CN212905144U

CN212905144U - High-precision measuring system for ultrahigh impedance of low-voltage device

Info

Publication number: CN212905144U
Application number: CN202021145564.1U
Authority: CN
Inventors: 王海来; 孔祥儒; 康明勇
Original assignee: Intelligent Automation Equipment Zhuhai Co Ltd
Current assignee: Intelligent Automation Equipment Zhuhai Co Ltd; Intelligent Automation Zhuhai Co Ltd
Priority date: 2020-06-19
Filing date: 2020-06-19
Publication date: 2021-04-06
Anticipated expiration: 2030-06-19

Abstract

The utility model provides a low pressure device ultrahigh impedance's high accuracy measurement system simple structure, with low costs, efficient, performance is strong. The utility model discloses a MCU (1), exchange source signal generating device (2), serial ports isolator (U9), port isolator (U16), sinusoidal signal isolating device (U18), direct current source signal generating device (3), direct current source auto-change over device (4), impedance measurement device (5), data collection station (6), test resistance analog switch (7) and power, be provided with shield assembly (8) in the product periphery that awaits measuring, MCU (1) passes through port isolator (U16) respectively with impedance measurement device (5) data collection station (6) reach test resistance analog switch (7) are connected, be provided with protection ring (9) between impedance measurement device (5) and the product that awaits measuring, the power is the power supply of whole measurement system. The utility model discloses can be applied to the test field.

Description

High-precision measuring system for ultrahigh impedance of low-voltage device

Technical Field

The utility model relates to a test field especially relates to a be applied to G Europe (1 x 10)¹⁴＞X_R＞1×10⁹Ohm) even T ohm and the voltage tolerance of the material per se is lower (less than 2-5 volts), and the high-precision measurement system of the ultrahigh impedance of the low-voltage device is used for testing the direct current impedance and the alternating current impedance of the precision device.

Background

The higher the impedance of the common insulating material is, the higher the voltage endurance is, so the measurement is generally performed by using a high-voltage instrument (0-KV), such as a megger and the like. However, when measuring materials with low withstand voltage (< 2V, even lower) and high impedance, the high voltage testing method can not be normally applied. The main factors affecting the measurement accuracy at low voltage include:

1. the influence of noise of the resistor is particularly prominent;

2. exciting self-body noise;

the effects of EMI (electromagnetic interference);

4. and testing the leakage current and the leakage voltage of the network.

At present, when the resistance of more than 1G ohm is measured, the static meter, the SMU, the picoammeter, the voltage source, the high impedance meter and the like are used for measurement. The measurement mode of the electrometer needs to be configured with a voltage source or a current source, so that the precise measurement of the high resistance is realized by using a method of externally connecting a voltage source (source meter) and the electrometer or a picoammeter, so as to obtain the measurement voltage or current, and finally calculating the resistance value by using the ohm's law, as shown in fig. 1 and 2. The meter test method using the source meter and the electrometer can directly obtain the test value. Fig. 1 and 2 show high resistance measurement realized by a general electrometer (electrostatic voltmeter) and a high resistance meter instrument, and the characteristics of the high resistance measurement are that the electrometer (electrostatic voltmeter) and an excitation source (a voltage source or a current source) are separated into two parts. In addition, a source meter and an electrometer are integrated into one instrument by a high-resistance measuring instrument which is popular in the market, such as instrument equipment with the model number of B2985A and the like, and then the high resistance is measured by connecting a special matching adapter for the instrument, so that a test value can be directly read on an instrument panel without additional calculation.

Another method is to use a common digital multimeter to calculate the high resistance by reading the voltage, the principle of which is shown in fig. 3. FIG. 3 shows that an external current source is used to supply a constant current to a device under test, and then an operational amplifier is used as a buffer, wherein V1 ≈ V0, so that a common digital multimeter with lower cost can measure the high resistance of Rx.

In addition, an integrated excitation source (a voltage source or a current source) and a buffer can be built in to form a measuring circuit for high-resistance measurement. In the current circuit measurement technology of many test instrument boards, a current source of a circuit board is used, and then an operational amplifier is used as a buffer of an input signal, as shown in fig. 4 and 5. Fig. 4 is a schematic diagram of high-resistance measurement of an electrometer with a built-in current source, and fig. 5 is a schematic diagram of high-resistance measurement of an electrometer with a protection ohm type.

The measured resistance calculation formulas in fig. 4 and 5 are as follows:

R_X=V₁/(V_Sxr) (expression 1)

R_X=V₁I (expression 2)

The test method shown in fig. 1, 2 and 3 is to realize the measurement of high resistance by the cooperation of instruments and meters. Fig. 4 and 5 are completely the measurement method of the autonomous circuit instrument board card. But its measurement quality is very limited by the electrical parameter performance of the operational amplifier itself.

