CN102636699A - Capacitance measuring device - Google Patents
Capacitance measuring device Download PDFInfo
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- CN102636699A CN102636699A CN2012100891257A CN201210089125A CN102636699A CN 102636699 A CN102636699 A CN 102636699A CN 2012100891257 A CN2012100891257 A CN 2012100891257A CN 201210089125 A CN201210089125 A CN 201210089125A CN 102636699 A CN102636699 A CN 102636699A
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Abstract
The invention relates to a capacitance measuring device, which comprises a single chip microcomputer controller serving as a core, a charging circuit and a charging detecting circuit, wherein the charging circuit and the charging detecting circuit are used with the single chip microcomputer controller. The capacitance measuring device is characterized in that the single chip microcomputer controller is a single chip microcomputer minimum system consisting of a single chip microcomputer and a peripheral circuit of the single chip microcomputer, a voltage follower, a fixed resistor and a bidirectional electronic switch are sequentially connected to form the charging circuit, a control end of the bidirectional electronic switch is linked with an I/O (input/output) port of the single chip microcomputer, the charging detecting circuit consists of a charging voltage comparator, a non-inverting input end of the charging voltage comparator is connected one end of the electronic switch and one end of a capacitor to be measured, an inverting input end of the charging voltage comparator is connected with a reference voltage source, and an output end of the charging voltage comparator is linked with another I/O port of the single chip microcomputer. The bidirectional electronic switch is controlled by PWM (pulse-width modulation) pulses modulated by the single chip microcomputer to charge the capacitor to be measured, and the capacity of the capacitor to be measured is calculated by the single chip microcomputer according to an RC (resistance-capacitance) charging and discharging zero-state response equation.
Description
Technical field
The present invention relates to the field of measurement of electric variable, be specifically related to a kind of measurement of electric capacity.
Background technology
Capacitance measurement has a wide range of applications in the present engineering field, yet in the plurality of applications occasion, also increasingly high for the requirement of the measuring accuracy of the measurement of unknown capacity electric capacity and electric capacity.Capacitance measurement circuit is studied carefully its principle of work at present, mainly contains LC resonant mode capacitance measurement circuit, bridge type capacitance measurement circuit, RC oscillatory type capacitance measurement circuit, RC charging/discharging type capacitance measurement circuit.
Yet all there is weak point in above-mentioned metering circuit:
The measuring accuracy of LC resonant mode capacitance measurement circuit usually receives following condition influence: the distributed capacitance of wiring place and telefault is crossed conference and is caused error; When resonance frequency was too high, wiring and lead-in wire also can be participated in resonance, cause measuring error; The quality factor of resonant tank are low excessively, cause the loop tuning curve too smooth, are difficult to find out tuning-points, cause measuring error;
Though bridge type capacitance measurement circuit measuring accuracy is higher, operation is complicated, and the frequency of signal source and the structure of electric bridge are bigger to the influence of measuring accuracy;
Though RC oscillatory type capacitance measurement circuit is simple in structure, during actual the use, proofread and correct trouble, and range is limited, when wide region is tested or measured, need the manual switchover range;
RC charging/discharging type capacitance measurement circuit is when measuring low capacity electric capacity; Often precision and range are limited, improve precision or range extension like need, need the resistance of bigger charging and discharging circuit; It is big as far as possible to make that RC discharges and recharges constant, so then needs the manual switchover range.
Summary of the invention
Deficiency in view of prior art; The invention provides a kind of simple in structure; High and the capacitance measuring device that can automatic switching range of measuring accuracy, this install based on the RC charge-discharge principle, regulates through single-chip microcomputer and exports adjustable pwm pulse; Prolong capacitor charging time, change range and reduce the purpose of measuring error thereby reach according to capacitance.
