CN108828322A - A kind of low capacity capacitor high-speed detection circuit - Google Patents
A kind of low capacity capacitor high-speed detection circuit Download PDFInfo
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- CN108828322A CN108828322A CN201810436581.1A CN201810436581A CN108828322A CN 108828322 A CN108828322 A CN 108828322A CN 201810436581 A CN201810436581 A CN 201810436581A CN 108828322 A CN108828322 A CN 108828322A
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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
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Abstract
A kind of low capacity capacitor high-speed detection circuit, including single-chip microcontroller, the PC machine being bi-directionally connected with single-chip microcontroller, pass through electronic switch K1, K2 excitation power supply Ui1 and excitation power supply Ui2 for connecting corresponding to single-chip microcontroller, excitation power supply output signal U i is connect with measured capacitance CX, standard capacitance CN, an exciting current is generated on measured capacitance CX and standard capacitance CN, it is added to transformer bridges detection circuit, and output voltage Uo1 is generated in its output end, Uo1 is connected in amplifying circuit, passes through amplifying circuit output signal Uo；Amplifying circuit and amplification factor adjust circuit connection, and amplification factor adjusts circuit and connect with single-chip microcontroller；Uo and Ui is connect by phase detecting circuit with single-chip microcontroller, Uo and UREFIt is connect by voltage comparator circuit with single-chip microcontroller；Uo is connect by VPC conversion circuit with single-chip microcontroller；The error stepping indication signal circuit and capacitance value data display circuit being connect with single-chip microcontroller output signal.Measuring speed of the present invention is up to 100/second, and the stability of measurement is more preferable, precision is higher.
Description
Technical field
The present invention relates to capacitive detection circuits, and in particular to using the electricity of transformer bridges balancing circuitry measurement small capacitances
Road.
Background technique
Currently, low value capacitor is more and more praised highly by electronics industry, demand is also increasing.Enterprise is
It further reduces the cost, requirements at the higher level is proposed to the detection of capacitor, the present common capacitance detecting instrument of domestic enterprise has HP-
4278A, LCR101 and CDF-X.But these measuring device measuring speeds are slower, cannot all be recorded to the data of measurement,
Statistics and analysis.Therefore, scientific and technical personnel and user are improved and have been transformed to existing capacitance measuring instrument.
Existing patent《Capacitance detecting device》The patent No.：CN102590635A, which can be than adjustment
Offset is adjusted with the minimum value higher precision of capacity cell.《Capacitance determining method》The patent No.：CN102375628A, the invention
Capacitance determining method, capacitor and impedance in noise suppression effect and lifting process can reach using the method for capacitor charge and discharge
Change the purpose of tolerance.《Capacitive detection circuit》The patent No.：CN103487662A, the capacitance determining method of the invention is using electricity
Volume parallel circuit will not cause the decline of signal-to-noise ratio in the detection process in the case where not reducing detection voltage conditions.
All there are some problems in above measuring instrument and patent solution.First, the speed of measurement is slower, Bu Nengman
The requirement of sufficient manufacturing enterprise.Second, measurement range is wider, and the cost performance of instrument is low.The data of third, measurement cannot be total with user
It enjoys, it is controversial that the measurement standard between enterprise and user is easy to produce error.4th, most of instrumentation and testing methods are all adopted
It is more demanding to signal source with the method for balanced bridge, and environmental parameter is required also very high.When temperature, humidity variation compared with
When big, measurement accuracy can decline an order of magnitude.
Summary of the invention
The invention proposes a kind of low capacity capacitor high-speed detection circuits, using transformer principle of balance bridge to small capacitances
It measures.By generating an exciting current, the size of exciting current in primary winding compared with standard capacitance
Error between measurement capacitor and standard capacitance is directlyed proportional.Two-way biography of the PC machine as host computer, with chip microcontroller data
It is defeated, the process of low capacitance measurement is controlled, error compensation, analysis and management are carried out to the data of measurement, pass through internet
With user sharing measurement data.
The invention is realized by the following technical scheme：
A kind of low capacity capacitor high-speed detection circuit, including single-chip microcontroller are bi-directionally connected with single-chip microcontroller and realize data double-way transmission
PC machine；PC machine controls the process of low capacitance measurement, carries out error compensation, analysis and management to the data of measurement, passes through
Internet and user sharing measurement data.
Single-chip microcontroller accordingly connects excitation power supply Ui1 and excitation power supply Ui2 by electronic switch K1 and K2, to excitation power supply
Ui1 and excitation power supply Ui2 are selected；As measured capacitance CX<When 20pF, excitation power supply Ui1 is connected；When measured capacitance CX >=
When 20pF, excitation power supply Ui2 is connected.