In the prior art, when the high resistance of more than 100G is measured, and the test voltage is less than or equal to 1V, the directional movement of the charges in the electric field is extremely easy to be disturbed by power frequency radiation because the voltage loaded at the two ends of the measured object is too low. The object to be tested has extremely high impedance, radiation can be easily transmitted to two ends of the measuring instrument through space and metal or low-resistance non-conductors, low-frequency harmonic waves of 0-150 Hz can be loaded on the signal to be tested, and the time for achieving a stable test state is long. To ensure faster and more accurate testing, the voltage of the current or voltage source must be adjusted relatively high, typically to > 1V, or even higher, to reduce the thermal noise effects of the resistor itself. And the test conditions were tested in very demanding shielding environments (> 60dB isolation). However, such a voltage division test has no dynamic response capability, and it is still necessary to wait for the electric fields at the two ends of the object to be measured to be stable before accurately testing the resistance value, and the test time is still long.

Since the existing measurement technology is basically a mode of partial pressure test, instruments with high precision, such as a picometer, an electrometer, a voltage source and the like, are required firstly. In addition, the test apparatus is easily affected by EMI (electromagnetic interference) in an external environment, an electrostatic field, temperature and humidity of a natural environment, and the like, so a good shielding environment must be established, the test cost is very high, and unnecessary waste is caused. The volume occupied by the test instrument and the measuring equipment is large, and the test instrument and the measuring equipment are difficult to be introduced into the quantitative production.

In addition, there are very many materials on the market that have a low withstand voltage and a high resistance. The existing testing method often causes breakdown or material fission of a tested object due to the problem of pressure resistance, so that the characteristics and the service life of the material are reduced. When the insulation DC impedance and AC impedance of the tested device (material) exceed G omega (1 x 10)⁹Ohm) and when the ultrahigh impedance is measured, the electrical parameters of the tested materials are sensitively changed after the test voltage for the tested materials is more than 2 volts, and the tested materials are in a nonlinear low-voltage working state.

SUMMERY OF THE UTILITY MODEL

The utility model aims to solve the technical problem that overcome prior art not enough, provide a low pressure device ultra high impedance's high accuracy measurement system simple structure, with low costs, efficient, the performance is strong, this system design science, test accurate and be applicable to the volume production.

The technical proposal adopted by the utility model is that the system comprises

An MCU which is arranged independently and used for outputting test data to the measuring system and receiving test results,

an AC source signal generating device which is arranged independently and used for outputting AC sine exciting signals,

a serial port isolator and a port isolator for isolating data transmission coupled to the MCU,

a sinusoidal signal isolation device for isolating the AC sinusoidal excitation signal output by the AC source signal generation device,

a DC source signal generating device for generating a DC source signal,

a DC source switching device for switching the positive and negative phase DC sources,

an impedance measuring device for measuring the impedance of a product to be measured,

a data collector for collecting the impedance measurement data of the product to be measured,

a test resistor analog switch for setting different resistance values of the test resistor, and a power supply,

a shielding device is arranged at the periphery of a product to be tested, the output end of the test resistance analog switch is connected with the product to be tested, the test resistance analog switch is provided with a plurality of test resistances, the direct current source signal generating device is connected with the impedance measuring device through the direct current source switching device, the output end of the impedance measuring device is connected with the input end of the test resistance analog switch, the impedance measuring device is connected with the data collector after sampling, the serial port isolator is respectively connected with the MCU and the data collector, the output end of the sinusoidal signal isolating device is respectively connected with the impedance measuring device and the data collector through a third relay, the MCU is respectively connected with the impedance measuring device, the data collector and the test resistance analog switch through the port isolator, a protection ring is arranged between the impedance measuring device and a product to be measured, and the power supply supplies power to the whole measuring system.

The serial port isolator, the sinusoidal signal isolating device, the direct current source signal generating device, the direct current source switching device, the impedance measuring device, the data acquisition unit and the test resistance analog switch are all arranged on the same PCB.

The direct current source signal generating device comprises a DAC (digital-to-analog converter), a twenty-second low-dropout linear regulator, a high-precision voltage divider, a phase inverter and a buffer, wherein the twenty-second low-dropout linear regulator is connected with the high-precision voltage divider to form a high-precision voltage source, the DAC is used for providing a set value voltage source for the direct current impedance measuring device, and the high-precision voltage source is switched with the set value voltage source through a channel switcher.

