CN108828322B - High-speed detection circuit of low-capacity capacitor - Google Patents
High-speed detection circuit of low-capacity capacitor Download PDFInfo
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- CN108828322B CN108828322B CN201810436581.1A CN201810436581A CN108828322B CN 108828322 B CN108828322 B CN 108828322B CN 201810436581 A CN201810436581 A CN 201810436581A CN 108828322 B CN108828322 B CN 108828322B
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- 239000003990 capacitor Substances 0.000 title claims abstract description 86
- 238000001514 detection method Methods 0.000 title claims abstract description 62
- 230000005284 excitation Effects 0.000 claims abstract description 40
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- 238000005259 measurement Methods 0.000 claims description 27
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2605—Measuring capacitance
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
Abstract
The low-capacity capacitor high-speed detection circuit comprises a single chip microcomputer, a PC (personal computer) which is in bidirectional connection with the single chip microcomputer, an excitation power supply Ui1 and an excitation power supply Ui2 which are correspondingly connected with the single chip microcomputer through electronic switches K1 and K2, an excitation power supply output signal Ui is connected with a tested capacitor CX and a standard capacitor CN, an excitation current is generated on the tested capacitor CX and the standard capacitor CN, the excitation current is added to a transformer bridge detection circuit, an output voltage Uo1 is generated at an output end of the excitation current, the Uo1 is received into an amplifying circuit, and the signal Uo is output through the amplifying circuit; the amplifying circuit is connected with the amplifying multiple adjusting circuit, and the amplifying multiple adjusting circuit is connected with the singlechip; uo and Ui are connected with the singlechip through a phase detection circuit, and Uo and U REF The voltage comparison circuit is connected with the singlechip; the Uo is connected with the singlechip through a VPC conversion circuit; an error grading indication signal circuit and a capacitance value data display circuit which are connected with the output signal of the singlechip. The invention has the advantages of measuring speed up to 100 grains/second, better measuring stability and higher measuring precision.
Description
Technical Field
The invention relates to a capacitance detection circuit, in particular to a circuit for measuring small capacitance by adopting a transformer bridge balance circuit.
Background
Currently, small-capacity capacitors are increasingly favored by the electronics industry, and the demand thereof is also increasing. In order to further reduce the cost, enterprises put higher requirements on capacitance detection, and the capacitance detectors commonly used by domestic enterprises at present comprise HP-4278A, LCR101 and CDF-X. However, these measuring devices have a relatively slow measuring speed and are not capable of recording, counting and analyzing the measured data. Accordingly, technicians and users have improved and retrofitted existing capacitance measuring instruments.
Existing patent 'capacitance detection device' patent number: CN102590635a, which is capable of adjusting the offset with higher accuracy than the minimum value of the capacitive element for adjustment. Capacitance detection method patent number: in the capacitance detection method of CN102375628A, the purposes of noise suppression effect and improving the tolerance of capacitance and impedance change in the process can be achieved by adopting a capacitance charge-discharge method. Capacitive detection circuit patent number: CN103487662a, the capacitive detection method of the invention adopts a capacitive integrating circuit, and the signal-to-noise ratio is not reduced under the condition of not reducing the detection voltage in the detection process.
Both the above measuring instrument and the patent solutions have some problems. First, the speed of measurement is slow, and the requirements of manufacturing enterprises cannot be met. Secondly, the measuring range is wider, and the cost performance of the instrument is low. Third, the measured data cannot be shared with the user, and the measurement standards between the enterprise and the user are subject to errors causing disputes. Fourth, most instruments and measurement methods use a balanced bridge method, which has high requirements on signal sources and environmental parameters. When the temperature and humidity change is large, the measurement accuracy is reduced by an order of magnitude.
Disclosure of Invention
The invention provides a low-capacity capacitor high-speed detection circuit which adopts a transformer balance bridge principle to measure a low capacity capacitor. An excitation current is generated in the primary winding of the transformer by comparison with the standard capacitance, the magnitude of the excitation current being proportional to the error between the measured capacitance and the standard capacitance. The PC is used as an upper computer, realizes the bidirectional transmission of data with the singlechip, controls the process of measuring the small capacitance, performs error compensation, analysis and management on the measured data, and shares the measured data with a user through the Internet.
The invention is realized by the following technical scheme:
the low-capacity capacitor high-speed detection circuit comprises a singlechip and a PC (personal computer) which is connected with the singlechip in a bidirectional manner to realize data bidirectional transmission; the PC controls the measuring process of the small capacitance, performs error compensation, analysis and management on measured data, and shares the measured data with a user through the Internet.
The singlechip is correspondingly connected with an excitation power supply Ui1 and an excitation power supply Ui2 through electronic switches K1 and K2, and selects the excitation power supply Ui1 and the excitation power supply Ui2; when the measured capacitance CX is smaller than 20pF, the exciting power supply Ui1 is switched on; when the measured capacitance CX is more than or equal to 20pF, the excitation power supply Ui2 is connected.