Excitation power supply Ui1, Ui2 output signal U i is connect with measured capacitance CX, standard capacitance CN, in measured capacitance CX and mark
An exciting current is generated on pseudo-capacitance CN, transformer bridges detection circuit is added to, in the output of transformer bridges detection circuit
End generates an output voltage Uo1, when CX=CN, Uo1=0；As CX ≠ CN, Uo1=K △ C, K are proportionality coefficient, are divided by circuit
Cloth capacitor and contact resistance influence, and when circuit determines, K is constant；It can be automatic by the measurement to standard capacitance before use
Obtain K value.
Uo1 is connected in amplifying circuit, passes through amplifying circuit output signal Uo；Amplifying circuit connects amplification factor and adjusts electricity
Road, amplification factor adjust circuit and connect with single-chip microcontroller.Amplification factor, which is controlled, by single-chip microcontroller adjusts circuit automatic adjustment times magnification
Number guarantees to make signal Uo reach bigger numerical in the distortionless situation of signal Uo, guarantee that the measuring accuracy of small capacitances can reach
To 0.01%；Improve measuring accuracy.
The signal Uo and signal Ui is connect by the output signal YC of phase detecting circuit with single-chip microcontroller, phase-detection
Circuit carries out phase-detection to signal Ui and signal Uo, judges the size relation of measured capacitance CX Yu standard capacitance CN；When YC=0
When, then two voltage inversions of Ui and Uo, CX>CN；As YC=1, then two arc in phase of Ui and Uo, CX<CN.
The output voltage Uo and reference voltage UREF Connected by the output signal YA and single-chip microcontroller of voltage comparator circuit
It connects, voltage comparator circuit is to output voltage Uo and reference voltage UREFVoltage comparison is carried out, as output voltage Uo<UREF, YA=0 is defeated
Enter single-chip microcontroller, single-chip microcontroller outputs a control signal to amplification factor and adjusts circuit, adjusts the amplification factor that amplification factor adjusts circuit；
As output voltage Uo>UREF, YA=1 is input to single-chip microcontroller, then output signal U o meets design requirement.
The output signal U o is analog signal, is connect by VPC conversion circuit with single-chip microcontroller, and analog signal Uo is turned
It is changed to digital signal YB；Single-chip microcontroller gives PC machine data transfer, and the capacitance and mistake of measured capacitance device CX are calculated by PC machine
Difference shelves signal.The pulse width of digital signal YB is directly proportional to the size of analog signal Uo.Believed by single-chip microcontroller recording impulse
Number width, so as to calculate the size of output voltage Uo, while calculating according to the size of Uo the electricity of measured capacitance CX
Capacitance.
The capacitance error stepping indication signal circuit is connect with single-chip microcontroller output signal, capacitance error stepping instruction letter
Eight grades of instructions of number circuit point, with eight LED diode displayings.
The capacitance value data display circuit is connect with single-chip microcontroller output signal, the capacitance value data display circuit
Using LED display, the capacitance of measured capacitance CX is shown.
Further, the excitation power supply Ui1 is the 12V sine ac power supply of 1MHz, and excitation power supply Ui2 is 500KHz
12V sine ac power supply.
Further, when the excitation power supply is more than or equal to 10 signal periods, capacitive detection circuit enters stable shape
State can effectively measure the capacitance of measured capacitance device CX.
（Three）Beneficial effect
A kind of low capacity capacitor high-speed detection circuit proposed by the present invention has below beneficial to effect compared with prior art
Fruit：
（1）Using transformer balanced bridge detection circuit, small capacitances are measured using transformer principle of balance bridge.Pass through
Measured capacitance generates an exciting current, excitation electricity compared with standard capacitance in two secondary windings of three-winding transformer
Error delta C between the size of stream and measurement capacitor CX and standard capacitance CN is directly proportional；Eliminate environmental parameter and distribution parameter
Influence.The stability of measurement is more preferable, precision is higher.
（2）The amplification factor of amplifying circuit is controlled by single-chip microcontroller and realizes automatic adjustment, guarantees that output voltage is distortionless
In the case of reach bigger numerical to improve measurement accuracy.
（3）Using PC machine as host computer, controlled by process of the PC machine to low capacitance measurement, to the data of measurement
Error compensation, analysis and management are carried out, internet and user sharing measurement data are passed through.
（4）Measurement range is reduced, actual measurement range is 0.1pF-200pF；Make measurement accuracy more accurate,
Accelerate measuring speed；Measurement accuracy 0.01%, measuring speed are 100/second.
Detailed description of the invention
Fig. 1 is detection circuit functional block diagram of the invention.
Fig. 2 is circuit diagram of the invention.
Fig. 3 is work flow diagram of the invention.