The impedance measuring device comprises a third low power consumption amplifier, a measuring operational amplifier and an instrument amplifier, the output end of the third low power consumption amplifier is connected with the negative input end of the measurement operational amplifier, the positive input end of the third low power consumption amplifier, the positive input end of the measurement operational amplifier and the negative input end of the instrumentation amplifier are communicated, the output end of the instrumentation amplifier is connected with the data collector, one end of the test resistance analog switch is connected with the output end of the measurement operational amplifier, the other end is connected with the input end of a product to be tested, the protection ring is connected with the negative input end of the measurement transporting and amplifying device and is connected with the input end of a product to be measured, a fourth relay is arranged between the positive input end of the measurement operational amplifier and the output ends of the phase inverter and the buffer, and a first relay is arranged between the output end of the third low-power amplifier and the negative input end of the measurement operational amplifier.

The device comprises a product to be tested, a test resistance analog switch and a shielding device, wherein a second relay and a three-coaxial connector are further arranged between the product to be tested and the test resistance analog switch, the product to be tested is connected to the three-coaxial connector, the three-coaxial connector is connected with the second relay, the shielding device is an EMI shielding box, and the EMI shielding box is connected with a voltage source through a reference voltage source device.

The power is single power input, dual power output's isolation power, the power includes dual output isolation power, first low-dropout linear regulator, second low-dropout linear regulator, third low-dropout linear regulator, fifth low-dropout linear regulator and sixth linear regulator, first low-dropout linear regulator third low-dropout linear regulator with sixth linear regulator all with dual output isolation power's output all the way is connected, second low-dropout linear regulator with fifth low-dropout linear regulator all with dual output isolation power's another way output is connected.

The utility model has the advantages that: the utility model discloses in, the fixed voltage value that direct current source signal generating device output was set for arrives the cophase input end of direct current impedance measuring device's measurement fortune ware, accomplish direct current measurement's malleation and establish, at this moment, the product that awaits measuring, direct current measurement resistance, measure fortune ware, form a closed circuit of establishing ties between the constant voltage source and the ground, in this closed circuit, the resistance change of the product that awaits measuring can arouse the change of measuring fortune ware input end voltage, the voltage of definition this change is differential voltage, after carrying out amplification treatment to this differential voltage, utilize the passageway auto-change device to transmit this differential voltage value to MCU in, obtain the voltage value under the forward current condition; then, a fourth relay is switched on, the negative voltage of the direct current measurement is input to the in-phase end of the measurement operation and amplification device through the phase inverter, the negative voltage establishment of the direct current measurement is completed, two ends of a product to be measured obtain a negative voltage source with reverse current, a closed loop in series is formed among the product to be measured, the direct current measurement resistor, the measurement operation and amplification device, the constant measurement voltage source and the ground, in the closed loop, reverse current is divided by the measurement operation and amplification device, namely, a reverse negative voltage value is obtained, after the differential voltage is amplified, the differential voltage value is transmitted to the MCU through the channel switching device, and therefore, a voltage value under the condition of reverse current is obtained; setting the DAC of the direct current source signal generating device to 0V output again, and reading a zero potential voltage value from the channel switching device in a closed test loop formed by the product to be tested, the direct current measuring resistor, the measuring operational amplifier and the ground in series; because the direct current measuring resistor is a known set value, impedance values under the conditions of positive current, negative current and zero potential current are respectively obtained by utilizing the relation between the known resistance value and voltage drop, and then the impedance of a product to be measured is obtained by utilizing the averaging; the relay is connected to a measuring circuit which can be switched to alternating current impedance, a signal generated by the alternating current source signal generating device is coupled to the alternating current operational amplifier through the isolation coupling device, then passes through the alternating current measuring resistor, the second relay and a product to be measured to form a testing loop, an alternating current measuring voltage signal is read through the channel switching device, and then the alternating current impedance of the product to be measured can be obtained through the known alternating current measuring resistor; the event the utility model discloses the system can be fast accurate accomplish the high accuracy measurement of the product that awaits measuring, and the working property is superior, and the design of this system has the scientificity, and its is small, easily realizes the accurate test of the high accuracy of this type of high impedance measurement demand when the quantization production, also is applicable to the verification test and scientific research clearance and so on of product research and development stage.

