CN103487775B - Intelligent digital micro resistor standard device - Google Patents

Abstract

Intelligent digital micro resistor standard device, be narrow in order to solve the measurement range existed the measurement of micro-ohmmeter at present, accuracy is low, poor stability, carrying working current is little, can not carry out the technical matterss such as gamut detects automatically, and measuring process is loaded down with trivial details design there being the instrument of communication interface.This device is made up of standard set-up main body, guidance panel and electronic circuit; Completed the precise acquisition of electric current by the DC current proportioner in electronic circuit and current sampler, use 20 figure place weighted-voltage D/A converters to export the voltage of high precision and high stability.Beneficial effect: achieve wide region, pin-point accuracy, high stability, micro-resistance value that carrying working current is large exports; Achieve and automatically detect there being the instrument of communication interface to carry out gamut; The inspection software of design, achieves the quick operating mode of hommization, makes work efficiency improve 60%.

Description

Intelligent digital micro resistor standard device

technical field:

The present invention relates to a kind of standard set-up examining and determine or calibrate micro-resistance class testing instrument, particularly relate to a kind of intelligent digital micro resistor standard device.For examining and determine or calibrate the DC micro-electric resistance tester be widely used in electric system and electric apparatus manufacture.Also for Estimate of Resistance for DC Low Resistance Meter, micro-resistance class testing instrument such as direct current resistance high speed tester carry out examining and determine or calibrating.

background technology:

How accurately measuring feeble signal is now the emerging scientific research task of domestic and international metrology and measurement industry, as being widely used in DC micro-electric resistance tester in electric system and electric apparatus manufacture for measuring the direct current resistance of the direct current resistance of electric wire and transformer, mutual inductor, reactor, motor even load, its accuracy directly has influence on the quality of product quality, this is also the metrology and measurement difficult point faced at present, and can capture this difficult problem have become the important symbol weighing measurement technology mechanism detectability.

Along with the application of new technology and microresistivity survey technology are maked rapid progress, require that the measurement means detecting all kinds of tester will adapt to it.But, domestic and international calibrating/calibration to micro-resistance meter at present has also come in employing multiple stage DC resistance box and measuring resistance combination, its measuring process is complicated and accuracy is difficult to ensure, by the understanding to the domestic and international measuring technique about micro-ohmmeter, mainly to there is following technological deficiency:

1. measurement range is narrow, and measured resistance value exists discontinuous.Low and the implacable measurement requirement of small resistance value accuracy due to DC resistance box; Measuring resistance accuracy can meet the demands, but its resistance value exists again discontinuous defect, therefore there is blind area to the measurement of micro-ohmmeter, cannot meet the demands.

2. accuracy is low, poor stability.(1) resistance box measuring micro-ohmmeter because of the accuracy within the scope of its small resistance value low, the measurement that therefore can not meet various types of micro-ohmmeter requires that (2) are because micro-resistance is because of the little interference being very easily subject to the factors such as external environment in measuring process of its resistance, therefore the stability of measurement result and poor repeatability, this is just difficult to the accuracy ensureing to measure.

3. carry working current little.For adapting to economic development both at home and abroad, in electric system and electric apparatus manufacture, new product emerges in an endless stream, the new equipment detecting these products is also constantly used in product testing and type approval test thereupon and goes, as detect motor, transformer coil resistance micro-ohmmeter its carrying working current reach 60A, we cannot measure with traditional detection method at all like this.

4. pair there is the tested instrument of communication interface automatically not detect accurately.Along with the development of science and technology, measured equipment has communication interface usually, and can only manual operation with traditional detection method, and inefficiency, testing staff's working strength is large, cannot adapt with current work rhythm efficiently.

5. measuring process is loaded down with trivial details, and the measurement introduced in measuring process is greatly uncertain, inefficiency.At least will use three resistance boxes and some measuring resistances with traditional detection method, measuring process is very loaded down with trivial details, and the measurement introduced in measuring process is uncertain also very large, testing staff's inefficiency.

summary of the invention:

In order to solve the domestic and international measurement to micro-resistance meter at present, to there is value discontinuous in the present invention, measurement range is narrow, accuracy is low, poor stability, carrying working current is little, gamut accurately can not be carried out to there being the tested instrument of communication interface automatically to detect, the measurement introduced in measuring process is greatly uncertain, measuring process is loaded down with trivial details, the technical matterss such as inefficiency, provide a kind of intelligent digital micro resistor standard device, this device by standard set-up main body, guidance panel and electronic circuit three part form; Described electronic circuit is formed primarily of DC current proportioner, 20 figure place weighted-voltage D/A converters, resistance in kind, current sampler, microcomputer controller and lcd touch display; The output current I1 of measured instrument through C1, C2 or, input to matrix switch 1, described DC current proportioner is inputed to again after the range that matrix switch 1 is switched to selection, I1 is converted to magnetic flux balanced balanced current I2 through described DC current proportioner, magnetic flux balanced balanced current I2 produces a voltage through described current sampler, and this magnitude of voltage is transferred to the precise acquisition completing magnetic flux balanced balanced current in RAM9 microcomputer controller; According to the magnetic flux balanced balanced current I2 collected, the resistance value R that will export is set by lcd touch display, these resistance value data are controlled 20 figure place weighted-voltage D/A converters by RAM9 microcomputer controller and exports a magnitude of voltage analog quantity meeting U=I2R to matrix switch 2, control by matrix switch 2 the current potential input end that this magnitude of voltage exports to measured instrument, realize the output of the micro-resistance value of simulation; Described resistance in kind is fixed value resistance, is accepted the resistance value detected needed for described lcd touch display setting, then carry out the switching of fixed value resistance and the output of fixed value resistance through RAM9 microcomputer controller gating matrix switch 2 by inspection software.