Label and components mark in attached drawing：1- single chip circuit, 2- excitation power supply, 3- transformer bridges detection electricity
Road, 4- two-stage amplifying circuit, 5- amplification factor adjust circuit, 6- voltage comparator circuit, 7-VPC conversion circuit, 8- phase bit comparison
Circuit, 9- capacitance error stepping indication signal circuit, 10- capacitance value data display circuit, 11- Singlechip clock circuit, 12- are mono-
Piece machine power-on reset circuitry, 13- single-chip microcontroller and PC machine RS232 interface circuit form.
Specific embodiment
Following will be combined with the drawings in the embodiments of the present invention, and technical solution in the embodiment of the present invention carries out clear, complete
Site preparation description.Described embodiments are only a part of the embodiments of the present invention, instead of all the embodiments.This is not being departed from
Under the premise of invention design concept, all variations and modifications that ordinary people in the field makes technical solution of the present invention,
Protection scope of the present invention should be dropped into.
Embodiment：
As shown in Figure 1：A kind of low capacity capacitor high-speed detection circuit, including single-chip microcontroller are bi-directionally connected realization data with single-chip microcontroller
The PC machine of transmitted in both directions；PC machine controls the process of low capacitance measurement, to the data of measurement carry out error compensation, analysis and
Management, passes through internet and user sharing measurement data.
Single-chip microcontroller accordingly connects excitation power supply Ui1 and excitation power supply Ui2 by electronic switch K1 and K2, to excitation power supply
Ui1 and excitation power supply Ui2 are selected；As measured capacitance CX<When 20pF, excitation power supply Ui1 is connected；When measured capacitance CX >=
When 20pF, excitation power supply Ui2 is connected.
The excitation power supply Ui1 is the 12V sine ac power supply of 1MHz, and the 12V that excitation power supply Ui2 is 500KHz is sinusoidal
AC power source.When excitation power supply is more than or equal to 10 signal periods, capacitive detection circuit enters stable state, can effectively measure
The capacitance of measured capacitance device CX.
Excitation power supply output signal U i is connect with measured capacitance CX, standard capacitance CN, in measured capacitance CX and standard capacitance
An exciting current is generated on CN, is added to transformer bridges detection circuit, is generated in the output end of transformer bridges detection circuit
One output voltage Uo1, when CX=CN, Uo1=0；As CX ≠ CN, Uo1=K △ C, K are proportionality coefficient, by the distribution capacity of circuit
It is influenced with contact resistance, when circuit determines, K is constant；K can be automatically obtained by the measurement to standard capacitance before use
Value.
Uo1 is connected in amplifying circuit, passes through amplifying circuit output signal Uo；Amplifying circuit connects amplification factor and adjusts electricity
Road, amplification factor adjust circuit and connect with single-chip microcontroller.Amplification factor, which is controlled, by single-chip microcontroller adjusts circuit automatic adjustment times magnification
Number guarantees to make Uo reach bigger numerical in the distortionless situation of Uo, guarantee that the measuring accuracy of small capacitances can reach 0.01%；
Improve measuring accuracy.
The signal Uo and signal Ui is connect by the output signal YC of phase detecting circuit with single-chip microcontroller, phase-detection
Circuit carries out phase-detection to signal Ui and signal Uo, judges the size relation of measured capacitance CX Yu standard capacitance CN；When YC=0
When, then two voltage inversions of Ui and Uo, CX>CN；As YC=1, then two arc in phase of Ui and Uo, CX<CN.
The output voltage Uo and reference voltage UREF Connected by the output signal YA and single-chip microcontroller of voltage comparator circuit
It connects, voltage comparator circuit is to output voltage Uo and reference voltage UREFVoltage comparison is carried out, as output voltage Uo<UREF, YA=0 is defeated
Enter single-chip microcontroller, single-chip microcontroller outputs a control signal to amplification factor and adjusts circuit, adjusts the amplification factor that amplification factor adjusts circuit；
As output voltage Uo>UREF, YA=1 is input to single-chip microcontroller, then output signal U o meets design requirement.
The signal Uo is analog signal, is connect by VPC conversion circuit with single-chip microcontroller, analog signal Uo is converted to
Digital signal YB；Single-chip microcontroller gives PC machine data transfer, and the capacitance and error point of measured capacitance device CX are calculated by PC machine
Shelves signal.The pulse width of digital signal YB is directly proportional to the size of analog signal Uo.Pass through single-chip microcontroller recording pulse signal
Width so as to calculate the size of output voltage Uo, while calculating according to the size of Uo the capacitance of measured capacitance CX.
The capacitance error stepping indication signal circuit is connect with single-chip microcontroller output signal, capacitance error stepping instruction letter
Eight grades of instructions of number circuit point, with eight LED diode displayings.