Drawings

FIG. 1 is a simplified schematic diagram of a prior art high resistance measurement using an electrometer and an external voltage source;

FIG. 2 is a simplified schematic diagram of a prior art high resistance measurement using an electrometer and an external current source;

FIG. 3 is a simplified schematic of a prior art high resistance measurement using a real current source and a digital multimeter;

FIG. 4 is a simplified schematic diagram of a prior art electrometer high resistance measurement with a built-in current source;

FIG. 5 is a simplified schematic diagram of a prior art high resistance measurement of an electrometer with protected ohm;

FIG. 6 is a block diagram of a simple structure of the circuit of the present invention;

FIG. 7 is a circuit schematic of the AC signal isolation circuit;

FIG. 8 is a circuit schematic of the communication data isolation circuit;

FIG. 9 is a circuit schematic of the DAC;

FIG. 10 is a circuit schematic of the high precision voltage source;

fig. 11 is a schematic circuit diagram of the fifth relay;

FIG. 12 is a circuit schematic of the buffer and inverter;

fig. 13 is a schematic diagram of the high resistance measurement circuit of the present invention;

FIG. 14 is a schematic circuit diagram of the shielding device;

fig. 15 is a schematic circuit diagram of the fourth relay;

FIG. 16 is a circuit schematic of the ADC analog-to-digital converter;

FIG. 17 is a circuit schematic of the dual output isolated power supply;

FIG. 18 is a circuit schematic of the first low dropout linear regulator;

FIG. 19 is a circuit schematic of the second LDO;

fig. 20 is a circuit schematic of the third low dropout linear regulator;

fig. 21 is a circuit schematic of the fifth low dropout linear regulator;

fig. 22 is a circuit schematic of the sixth linear regulator;

fig. 23 is a data diagram collected in the ac impedance measurement state according to the embodiment of the present invention.

Detailed Description

As shown in fig. 6, the system of the present invention comprises

An MCU1 which is arranged independently and used for outputting test data to the measuring system and receiving test results,

an AC source signal generating device 2 which is arranged independently and is used for outputting AC sine exciting signals,

a serial port isolator U9 and a port isolator U16 for isolating data transmission coupling the MCU1,

a sinusoidal signal isolation device U18 for isolating the AC alternating current sinusoidal excitation signal output by the AC source signal generation device 2,

a dc source signal generating means 3 for generating a dc source signal,

a DC source switching device 4 for switching the positive and negative phase DC sources,

an impedance measuring device 5 for measuring the impedance of the product to be measured,

a data collector 6 for collecting the impedance measurement data of the product to be measured,

a test resistor analog switch 7 for setting different resistance values of the test resistor, and a power supply,

be provided with shield assembly 8 at the product periphery that awaits measuring, test resistance analog switch 7's output is connected with the product that awaits measuring, test resistance analog switch 7 is provided with a plurality of ways test resistance Rs, direct current source signal generating device 3 passes through direct current source auto-change over device 4 with impedance measurement device 5 connects, impedance measurement device 5's output with test resistance analog switch 7's input is connected impedance measurement device 5 sample back with data collection station 6 connects, serial port isolator U9 respectively with MCU1 with data collection station 6 connects, sinusoidal signal isolating device U18's output pass through third relay K3 respectively with impedance measurement device 5 with data collection station 6 connects, MCU1 passes through port isolator U16 respectively with impedance measurement device 5, data collection station 6 connects, MCU1 passes through, The data acquisition unit 6 is connected with the test resistance analog switch 7, a protection ring 9 is arranged between the impedance measurement device 5 and a product to be measured, and the power supply supplies power to the whole measurement system. The model of the MCU is selected from STM32F103ZET 6.

The serial port isolator U9, the port isolator U16, the sinusoidal signal isolation device U18, the direct current source signal generation device 3, the direct current source switching device 4, the impedance measurement device 5, the data acquisition device 6 and the test resistance analog switch 7 are all arranged on the same PCB.

The direct current source signal generating device 3 comprises a DAC (digital-to-analog converter) U10, a twenty-second low dropout linear regulator U22, a high-precision voltage divider U21, an inverter U20A and a buffer U20B, the twenty-second low dropout linear regulator U22 is connected with the high-precision voltage divider U21 to form a high-precision voltage source, the DAC U10 provides a set value voltage source for the direct current impedance measuring device 5, and the high-precision voltage source is switched with the set value voltage source through a channel switch U15.

The impedance measuring device 5 comprises a third low-power amplifier U14A, a measurement operational amplifier U12 and an instrumentation amplifier U11, wherein an output end of the third low-power amplifier U14A is connected with a negative input end of the measurement operational amplifier U12, a positive input end of the third low-power amplifier U14A, a positive input end of the measurement operational amplifier U12 and a negative input end of the instrumentation amplifier U11 are communicated, an output end of the instrumentation amplifier U11 is connected with the data collector 6, one end of the test resistance analog switch 7 is connected with an output end of the measurement operational amplifier U12, the other end of the test resistance analog switch is connected with an input end of a product to be measured, the guard ring 9 is connected with a negative input end of the measurement operational amplifier U12 and an input end of the product to be measured, a fourth relay K4 is arranged between a positive input end of the measurement operational amplifier U12 and output ends of the phase inverter U20A and the buffer U20B, a first relay K1 is arranged between the output end of the third low power consumption amplifier U14A and the negative input end of the measurement operational amplifier U12.