The excitation power supply Ui1, ui2 output signal Ui is connected with the tested capacitor CX, the standard capacitor CN, generates an excitation current on the tested capacitor CX and the standard capacitor CN, adds to the transformer bridge detection circuit, generates an output voltage Uo1 at the output end of the transformer bridge detection circuit, when CX=CN, uo1=0; when CX is not equal to CN, uo1=K delta C, K is a proportionality coefficient, and is influenced by the distributed capacitance and the contact resistance of the circuit, and when the circuit is determined, K is a constant; the K value can be obtained automatically by measuring the standard capacitance before use.
Uo1 is connected to the amplifying circuit, and a signal Uo is output through the amplifying circuit; the amplifying circuit is connected with the amplifying multiple adjusting circuit, and the amplifying multiple adjusting circuit is connected with the singlechip. The single chip microcomputer controls the amplification factor adjusting circuit to automatically adjust the amplification factor, so that the signal Uo reaches a larger value under the condition of ensuring that the signal Uo is not distorted, and the measurement accuracy of the small capacitor can reach 0.01%; the measurement accuracy is improved.
The signal Uo and the signal Ui are connected with the singlechip through an output signal YC of the phase detection circuit, the phase detection circuit carries out phase detection on the signal Ui and the signal Uo, and the size relation between the tested capacitor CX and the standard capacitor CN is judged; when yc=0, then the two voltages Ui and Uo are inverted, CX > CN; when yc=1, then the two voltages Ui and Uo are in phase, CX < CN.
The output voltage Uo and the reference voltage U REF The output signal YA of the voltage comparison circuit is connected with the singlechip, and the voltage comparison circuit outputs the voltage Uo and the reference voltage U REF Comparing the voltages, when outputting the voltage Uo<U REF Ya=0 is input into a singlechip, and the singlechip outputs a control signal to a magnification adjusting circuit to adjust the magnification of the magnification adjusting circuit; when outputting the voltage Uo>U REF YA=1 is input to the singlechip, and the output signal Uo meets the design requirement.
The output signal Uo is an analog signal and is connected with the singlechip through the VPC conversion circuit to convert the analog signal Uo into a digital signal YB; the single chip microcomputer transmits the measurement data to the PC, and the PC calculates the capacitance value and the error grading signal of the capacitor CX to be measured. The pulse width of the digital signal YB is proportional to the magnitude of the analog signal Uo. The width of the pulse signal is recorded by the singlechip, so that the magnitude of the output voltage Uo can be calculated, and meanwhile, the capacitance value of the measured capacitor CX is calculated according to the magnitude of the Uo.
The capacitive error step indication signal circuit is connected with the output signal of the singlechip, and indicates in eight steps and is displayed by eight LED light emitting diodes.
The capacitance value data display circuit is connected with the output signal of the singlechip, and the capacitance value data display circuit adopts an LED display screen to display the capacitance value of the tested capacitor CX.
Furthermore, the exciting power supply Ui1 is a 12V sinusoidal alternating current power supply of 1MHz, and the exciting power supply Ui2 is a 12V sinusoidal alternating current power supply of 500 KHz.
Furthermore, when the excitation power supply is larger than or equal to 10 signal periods, the capacitance detection circuit enters a stable state, and the capacitance value of the capacitor CX to be detected can be effectively measured.
(III) beneficial effects
Compared with the prior art, the low-capacity capacitor high-speed detection circuit provided by the invention has the following beneficial effects:
(1) The transformer balance bridge detection circuit is adopted, and the transformer balance bridge principle is adopted to measure the small capacitance. Generating an excitation current in two secondary windings of the three-winding transformer through comparison of the measured capacitance and the standard capacitance, wherein the excitation current is proportional to the error delta C between the measured capacitance CX and the standard capacitance CN; the influence of the environmental parameters and the distribution parameters is eliminated. The stability of measurement is better, the precision is higher.
(2) The amplification factor of the amplifying circuit is automatically adjusted by the control of the singlechip, so that a larger value is achieved under the condition of ensuring that the output voltage is not distorted, and the measurement precision is improved.
(3) The PC is used as an upper computer, the PC is used for controlling the measuring process of the small capacitor, error compensation, analysis and management are carried out on measured data, and the measured data is shared with a user through the Internet.
(4) The measuring range is reduced, and the actual measuring range is 0.1pF-200pF; the measurement accuracy is more accurate, and the measurement speed is also increased; the measurement accuracy was 0.01%, and the measurement speed was 100 grains/second.
Drawings
Fig. 1 is a schematic block diagram of a detection circuit of the present invention.
Fig. 2 is a schematic circuit diagram of the present invention.
Fig. 3 is a flow chart of the operation of the present invention.
The marks and parts in the drawings are marked: the power supply circuit comprises a 1-singlechip circuit, a 2-excitation power supply, a 3-transformer bridge detection circuit, a 4-two-stage amplifying circuit, a 5-amplifying factor regulating circuit, a 6-voltage comparing circuit, a 7-VPC converting circuit, an 8-phase comparing circuit, a 9-capacitance error step indication signal circuit, a 10-capacitance value data display circuit, an 11-singlechip clock circuit, a 12-singlechip start-up reset circuit, a 13-singlechip and PC RS232 interface circuit.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. The described embodiments are only some, but not all, embodiments of the invention. Various modifications and improvements of the technical scheme of the invention, which are made by those skilled in the art, are included in the protection scope of the invention without departing from the design concept of the invention.