The technical scheme that the present invention addresses the above problem is following:
A kind of capacitance measuring device, it comprises with the singlechip controller is core, is equipped with charging circuit and the capacitance measurement circuit that the charging testing circuit constitutes, it is characterized in that,
Described singlechip controller is the single-chip minimum system that single-chip microcomputer and peripheral circuit thereof constitute;
Described charging circuit is connected to form by voltage follower, fixed value resistance and bidirectional electronic switch successively; Wherein, the control end of described bidirectional electronic switch links with an I/O mouth of said single-chip microcomputer;
Described charging testing circuit is the charging voltage comparer, and the normal phase input end of this charging voltage comparer cross-over connection over the ground has testing capacitance, and inverting input is provided with reference voltage source, and output terminal is connected with an I/O mouth of single-chip microcomputer;
The input end of described voltage follower is connected with an I/O mouth of single-chip microcomputer, and output terminal links to each other with the normal phase input end of bidirectional electronic switch with the charging voltage comparer through said fixed value resistance; Described single-chip microcomputer modulates pwm pulse, and to control described bidirectional electronic switch be testing capacitance charging, calculates the capacity of testing capacitance by single-chip microcomputer by following formula (II),
In the formula (II), C
XThe capacity of expression testing capacitance, d representes the dutycycle of pwm pulse, and T representes the cycle of pwm pulse, and N representes the number of pwm pulse, and R representes the resistance of said resistance, U
hThe output voltage of expression voltage follower, U
RPFTesting capacitance voltage during expression charging voltage comparator toggles.
For the stability and the measuring accuracy that improve circuit, capacitance measuring device of the present invention also comprises a pulse shaping circuit, between the control end that this circuit string is located at described bidirectional electronic switch and the I/O mouth of the single-chip microcomputer that is connected.
For fear of the influence of the remaining capacity of testing capacitance to measuring accuracy; Capacitance measuring device of the present invention also can comprise a remaining capacity detecting device; This remaining capacity detecting device is made up of another voltage comparator; Its positive and inverting input cross-over connection are in the two ends of testing capacitance, and output terminal is connected with an I/O mouth of single-chip microcomputer; Wherein, the inverting input of said another voltage comparator is connected on the node of normal phase input end and testing capacitance of said charging voltage comparer.
The principle of work of capacitance measuring device of the present invention is following:
A) testing capacitance is inserted and after singlechip controller powers on; Single-chip microcomputer promptly begins according to program setting configuration impulse meter; And the dutycycle in cycle and when charging of pwm signal is set; Simultaneously, single-chip microcomputer makes voltage follower output LOW voltage and make bidirectional electronic switch closed always through the I/O mouth, with possibly discharging by remaining electric charge in the testing capacitance;
B) whether single-chip microcomputer is pressed by manual work through I/O mouth detection measurement button;
C) when detecting the measurement button, presses by single-chip microcomputer; Then single-chip microcomputer makes the constant high voltage of voltage follower output voltage values through the I/O mouth; As charge voltage source, simultaneously, single-chip microcomputer output pwm pulse drives bidirectional electronic switch; Make that voltage follower is that testing capacitance provides electric charge by the preset time interval, and the number of the pwm pulse of totally being exported;
D) the charging voltage comparer compares the voltage and the reference voltage of testing capacitance, and single-chip microcomputer judges whether testing capacitance voltage reaches reference voltage simultaneously; If testing capacitance voltage reaches reference voltage, then charging voltage comparer output voltage upset, single-chip microcomputer stops counting, and utilizes RC to discharge and recharge the capacity that the corresponding equation of zero condition is calculated testing capacitance according to the pulse number of counting.
Compared with prior art, the present invention has the following advantages:
1, capacitance measuring device of the present invention only need once discharge and recharge the cubic content measurement that can accomplish measured capacitance; Measuring speed is fast; Precision is high; And can be through program setting or the cycle and the dutycycle of pwm pulse artificially are set, combine some statistical algorithms again, also can further improve measuring accuracy through repeatedly discharging and recharging measurement;
2, capacitance measuring device of the present invention can be adjusted capacitor charging time through the dutycycle and the cycle of single-chip microcomputer adjustment pwm pulse, and is not only simple in structure, and need not manually to select range.
Description of drawings
Fig. 1 is the circuit theory diagrams of a specific embodiment of capacitance measuring device according to the invention.
Fig. 2 is the circuit theory diagrams of a specific embodiment of bidirectional electronic switch according to the invention.
Fig. 3 is the circuit theory diagrams of another specific embodiment of capacitance measuring device according to the invention.
Fig. 4 is the circuit theory diagrams of a specific embodiment of pulse shaping circuit according to the invention.
Fig. 5 is the circuit theory diagrams of another specific embodiment of pulse shaping circuit according to the invention.
Fig. 6 is the SCM program process flow diagram of capacitance measuring device shown in Figure 1.
Fig. 7 is the SCM program process flow diagram of capacitance measuring device shown in Figure 3.