The product to be tested and the test resistor analog switch 7 are further provided with a second relay K2 and a triaxial connector J4, the product to be tested is connected to the triaxial connector J4, the triaxial connector J4 is connected to the second relay K2, the shielding device 8 is an EMI shielding box, and the EMI shielding box is connected with a voltage source through a reference voltage source device U8.

The power is single power input, dual power output's isolation power supply, the power includes dual output isolation power U4, first low-dropout linear regulator U1, second low-dropout linear regulator U2, third low-dropout linear regulator U3, fifth low-dropout linear regulator U5 and sixth linear regulator U6, first low-dropout linear regulator U1 third low-dropout linear regulator U3 with sixth linear regulator U6 all with output of dual output isolation power U4 is connected all the way, second low-dropout linear regulator U2 with fifth low-dropout linear regulator U5 all with another way output of dual output isolation power U4 is connected.

Here, considering signal collection precision and the number of required independent signal channels, the utility model discloses select the chip that model is AD7175 as data collection station, this chip possesses 24 bits, 250KSPS data sampling rate, and integrated sigma-delta type analog-to-digital converter is fit for the high resistance measuring signal input of low bandwidth, and built-in digital filter can export data with 27.27 SPSThe rate synchronously inhibits the frequency multiplication of 50 Hz/60 Hz and power frequency (100 Hz/120 Hz), and the inhibiting capability reaches 86dB, so that the radiation influence of power frequency noise in the measuring process is well reduced. Specifically, the signals for DC impedance measurement are read from the DC differential signal input channels ADC _ AIN0, ADC _ AIN1, and the signals for AC impedance measurement are read from the AC differential signal input channels ADC _ AIN2, ADC _ AIN3, set at V_REFBoth the dc and ac sine wave amplitude signals are read from the signal read channel ADC _ AIN 4.

As shown in fig. 13 and 14, here, the reason why the shielding device 8 is provided is as follows: because the measuring loop has inherent characteristics of high impedance and is very easy to absorb a peripheral piezoelectric magnetic field, a measuring circuit can be disturbed in an electromagnetic field mode no matter in a power frequency electric field or an electrostatic field, and the interference can appear in a measured effective signal in a noise superposition mode, so that a measuring error is generated. In order to solve the EMC problem in the measurement, the electromagnetic disturbance is generally conducted and radiated in two ways, so a shielding device is needed to isolate and shield the electromagnetic disturbance.

As shown in fig. 18 to fig. 22, the power supply is an isolated power supply with single power input and dual power outputs, the power supply includes a dual-output isolated power supply U4, a first low dropout linear regulator U1, a second low dropout linear regulator U2, a third low dropout linear regulator U3, a fifth low dropout linear regulator U5 and a sixth linear regulator U6, the first low dropout linear regulator U1, the third low dropout linear regulator U3 and the sixth linear regulator U6 are all connected to one output of the dual-output isolated power supply U4, and the second low dropout linear regulator U2 and the fifth low dropout linear regulator U5 are all connected to the other output of the dual-output isolated power supply U4.

The utility model discloses consider the noise problem that anti-interference and conduction harass arouse, choose the isolation power module of single power input, dual supply 12V, 500mA output for use as the power. Through tests, the voltage suppression ratio of an operational amplifier direct-current working area in the circuit is excellent. However, in consideration of the characteristic that the performance of the ac signal is reduced due to the increase in frequency, in order to reduce the noise of the power supply rail, low dropout linear regulators LT3042 and LT3094 having an excellent common mode rejection ratio are selected as the regulated output of the dual power supplies for suppressing the switching noise generated from the isolated power supply terminals. While the second low dropout linear regulator U2 also serves to isolate noise in an unknown multi-spectral range outside the high impedance measurement circuit.