Examples:
as shown in fig. 1: the low-capacity capacitor high-speed detection circuit comprises a singlechip and a PC (personal computer) which is connected with the singlechip in a bidirectional manner to realize data bidirectional transmission; the PC controls the measuring process of the small capacitance, performs error compensation, analysis and management on measured data, and shares the measured data with a user through the Internet.
The singlechip is correspondingly connected with an excitation power supply Ui1 and an excitation power supply Ui2 through electronic switches K1 and K2, and selects the excitation power supply Ui1 and the excitation power supply Ui2; when the measured capacitance CX is smaller than 20pF, the exciting power supply Ui1 is switched on; when the measured capacitance CX is more than or equal to 20pF, the excitation power supply Ui2 is connected.
The exciting power supply Ui1 is a 12V sinusoidal alternating current power supply of 1MHz, and the exciting power supply Ui2 is a 12V sinusoidal alternating current power supply of 500 KHz. When the excitation power supply is larger than or equal to 10 signal periods, the capacitance detection circuit enters a stable state, and the capacitance value of the capacitor CX to be detected can be effectively measured.
The excitation power supply output signal Ui is connected with the tested capacitor CX and the standard capacitor CN, an excitation current is generated on the tested capacitor CX and the standard capacitor CN and is added to the transformer bridge detection circuit, an output voltage Uo1 is generated at the output end of the transformer bridge detection circuit, and when CX=CN, uo1=0; when CX is not equal to CN, uo1=K delta C, K is a proportionality coefficient, and is influenced by the distributed capacitance and the contact resistance of the circuit, and when the circuit is determined, K is a constant; the K value can be obtained automatically by measuring the standard capacitance before use.
Uo1 is connected to the amplifying circuit, and a signal Uo is output through the amplifying circuit; the amplifying circuit is connected with the amplifying multiple adjusting circuit, and the amplifying multiple adjusting circuit is connected with the singlechip. The single chip microcomputer controls the amplification factor adjusting circuit to automatically adjust the amplification factor, so that under the condition that the Uo is not distorted, the Uo reaches a larger value, and the measurement accuracy of the small capacitor can reach 0.01%; the measurement accuracy is improved.
The signal Uo and the signal Ui are connected with the singlechip through an output signal YC of the phase detection circuit, the phase detection circuit carries out phase detection on the signal Ui and the signal Uo, and the size relation between the tested capacitor CX and the standard capacitor CN is judged; when yc=0, then the two voltages Ui and Uo are inverted, CX > CN; when yc=1, then the two voltages Ui and Uo are in phase, CX < CN.
The output voltage Uo and the reference voltage U REF The output signal YA of the voltage comparison circuit is connected with the singlechip, and the voltage comparison circuit outputs the voltage Uo and the reference voltage U REF Comparing the voltages, when outputting the voltage Uo<U REF Ya=0 is input into a singlechip, and the singlechip outputs a control signal to a magnification adjusting circuit to adjust the magnification of the magnification adjusting circuit; when outputting the voltage Uo>U REF YA=1 is input to the singlechip, and the output signal Uo meets the design requirement.
The signal Uo is an analog signal and is connected with the singlechip through the VPC conversion circuit to convert the analog signal Uo into a digital signal YB; the single chip microcomputer transmits the measurement data to the PC, and the PC calculates the capacitance value and the error grading signal of the capacitor CX to be measured. The pulse width of the digital signal YB is proportional to the magnitude of the analog signal Uo. The width of the pulse signal is recorded by the singlechip, so that the magnitude of the output voltage Uo can be calculated, and meanwhile, the capacitance value of the measured capacitor CX is calculated according to the magnitude of the Uo.
The capacitive error step indication signal circuit is connected with the output signal of the singlechip, and indicates in eight steps and is displayed by eight LED light emitting diodes.
The capacitance value data display circuit is connected with the output signal of the singlechip, and the capacitance value data display circuit adopts an LED display screen to display the capacitance value of the tested capacitor CX.
As shown in FIG. 2, the low-capacity capacitor high-speed detection circuit comprises a single chip microcomputer circuit, a single chip microcomputer clock circuit, a single chip microcomputer start-up reset circuit, an excitation power supply, a transformer bridge detection circuit, a two-stage amplification circuit, an amplification factor adjustment circuit, a voltage detection rectification filter circuit, an amplification output rectification filter circuit, a voltage detection comparison circuit, a VPC conversion circuit, a phase comparison circuit, a capacitor error step indication signal circuit, a capacitor value data display circuit and a single chip microcomputer RS232 interface circuit.
U1 is a singlechip and adopts AT89C 52. The 32 th to 39 th pins of the P0 port of U1 are respectively connected with the 9 th to 2 nd pins of a pull-up resistor RP1, and the 1 st pin of RP1 is connected with +5V.