Voltage waveform view when Fig. 8 is capacitance measuring device according to the invention work.
Specific embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is done further detailed description, but this embodiment should not be construed as limitation of the present invention.
Fig. 1 is the circuit theory diagrams of the basic scheme of capacitance measuring device according to the invention.Referring to Fig. 1,
Singlechip controller is made up of single-chip microcomputer (ATmega16) and the start-up circuit be made up of resistance R 1, R2 and button AN, wherein, and the power input of single-chip microcomputer and constant voltage source U
hConnect, the I/O mouth PB1 of single-chip microcomputer is connected to constant voltage source U through resistance R 2 with R1
h, an end ground connection of button, the other end and resistance R 2 are connected with node between R1.
Charging circuit connects to form for voltage follower A1, fixed value resistance R4 and the bidirectional electronic switch S that is connected into by amplifier successively.Wherein, The normal phase input end of said voltage follower A1 is connected with the I/O mouth PA0 of single-chip microcomputer (ATmega16); Output terminal is through deciding the positive voltage terminal that resistance resistance R 4 and bidirectional electronic switch S are connected to testing capacitance, and the control end of bidirectional electronic switch S is connected with the I/O mouth PB3 of single-chip microcomputer (ATmega16).Referring to Fig. 2; Described bidirectional electronic switch S is made up of with the drain electrode reverse parallel connection the N channel field-effect pipe G1 of 2 ultralow internal resistances and the source electrode of G2; Wherein, The major loop of the source electrode of G1 and G2 and the described bidirectional electronic switch S of drain electrode formation, the grid parallel connection of G1 and G2 is as the control end of described bidirectional electronic switch S.
The charging testing circuit is high speed charging voltage comparer A2, and wherein, the normal phase input end of described high speed charging voltage comparer A2 links to each other with the positive voltage port and the electronic switch of testing capacitance, and the inverting input of A2 connects a reference voltage source V
Ref, the reference voltage source voltage U
REF＜U
h, the output terminal of A2 links to each other with the I/O mouth PD2 of single-chip microcomputer (ATmega16).
Referring to Fig. 6, the course of work of this device is following:
A) with testing capacitance C
XAfter access and singlechip controller power on; Single-chip microcomputer promptly begins according to program setting configuration impulse meter; And the cycle T of pwm pulse and the dutycycle d in when charging be set; Simultaneously, single-chip microcomputer makes voltage follower A1 output LOW voltage and make bidirectional electronic switch S closed always through I/O mouth PA0, with testing capacitance C
XInterior possibly release by remaining electric charge, because voltage follower A1 is output as low-voltage at this moment, so only is positioned at the N channel field-effect pipe conducting work of discharge loop in the bidirectional electronic switch, the N channel field-effect pipe that is in charge circuit instead ends partially.Because testing capacitance C
XVoltage is lower than the reference voltage source voltage U at this moment
REF, so charging voltage comparer A2 is output as low level;
B) whether single-chip microcomputer is pressed by manual work through I/O mouth PB1 detection measurement button AN;
C) AN presses if single-chip microcomputer detects the measurement button, and it is U that single-chip microcomputer makes the voltage follower output voltage values through I/O mouth PA0
hHigh voltage, as charge voltage source, simultaneously, single-chip microcomputer output pwm pulse drives bidirectional electronic switch S, makes that voltage follower A1 is testing capacitance C with the constant time interval
XElectric charge is provided, and impulse meter also begins to measure the number of the pwm pulse of single-chip microcomputer output simultaneously.Because this moment, voltage follower A1 was output as high voltage, so only was positioned at the N channel field-effect pipe conducting work of charge circuit in the bidirectional electronic switch, the N channel field-effect pipe that is in discharge loop instead ends partially;
D) referring to Fig. 8, when this figure is the electric capacity charging, capacitance voltage waveform and output pwm pulse waveform synoptic diagram, charging voltage comparer A2 is with testing capacitance C
XVoltage and reference voltage U
REFRelatively, single-chip microcomputer is judged testing capacitance C
XWhether voltage reaches reference voltage U
REF, if testing capacitance C
XVoltage reaches reference voltage U
REF, then high level to single-chip processor i/o mouth PD2 is exported in charging voltage comparer A2 upset, and at this moment, impulse meter stops counting, according to the pulse number N that this moment, the impulse meter meter got.Can get RC according to the RC charge-discharge principle and discharge and recharge the corresponding equation I of zero condition):
In the formula, U
CThe testing capacitance C constantly time the for t
XVoltage, U
LBe charge or discharge initial time testing capacitance voltage, U
∞For electric capacity is full of or electric capacity voltage when draining fully fully, during charging process, U
∞Equal charge power supply voltage, during discharge process, U
∞Equal 0.