The guard ring is described herein as follows. As shown in fig. 13, since the current in the impedance circuit to be measured is extremely small, the charges in the current leak to the electrodes with different potentials, and thus the static charges outside the high-resistance measurement circuit flow into the high-resistance measurement circuit or are affected by the piezoelectric effect of the electrode material near the circuit, and the charges flowing into the high-resistance measurement circuit will seriously affect the measurement. In order to avoid the creeping leakage of the charges, a protection ring is designed and surrounded around the measurement main loop, so that the potential of the protection ring is equal to the potential of a measurement signal source, and the creeping leakage problem of the charges is further solved. The utility model discloses in, measure and carry and put ware U12, exchange and carry 8 th foot of putting ware U16 and directly connect with high impedance device (including direct current measuring resistance Rz (R36), exchange measuring resistance Rj (R52) and with the product that awaits measuring), and intermediate junction test cable, like three coaxial connector of J4 output and coaxial cable, a protection ring need be established to longer network. The utility model discloses in, to input into the VREF signal of measuring fortune amplifier U12, the 1 st foot of interchange fortune amplifier U16, also input into third low power consumption amplifier U14A simultaneously (the model is ADA 4522), a follower circuit has been constituteed to third low power consumption amplifier U14A, the output signal of the 1 st foot of third low power consumption amplifier U14A is as protection ring 9, make the electric potential of the part of being protected equal with the point location of measuring the signal source, thereby avoid external noise interference.

The utility model discloses in, the process of direct current impedance measurement is as follows:

as shown in FIG. 13, firstly, 1V voltage is set through a DAC digital-to-analog converter U10 in the direct current source signal generating device 4, or a high-precision voltage source consisting of a twenty-second low dropout linear regulator U22 and a high-precision voltage divider U21 is connected to set a fixed voltage value of 1.024V, and the set fixed voltage value is controlled by a relayConstant measurement voltage source V_REFInputting the voltage to the non-inverting terminal of the measuring operational amplifier U12, thus completing V_REFThe positive pressure of (2) is established. Common mode levels at two ends of IN + \ IN-of

pins

1 and 8 of virtual short characteristics of the operational amplifier U12 are kept unchanged at 1V (or 1.024V), so that the levels at two ends of a product to be tested are also kept unchanged at 1V (or 1.024V), and thus the product to be tested (Rx), a direct current measuring resistor Rz (R36), the measurement operational amplifier U12 and a constant measurement voltage source V are obtained_REFThe analog ground AGND forms a series closed loop. The current change caused by the resistance change of the product to be measured is finally reflected on the voltage division of the 1 st pin and the 6 th pin of the measurement operational amplifier U12, that is, the current change caused by different impedance values can cause the voltage change of the 1 st pin and the 6 th pin of the measurement operational amplifier U12, and the voltage is defined as a forward voltage value V under the condition of forward current_{O_P1V}(ii) a Forward voltage value V_{O_P1V}The differential voltage is input to a direct current instrument amplifier U11 (model is AD 8422) for amplification in a differential voltage mode, the amplified differential mode voltage is transmitted to the input ends of direct current differential signal input channels AIN0 and AIN1 of a channel switching device U7 as a first channel through a thirty-second resistor R32 and a forty-fourth resistor R40, and a microprocessor can read V after digital-to-analog conversion_{O_P1V}The voltage value of (2) is used for impedance calculation.

Measuring forward voltage value V_{O_P1V}Then, as long as the fourth relay K4 is turned on, the previously set 1V voltage is input to the non-inverting terminal (1 pin) of the measurement amplifier U12 through the inverter U20A, thus completing the constant measurement voltage source V_REFThe negative pressure of (2) is established. The two ends of the product to be measured can obtain a-1V voltage source with opposite current directions, so that the product to be measured Rx, the direct current measuring resistor Rz (R36), the measuring operational amplifier U12 and the constant measuring voltage source V are obtained_REFThe analog ground AGND forms a series closed loop. The reverse current is divided by a measuring operational amplifier U12 (pin 1 and pin 6) to obtain a reverse voltage value V under the condition of reverse current_{O_N1V}. Here, the dc instrumentation amplifier U11 and the follower U13 form a circuit with a common mode reference voltage point of 2.5V. The level of a 6 th pin REF of a direct current instrument amplifier U11 is raised and stabilized at 2.5V, so that the direct current instrumentThe common mode reference point voltage of the amplifying circuit of the amplifier U11 is 2.5V, the voltage of the reference point of the 4 th pin (REFOUT) of the ADC U7 in the channel switching device is also set to 2.5V (the 4 th pin of the ADC U7 and the 3 rd pin of the follower U13 are the same network signal), and the input ends of AIN0 and AIN1 of the ADC U7 can read the inverted negative voltage value V_{O_N1V}. The absolute value of the forward impedance measurement voltage value and the absolute value of the reverse impedance measurement voltage value can be ensured to be consistent, and the consistency of the output impedance of the positive signal source and the negative signal source is further ensured.