The singlechip clock circuit consists of a capacitor C7, a capacitor C8 and a crystal oscillator X1, wherein one end of the C7 is grounded, and the other end of the C7 is connected with a 19 th pin of U1; one end of the C8 is grounded, and the other end of the C8 is connected with the 18 th pin of the U1; x1 is connected in parallel with pins 18 and 19 of U1. The frequency of crystal oscillator X1 was chosen to be 11.0592MHz.
The singlechip power-on reset circuit consists of a resistor R23 and a capacitor C9, and realizes the power-on reset function of the singlechip. Wherein the positive electrode of C9 is connected with +5V, the negative electrode is connected with R23, and the other end of R23 is grounded. The connection point of R23 and C9 is connected with the 9 th pin of U1.
The excitation power supply consists of an alternating current signal source Ui1 (12V alternating current power supply of 1 MHz), an alternating current signal source Ui2 (12V alternating current power supply of 500 KHz) and an electronic switch U2: a and U2: and B is composed of. One end of Ui1 is grounded, and the other end of Ui1 is connected with U2: pin 1 of a, U2: pin 13 of A is connected to port P1.0 of U1. One end of Ui2 is grounded, and the other end of Ui2 is connected with U2: 11 th pin of B, U2: the 12 pins of B are connected with the P1.1 port of U1. The 2 nd pin of Ui1 is connected with the 10 th pin of Ui2, and the output signal is Ui. When p1.0=1, ui=ui1; when p1.1=1, ui=ui2. And under the control of the singlechip U1, P1.0 and P1.1 are forbidden to be 1 at the same time, so that the short circuit of Ui1 and Ui2 is prevented.
The transformer bridge detection circuit consists of resistors R1 and R2, a measured capacitor CX, a standard capacitor CN and a three-winding transformer TR1, wherein the transformation ratio of the transformer is 1:1:1. wherein, R1 and R2 are connected in series in the transformer bridge, and the function is to eliminate the resistance generated by contact resistance, wire resistance and the like in the measuring circuit so as to improve the measuring precision. One end of R1 is connected with U2: the 2 nd pin of A is connected, and the other end and the CN of R1 are connected, and R2 one end and U2: the 2 nd pin of A is connected, and the other end of R2 is connected with CX. One end of CN is connected with the 5 th pin of R1 and the other end of CN is connected with the 5 th pin of TR 1. CX one end connects R2, CX other end TR 1's 1 pin. The 1 st pin and the 5 th pin of the TR1 are the synonym terminals. When cx=cn, the transformer bridge balances, uo1 is 0. When cx+.cn, uo1=kΔc, K is the scaling factor, affected by the distributed capacitance and contact resistance of the circuit. K is a constant when the circuit is determined. The value of K can be obtained automatically by measurement of the standard capacitance before use. Pins 2, 4 and 8 of TR1 are grounded. The 7 th pin and the 1 st pin of the TR1 are the same-name terminals, and the 7 th pin output voltage Uo1 of the TR1 is applied to the same-phase terminal of the first-stage voltage amplifying circuit through R26.
The amplifying circuit is composed of a two-stage amplifying circuit and an amplifying multiple adjusting circuit. The first-stage amplifying circuit is an in-phase proportional operational amplifying circuit, the input resistance is large, and the influence on the balanced bridge excitation signal is reduced. The first stage amplifying circuit is composed of an operational amplifier U8, resistors R26, R27 and R28. The U8 adopts AD711AP, the 3 rd pin of the U8 is connected with R26, the other end of the R26 is connected with the 7 th pin of TR1, the input signal is Uo1, the 7 th pin of the U8 is connected with +5V, the 4 th pin of the U8 is connected with-5V, dual power supply is adopted for supplying power, the 2 nd pin of the U8 is connected with R27, and the other end of R27 is grounded; a feedback resistor R28 connected to U8 at 2 nd,And between the 6 pins, the 6 th pin of U8 is an output end, the output voltage is Uo2, and the output voltage is applied to the second-stage amplifying circuit through R3. The second-stage amplifying circuit is composed of an operational amplifier U3, resistors R3, R4, R5, R6, R7 and R8, wherein the U3 adopts an AD711AP, a U3 pin is connected with the R3, the other end of the R3 is connected with a U8 pin 6, an input signal is Uo2, a U3 pin 7 is connected with +5V, a U3 pin 4 is connected with-5V, dual power supply is adopted, the U3 pin 2 is connected with the R4, and the other end of the R4 is grounded; one end of each feedback resistor R5, R6, R7 and R8 is commonly connected to the 6 th pin of U3, the 6 th pin of U3 is an output end, the output voltage is Uo, and the other ends of R5, R6, R7 and R8 are respectively connected to the electronic switch U2: C. u2: D. u2: A. u2: pins 4, 8, 1, 11 of B are connected to pin 2 of U3 through electronic switches; electronic switch U2: C. u2: D. u2: A. u2: pins 5, 6, 13 and 12 of the B are respectively connected with ports P1.2, P1.3, P1.4 and P1.5 of the singlechip U1; electronic switch U2: C. u2: D. u2: A. u2: pins 3, 9, 2 and 10 of B are connected together and commonly connected to pin 6 of U3. The singlechip sends out instructions to control the electronic switch U2 through P1.2, P1.3, P1.4 and P1.5: C. u2: D. u2: A. u2: b, thereby realizing the automatic adjustment of the amplification factor of the second-stage voltage amplifying circuit, wherein the basis of the automatic adjustment of the amplification factor is that the output voltage is larger than the reference voltage U REF 。