Feature of the present invention and beneficial effect: adopt this device can hinder tester, Estimate of Resistance for DC Low Resistance Meter to DC micro-electric both domestic and external, micro-resistance class testing instrument such as direct current resistance high speed tester carry out examining and determine or calibrating.Solve a detection difficult problem for DC micro-electric resistance.Achieve pin-point accuracy and the high stability of micro-resistance value; And the measurement range of micro-resistance value is wide, carrying working current is large; Achieve and automatically detect there being the tested instrument of communication interface to carry out gamut accurately.The inspection software of design, achieves the simple and fast mode of operation of hommization, makes work efficiency improve 60%.Be embodied in:

(1) this standard measurement device wide ranges, carrying working current is large.Micro-resistance output area is:

0.1 μ Ω ~ 20m Ω continuously adjustabe, maximum carrying working current 60A;

1 μ Ω ~ 200m Ω continuously adjustabe, maximum carrying working current 10A;

10 μ Ω ~ 2 Ω continuously adjustabe, maximum carrying working current 1A;

100 μ Ω ~ 20 Ω continuously adjustabe, maximum carrying working current 0.1A.

And when working current is maximum current, can charged adjustment micro-resistance value that will export.

Resistance (15 fixed value resistances) output area in kind is:

20Ω，100Ω,190Ω,200Ω,1kΩ,1.9kΩ,2kΩ,10kΩ,19kΩ,

20kΩ,100kΩ,190kΩ,200kΩ,1MΩ,1.9MΩ。

(2) can meet and automatically detect there being the tested instrument of communication interface to carry out gamut accurately.

(3) intelligent digital micro resistor standard device class of accuracy 0.01 grade

The accuracy of intelligent digital micro resistor standard device and stability high.20 figure place weighted-voltage D/A converters of device can export high stability and high-precision voltage, DC current proportioner and current sampler complete the precise acquisition of electric current, which reduces the deviation that micro-resistance exports, achieve pin-point accuracy and the high stability of this standard device.

(5) inspection software provided, achieve the simple and fast mode of operation of hommization, solve measuring process loaded down with trivial details, the measurement introduced in measuring process is greatly uncertain, ineffective problem.

accompanying drawing illustrates:

Fig. 1 one-piece construction schematic diagram

Lcd touch display schematic diagram on Fig. 2-Fig. 4 panel

The fundamental diagram of Fig. 5 electronic circuitry part

Fig. 6 inspection software workflow diagram

Figure 71 0V reference power circuit schematic diagram

A winding of Fig. 8 DC magnetic modulator, Secondary Winding structural representation

The structural representation of Fig. 9 DC magnetic modulator

Coils arrangement figure on Figure 10 DC magnetic modulator iron core

Figure 11 DC magnetic modulator circuit schematic diagram

Figure 12 peak difference wave detector and automatic balancing circuit schematic diagram

Figure 13 power amplifier and current sampler circuit theory diagrams

Figure 14 driving source circuit theory diagrams

Figure 15 ARM9 microcomputer controller and AD5791D/A chip interface schematic diagram

Figure 16 working power circuit schematic diagram

embodiment:

Referring to Fig. 1-Figure 16; intelligent digital micro resistor standard device; this device by standard set-up main body, guidance panel and electronic circuit three part form, described electronic circuit is formed primarily of DC current proportioner, 20 figure place weighted-voltage D/A converters, resistance in kind, current sampler, microcomputer controller and lcd touch display; The output current I1 of measured instrument through C1, C2 or, input to matrix switch 1, described DC current proportioner is inputed to again after the range that matrix switch 1 is switched to selection, I1 is converted to magnetic flux balanced balanced current I2 through described DC current proportioner, magnetic flux balanced balanced current I2 produces a voltage through described current sampler, and this magnitude of voltage is transferred to the precise acquisition completing magnetic flux balanced balanced current in RAM9 microcomputer controller; According to the magnetic flux balanced balanced current I2 collected, the resistance value R that will export is set by lcd touch display, these resistance value data are controlled 20 figure place weighted-voltage D/A converters by RAM9 microcomputer controller and exports a magnitude of voltage analog quantity meeting U=I2R to matrix switch 2, control by matrix switch 2 the current potential input end that this magnitude of voltage exports to measured instrument, realize the output of the micro-resistance value of simulation; Described resistance in kind is fixed value resistance, is accepted the resistance value detected needed for described lcd touch display setting, then carry out the switching of fixed value resistance and the output of fixed value resistance through RAM9 microcomputer controller gating matrix switch 2 by inspection software.

Wherein:

Described guidance panel is made up of power switch 1, relay indicating light 2, communication interface 3, lcd touch display 4, current wiring terminal A5, electric potential connection terminal 6 and current wiring terminal B7, described communication interface 3 is for transmitting the related data of intelligent digital micro resistor standard device, the gamut having the tested instrument of communication interface to carry out is detected automatically, also can external computer as the controller of this standard device, this communication interface can also be upgraded to software; Described lcd touch display 4 is for arranging the resistance value that will export, and working current during display measurement; Described current wiring terminal A5, be as working current≤10A, micro-resistance exports the current wiring terminal of measurement range when 0 ~ 1.9M Ω; Described electric potential connection terminal 6 is electric potential connection terminals when exporting micro-resistance; Described current wiring terminal B7, be as working current≤60A, micro-resistance exports the current wiring terminal of measurement range when 0 ~ 20m Ω.