The capacitance value data display circuit is connect with single-chip microcontroller output signal, the capacitance value data display circuit
Using LED display, the capacitance of measured capacitance CX is shown.
As shown in Fig. 2, a kind of low capacity capacitor high-speed detection circuit includes single chip circuit, further include in single chip circuit
Singlechip clock circuit and single-chip microcontroller power-on reset circuitry, excitation power supply, transformer bridges detection circuit, two-stage amplifying circuit,
Amplification factor adjusting circuit, voltage detecting current rectifying and wave filtering circuit, amplification output rectifier and filter, voltage detecting comparison circuit,
VPC conversion circuit, phase-comparison circuit, capacitance error stepping indication signal circuit, capacitance value data display circuit, single-chip microcontroller with
PC machine RS232 interface circuit composition.
U1 is single-chip microcontroller, using AT89C52.The 32nd~39 pin of the port P0 of U1 respectively with the 9th of pull-up resistor RP1~
The connection of 2 pins, the 1st pin of RP1 are connect with+5V.
Singlechip clock electricity routing capacitance C7, capacitor C8 and crystal oscillator X1 composition, wherein the one end C7 is grounded, and C7 is another
Terminate at the 19th pin of U1；The one end C8 ground connection, another the 18th pin for terminating at U1 of C8；X1 is connected in parallel on the 18th of U1 the, 19 and draws
On foot.The frequency of crystal oscillator X1 is selected as 11.0592MHz.
Single-chip microcontroller power-on reset circuitry is made of resistance R23 and capacitor C9, realizes the power-on reset function of single-chip microcontroller.Wherein
C9 anode meets+5V, and cathode is connect with R23, the other end ground connection of R23.The tie point of R23 and C9 and the 9th pin of U1 connect.
Excitation power supply is by alternating message source Ui1（The 12V AC power source of 1MHz）, alternating message source Ui2（The 12V of 500KHz
AC power source）, electronic switch U2：A and U2：B composition.The one end Ui1 ground connection, another termination U2 of Ui1：The 1st pin of A, U2：A's
13rd pin connects the port P1.0 of U1.The one end Ui2 ground connection, another termination U2 of Ui2：The 11st pin of B, U2：12 feet of B connect U1's
The port P1.1.The 2nd pin of Ui1 is connected with the 10th pin of Ui2, as output, output signal Ui.As P1.0=1, Ui=
Ui1；As P1.1=1, Ui=Ui2.It is controlled by single-chip microcontroller U1, forbids P1.0 and P1.1 while being 1, prevent Ui1 and Ui2 short
Road.
Transformer bridges detection circuit is by resistance R1, R2, measured capacitance CX, standard capacitance CN and three-winding transformer TR1
Composition, the no-load voltage ratio of transformer are 1：1：1.Wherein concatenated R1 and R2 in transformer bridges, function are eliminated in measuring circuit
The resistance of the generations such as contact resistance, conductor resistance is to improve measurement accuracy.The one end R1 and U2：The 2nd pin of A connects, and R1's is another
One end is connected with CN, the one end R2 and U2：The 2nd pin of A connects, and the other end of R2 is connected with CX.CN mono- terminates R1, and CN is another
Hold the 5th pin of TR1.CX mono- terminates R2,1 pin of CX other end TR1.The 1st pin of TR1 and the 5th pin are different name end.When
When CX=CN, transformer bridges balance, Uo1 0.As CX ≠ CN, Uo1=K △ C, K are proportionality coefficient, by the distribution electricity of circuit
Hold and contact resistance influences.When circuit determines, K is constant.K can be automatically obtained by the measurement to standard capacitance before use
Value.The pin of the 2nd, 4 and 8 of TR1 is grounded.The the 7th and the 1st pin of TR1 is Same Name of Ends, the 7th pin output voltage Uo1 of TR1
The in-phase end of first order voltage amplifier circuit is added to by R26.