Thirdly, the channel setting is unchanged, the DAC digital-to-analog converter U10 is set to be 0V, the test loop is the same as the above, and the zero potential voltage value V can be read by the input ends of AIN0 and AIN1 of the ADC analog-to-digital converter U7_{O_0V}。

By means of a measured forward voltage value V_{O_P1V}Reverse voltage value V_{O_N1V}And a zero potential voltage value V_{O_0V}And the known direct current measurement resistor Rz (R36) can respectively calculate the impedance values of the product to be measured under three conditions, and then the impedance values are averaged to obtain the impedance of the product to be measured.

The utility model discloses a measurement process of alternating current impedance as follows:

an alternating current source signal generating device (namely a direct digital frequency synthesizer, hereinafter abbreviated as DDS) is set to be a 10Hz alternating current sine wave with the amplitude of 1Vpp (set according to the impedance of a product to be tested), and a first relay K1, a second relay K2 and a first pressing relay K3 are switched to an alternating current impedance testing loop. The 10Hz alternating current sine wave is coupled to the 1 st pin of the alternating current operational amplifier U16 through the linear isolator U18 and the first relay K1, and then forms a test loop through the alternating current measuring resistor Rj (R52, 100M ohm resistor), the second relay K2, the triaxial connector J4 and a product to be tested. The measurement voltage signal is read as an input of an ac differential signal input channel (ADC _ AIN2, ADC _ AIN 3) and an input of a signal read channel (ADC _ AIN 4) of the ADC analog-to-digital converter U7. At a set frequency, the AC impedance is much smaller than the DC impedance, so the sampling resistance of the AC measuring resistor Rj (R52) is as small as possible, and the AC instrumentation amplifier U15 is considered at the ACThe nonlinearity of the current amplification circuit is obtained by using a circuit model having a gain G =1 as much as possible. Thus, the sine wave signal V input after being generated by the DDS can be tested and obtained_REFEffective value of (V)_{REF_RMS}And a sine wave signal V obtained by shunting of the operational amplifier_OEffective value of (V)_{O_RMS}Then, an ac impedance value is obtained from the known ac measurement resistor Rj.

The principle of the measurement signal channel of the alternating-current impedance is basically consistent with that of the measurement signal channel of the direct-current impedance, and the measurement signal channel of the alternating-current impedance is greatly different in the acquisition and metering modes for obtaining the sine wave amplitude. If an AC sine wave signal frequency of 10Hz is used as a test signal source, the signal source period is 100mS (100 mS), and four or fifty level data of 2 to 3 complete periods are collected to calculate the RMS effective value using a sampling rate of about 200Hz, as shown in fig. 23, a higher sampling rate may be set, and more distributed data may be collected to calculate to obtain a more accurate effective value. In the present embodiment, the purpose of using low-frequency sampling is to control the signal bandwidth, and the low-frequency interference is better suppressed by using the 50Hz and 60 Hz filter characteristics of the ADC analog-to-digital converter U7 itself.

The utility model discloses an impedance measurement range can be through adjusting the measuring voltage V of loading at the product both ends that await measuring_REFThe voltage amplitude of the voltage can also realize a broadband measurement range from 50M ohm to 100T ohm by changing the resistance value of the direct current measurement resistor Rz or the alternating current measurement resistor Rj. Furthermore, the utility model discloses a high resistance is measured and is all had certain requirement to test environment and natural environment, and at first the device that is surveyed should keep dry, can be true reflect the physical characteristics of device.

High accuracy measurement system can be applied to and measure and exceed G Europe (1X 10)¹⁴＞X_R＞1×10⁹Ohm) and the voltage endurance of the material itself is low (< 2-5 volts), in particular to measure the direct current impedance and the alternating current impedance of the sensors, electronic devices, semiconductor devices and other components which can normally work only under low voltage. For example, the method can be applied to the height of a semiconductor deviceThe high-precision test of input impedance, the direct current and alternating current high-impedance test of a chemical sensor and the alternating current high-impedance test of a capacitive sensor are extremely widely applied. In addition, the system is also suitable for surface resistance and volume resistance tests of low-voltage-resistant insulating materials, and the characteristic parameters of the insulation direct current impedance and the insulation alternating current impedance of a tested device (material) exceed G ohm and even reach T ohm. The method can also be applied to analytical instruments and meters and measuring equipment, and measurement in the material research and development process, impedance test of biomedicine, inspection of semiconductor devices and electronic product test. The technology has the characteristic of easy quantitative production test application, and is favorable for obtaining accurate impedance data of the material to be tested in a laboratory or a processing plant and carrying out characteristic analysis and quality monitoring on the material to be tested.