Described DC current proportioner is made up of driving source, DC magnetic modulator, peak difference wave detector, self-equilibrating circuit and power amplifier, the ratio value of turn ratio is formed by described DC magnetic modulator, the power amplifier in the Secondary Winding loop of DC magnetic modulator is driven by described power amplifier, d. c. voltage signal is converted to magnetic flux balanced balanced current I2, make the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, is zero to the direct current flux in DC magnetic modulator iron core, detected in DC magnetic modulator by described peak difference wave detector and detect the amplitude being twice in the burst pulse of excitation frequency and polarity that winding induces, by automatic balancing circuit, peak difference wave detector is exported to direct current spike pulse and the Zero flux balanced signal of automatic balancing circuit again, after amplification, export to the drive singal of described power amplifier as this power amplifier, described driving source is the square wave power that described DC magnetic modulator enters duty, described DC magnetic modulator detects in detection winding that under the excitation of described driving source direct current Zero flux balanced signal converts d. c. voltage signal to magnetic flux balanced balanced current I2 through amplifying Driver amplifier, make the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, the direct current flux in DC magnetic modulator iron core is made to be zero, electric current compares relevant to the turn ratio and is inverse ratio, realize DC current 60A, 10A, 1A, 0.1A converts DC current 60mA to respectively, 100mA, 100mA, 10mA.

Described 20 figure place weighted-voltage D/A converters are made up of 10V reference power supply, voltage follower, AD5791D/A chip and communication interface, direct current 10V voltage is exported by described 10V reference power supply, as the working standard power supply of AD5791D/A chip, convert digital quantity to controllable analog output by RAM9 microcomputer controller control AD5791D/A chip, the voltage being improved AD5791D/A chip by voltage follower exports load capacity.

Described current sampler is made up of 71/2 digital voltmeter and resistor network, by the magnetic flux balanced balanced current I2 obtained from described DC current proportioner, produces a voltage, measure this voltage by 71/2 digital voltmeter on resistor network.

The effect of each circuit module of electronic circuitry part of intelligent digital micro resistor standard device and principle of work:

The effect of DC current proportioner: be convert DC current 60A, 10A, 1A, 0.1A to DC current 60mA respectively, 100mA, 100mA, 10mA.

The effect of DC magnetic modulator: form three ratio value K(and turn ratio): 0.001,0.01,0.1

DC current proportioner

The effect of power amplifier: drive the Secondary Winding of DC magnetic modulator to be converted to by d. c. voltage signal

Magnetic flux balanced balanced current I2, makes the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, makes the direct current flux in DC magnetic modulator iron core be zero.

The effect of current sampler: magnetic flux balanced balanced current I2 produces a voltage on resistor network, by 71/2

This voltage measured by digital voltmeter, and this magnitude of voltage is transferred to RAM9 microcomputer controller, completes the precise acquisition of magnetic flux balanced balanced current.

The effect of peak difference wave detector: peak difference wave detector effect is to detect in DC magnetic modulator and detects the amplitude being twice in the burst pulse of excitation frequency and polarity that winding induces.

The effect of automatic balancing circuit: direct current spike pulse and the Zero flux balanced signal of peak difference wave detector being exported to automatic balancing circuit, exports to the drive singal of power amplifier as this power amplifier after amplification.

The effect of driving source: driving source is the power supply that DC magnetic modulator enters duty, it produces, and a frequency is 800HZ, voltage is the square wave power of 300V.DC magnetic modulator can detect direct current Zero flux balanced signal under the excitation of driving source in detection winding.

The effect of working power: export 18V DC voltage to driving source as working power by working power; Output ± 15V DC voltage to automatic balancing circuit as working power, output ± 30V DC voltage to power amplifier circuit as working power.

The effect of 10V reference power supply: 10V reference power supply exports high stability, and high-precision direct current 10V voltage, as the working standard power supply of AD5791D/A chip.

The effect of AD5791D/A chip and voltage follower: the effect of AD5791D/A chip converts digital quantity to controllable analog output.The effect of AD5791D/A chip is the resistance value R that will export that will lcd touch display be arranged, and this digital quantity is controlled 20 figure place weighted-voltage D/A converters by RAM9 microcomputer controller and exports a magnitude of voltage analog quantity.The voltage of AD5791D/A chip exports and is controlled by RAM9 microcomputer controller.The voltage of AD5791D/A chip according to the instruction of RAM9 microcomputer controller, the magnitude of voltage required for output.

The voltage that voltage follower mainly improves AD5791 chip exports load capacity.

The effect of matrix switch: C1, C2 or, the matrix switch 1 of end mainly switches the number of turn of the primary winding of the DC magnetic modulation of DC current proportioner, as 1 circle (range 20m Ω), 10 circles (range 200m Ω), 100 circles (range 2 Ω, 20 Ω).

The matrix switch 2 of P1, P2 end a: part controls micro-resistance and exports, another part switches 15 resistance in kind (i.e. fixed value resistance) and fixed value resistance exports.

The effect of RAM9 microcomputer controller: the instruction of the chip of control criterion device, the signal of lcd touch display, matrix switch fill order, resistance output order, data export and are all completed by RAM9 microcomputer controller.

