phase amplification circuit part 5 is the interchange small voltage amplifier on the measured capacitance.Because the voltage on the measured capacitance about 1mV～1V, for expanded range needs, amplifies 100,10,1 with tested voltage as required, after this voltage be added on the normal impedance 6 produce measured current I
2, normal impedance is the accurate mica capacitor of 1 a μ F, its error criterion is 2 * 10
-4
The in-phase amplification circuit block diagram as shown in Figure 2.Take the precision instrumentation amplifier AD623 of AD company as core design amplifier circuit, amplify the voltage signal on the electric capacity.But the input impedance of the differential amplification mode Effective Raise amplifying circuit of AD623 improves the matching degree of its balanced, symmetrical, and effect ground reduces the impact of common mode interference.Amplifying circuit is selected three outer meeting resistances, changes gain amplifier.Increase simultaneously the undesired signal after high and low pass filter circuit filtering is amplified.Simultaneously, in order to reduce the impact on rear class output, adopt the alternating voltage follow circuit to reduce output impedance, improve the load capacity of output circuit.
Current comparator part 4 is the cores of regulating proportional balancing method.During work, with the electric current I on the standard capacitance
1With the electric current I on the normalized current shunt
2Access respectively comparator once and Secondary Winding, inject poor stream by poor current test instrument to comparator and make its balance, and measure poor stream, calculate I
1, I
2Ratio.
Comparator adopts compensation design, and its design concept as shown in Figure 3.At main iron core S
aCoiling nulling coil N reaches the standard grade
D, then add the ground floor shielding iron core.Coiling compensating coil N on shielding iron core and main iron core
BAdd again second layer shielding iron core S
b, the while is as the iron core of auxiliary mutual inductor.On the iron core of all coilings around referring to N
1And N
2The ratio coil, secondary coil and compensating ring equal turn numbers, i.e. N
2=N
BThe primary current of compensation comparator is I
1, secondary current is I
2+ I
B, when the main iron core of comparator is in zero magnetic flux state, have
I
1N
1+I
2N
2+I
BN
B0 （5）
Electric current I during work on the standard capacitance
1With the electric current I on the normalized current shunt
2Meet respectively N
1And N
2Coil, poor current test instrument meets compensating coil N
B, to compensating coil input Xiao Dian Liu ⊿ I, zero indicator meets magnetic test coil N
DWhen the zero indicator nulling, during the interior magnetic potential balance of iron core:
I
1N
1+I
2N
2+I
BN
B+⊿INN
B+⊿IxN
B=0 （6）
Qi Zhong ⊿ Ix is measured current I
1, I
2Difference between current, bring formula (1) into (2)
⊿Ix＝-⊿I （7）
Reading by poor current test instrument Du Chu ⊿ I/I can calculate I
1And I
2Ratio poor.
Working current in the device on the comparator is a milliampere magnitude weak current, causes easily larger measuring error, the accuracy that impact is measured.Error on the comparator mainly contains capacitive error and two components of magnetic error.The capacitive error be since inner (interlayer, the turn-to-turn) winding of comparator winding over the ground and exist distributed capacitance and potential difference (PD) to cause between each winding, it is the principal element that affects the accuracy of weak current comparator.Adopt the capacitance compensation method in order to eliminate the capacitive error, the error of distributed capacitance is reduced to minimum.The magnetic error mainly is because the error that main iron core each point magnetoconductivity is different, the detection winding technique is inhomogeneous, core section is inconsistent, iron core is non-linear and the magnetic dispersion of existence causes.Adopt the method for magnetic shielding, the magnetic error is reduced, magnetic shielding is rolled into by the high permeability magnetic material of saturation magnetic induction degree, around detect with the compensation winding outside, in order to shielding once, leakage field and the extraneous stray magnetic field of Secondary Winding.Simultaneously once, keep close-coupled between Secondary Winding, to reduce leakage flux, for this reason, once, Secondary Winding adopts even distributed winding.The homogeneity of cross section and magnetoconductivity should be good everywhere for main iron core.For this reason, require the width of alloy band consistent, even thickness, band material with whole piece without the even coiled ring-type of seam alloy band, layer insulation is good, without short circuit.Iron core is wanted homo genizing annelaing, and temperature is even everywhere for workpiece during thermal treatment, does not make the iron core distortion.Should there be residual mechanical stresses after processing and assembling.
Should be appreciated that the above detailed description of the technical solution of the utility model being carried out by preferred embodiment is illustrative and not restrictive.Those of ordinary skill in the art can make amendment to the technical scheme that each embodiment puts down in writing on the basis of reading the utility model instructions, perhaps part technical characterictic wherein is equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution break away from the spirit and scope of each embodiment technical scheme of the utility model.
Claims (6)
1. large capacitance measuring device of low frequency, it is characterized in that, this measurement mechanism comprises current source, isolation shunt, normalized current shunt, current comparator, standard capacitance, in-phase amplification circuit and detected element, described current source successively through, isolation shunt, normalized current shunt, current comparator, standard capacitance be to in-phase amplification circuit, described isolation shunt links to each other with the current input terminal of detected element respectively with the normalized current shunt, and described in-phase amplification circuit is connected with the voltage input end of detected element; Described current comparator also is connected with the zero indicator that is used to indicate magnetic potential balance in the current comparator iron core and is used for the relatively poor current test instrument of current comparator two ends electric current.
2. the large capacitance measuring device of a kind of low frequency according to claim 1, it is characterized in that, described in-phase amplification circuit comprises sampling amplifier, Hi-pass filter, low-pass filter and voltage follower, described sampling amplifier successively through Hi-pass filter, low-pass filter to voltage follower.