Amplifying circuit adjusts circuit by two-stage amplifying circuit and amplification factor and forms.First order amplifying circuit is in-phase proportion
Operational amplification circuit, input resistance is big, reduces the influence to balanced bridge pumping signal.First order amplifying circuit is put by operation
Big device U8, resistance R26, R27 and R28 are constituted.U8 uses AD711AP, and the 3rd pin of U8 meets R26, and the of another termination TR1 of R26
7 pins, the 7th pin of input signal Uo1, U8 meet+5V, and the 4th pin of U8 meets -5V, and using dual power supply, the 2nd pin of U8 is connect
The other end of R27, R27 are grounded；Feedback resistance R28 is connected between U8 the 2nd, 6 pins, and the 6th pin of U8 is output end, output electricity
Pressure is Uo2, is added to second level amplifying circuit by R3.Second level amplifying circuit by operational amplifier U3 and resistance R3, R4, R5,
R6, R7, R8 are constituted, and U3 uses AD711AP, and the 3rd pin of U3 meets R3, another the 6th pin of termination U8 of R3, input signal Uo2,
The 7th pin of U3 meets+5V, and the 4th pin of U3 meets -5V, and using dual power supply, the 2nd pin of U3 connects R4, the other end ground connection of R4；Instead
Feed resistance one end R5, R6, R7, R8 is connect jointly in the 6th pin of U3, and the 6th pin of U3 is output end, output voltage Uo, R5,
R6, R7, R8 other end meet electronic switch U2 respectively：C,U2：D,U2：A,U2：B the 4th, 8,1,11 pins, pass through electronic switch
It is connected to the 2nd pin of U3；Electronic switch U2：C,U2：D,U2：A,U2：B the 5th, 6,13,12 pins meet single-chip microcontroller U1 respectively
The port P1.2, P1.3, P1.4, P1.5；Electronic switch U2：C,U2：D,U2：A,U2：B the 3rd, 9,2,10 pins connect one
It rises, is connected to the 6th pin of U3 jointly.Single-chip microcontroller issues instruction control electronic switch U2 by P1.2, P1.3, P1.4, P1.5：C,
U2：D,U2：A,U2：B, thus realize the automatic adjustment to second level tension discharge road amplification factor, amplification factor automatic adjustment
Foundation be exactly that output voltage is greater than reference voltage UREF。
Voltage comparator circuit adjusts the foundation of circuit as amplification factor, is examined by voltage detecting current rectifying and wave filtering circuit, voltage
Survey comparison circuit, phase inverter composition.Voltage detecting current rectifying and wave filtering circuit is made of diode D1, capacitor C1, C2 and resistance R11,
C1 is filtering storage capacitor, and C1 effect is exactly to keep the voltage UDC1 of D1 rectification output smooth；C2 is high-frequency filter capacitor, the work of C2
With being exactly the influence for reducing high-frequency signal to circuit job stability；Resistance R11 is release resistance, and the function of R11 is exactly one
It after secondary voltage compares, is quickly releasing on C1 and stores electricity, guarantee the accuracy that voltage compares next time, release time.
Diode D1 uses 1N4148, rectifies to the output signal U o of U3, and D1 anode connects the 6th pin of U3, and cathode meets capacitor C1
One end, C1 mono- terminate the cathode of D1, C1 other end ground connection, and C2 mono- terminates the cathode of D1, C2 other end ground connection, and R11 mono- terminates D1
Cathode, the R11 other end ground connection, τ1=5×R11×C1=5×0.047×106×1×103≈0.25×10-3S=0.25mS.Electricity
Pressure detection comparison circuit is by voltage comparator U9：A, resistance R9, R10, R25 is formed.U9：A uses TLC393, U9：The 8th pin of A
Meet+5V；4th pin ground connection；The cathode of 3rd pin D1, as U9：A input terminal, input signal UDC1.A termination of R10+
Another termination R9 of 5V, R10, R9 other end ground connection, R9, R10 tie point connect in U9：The 2nd pin of A.R9 and R10 series connection partial pressure
To U9：A provides a reference voltage UREF（UREF=5×R9/（R10+R9）=0.5V）, U9：The 1st pin of A meets U10：Draw the 1st of A
Foot is the output end of voltage comparison result, output signal YA1.R25 is pull-up resistor, and is connected in U9：A the 1st, 8 pins
On.As UDC1≤0.5V, YA1=0, as UDC1 0. 5 V of >, YA1=1.Phase inverter U10：The 1st pin of A meets U9：A's is defeated
The 1st pin of outlet, U10：The 1st pin of A meets the port P3.2 of single-chip microcontroller U1, phase inverter U10：The 2nd pin of A is output, defeated
Signal is YA2 out.U10：The 2nd pin of A is connected to the port P3.2 of single-chip microcontroller U1.According to the signal of YA2, single-chip microcontroller is analysed whether
Carry out voltage amplification factor adjusting.When YA2=1, continue that amplification factor is adjusted, until YA2=0, stop to times magnification
Number is adjusted.Using phase inverter U10：A is connected with U1, ensure that the level of output signal YA2 meets single-chip microcontroller to input signal
The requirement of level improves circuit stability.