The connected mode of RAM9 microcomputer controller and interlock circuit module:

RAM9 microcomputer controller is connected with lcd touch display and connects with computer display interface device line VGA;

RAM9 microcomputer controller and 71/2 digital voltmeter carry out communication by RS232 interface;

RAM9 microcomputer controller and 20 figure place weighted-voltage D/A converters carry out communication by RS232 interface;

RAM9 microcomputer controller and two matrix switches carry out communication by RS232 interface.

USB communication interface: send instruction by lcd touch display, control through RAM9 microcomputer controller, the relevant data of this standard device can be transmitted by communication interface, automatically can be detected there being the tested instrument of communication interface to carry out gamut accurately by communication interface, can also be upgraded to inspection software by communication interface, also can directly control this standard device by external computer.

Principle of work:

The output current I1 of measured instrument through C1, C2 or, input to matrix switch 1, the winding being input to corresponding DC magnetic modulator after selected range is switched to again through matrix switch 1, and magnetic potential is produced on a winding, thus magnet ring is magnetized, once, when the number of turn is unequal in Secondary Winding, direct current flux in iron core, is just had to exist.In the square wave input that driving source produces to the excitation winding and detection winding of DC magnetic modulator, iron core is entered saturated, the burst pulse being twice in excitation frequency will be induced in the detection winding of DC magnetic modulator, and amplitude and the polarity of this pulse is detected by peak difference wave detector, the Zero flux balanced signal exported through peak difference wave detector exports the individual Zero flux balanced signal through amplifying through automatic balancing circuit, this Zero flux balanced signal through amplification drives the power amplifier in Secondary Winding loop to convert d. c. voltage signal to magnetic flux balanced balanced current I2, make the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, the direct current flux in DC magnetic modulator iron core is made to be zero, electric current compares relevant to the turn ratio and is inverse ratio, very accurate due to the coiling of DC magnetic modulator winding, therefore form a very accurate DC current proportioner of ratio.DC current proportioner according to wanted switching range according to turn ratio K=0.001(60mA/60A), 1T/1000T; K=0.01(100mA/10A) 10T/1000T; K=0.1(100mA/1A), 100T/1000T; K=0.1(10mA/0.1A), 100T/1000T by the output current value I1 of measured instrument through DC current proportioner output current value I2, magnetic flux balanced balanced current I2 produces a voltage on resistor network, this voltage is measured by 71/2 digital voltmeter, this magnitude of voltage is transferred to RAM9 microcomputer controller, completes the precise acquisition of magnetic flux balanced balanced current.The object detecting this electric current to know the relative error of tested instrument output current I1 and output voltage this relative error corresponding.After collecting magnetic flux balanced balanced current I2, lcd touch display arranges the resistance value R(digital quantity that will export), this digital quantity is controlled 20 figure place weighted-voltage D/A converters by RAM9 microcomputer controller and exports a magnitude of voltage analog quantity meeting U=I2R to matrix switch 2, control by matrix switch 2 the current potential input end that this magnitude of voltage exports to measured instrument, thus achieve the output of simulating micro-resistance value.Resistance in kind is fixed value resistance.Pass through to click lcd touch display according to the resistance value of required detection by inspection software, control through RAM9 microcomputer controller, control the switching of fixed value resistance and the output of fixed value resistance by matrix switch 2.18V DC voltage is exported to driving source as working power by working power; Output ± 15V DC voltage to automatic balancing circuit as working power, output ± 30V to power amplifier circuit as working power.Instruction is sent by lcd touch display, control through RAM9 microcomputer controller, the related data of this standard device is transmitted by communication interface, automatically detected there being the tested instrument of communication interface to carry out gamut accurately by communication interface, by communication interface, inspection software is upgraded, also can directly control this standard device by external computer.

Embodiment

Referring to Fig. 1, one-piece construction schematic diagram.

This device primarily of standard set-up main body, guidance panel and electronic circuit three part composition.Wherein:

Described guidance panel is provided with:

Power switch 1: control on/off, when power supply is connected, pilot lamp is bright;

Relay indicating light 2: the driving source working station indicator in DC current proportioner.When duty is normal, pilot lamp is bright; During working state abnormal, pilot lamp does not work;

Communication interface 3: this interface, for transmitting the relevant data of intelligent digital micro resistor standard device, detects automatically to the gamut having the tested instrument of communication interface to carry out, also can directly control this standard set-up by external computer; This communication interface can also be upgraded to software.

Lcd touch display 4: the resistance value that export is set, and working current during display measurement;

Current wiring terminal A5 when micro-resistance exports: as working current≤10A, micro-resistance exports the current wiring terminal of measurement range when 0 ~ 1.9M Ω;

Electric potential connection terminal 6 when micro-resistance exports: export electric potential connection terminal during micro-resistance;

Current wiring terminal B7 when micro-resistance exports: as working current≤60A, micro-resistance exports the current wiring terminal of measurement range when 0 ~ 20m Ω.

Referring to Fig. 2-Fig. 4, lcd touch display schematic diagram on panel.