Claims

1. The utility model provides a high accuracy measurement system of low-voltage device superelevation impedance which characterized in that: the system comprises

An MCU (1) which is arranged independently and used for outputting test data to the measuring system and receiving test results,

an AC source signal generating device (2) which is arranged independently and is used for outputting AC sine exciting signals,

a serial port isolator (U9) and a port isolator (U16) for isolating data transmissions coupling the MCU (1),

a sinusoidal signal isolation device (U18) for isolating an AC alternating current sinusoidal excitation signal output by the AC source signal generation device (2),

a direct current source signal generating means (3) for generating a direct current source signal,

a direct current source switching device (4) for switching positive and negative phase direct current sources,

an impedance measuring device (5) for measuring the impedance of a product to be measured,

a data collector (6) for collecting the impedance measurement data of the product to be measured,

a test resistor analog switch (7) for setting different resistance values of the test resistor, and a power supply,

be provided with shield assembly (8) at the product periphery that awaits measuring, the output of test resistance analog switch (7) is connected with the product that awaits measuring, test resistance analog switch (7) are provided with a plurality of ways test resistance (Rs), direct current source signal generating device (3) pass through direct current source auto-change over device (4) with impedance measurement device (5) are connected, the output of impedance measurement device (5) with the input of test resistance analog switch (7) is connected impedance measurement device (5) sample the back with data collection station (6) are connected, serial port isolator (U9) respectively with MCU (1) and data collection station (6) are connected, the output of sinusoidal signal isolating device (U18) pass through third relay (K3) respectively with impedance measurement device (5) and data collection station (6) are connected, MCU (1) pass through port isolator (U16) respectively with impedance measurement device (5), data collection station (6) reach test resistance analog switch (7) are connected, be provided with protection ring (9) between impedance measurement device (5) and the product that awaits measuring, the power is the power supply of whole measurement system.

2. The system of claim 1, wherein the system comprises: the serial port isolator (U9), the port isolator (U16), the sinusoidal signal isolation device (U18), the direct current source signal generation device (3), the direct current source switching device (4), the impedance measurement device (5), the data acquisition unit (6) and the test resistance analog switch (7) are all arranged on the same PCB.

3. The system of claim 2, wherein the system comprises: the direct current source signal generating device (3) comprises a DAC (digital-to-analog converter) (U10), a twenty-second low dropout linear regulator (U22), a high-precision voltage divider (U21), an inverter (U20A) and a buffer (U20B), the twenty-second low dropout linear regulator (U22) and the high-precision voltage divider (U21) are connected to form a high-precision voltage source, the DAC (digital-to-analog converter) (U10) provides a set-point voltage source for the impedance measuring device (5), and the high-precision voltage source and the set-point voltage source are switched through a channel switch (U15).

4. The system of claim 3, wherein the system comprises: the impedance measuring device (5) comprises a third low-power amplifier (U14A), a measuring operational amplifier (U12) and an instrument amplifier (U11), wherein the output end of the third low-power amplifier (U14A) is connected with the negative input end of the measuring operational amplifier (U12), the positive input end of the third low-power amplifier (U14A), the positive input end of the measuring operational amplifier (U12) and the negative input end of the instrument amplifier (U11) are communicated, the output end of the instrument amplifier (U11) is connected with the data collector (6), one end of the test resistance analog switch (7) is connected with the output end of the measuring operational amplifier (U12), the other end of the test resistance analog switch is connected with the input end of a product to be measured, the protection ring (9) is connected with the negative input end of the measuring operational amplifier (U12) and is connected with the input end of the product to be measured, and the positive input end of the measuring operational amplifier (U12) is connected with the phase inverter (U20A) and the output end of the buffer (U20B A fourth relay (K4) is arranged between the first relay and the second relay, and a first relay (K1) is arranged between the output end of the third low power consumption amplifier (U14A) and the negative input end of the measurement operational amplifier (U12).

5. The system of claim 1, wherein the system comprises: the product that awaits measuring with still be provided with between test resistance analog switch (7) including second relay (K2) and triaxial connector (J4), the product that awaits measuring is connected on triaxial connector (J4), triaxial connector (J4) with second relay (K2) are connected, shield assembly (8) are EMI shielding box, EMI shielding box is connected with the voltage source through reference voltage source device (U8).

6. The system of claim 1, wherein the system comprises: the power is single power input, dual power output's isolation power supply, the power includes dual output isolation power (U4), first low-dropout linear regulator (U1), second low-dropout linear regulator (U2), third low-dropout linear regulator (U3), fifth low-dropout linear regulator (U5) and sixth linear regulator (U6), first low-dropout linear regulator (U1), third low-dropout linear regulator (U3) with sixth linear regulator (U6) all with the output of dual output isolation power (U4) is connected all the way, second low-dropout linear regulator (U2) with fifth low-dropout linear regulator (U5) all with the output of another way of dual output isolation power (U4) is connected.