In step d), U
C=U
REF, U
L=0, U
∞=U
h, t=dTN, resistance is known, thereby can get capacitance computing formula II):
Formula can be calculated testing capacitance appearance value thus.Among the formula II, the definition of each code name is identical with the said formula II of summary of the invention part.
Testing capacitance charge for the first time accomplish record capacitance after, can return step a) based on demand through program or artificial the setting, change the cycle or the dutycycle of pwm pulse, repeatedly discharge and recharge, thereby further improve certainty of measurement.To reduce dutycycle raising measuring accuracy is example, to same testing capacitance C
X,, suppose the dutycycle d of current pwm pulse because measuring error is directly proportional with measuring speed
1, obtaining pulse number is N
1, the dutycycle of pwm pulse is reduced to d
2, obtaining pulse number is N
2, the ratio N of umber of pulse is then arranged
1: N
2=k, 0＜k＜1, the measuring error of then dwindling after the dutycycle has reduced before
This shows that dutycycle is more little, measuring accuracy is high more.
Fig. 3 is an improvement project embodiment illustrated in fig. 1, and this scheme has been set up a pulse shaping circuit and remaining capacity detecting device.Wherein, said pulse shaping circuit is connected between the control end of I/O mouth PB3 and bidirectional electronic switch S of single-chip microprocessor MCU and connects; Described remaining capacity detecting device is made up of voltage comparator A3, and its positive and inverting input cross-over connection are in testing capacitance C
XTwo ends, output terminal is connected with the I/O mouth PD1 of single-chip microcomputer (ATmega16), the inverting input of said voltage comparator A3 is connected to normal phase input end and the testing capacitance C of charging voltage comparer A2
XNode on.
Fig. 4 is a kind of specific embodiments of pulse shaping circuit described in the improvement project shown in Figure 3; This scheme is made up of push-pull circuit and the resistance R 8 that NPN type triode Q3 and positive-negative-positive triode Q4 form; Wherein, The pwm pulse output I/O mouth of single-chip microcomputer is connected to the emitter-base bandgap grading of NPN type triode Q3 and the emitter-base bandgap grading of positive-negative-positive triode Q4 through resistance R 8, and the collector of NPN type triode Q3 connects constant voltage source U
h, the grounded collector of positive-negative-positive triode Q4, the control end of bidirectional electronic switch S is connected to the emitter-base bandgap grading of NPN type triode Q3 and the emitter-base bandgap grading of positive-negative-positive triode Q4.
Fig. 5 is the another kind of specific embodiments of pulse shaping circuit described in the improvement project shown in Figure 3, and this scheme is by NPN type triode Q1, positive-negative-positive triode Q2; Resistance R 5, R6, R7; Pulse transformer T constitutes; Wherein, the pwm pulse of single-chip microcomputer output I/O mouth is connected to the emitter-base bandgap grading of NPN type triode Q1 and the emitter-base bandgap grading of positive-negative-positive triode Q2 through resistance R 5, and the collector of NPN type triode Q1 connects constant voltage source U
hThe grounded collector of positive-negative-positive triode; The former limit of pulse transformer T is connected to the connected node of emitter-base bandgap grading of emitter-base bandgap grading and the positive-negative-positive triode Q2 of NPN type triode Q1 respectively; And ground connection, an end of pulse transformer T secondary is connected to the control end of bidirectional electronic switch S, the source electrode of 2 FETs among the other end of secondary and the bidirectional electronic switch S after resistance R 6 and resistance R 7 dividing potential drops.