Measurement range selection 8: click lcd touch display 8, selects range 20m Ω;

Measurement range selection 9: click lcd touch display 9, selects range 200m Ω;

Measurement range selection 10: click lcd touch display 10, selects range 2 Ω;

Measurement range selection 11: click lcd touch display 11, selects range 20 Ω;

Resistance 12 in kind: click lcd touch display 12, select resistance function in kind;

Rising adjustment 13: in click lcd touch display 13 ▲, upwards regulate this bit digital,

Stepped intervals is 1;

Decline adjustment 14: click the ▼ in lcd touch display 14, regulates this bit digital downwards,

Stepped intervals is 1;

Duty 15: during display ON, the resistance value of setting is at output state; Intelligence during display OFF

The digital micro-resistor standard device of energy not output resistance;

Measurement unit 16: the measurement unit of the micro-resistance value set by display;

Arrange micro-resistance value 17(at range 20m Ω, 200m Ω, 2 Ω, in 20 Ω): the micro-resistance value set by display;

Measurement unit 18: the measurement unit of working current;

Working current 19: the set working current exporting micro-resistance value (at range 20m Ω, 200m Ω, 2 Ω, in 20 Ω) of display;

Reset 20: the zero-bit eliminating current sampler, makes tested current value more accurate.

Select resistance value 21 in kind: click lcd touch display 21 and select resistance value in kind;

Measurement unit 22: the measurement unit of the resistance value in kind selected by display;

Resistance value 23 in kind: the resistance value in kind selected by display;

Display window 24: after clicks keyboard, shows the numerical value inputted;

Determining 25: after clicks keyboard, press this key, being directly presented on main interface by clicking the numerical value inputted;

Remove 26: when numerical key is clicked and made a mistake, press this key, remove the numerical value clicked;

Backspace 27: when numerical key is clicked and made a mistake, press this key and once move back forward one;

Exit 28: exit this interface;

Numerical key 29: clicks keyboard can directly key in the resistance value that will export.

Referring to Fig. 5, the fundamental diagram of electronic circuitry part.

The output resistance of intelligent digital micro resistor standard device has two kinds:

1, micro-resistance is simulated:

The output current I1 of measured instrument inputs to matrix switch 1 through C1, C2 (or), the winding being input to corresponding DC magnetic modulator after selected range is switched to again through matrix switch 1, and magnetic potential is produced on a winding, thus magnet ring is magnetized, once, when the number of turn is unequal in Secondary Winding, direct current flux in iron core, is just had to exist.18V DC voltage is exported to driving source as working power by working power; Output ± 15V DC voltage to automatic balancing circuit as working power, output ± 30V to power amplifier circuit as working power.In the square wave input that driving source produces to the excitation winding and detection winding of DC magnetic modulator, iron core is entered saturated, the burst pulse being twice in excitation frequency will be induced in the detection winding of DC magnetic modulator, and amplitude and the polarity of this pulse is detected by peak difference wave detector, the Zero flux balanced signal exported through peak difference wave detector exports the individual Zero flux balanced signal through amplifying through automatic balancing circuit, this Zero flux balanced signal through amplification drives the power amplifier in Secondary Winding loop to convert d. c. voltage signal to magnetic flux balanced balanced current I2, make the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, the direct current flux in DC magnetic modulator iron core is made to be zero, electric current compares relevant to the turn ratio and is inverse ratio, because DC magnetic modulator winding can coiling very accurate, therefore a very accurate DC current proportioner of ratio can be formed.DC current proportioner according to wanted switching range according to turn ratio K=0.001(60mA/60A), 1T/1000T; K=0.01(100mA/10A) 10T/1000T; K=0.1(100mA/1A), 100T/1000T; K=0.1(10mA/0.1A), 100T/1000T by the output current value I1 of measured instrument through DC current proportioner output current value I2, magnetic flux balanced balanced current I2 produces a voltage on resistor network, this voltage is measured by 71/2 digital voltmeter, this magnitude of voltage is transferred to RAM9 microcomputer controller, completes the precise acquisition of magnetic flux balanced balanced current.After collecting magnetic flux balanced balanced current I2, lcd touch display arranges the resistance value R(digital quantity that will export), this digital quantity is controlled 20 figure place weighted-voltage D/A converters by RAM9 microcomputer controller export a magnitude of voltage analog quantity (1. this magnitude of voltage can meet U=I2R in intelligent digital micro resistor standard device, 2. this magnitude of voltage is supplied to 20 figure place weighted-voltage D/A converter working stamndard by 10V reference power supply, thus it is high to make 20 figure place weighted-voltage D/A converters export accuracy, the magnitude of voltage analog quantity of good stability) to matrix switch 2, the current potential input end that this magnitude of voltage exports to measured instrument is controlled by matrix switch 2, thus achieve the output of simulating micro-resistance value.The object detecting this electric current to know the relative error of tested instrument output current I1 and output voltage this relative error corresponding.

2, resistance in kind is fixed value resistance.By the resistance value of inspection software by required detection, obtaining by clicking lcd touch display, controlling through RAM9 microcomputer controller, and namely controlling the switching of 15 fixed value resistances and the output of fixed value resistance by matrix switch 2.

Be combined with D/A digital to analog converter by described DC current proportioner, abundant utilization DC current proportioner, to the program-controlled property of the accurate measurement of electric current and high precision digital-to-analogue technology export voltage, achieves and automatically detects there being the tested instrument of communication interface to carry out gamut accurately.

The high stability exported by described 20 figure place weighted-voltage D/A converters and high-accuracy voltage, and the precise acquisition of electric current is completed by described DC current proportioner and resistance network, 71/2 digital voltmeter, not only reduce the deviation that micro-resistance exports, also improve accuracy and the stability of standard set-up.