The voltage comparison circuit is used as the basis of the amplification factor regulating circuit and consists of a voltage detection rectifying and filtering circuit, a voltage detection comparison circuit and an inverter. The voltage detection rectifying and filtering circuit consists of a diode D1, capacitors C1 and C2 and a resistor R11, wherein C1 is a filtering energy storage capacitor, and the function of C1 is to smooth the voltage UDC1 rectified and output by the D1; c2 is a high-frequency filter capacitor, and the effect of C2 is to reduce the influence of a high-frequency signal on the working stability of the circuit; the resistor R11 is a release resistor, and the function of the resistor R11 is to quickly release the stored electric quantity on the C1 after one voltage comparison is finished, so that the accuracy of the next voltage comparison and the release time are ensured. The diode D1 rectifies the output signal Uo of U3 by 1N4148, the positive electrode of D1 is connected with the 6 th pin of U3, the negative electrode is connected with one end of a capacitor C1, one end of C1 is connected with the negative electrode of D1, the other end of C1 is connected with the ground, one end of C2 is connected with the negative electrode of D1, the other end of C2 is connected with the ground, one end of R11 is connected with the negative electrode of D1, the other end of R11 is connected with the ground, and tau is connected with the ground 1 =5×R11×C1=5×0.047×10 6 ×1×10 3 ≈0.25×10 -3 S=0.25 mS. The voltage detection comparison circuit is composed of a voltage comparator U9: A. resistors R9, R10, R25. U9: a employs TLC393, U9: pin A8 is connected with +5V; the 4 th pin is grounded; negative electrode of 3 rd pin D1 as U9: and an input end A, wherein an input signal is UDC 1. One end of R10 is connected with +5V, the other end of R10 is connected with R9, the other end of R9 is grounded, and the connection point of R9 and R10 is connected with U9: pin 2 of a. R9 and R10 are divided in series to U9: a provides a reference voltage U REF （U REF =5×r9/(r10+r9) =0.5v), U9: pin a1 connects U10: the 1 st pin of A is the output end of the voltage comparison result, and the output signal is YA 1. R25 is a pull-up resistor and is coupled to U9: pins 1 and 8 of A. Ya1=0 when UDC1 is 0.5V or less, ya1=1 when UDC1 > 0.5V. Inverter U10: pin 1 of a connects U9: output end 1 st pin of A, U10: the 1 st pin of A is connected with the P3.2 port of the singlechip U1, and the inverter U10: the 2 nd pin of A is output, and the output signal is YA 2. U10: the 2 nd pin of A is connected to the P3.2 port of the singlechip U1. And according to the signals of YA2, the singlechip analyzes whether voltage amplification factor adjustment is required. When ya2=1, the adjustment of the magnification is continued until ya2=0, and the adjustment of the magnification is stopped. Inverter U10 is used: a is connected with U1, so that the level of an output signal YA2 meets the requirement of a singlechip on the level of an input signal, and the stability of a circuit is improved.
The VPC conversion circuit consists of an amplifying output rectifying and filtering circuit and a voltage/pulse width conversion circuit. The amplifying output rectifying and filtering circuit consists of a diode D3, capacitors C3 and C4, a resistor R24 and an inductor L1. And C3, C4 and L1 form a pi filter circuit, and the ripple coefficient (ripple voltage is smaller than 5 mV) of the UDC2 is reduced, so that the signal is more stable, and the measurement accuracy is improved. R24 is a release resistor, and the function of R24 is to quickly release the stored electric quantity on C3, L1 and C4 after one capacitance measurement is finished, so that the precision of the next capacitance measurement is ensured. The diode D3 rectifies the output signal Uo of U3 by adopting 1N4148, the positive electrode of D3 is connected with the 6 th pin of U3, the negative electrode is connected with the capacitor C3, one end of C3 is connected with the negative electrode of D3, the other end of C3 is connected with the ground, one end of L1 is connected with the negative electrode of D3, and the other end of L1 is connected with R24; one end of R24 is connected with L1, and the other end of R24 is grounded. The output signal Uo of the U3 is amplified and output to a rectifying and filtering circuit and then is output to be a direct-current voltage UDC2.