VPC conversion circuit is made of amplification output rectifier and filter, voltage/pulse-width conversion circuit.Amplification output rectification
Filter circuit is made of two pole D3, capacitor C3, C4, resistance R24 and inductance L1.C3, C4 and L1 form a л type filter circuit,
Reduce the ripple factor of UDC2（Ripple voltage is less than 5mV）Keep signal more stable, to improve the precision of measurement.R24 is release
Resistance, the function of R24 are exactly the storage electricity being quickly releasing on C3, L1, C4, under guarantee after a capacitance measurement
The precision of capacitance measurement.For diode D3 using 1N4148, rectify to the output signal U o of U3, D3 anode connects the of U3
6 pins, cathode meet capacitor C3, and C3 mono- terminates D3 cathode, C3 other end ground connection, and L1 mono- terminates D3 cathode, another termination R24 of L1；
R24 mono- terminates L1, R24 other end ground connection.The output signal U o of U3 is exported after amplifying output rectifier and filter as direct current
Voltage UDC2.
Voltage/pulse-width conversion circuit is by phase inverter U6：B, resistance R30, R29, R12, R31, capacitor C5, diode D2, ratio
Compared with device U5：A composition.Using phase inverter U6：The purpose of B is to increase output electric current, improves carrying load ability, phase inverter U6：B the 3rd draws
Foot meets the port P1.6 of single-chip microcontroller U1, phase inverter U6：The 4th pin of B connects the cathode of D2.Phase inverter U6：B effect is by single-chip microcontroller
The instruction reverse phase that the port P1.6 issues, exports a capacitor C5 charge and discharge control signal YB1.As YB1=1, diode D2 is cut
Only, it is charged by R30 to capacitor C5；As YB1=0, diode D2 conducting, C5 is discharged by R30, R29, D2. R29,C5,
R30, D2 constitute capacitor C5 charge-discharge circuit, and D2 can accelerate C5 to discharge, and shorten discharge time, it is ensured that electric discharge terminates C5 every time
The voltage at both ends is 0；R30 buffers charge and discharge surge, reduces the harmonic radiation and interference of circuit.R30 mono- terminates U6：Draw the 4th of B
Foot, the other end ground connection of R30 another termination C5, C5；D2 cathode meets U6：The 4th pin of B, anode connect R29, another termination of R29
Ground.The tie point of R30 and C5 is in parallel with the tie point of D2 and R29 to be followed by U5：The 3rd pin of A；U5：The 3rd pin both ends of A
Voltage is exactly capacitor C5 both end voltage UC5, U5：The 2nd pin of A connects R12, one end of another termination R24 of R12；U5：Draw the 2nd of A
Foot both end voltage is exactly UDC2, U5：The 8th pin of A meets+5V；4th pin ground connection；R31 is pull-up resistor, and is connected in U5：A
The 1st, on 8 pins.U5：The 1st pin of A meets phase inverter U6：The 1st pin of A；Phase inverter U6：The 2nd pin of A connects in single-chip microcontroller
The port P1.7 of U1, when P1.6=1, C5 are discharged by R29, R30 and D2；At the end of electric discharge, UC5=0, and UC5 < UDC2,
YB2=0,YB3=1；As P1.6=0, C5 is charged by R30, P1.7=1, single-chip microcontroller U1 Open Timer device, starts timing, with UC5 by
Edge up it is high, when UC5 is greater than UDC2, YB2=1, YB3=0, single-chip microcontroller U1 closes timer, stops timing, and P1.7=0 stops to C5
Charging.UDC2 is bigger, the capacitor C5 charging time is longer, and the C5 charging time is tw=R30 × C5 × ln ((5-UCD2)/5), most
Big charging time twmax= R30×C5=10×103×0.1×10-6=1×10-3S=1mS。
Phase-comparison circuit is by excitation power supply Ui phase detecting circuit, second level amplifying circuit output signal Uo phase-detection
Circuit, phase-comparison circuit and shaping circuit composition.Excitation power supply Ui phase detecting circuit is by voltage comparator U5：B, resistance
R33, R32, R34 composition.U5：The 8th pin of B meets+5V；4th, 6 pins are grounded；R33 mono- terminates U2:The 2nd pin of A, it is another
End is connect with R32, and the other end ground connection of R32 connects the tie point of R33 and R32 in U5：The 5th pin of B；R34 is pull-up resistor
And it is connected in U5：B the 7th, 8 pins.U5：The 7th pin of B is output end, output signal YC1, resistance R33 and R32 series connection
Bleeder circuit Ui is reduced after with zero balancing, work as Ui>0, YC1=1, work as Ui<0, YC1=0.Second level amplifying circuit output signal Uo
Phase detecting circuit is by voltage comparator U11：A, resistance R38, R39 is formed.U11：The 8th pin of A meets+5V；2nd, 4 pins connect
Ground；R38 mono- terminates the 6th pin of U3, another termination U11 of R38：The 3rd pin of A；R39 is pull-up resistor and is connected in U11：A
The 1st, 8 pins.U11：The 1st pin of A is output end, and output signal YC2 works as Uo>0, YC2=1；Work as Uo<0, YC2=0.Phase
Bit comparison circuit is by XOR gate U12：A composition.U12：The 1st pin of A meets U11：The 1st pin of A；U12：The 2nd pin of A connects
U5：The 7th pin of B, U12：The 3rd pin of A is output end, output signal YC3, when YC1 ≠ YC2, YC3=1；YC1=YC2,
YC3=0.Shaping circuit is by resistance R35, capacitor C6 and Schmidt trigger U13：A composition.R35, C6 constitute filter circuit, eliminate
Because of spike wave interference caused by Ui and Uo phase shift.A termination U12 of R35：The 3rd pin of A, another termination U13：Draw the 1st of A
Foot；U13：The 3rd pin of A connects the port P3.3 of single-chip microcontroller U1.When YC1 and YC2 reverse phase, P3.3=0 illustrates CX>CN；When
YC1And YC2With P3.3=1 when phase, illustrate CX<CN.