Related data is transmitted by communication interface, not only achieve and automatically detected there being the tested instrument of communication interface to carry out gamut accurately by communication interface, also upgrading by communication interface to inspection software and realize external computer directly controls this standard device.

Referring to Fig. 6, inspection software workflow:

C# language is adopted to programme to AD5791D/A chip.

After intelligent digital micro resistor standard device start enters duty, first judge whether user selects material object

Does resistance export?

Be then select resistance value in kind, perform matrix switch switching command.According to the resistance value selected, point

Hit lcd touch display, lcd touch display shows the resistance value in kind that will export;

No, then select the micro-resistance range 20m Ω of simulation, 200m Ω, 2 Ω or 20 Ω, according to the mould selected

Intend micro-resistance range, matrix switch performs instruction, enter selected range, gather and the current value that exports after DC current proportioner of the output current value measuring measured instrument, corresponding magnitude of voltage is calculated again according to the resistance value that will export shown after click lcd touch display, then this magnitude of voltage is exported by 20 figure place weighted-voltage D/A converters, and the micro-resistance value of simulation selected by exporting.

Check Fig. 7,10V reference power supply schematic diagram.

Mains 220V inputs through transformer B step-down, forms rectifying and wave-filtering, alternating current is become direct current by diode D1, D2, electric capacity C1.Direct current is through first order voltage stabilizing, namely through LM337 Voltage stabilizing module by voltage stabilization at direct current 15V, again through second level voltage stabilizing, the amplification of power supply adopts low drifting operating amplifier A, this voltage adopts multiple resistance to be sitting on same matrix the ratio of sampling resistor is not changed because of variation of ambient temperature by band calibration cell high stability stabilivolt LM399 and sampling resistor R5, R6() voltage that exports afterwards compares Correctional tube (BG1, BG2 two triodes), export high stability, high-precision 10V DC voltage.This direct current 10V voltage exported, as the working standard power supply of AD5791D/A chip.+ 10V connects the VREFPS(3 pin of AD5791D/A chip), 0V connects the VREFPF(4 pin of AD5791D/A chip).

Referring to Fig. 8-Figure 10, the structural representation of DC magnetic modulator.

DC magnetic modulator is a kind of toroidal transformer device (referring to Fig. 8, Fig. 9) of Multiple coil, and it comprises excitation winding, detects winding, and winding, a Secondary Winding, their arrangement is referring to Figure 10.

Referring to Figure 11, DC magnetic modulator fundamental diagram.

Magnet ring is wound with a winding W1, Secondary Winding W2 and detection winding W examines and excitation winding.The working current of micro-resistance meter and primary current I1 through C1, C2 or, flow through W1, it produces magnetic potential I1W1 on W1, thus is magnetized by magnet ring, once, when the number of turn is unequal in Secondary Winding, just has direct current flux to exist in iron core.

The frequency that driving source produces is 800HZ, voltage is that the square wave input of 300V is in excitation winding and detection winding, iron core is entered saturated, and the burst pulse being twice in excitation frequency is induced in the detection winding of DC magnetic modulator, and amplitude and the polarity of this pulse is detected by peak difference wave detector, the direct current Zero flux balanced signal exported through peak difference wave detector exports a Zero flux balanced signal through amplifying through automatic balancing circuit, this direct current Zero flux balanced signal through amplification drives the power amplifier in Secondary Winding loop to convert d. c. voltage signal to magnetic flux balanced balanced current I2, magnetic flux balanced balanced current I2 flows through W2, produce magnetic potential I2W2, now the magnetic potential of a winding is equal with the magnetic potential of Secondary Winding, but direction is contrary, the direct current flux in DC magnetic modulator iron core is made to be zero.

Magnetic flux balanced balanced current I2 flows through W2, produces magnetic potential I2W2 and contrary with I1W1 direction.When

During I2W2=I1W1, I2 will remain unchanged, therefore have: I2/I1=W1/W2, direct current flux in iron core is made to be zero, electric current than relevant to the turn ratio and in inverse ratio, due to winding W can coiling very accurately, so instrument forms a very accurate DC current proportioner of ratio.One time winding W1 has three windings, is respectively 1 circle (1T), 10 circles (10T), 100 circles (100T).Secondary Winding W2 is only a winding, is 1000 circles (1000T), therefore forms three ratio value K(and turn ratio): 0.001,0.01,0.1.

Referring to Figure 12, peak difference wave detector and automatic balancing circuit schematic diagram.

Peak difference wave detector effect is to detect in DC magnetic modulator and detects the amplitude being twice in the burst pulse of excitation frequency and polarity that winding induces.From DC magnetic modulator 10,11 terminals export 1,2 terminals of a non-zero magnetic flux signal (i.e. alternating signal) to peak difference wave detector, pass through D3, D4, C3, C4 become alternating signal into Unidirectional direct-current signal, through C5, R3 filtering, after filtering high-frequency interferencing signal, export direct current spike pulse (i.e. Zero flux balanced signal) to automatic balancing circuit 3 pin through R4, C6 resistive-capacitive voltage divider.

From working power output ± 15V DC voltage to the A2 comparison amplifier of automatic balancing circuit, the direct current spike pulse (i.e. Zero flux balanced signal) exported by peak difference wave detector is input to automatic balancing circuit 3 pin, exports 4 pin of a direct current Zero flux balanced signal be exaggerated to power amplifier by A2 comparison amplifier.

Referring to Figure 13, power amplifier and current sampler circuit theory diagrams.