Referring to Fig. 7), the course of work of the once charging of improvement project shown in Figure 3 is following:
A) step a) with the course of work shown in Figure 6 is identical;
B) step b) with the course of work shown in Figure 6 is identical;
C) AN presses if single-chip microcomputer detects the measurement button, and then single-chip microcomputer detects testing capacitance C through I/O mouth PD1
XRemaining capacity whether drain;
D) if single-chip microcomputer detects testing capacitance C
XRemaining capacity drain, then to make the voltage follower output voltage values through I/O mouth PA0 be U to single-chip microcomputer
hHigh voltage, as charge voltage source, simultaneously, single-chip microcomputer output pwm pulse drives bidirectional electronic switch S, makes that voltage follower A1 is testing capacitance C with the constant time interval
XElectric charge is provided, and impulse meter also begins to measure the number of the pwm pulse of single-chip microcomputer output simultaneously;
E) step d) with the course of work shown in Figure 6 is identical.
Claims (3)
1. capacitance measuring device, it comprises with the singlechip controller is core, is equipped with charging circuit and the capacitance measurement circuit that the charging testing circuit constitutes, it is characterized in that,
Described singlechip controller is the single-chip minimum system that single-chip microcomputer and peripheral circuit thereof constitute;
Described charging circuit is connected to form by voltage follower, fixed value resistance and bidirectional electronic switch successively; Wherein, the control end of described bidirectional electronic switch links with an I/O mouth of said single-chip microcomputer;
Described charging testing circuit is the charging voltage comparer, and the normal phase input end of this charging voltage comparer cross-over connection over the ground has testing capacitance, and inverting input is provided with reference voltage source, and output terminal is connected with an I/O mouth of single-chip microcomputer;
The input end of described voltage follower is connected with an I/O mouth of single-chip microcomputer, and output terminal links to each other with the normal phase input end of bidirectional electronic switch with the charging voltage comparer through said fixed value resistance; Described single-chip microcomputer modulates pwm pulse, and to control described bidirectional electronic switch be testing capacitance charging, calculates the capacity of testing capacitance by single-chip microcomputer by following formula (II),
In the formula (II), C
XThe capacity of expression testing capacitance, d representes the dutycycle of pwm pulse, and T representes the cycle of pwm pulse, and N representes the number of pwm pulse, and R representes the resistance of said resistance, U
hThe output voltage of expression voltage follower, U
RPFTesting capacitance voltage during expression charging voltage comparator toggles.
2. a kind of capacitance measuring device according to claim 1 is characterized in that it also comprises a pulse shaping circuit, between the control end that this circuit string is located at described bidirectional electronic switch and the I/O mouth of the single-chip microcomputer that is connected.
3. a kind of capacitance measuring device according to claim 1 and 2; It is characterized in that; It also comprises a remaining capacity detecting device; This remaining capacity detecting device is made up of another voltage comparator, and its positive and inverting input cross-over connection are in the two ends of testing capacitance, and output terminal is connected with an I/O mouth of single-chip microcomputer; Wherein, the inverting input of said another voltage comparator is connected on the node of normal phase input end and testing capacitance of said charging voltage comparer.
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| CN108196129A (en) * | 2018-01-05 | 2018-06-22 | 电子科技大学 | A kind of capacitance measuring device |
| CN109716534A (en) * | 2016-09-23 | 2019-05-03 | 艾思玛太阳能技术股份公司 | Solar energy module, photovoltaic apparatus and the method for voltage limit |
| CN110411987A (en) * | 2019-08-30 | 2019-11-05 | 北京智芯微电子科技有限公司 | The signal processing system and signal processing method of SF6 gas sensor |
| CN114002511A (en) * | 2021-11-16 | 2022-02-01 | 中国北方车辆研究所 | Distributed capacitance testing device for electrically-driven special vehicle |
| CN115078844A (en) * | 2022-06-01 | 2022-09-20 | 中国第一汽车股份有限公司 | Y capacitor test method, test equipment, storage medium and processor |
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| CN109716534A (en) * | 2016-09-23 | 2019-05-03 | 艾思玛太阳能技术股份公司 | Solar energy module, photovoltaic apparatus and the method for voltage limit |
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| CN114002511A (en) * | 2021-11-16 | 2022-02-01 | 中国北方车辆研究所 | Distributed capacitance testing device for electrically-driven special vehicle |
| CN114002511B (en) * | 2021-11-16 | 2023-07-28 | 中国北方车辆研究所 | Distributed capacitance testing device for electrically driven special vehicle |
| CN115078844A (en) * | 2022-06-01 | 2022-09-20 | 中国第一汽车股份有限公司 | Y capacitor test method, test equipment, storage medium and processor |
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Application publication date: 20120815 |