3. the large capacitance measuring device of a kind of low frequency according to claim 1 is characterized in that, described detected element links to each other with a test fixture, and this test fixture links to each other with voltage output end with the current input terminal of detected element with the protected type twisted-pair feeder of banana head.
4. the large capacitance measuring device of a kind of low frequency according to claim 1, it is characterized in that, described current comparator adopts the connected mode of compensation winding and ratio winding parallel, and the ratio winding of current comparator, compensation winding, detection winding all adopt omnidirectional coiling and magnetic shielding line to draw, and detect simultaneously the magnetic shielding ground connection of winding.
5. the large capacitance measuring device of a kind of low frequency according to claim 4 is characterized in that, limit screen, interior screen, three layers of shielding construction of outer screen are adopted in described magnetic shielding.
6. the large capacitance measuring device of the described a kind of low frequency of arbitrary claim is characterized in that according to claim 1-5, and an internal resistance of described comparator is less than 1 Ω, and the secondary internal resistance is less than 32m Ω.
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| CN 201220628492 CN202886483U (en) | 2012-11-23 | 2012-11-23 | Low-frequency large-capacitance measuring device |
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Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104377034A (en) * | 2014-11-28 | 2015-02-25 | 金攀 | Novel capacitor |
| CN105161290A (en) * | 2015-07-10 | 2015-12-16 | 中国船舶重工集团公司第七一〇研究所 | Annealing device for magnetic core of giant magneto impedance sensor |
| CN105929250A (en) * | 2016-07-08 | 2016-09-07 | 云南电力试验研究院(集团)有限公司 | Low-frequency measurement method for core loss of ferromagnetic element |
| CN106199209A (en) * | 2016-09-22 | 2016-12-07 | 申积良 | A kind of full-automatic general AC bridge |
| CN106324539A (en) * | 2015-07-01 | 2017-01-11 | 中国电力科学研究院 | High-precision current comparator |
| CN107315159A (en) * | 2017-07-11 | 2017-11-03 | 北京东方计量测试研究所 | Trace to the source circuit and the method for a kind of bulky capacitor |
| CN111060749A (en) * | 2019-11-25 | 2020-04-24 | 北京东方计量测试研究所 | Low-field quantum resistance measuring instrument |
| CN112630493A (en) * | 2020-12-29 | 2021-04-09 | 北京无线电计量测试研究所 | Wide frequency divider |
| CN113985176A (en) * | 2021-10-29 | 2022-01-28 | 上海市计量测试技术研究院 | Device for synchronously sampling and calibrating broadband alternating current shunt |
| CN116338556A (en) * | 2023-05-26 | 2023-06-27 | 上海置信电气有限公司 | Error tracing device and method for wide-range standard current transformer |
| CN117075021A (en) * | 2023-08-10 | 2023-11-17 | 武汉岸峰电子科技有限公司 | Automatic bridge balancing method and device for digital direct current comparator |
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- 2012-11-23 CN CN 201220628492 patent/CN202886483U/en not_active Expired - Fee Related
Cited By (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104377034A (en) * | 2014-11-28 | 2015-02-25 | 金攀 | Novel capacitor |
| CN106324539A (en) * | 2015-07-01 | 2017-01-11 | 中国电力科学研究院 | High-precision current comparator |
| CN106324539B (en) * | 2015-07-01 | 2019-06-14 | 中国电力科学研究院 | A kind of high-precision current comparator |
| CN105161290A (en) * | 2015-07-10 | 2015-12-16 | 中国船舶重工集团公司第七一〇研究所 | Annealing device for magnetic core of giant magneto impedance sensor |
| CN105161290B (en) * | 2015-07-10 | 2017-05-03 | 中国船舶重工集团公司第七一〇研究所 | Annealing device for magnetic core of giant magneto impedance sensor |
| CN105929250A (en) * | 2016-07-08 | 2016-09-07 | 云南电力试验研究院(集团)有限公司 | Low-frequency measurement method for core loss of ferromagnetic element |
| CN106199209A (en) * | 2016-09-22 | 2016-12-07 | 申积良 | A kind of full-automatic general AC bridge |
| 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 |
| CN107315159A (en) * | 2017-07-11 | 2017-11-03 | 北京东方计量测试研究所 | Trace to the source circuit and the method for a kind of bulky capacitor |
| CN111060749A (en) * | 2019-11-25 | 2020-04-24 | 北京东方计量测试研究所 | Low-field quantum resistance measuring instrument |
| CN111060749B (en) * | 2019-11-25 | 2022-05-24 | 北京东方计量测试研究所 | Low-field quantum resistance measuring instrument |
| CN112630493A (en) * | 2020-12-29 | 2021-04-09 | 北京无线电计量测试研究所 | Wide frequency divider |
| CN113985176A (en) * | 2021-10-29 | 2022-01-28 | 上海市计量测试技术研究院 | Device for synchronously sampling and calibrating broadband alternating current shunt |
| CN113985176B (en) * | 2021-10-29 | 2023-09-12 | 上海市计量测试技术研究院 | Device for synchronously sampling and calibrating broadband alternating current shunt |
| CN116338556A (en) * | 2023-05-26 | 2023-06-27 | 上海置信电气有限公司 | Error tracing device and method for wide-range standard current transformer |
| CN116338556B (en) * | 2023-05-26 | 2023-09-15 | 上海置信电气有限公司 | Error tracing device and method for wide-range standard current transformer |
| CN117075021A (en) * | 2023-08-10 | 2023-11-17 | 武汉岸峰电子科技有限公司 | Automatic bridge balancing method and device for digital direct current comparator |
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Granted publication date: 20130417 Termination date: 20151123 |