The voltage/pulse width conversion circuit is formed by an inverter U6: B. resistors R30, R29, R12, R31, capacitor C5, diode D2, comparator U5: and A is composed of. Inverter U6 is used: the purpose of B is to increase the output current and the load capacity, and the inverter U6: the 3 rd pin of the B is connected with the P1.6 port of the singlechip U1, and the inverter U6: and the 4 th pin of the B is connected with the cathode of the D2. Inverter U6: the function B is to invert the instruction sent by the port P1.6 of the singlechip and output a capacitor C5 charge and discharge control signal YB1. When yb1=1, diode D2 is turned off, charging capacitor C5 through R30; when yb1=0, diode D2 is turned on and C5 discharges through R30, R29, D2. R29, C5, R30 and D2 form a capacitor C5 charging and discharging circuit, D2 can accelerate C5 discharging, shorten discharging time and ensure that the voltage at two ends of C5 is 0 after each discharging; r30 buffers charge-discharge impact, reduces harmonic radiation and interference of the circuit. R30 is connected with U6: the other end of the pin 4 of the B is connected with C5, and the other end of the C5 is grounded; d2 negative electrode is connected with U6: and the 4 th pin of the B is connected with the anode of the R29, and the other end of the R29 is grounded. The connection point of R30 and C5 is connected in parallel with the connection point of D2 and R29 and then connected to U5: pin 3 of A; u5: the voltage at the two ends of the 3 rd pin of A is the voltage UC5 and U5 at the two ends of the capacitor C5: the 2 nd pin of A is connected with R12, and the other end of R12 is connected with one end of R24; u5: the voltage across pin 2 of A is UDC2, U5: the 8 th pin of A is connected with +5V; the 4 th pin is grounded; r31 is a pull-up resistor and is coupled to U5: pins 1 and 8 of A. U5: pin a1 is connected to inverter U6: pin 1 of A; inverter U6: the 2 nd pin of A is connected with the P1.7 port of the singlechip U1, and when P1.6=1, C5 discharges through R29, R30 and D2; when the discharge is finished, uc5=0, and uc5 < UDC2, yb2=0, yb3=1; when p1.6=0 and C5 is charged through R30, p1.7=1, the single chip microcomputer U1 starts the timer, starts timing, as UC5 gradually increases, when UC5 is greater than UDC2, yb2=1 and yb3=0, the single chip microcomputer U1 closes the timer, stops timing, p1.7=0, and stops charging C5. The larger UDC2 is, the longer the capacitor C5 is charged, and the C5 charging time is t w =r30×c5×ln ((5-UCD 2)/5), maximum charge time t wmax = R30×C5=10×10 3 ×0.1×10 -6 =1×10 -3 S=1mS。
Phase comparison circuitThe circuit consists of a circuit for detecting the phase of the exciting power supply Ui, a circuit for detecting the phase of the output signal Uo of the second-stage amplifying circuit, a phase comparison circuit and a shaping circuit. The exciting power Ui phase detection circuit is connected with a voltage comparator U5: B. resistors R33, R32, R34. U5: the 8 th pin of the B is connected with +5V; the 4 th pin and the 6 th pin are grounded; one end of R33 is connected with the pin 2 of U2:A, the other end is connected with R32, the other end of R32 is grounded, and the connection point of R33 and R32 is connected with U5: pin 5 of B; r34 is a pull-up resistor and is coupled to U5: pins 7 and 8 of B. U5: the 7 th pin of B is an output end, the output signal is YC1, the resistors R33 and R32 are connected in series with a voltage dividing circuit to reduce Ui and then compare with zero, when Ui>0, yc1=1, when Ui<0, yc1=0. The second-stage amplifying circuit output signal Uo phase detection circuit is composed of a voltage comparator U11: A. resistors R38 and R39. U11: the 8 th pin of A is connected with +5V; the 2 nd pin and the 4 th pin are grounded; one end of R38 is connected with the 6 th pin of U3, and the other end of R38 is connected with U11: pin 3 of A; r39 is a pull-up resistor and is coupled to U11: pins 1 and 8 of A. U11: the 1 st pin of A is the output end, the output signal is YC2, when Uo>0, yc2=1; when Uo<0, yc2=0. The phase comparison circuit is constituted by an exclusive or gate U12: and A is composed of. U12: pin 1 of a connects U11: pin 1 of A; u12: pin 2 of a connects U5: pin 7 of B, U12: the 3 rd pin of A is an output end, the output signal is YC3, when YC1 is not equal to YC2, YC3=1; yc1=yc2, yc3=0. The shaping circuit is composed of a resistor R35, a capacitor C6 and a Schmitt trigger U13: and A is composed of. R35 and C6 form a filter circuit to eliminate spike wave interference caused by Ui and Uo phase shift. One end of R35 is connected with U12: pin 3 of a, the other end of which is connected with U13: pin 1 of A; u13: the 3 rd pin of A is connected with the P3.3 port of the singlechip U1. P3.3=0 when YC1 and YC2 are inverted, indicating CX>A CN; when Y is C1 And Y C2 P3.3=1 at in-phase, explaining CX<CN。
The capacitance error step indication signal circuit consists of a decoder U7, resistors R15-R22 and light emitting diodes D7-D14. The capacitance error grading indication signal circuit realizes error grading indication, and the gear is set on the PC by a manufacturing enterprise or a user according to own standards. Pin 6 of U7 is connected with +5V; the 4 th pin and the 5 th pin of the U7 are grounded; pins 1, 2 and 3 of the U7 are respectively connected with pins 15, 16 and 17 of the singlechip U1 and serve as input ends of capacitance error gear indication data; pins 15, 14, 13, 12, 11, 10, 9 and 7 of U7 are respectively connected with cathodes D7-D14; anodes of D7-D14 are respectively connected with one ends of R15-R22; the other ends of R15 to R22 are connected with +5V.