The effect of power amplifier drives the Secondary Winding of DC magnetic modulator to be changed by d. c. voltage signal

Become magnetic flux balanced balanced current I2, make the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, makes the direct current flux in DC magnetic modulator iron core be zero.

From the direct current Zero flux balanced signal that automatic balancing circuit inputs through 4 pin, energy conversion is carried out through A3 power amplifier, DC current signal I2 is converted to by d. c. voltage signal, this electric current is exactly K times (K is turn ratio) of input current (namely by the working current of test examination instrument), electric current I 2 outputs to 12 terminals of DC magnetic modulator Secondary Winding 1000T, makes the direct current flux in DC magnetic modulator iron core be zero.A3 power amplifier ± 30V DC voltage is provided by working power.

Electric current I 2 is input on the resistance network of current sampler through 13 terminals of DC magnetic modulator Secondary Winding 1000T, I2 is by producing a voltage during resistance network, measure this voltage by 71/2 digital voltmeter, be transferred to RAM9 microcomputer controller, complete the precise acquisition of I2 current value.

Referring to Figure 14, driving source schematic diagram.

From, input 18V DC voltage is as working power.Driving source adopts and recommends self-sustained oscillation principle.Form square-wave oscillator by two 3AD30C triodes, the waveform exported by square-wave oscillator is square wave, and oscillation frequency is 800Hz, and voltage is 18V, then through transformer boost be peak-to-peak value voltage 300V.Wherein 7 pin of the excitation winding of DC magnetic modulator are delivered on a road, and another route 8 pin receives the detection winding of DC magnetic modulator.Driving source 9 pin receives peak difference wave detector low side (i.e. working power 0V end).(encourage winding 10 pin as shown in FIG., detect winding 11 pin and be connected to peak difference wave detector input end 1 pin.), driving source is the power supply that DC magnetic modulator enters duty, and the frequency that it produces is 800HZ, voltage is the square wave of 300V, makes DC magnetic modulator can detect direct current Zero flux balanced signal in detection winding under the excitation of driving source.

When square-wave oscillator is working properly, voltage is added on neon lamp through 1M Ω current-limiting resistance by peak-to-peak value voltage 300V, and neon lamp is bright, shows that driving source is working properly.

Referring to Figure 15, ARM9 microcomputer controller and AD5791D/A chip interface schematic diagram.

ARM9 microcomputer controller and AD5791D/A chip interface illustrate:

AD5791 has 3 line serial line interfaces (SYNC, SCLK and SDIN), it and SPI, QSPI, MICROWIRE interface standard and most devices compatible.

The interface circuit of ARM9 and AD5791, be connected with AD5791 by SPI universal serial bus by ARM9, SPI is full duplex transmission.This device adopts MISO mode from the main output of input, and SCK controls clock signal, and nSS doubles as synchronous effect for starting transmission.VCC is that digital power connects, connect the voltage in 2.7V to 5.5V scope, IOVCC is digital interface power pins, numeral threshold values level reference puts on the voltage of this pin, but magnitude of voltage can not be digital interface power pins more than VCC, IOVCC, numeral threshold values level reference puts on the voltage of this pin, but magnitude of voltage more than VCC, can not connect the effect that two electric capacity play decoupling in this circuit design, and is connected to DGND between VCC and IOVCC.It is positive benchmark driving voltage input (being supplied by 10V reference power supply), realize connecting the voltage within 5V to-2.5V, due to the special permission demand of AD5791 characteristic on this pin with on be connected a unity gain amplifier, be wherein positive reference voltage input (being supplied by 10V reference power supply).In the design, AD8676 is used as reference voltage buffer, and AD8675 is used as output buffer.For reaching rated linear degree, benchmark input end must use compulsory test impact damper.Output impedance due to AD5791 is 3.4K, therefore needs a voltage follower to drive low resistance, high capacitance load.AD5791 is voltage output type D/A conversion chip, but in order to improve output voltage accuracy and load capacity, so connect an AD8675 amplifier in input.

When designing the hardware interface circuit of ARM9 and AD5791, adopt using ARM9 as SPI main frame, AD5791 is as from machine.AD5791 only accepts the data of from host, then carries out D/A conversion and from VOUT pin output voltage to matrix switch 2.Serial line interface can adopt continous way serial clock working method.The SPICLK of ARM9 is as the clock input signal of AD5791, and data are at the negative edge input shift register of serial clock, and the highest clock rate with 35MHZ of data is transmitted.When SYNC remains low level in correct clock periodicity, continuous print SCLK clock source can only be used.Under gated clock pattern, the burst clock comprising definite clock periodicity must be adopted, after the clock period terminates, SYNC must be set to high level carry out latch data.First negative edge of SYNC starts write cycle time.SYNC after 24 clock falling edge, could must draw high by SCLK again.If drew high SYNC before the 24th SCLK negative edge, the data invalid of write.If have more than 24 SCLK negative edges before drawing high SYNC, input data are invalid equally.Input shift register upgrades at the rising edge of SYNC.If need other serial transmissions be carried out, SYNC must be dragged down again.After serial transmission terminates, data are sent to addressing register from input shift register automatically.Once write cycle completes, just can drag down LDAC while SYNC is high level, thus upgrade output.

Reset function (RESET)

AD5791 utilizes software RESET controlling functions to realize being reset to power-up state.RESET pin need not, be hard wired to IOVCC.

Asynchronous resetting function (CLR)

Clear operation is performed by the CLR position arranged in software control register.