Capacitance error stepping indication signal circuit is by decoder U7, resistance R15~R22 and light emitting diode D7~D14 group
At.Capacitance error stepping indication signal circuit realizes the instruction of error stepping, gear by manufacturing enterprise or user according to oneself
Standard is arranged in PC machine.The 6th pin of U7 meets+5V；U7 the 4th, 5 pins ground connection；The pin of the 1st, 2 and 3 of U7 connects respectively
The pin of the 15th, 16 and 17 of single-chip microcontroller U1, the input terminal as capacitance error gear designation date；U7 the 15th, 14,13,
12,11,10,9,7 pins connect the cathode of D7~D14 respectively；The anode of D7~D14 connects one end of R15~R22 respectively；R15~
Another termination+5V of R22.
Capacitance value data display circuit is made of liquid crystal screen displays LCD1 and variable resistance RV1, realizes measured capacitance device
The display of CX capacitance.The function of RV1 is to adjust the brightness of display lcd 1.Another termination of termination+a 5V, RV1 of RV1
Ground, the 1st pin of the activity termination LCD1 of RV1.The 2nd pin of LCD1 meets+5V；3rd pin ground connection；4th, 5,6 pins difference
It connects in the port P0.0, P0.1 and P0.2 of single-chip microcontroller U1；LCD1 the 7th, 8,9,10,11,12,13,14 pins connect single-chip microcontroller U1's
The port P2 shows the input port of data as measurement capacitor capacitance value.
The connection of single-chip microcontroller U1 and PC machine uses RS232 standard interface.Single-chip microcontroller and PC machine RS232 interface circuit by U14,
P1 and capacitor C10, C11, C12, C13 composition, U14 use MAX232 chip, and P1 uses 9 needle serial port sockets.C10 is connected in parallel on U14
The 1st, 3 pins；C11 is connected in parallel on the 4th of U14 the, 5 pins, and C12 mono- terminates the 2nd pin of U14, another termination+5V；The one end C13
Connect the 6th pin of U14, other end ground connection；The 9th pin of U14 connects in the port P3.0 of U1；The 10th pin of U14 connects U1's
The port P3.1；The 7th pin of U14 connects the 2nd pin of P1；The 8th pin of U14 connects the 3rd pin of P1.PC machine by P1 realize with
The bidirectional data transfers of single-chip microcontroller U1.
As shown in figure 3, " beginning " is the preparation before measurement, time 50μs±10μs." excitation power supply selection " is when tested
Capacitor CX<When 20pF, excitation power supply Ui1 is connected；As measured capacitance CX >=20pF, excitation power supply Ui2, time 10 are connectedμ
s±10μs." delay 1 " makes circuit stability by delay, effectively motivates to measured capacitance CX and standard capacitance CN, output voltage Uo
It remains unchanged, the time 2000μs±10μs." voltage amplification factor automatic adjustment " keeps output voltage Uo holding one suitable
Value, is conducive to Uo analog signal digital, to improve measurement accuracy, time 2000μs±10μs." delay 2 " is capacitance measurement
It prepares, the time 10μs±10μs." phase-detection " judges the size relation of measured capacitance CX Yu standard capacitance CN.As Ui and
Two voltage inversions of Uo, illustrate CX>CN；When two arc in phase of Ui and Uo, illustrate CX<CN, time 10μs±10μs." electricity
Voltage signal is converted into pulse width signal by pressure detection ", reads pulsewidth width to calculate output voltage UoSize, the time is
2000μs±10μs." data transmission and processing " are by the data of measurement（Phase, amplification factor, pulsewidth）It exports to PC machine, PC machine
According to output voltage Uo1=K Δ C, the capacitance of capacitor and the error gear of capacitor are calculated, PC machine is by the result of calculating（Quilt
Survey the capacitance and grade of errors of capacitor CX）It is transferred to single-chip microcontroller, single-chip microcontroller again exports signal, so that detection capacitance error
Corresponding indicator light is bright, and shows the capacitance values of measured capacitance CX, time 100 in display screenμs±10μs." end " prolongs
When for next time measurement prepare, 100μs±10μs.The time of whole cycle is T=50+10+2000+2000+10+10+2000+
100+100=7000μs.Theoretical measuring speed is 100/second up to 7 milliseconds/, actual measurement speed, and capacitive resolution reaches
0.01%。
Claims (7)
1. a kind of low capacity capacitor high-speed detection circuit, it is characterised in that：Including single-chip microcontroller, realization number is bi-directionally connected with single-chip microcontroller