The capacitance value data display circuit consists of a liquid crystal display LCD1 and a variable resistor RV1, and realizes the display of the capacitance value of the capacitor CX to be tested. The function of RV1 is to adjust the brightness of display LCD 1. One end of RV1 is connected with +5V, the other end of RV1 is grounded, and the active end of RV1 is connected with the 1 st pin of LCD 1. The 2 nd pin of the LCD1 is connected with +5V; the 3 rd pin is grounded; pins 4, 5 and 6 are respectively connected with ports P0.0, P0.1 and P0.2 of the singlechip U1; pins 7, 8, 9, 10, 11, 12, 13 and 14 of the LCD1 are connected with a P2 port of the singlechip U1 and serve as input ports for measuring capacitance value display data of the capacitor.
And the connection between the singlechip U1 and the PC adopts an RS232 standard interface. The singlechip and PC RS232 interface circuit comprises U14, P1, capacitors C10, C11, C12 and C13, wherein the U14 adopts MAX232 chip, and the P1 adopts 9-pin serial port socket. C10 is connected in parallel with pins 1 and 3 of U14; c11 is connected in parallel with pins 4 and 5 of U14, one end of C12 is connected with pin 2 of U14, and the other end is connected with +5V; one end of C13 is connected with the 6 th pin of U14, and the other end is grounded; the 9 th pin of U14 is connected with the P3.0 port of U1; the 10 th pin of U14 is connected with the P3.1 port of U1; the 7 th pin of U14 is connected with the 2 nd pin of P1; pin 8 of U14 is connected with pin 3 of P1. The PC realizes bidirectional data transmission with the singlechip U1 through P1.
As shown in FIG. 3, "start" is the preparation before measurement, time 50μs±10μs. "excitation Power supply selection" when the capacitance CX to be measured<When 20pF is reached, the excitation power supply Ui1 is turned on; when the measured capacitance CX is more than or equal to 20pF, the excitation power Ui2 is switched on for 10 timesμs±10μs. Delay 1 stabilizes the circuit by delaying, effectively excites the tested capacitor CX and the standard capacitor CN, and keeps the output voltage Uo unchanged for 2000 hoursμs±10μs. The voltage amplification factor is automatically adjusted to ensure that the output voltage Uo keeps a proper value, which is favorable for digitizing Uo analog signals to improve the measurement accuracy, and the time is 2000μs±10μs. "delay 2" provides for capacitance measurement for a time of 10μs±10μs. The phase detection judges the magnitude relation between the measured capacitor CX and the standard capacitor CN. When the voltages of Ui and Uo are inverted, CX is explained>A CN; when the voltages of Ui and Uo are in phase, CX is explained<CN, time of 10μs±10μs. "Voltage detection" converts the voltage signal into a pulse width signal, reads the pulse width to calculate the output voltage U o Is of size of 2000 aμs±10μs. The data transmission and processing outputs the measured data (phase, amplification factor and pulse width) to a PC, the PC calculates the capacitance value of the capacitor and the error gear of the capacitor according to the output voltage Uo1=KDeltaC, the PC transmits the calculated result (the capacitance value and the error grade of the capacitor CX to be measured) to a singlechip, and the singlechip outputs a signal to enable an indicator lamp corresponding to the error of the capacitor to be detected to be lightened, and the capacitance value of the capacitor CX to be measured is displayed on a display screen for 100 hoursμs±10μs. The "end" delay prepares for the next measurement, 100μs±10μs. The time of the whole period is t=50+10+2000+2000+10+10+2000+100+100=7000μs. The theoretical measurement speed can reach 7 milliseconds/grain, the actual measurement speed is 100 grains/second, and the capacitance resolution reaches 0.01 percent.