Referring to Figure 16, working power schematic diagram.

This power supply is the working power of supply DC current proportioner, and 220V alternating voltage is become 21V alternating voltage and 2 × 18V alternating voltage through transformer by civil power 220V.21V alternating voltage by 7818 Voltage stabilizing modules, is become stable 18V direct voltage output (3 pin are+18V, and 4 pin are 0V) through rectifying and wave-filtering by 21V alternating voltage.18V DC voltage is available to the working power of driving source.

This part 2 × 18V alternating voltage is become stable+15V DC voltage and-15V direct voltage output through rectifying and wave-filtering from 7815 and 7915 Voltage stabilizing modules by 2 × 18V alternating voltage.± 15V DC voltage is available to the working power of automatic balancing circuit.

2 × 18V alternating voltage again through rectifying and wave-filtering directly export ± 30V DC voltage is supplied to power amplifier circuit as working power.

Claims (3)

1. intelligent digital micro resistor standard device; this device by standard set-up main body, guidance panel and electronic circuit three part form, it is characterized in that: described electronic circuit is formed primarily of DC current proportioner, 20 figure place weighted-voltage D/A converters, resistance in kind, current sampler, microcomputer controller and lcd touch display; The output current I1 of measured instrument inputs to matrix switch 1 through C1, C2, described DC current proportioner is inputed to again after the range that matrix switch 1 is switched to selection, I1 is converted to magnetic flux balanced balanced current I2 through described DC current proportioner, magnetic flux balanced balanced current I2 produces a voltage through described current sampler, and this magnitude of voltage is transferred to the precise acquisition completing magnetic flux balanced balanced current in RAM9 microcomputer controller; According to the magnetic flux balanced balanced current I2 collected, the resistance value R that will export is set by lcd touch display, these resistance value data are controlled 20 figure place weighted-voltage D/A converters by RAM9 microcomputer controller and exports a magnitude of voltage analog quantity meeting U=I2R to matrix switch 2, control by matrix switch 2 the current potential input end that this magnitude of voltage exports to measured instrument, realize the output of the micro-resistance value of simulation; Described resistance in kind is fixed value resistance, is accepted the resistance value detected needed for described lcd touch display setting, then carry out the switching of fixed value resistance and the output of fixed value resistance through RAM9 microcomputer controller gating matrix switch 2 by inspection software;

Described DC current proportioner is made up of driving source, DC magnetic modulator, peak difference wave detector, automatic balancing circuit and power amplifier, the ratio value of turn ratio is formed by described DC magnetic modulator, the power amplifier in the Secondary Winding loop of DC magnetic modulator is driven by described power amplifier, d. c. voltage signal is converted to magnetic flux balanced balanced current I2, make the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, is zero to the direct current flux in DC magnetic modulator iron core, detected in DC magnetic modulator by described peak difference wave detector and detect the amplitude being twice in the burst pulse of excitation frequency and polarity that winding induces, by automatic balancing circuit, peak difference wave detector is exported to direct current spike pulse and the Zero flux balanced signal of automatic balancing circuit again, after amplification, export to the drive singal of described power amplifier as this power amplifier, described driving source is the square wave power that described DC magnetic modulator enters duty, described DC magnetic modulator detects in detection winding that under the excitation of described driving source direct current Zero flux balanced signal converts d. c. voltage signal to magnetic flux balanced balanced current I2 through amplifying Driver amplifier, make the magnetic potential of the magnetic potential of a winding and Secondary Winding equal, but direction is contrary, the direct current flux in DC magnetic modulator iron core is made to be zero, electric current compares relevant to the turn ratio and is inverse ratio, realize DC current 60A, 10A, 1A, 0.1A converts DC current 60mA to respectively, 100mA, 100mA, 10mA.

2. intelligent digital micro resistor standard device according to claim 1, it is characterized in that: described guidance panel is by power switch (1), relay indicating light (2), communication interface (3), lcd touch display (4), current wiring terminal A(5), electric potential connection terminal (6) and current wiring terminal B(7) form, described communication interface (3) is for transmitting the related data of intelligent digital micro resistor standard device, the gamut having the tested instrument of communication interface to carry out is detected automatically, also can external computer as the controller of this standard device, this communication interface can also be upgraded to software, described lcd touch display (4) is for arranging the resistance value that will export, and working current during display measurement, described current wiring terminal A(5), be as working current≤10A, micro-resistance exports the current wiring terminal of measurement range when 0 ~ 1.9M Ω, described electric potential connection terminal (6) is electric potential connection terminal when exporting micro-resistance, described current wiring terminal B(7), be as working current≤60A, micro-resistance exports the current wiring terminal of measurement range when 0 ~ 20m Ω.

Intelligent digital micro resistor standard device according to claim 1, it is characterized in that: described 20 figure place weighted-voltage D/A converters are made up of 10V reference power supply, voltage follower, AD5791D/A chip and communication interface, direct current 10V voltage is exported by described 10V reference power supply, as the working standard power supply of AD5791D/A chip, convert digital quantity to controllable analog output by RAM9 microcomputer controller control AD5791D/A chip, the voltage being improved AD5791D/A chip by voltage follower exports load capacity.

3. intelligent digital micro resistor standard device according to claim 1, it is characterized in that: described current sampler is made up of 71/2 digital voltmeter and resistor network, by the magnetic flux balanced balanced current I2 obtained from described DC current proportioner, on resistor network, produce a voltage, measure this voltage by 71/2 digital voltmeter.