According to the PC machine of transmitted in both directions；And pass through the electronic switch K1 and K2 excitation power supply Ui1 that connects corresponding to single-chip microcontroller and excitation electricity
Source Ui2；
Excitation power supply Ui1, Ui2 output signal U i is connect with measured capacitance CX, standard capacitance CN, in measured capacitance CX and standard electric
Hold and generate an exciting current on CN, be added to transformer bridges detection circuit, is produced in the output end of transformer bridges detection circuit
Raw output voltage Uo1, Uo1 are connected in amplifying circuit, pass through amplifying circuit output signal Uo；
Single-chip microcontroller adjusts circuit by amplification factor and connect with amplifying circuit；
The signal Uo and signal Ui is connect by the output signal YC of phase detecting circuit with single-chip microcontroller, phase detecting circuit
Phase-detection is carried out to signal Ui and signal Uo, judges the size relation of measured capacitance CX Yu standard capacitance CN；
The output voltage Uo and reference voltage UREF It is connect by the output signal YA of voltage comparator circuit with single-chip microcontroller, electricity
Press comparison circuit to output voltage Uo and reference voltage UREFVoltage comparison is carried out, the result obtained adjusts electricity as amplification factor
The foundation on road；
The signal Uo is analog signal, is connect by VPC conversion circuit with single-chip microcontroller, analog signal Uo is converted to number
Signal YB；Single-chip microcontroller gives PC machine data transfer, calculates the capacitance of measured capacitance device CX by PC machine and error stepping is believed
Number；
The capacitance error stepping indication signal circuit and capacitance value data display circuit being connect with single-chip microcontroller output signal.
2. a kind of low capacity capacitor high-speed detection circuit according to claim 1, it is characterised in that：The single-chip microcontroller is logical
Cross electronic switch K1 and K2 selection excitation power supply Ui1 and excitation power supply Ui2；As measured capacitance CX<When 20pF, excitation power supply is connected
Ui1；As measured capacitance CX >=20pF, excitation power supply Ui2 is connected.
3. a kind of low capacity capacitor high-speed detection circuit according to claim 1, it is characterised in that：As CX=CN, voltage
Uo1=0；As CX ≠ CN, Uo1=K △ C；K is proportionality coefficient, is influenced by the distribution capacity and contact resistance of circuit, when circuit is true
Periodically, K is constant；The value of K can be automatically obtained before use by the measurement to standard capacitance.
4. a kind of low capacity capacitor high-speed detection circuit according to claim 1, it is characterised in that：The excitation power supply
Ui1 is the 12V sine ac power supply of 1MHz, and excitation power supply Ui2 is the 12V sine ac power supply of 500KHz；The excitation electricity
When source is more than or equal to 10 signal periods, capacitive detection circuit enters stable state, can effectively measure the electricity of measured capacitance device CX
Capacitance.
5. a kind of low capacity capacitor high-speed detection circuit according to claim 1, it is characterised in that：The phase-detection electricity
Road carries out phase-detection to signal Ui and signal Uo, judges the size relation of measured capacitance CX Yu standard capacitance CN；As YC=0,
Then two voltage inversions of Ui and Uo, CX>CN；As YC=1, then two arc in phase of Ui and Uo, CX<CN.
6. a kind of low capacity capacitor high-speed detection circuit according to claim 1, it is characterised in that：The voltage compares
Circuit is to voltage Uo and reference voltage UREFVoltage comparison is carried out, as voltage Uo<UREF, the input single-chip microcontroller of YA=0, single-chip microcontroller output
It controls signal and adjusts circuit to amplification factor, adjust the amplification factor of amplifying circuit；In the case where guaranteeing the distortionless situation of signal Uo,
Biggish voltage signal is exported, signal Uo is made to reach bigger numerical, guarantees that the measurement accuracy of small capacitances can reach 0.01%；When
Output voltage Uo>UREF, YA=1 is input to single-chip microcontroller, then signal Uo meets design requirement.
7. a kind of low capacity capacitor high-speed detection circuit according to claim 1, it is characterised in that：The digital signal YB
Pulse width it is directly proportional to the size of analog signal Uo.
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