Claims (6)
1. A low-capacity capacitor high-speed detection circuit is characterized in that: the system comprises a singlechip and a PC (personal computer) which is connected with the singlechip in a bidirectional way to realize data bidirectional transmission; the single chip microcomputer circuit comprises an excitation power supply, a transformer bridge detection circuit, a two-stage amplification circuit, an amplification factor adjustment circuit, a voltage detection rectification filter circuit, an amplification output rectification filter circuit, a voltage detection comparison circuit, a VPC conversion circuit, a phase comparison circuit, a capacitance error step indication signal circuit, a capacitance value data display circuit and a PC RS232 interface circuit;
the singlechip is correspondingly connected with an excitation power supply Ui1 and an excitation power supply Ui2 of the singlechip through electronic switches K1 and K2; the excitation power supply Ui1 adopts a 12V alternating current power supply of 1MHz to form an alternating current signal source Ui1; the exciting power supply Ui2 adopts a 12V alternating current power supply of 500KHz to form an alternating current signal source Ui2; ui1 is connected with a P1.0 port of the singlechip after passing through the electronic switch K1, ui2 is connected with a P1.1 port of the singlechip after passing through the electronic switch K2, and Ui1 and Ui2 are connected as output signals, wherein the output signals are Ui; when p1.0=1, ui=ui1; when p1.1=1, ui=ui2; p1.0 and P1.1 are forbidden to be 1 at the same time under the control of a singlechip U1;
the exciting power supply Ui1, ui2 output signal Ui is connected with the measured capacitor CX, the standard capacitor CN, produces an exciting current on the measured capacitor CX and the standard capacitor CN, adds to the transformer bridge detection circuit, and the transformer bridge detection circuit comprises resistance R1, R2, measured capacitor CX, standard capacitor CN and three winding transformer TR1, and the transformation ratio of transformer is 1:1:1, connecting R1 and R2 in series in a transformer bridge;
generating an output voltage Uo1 at the output end of the transformer bridge detection circuit, wherein the Uo1 is connected to the amplifying circuit, and outputting a signal Uo through the amplifying circuit; the amplifying circuit consists of two stages of amplifying circuits and an amplifying multiple adjusting circuit, the first stage of amplifying circuit is an in-phase proportional operation amplifying circuit,
the second-stage amplifying circuit consists of an operational amplifier and a plurality of resistors, and the resistors are connected with the singlechip after passing through an electronic switch;
the singlechip is connected with the amplifying circuit through the amplifying factor adjusting circuit; the amplification factor regulating circuit consists of a voltage detection rectifying and filtering circuit, a voltage detection comparing circuit and an inverter, wherein the voltage detection rectifying and filtering circuit consists of a diode D1, capacitors C1 and C2 and a resistor R11; c1 is a filtering energy storage capacitor, C2 is a high-frequency filtering capacitor, and R11 is a release resistor;
the signal Uo and the signal Ui are connected with the singlechip through an output signal YC of the phase detection circuit, the phase detection circuit carries out phase detection on the signal Ui and the signal Uo, and the size relation between the tested capacitor CX and the standard capacitor CN is judged;
when cx=cn, the voltage uo1=0; when cx+.cn, uo1=kΔc; k is a proportionality coefficient, is influenced by the distributed capacitance and the contact resistance of the circuit, and is a constant when the circuit is determined; the value of K can be automatically obtained by measuring the standard capacitance before use; Δc is the error between the measured capacitance CX and the standard capacitance CN;
the output voltage Uo and the reference voltage U REF Through voltageThe output signal YA of the comparison circuit is connected with the singlechip, and the voltage comparison circuit outputs the voltage Uo and the reference voltage U REF Performing voltage comparison, wherein the obtained result is used as a basis of an amplification factor regulating circuit;
the signal Uo is an analog signal and is connected with the singlechip through the VPC conversion circuit to convert the analog signal Uo into a digital signal YB; the singlechip transmits the measurement data to the PC, and the PC calculates the capacitance value and the error grading signal of the capacitor CX to be measured;
the capacitive error step indication signal circuit and the capacitive value data display circuit are connected with the output signal of the singlechip.
2. The low capacitance high speed sensing circuit of claim 1, wherein: the singlechip selects an excitation power supply Ui1 and an excitation power supply Ui2 through electronic switches K1 and K2; when the measured capacitance CX is smaller than 20pF, the exciting power supply Ui1 is switched on; when the measured capacitance CX is more than or equal to 20pF, the excitation power supply Ui2 is connected.
3. The low capacitance high speed sensing circuit of claim 1, wherein: the exciting power supply Ui1 is a 12V sinusoidal alternating current power supply of 1MHz, and the exciting power supply Ui2 is a 12V sinusoidal alternating current power supply of 500 KHz; when the excitation power supply is larger than or equal to 10 signal periods, the capacitance detection circuit enters a stable state, and the capacitance value of the capacitor CX to be detected can be effectively measured.
4. The low capacitance high speed sensing circuit of claim 1, wherein: the phase detection circuit carries out phase detection on the signal Ui and the signal Uo and judges the magnitude relation between the tested capacitor CX and the standard capacitor CN; when yc=0, then the two voltages Ui and Uo are inverted, CX > CN; when yc=1, then the two voltages Ui and Uo are in phase, CX < CN.
5. The low capacitance high speed sensing circuit of claim 1, wherein: the voltage comparison circuit compares the voltage Uo with the reference voltage U REF Performing electric powerVoltage comparison, when voltage Uo<U REF YA=0 is input into a singlechip, and the singlechip outputs a control signal to an amplification factor regulating circuit to regulate the amplification factor of the amplification circuit; under the condition of ensuring that the signal Uo is not distorted, outputting a larger voltage signal to ensure that the signal Uo reaches a larger value, and ensuring that the measurement accuracy of the small capacitor can reach 0.01%; when outputting the voltage Uo>U REF Ya=1 is input to the singlechip, and the signal Uo meets the design requirement.
6. The low capacitance high speed sensing circuit of claim 1, wherein: the pulse width of the digital signal YB is proportional to the magnitude of the analog signal Uo.
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