CN1031428A - Differential capacitor metering circuit and multi-range measurement instrument - Google Patents
Differential capacitor metering circuit and multi-range measurement instrument Download PDFInfo
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- CN1031428A CN1031428A CN 88106571 CN88106571A CN1031428A CN 1031428 A CN1031428 A CN 1031428A CN 88106571 CN88106571 CN 88106571 CN 88106571 A CN88106571 A CN 88106571A CN 1031428 A CN1031428 A CN 1031428A
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Abstract
A kind of differential capacitor metering circuit and multirange capacitance meter belong to electrotechnical, electronic measuring method and device.The present invention has mainly adopted several cmos switches and measured capacitance, and reference capacitance has been formed one together and discharged and recharged bridge circuit, poor with the amplitude of two capacitance discharges electric currents of a charge measurement circuit measuring.This electric circuit characteristic is that required element is few, with low cost, the measuring accuracy height, good stability, inhibition ability to stray capacitance influences is strong, the multi-range measurement of this instrument is by changing frequency and the very easy realization of resistance value, and the survey frequency scope that can provide to 2MHz, can be measured differential capacitor and absolute capacitance from about 500Hz.
Description
The invention belongs to electrotechnical, electronic measuring method and device.
When carrying out capacitance measurement, between two pole plates and ground of capacitor, between two lines of capacitor and metering circuit and between these lines and the ground, all exist stray capacitance.The capacitive transducer that is used for commercial measurement, for avoiding the interference of external electromagnetic field, its pole plate and the conductively-closed often that goes between.As shown in Figure 1, the system after the shielding can equivalence be one three a terminal capacitance network, and wherein electric capacity [6] is two electric capacity between the pole plate, and electric capacity [7], [8] are respectively pole plate [1] and lead-in wire [2] thereof, the electric capacity between pole plate [3] and lead-in wire [4] thereof and the shielding [5].When the laboratory measurement capacitor, also often adopt concentric cable as measuring lead wire, therefore actual measured capacitance also the equivalent electrical circuit of available Fig. 1 represent.In order to measure electric capacity [6] exactly, must eliminate stray capacitance [7] and [8] for the influence of measuring.
Existing capacitance measurement method can be divided three classes: succusion, impedance measurement (comprising various bridge technologies) and charge and discharge electrical method.In general, based on the capacitance meter of succusion advantages such as circuit is simple, price is low, easy to use are arranged, but relatively more responsive for stray capacitance, it is bigger to drift about.Based on the capacitance meter of impedance method, can accomplish high precision, high stability reaches and is not subjected to stray capacitance influences, but the circuit more complicated, cost is higher, especially adopts the device of transformer bridges, and volume is bigger, and price is more expensive.Charge and discharge electrical method and have advantages such as circuit is simple, its degree of stability can accomplish to be better than slightly succusion.But adopt the circuit of mise-a-la-masse method at present, mostly relatively responsive to the influence of stray capacitance.Fig. 2 is one based on the typical circuit that charges and discharge electrical method.Once in 1984 by West Germany Endress ﹠amp; Hauser company has applied for patent.（Endress & Hauser patent 84087）。Electric capacity among the figure [6], [9] are respectively tested and reference capacitance.The circuit working principle is as follows, typically discharges and recharges in the cycle at one, and the preceding semiperiod, cmos switch [11] is opened, [10] closure, and power supply+Vc charges to measured capacitance [6] through [10].After charging finished, the electric charge of storage was in the electric capacity [6]
Q＝VcCx
Cx is the capacity of electric capacity [6] in the formula.In the later half cycle, switch [10] is opened, [11] closure, and electric capacity [6] is to by operational amplifier [13], the charge measurement circuit discharging that electric capacity [12] and [15] and resistance [14] are formed.Because the input end of metering circuit is in virtual ground potential, the electric charge in the electric capacity [6] all flows into metering circuit, and obtains a proportional output voltage of the quantity of electric charge [16] therewith thus.The circuit component of the right-hand part of Fig. 2 and parameter, identical with the left side, to form the differential comparator circuit of electric capacity [6] and electric capacity [9].
The shortcoming of circuit is shown in the figure two, and when charging, stray capacitance [7] also is charged to+Vc, the also measured circuit measuring of the electric charge in electric capacity during discharge [7].Therefore this circuit is to the stray capacitance sensitivity.Owing to comprise the electric capacity of cmos switch [10], [11] in the stray capacitance [7], these electric capacity are responsive to temperature, and this has limited the improvement of the degree of stability of entire circuit.
For reaching above-mentioned purpose, the present invention designs a kind of differential capacitor metering circuit that can suppress stray capacitance influences, by two above semiconductor switchs and measured capacitance, one of forming together of reference capacitance discharges and recharges bridge circuit and the charge measurement circuit constitutes, it is characterized in that first pole plate of measured capacitance in the said bridge circuit and the contact mutually of first pole plate of reference capacitance, link to each other with this charge measurement circuit by said first semiconductor switch, second pole plate of measured capacitance is by above-mentioned second semiconductor switch, link to each other with two mutually different supply voltages, second pole plate of reference capacitance links to each other with above-mentioned two supply voltages by the 3rd semiconductor switch.Make in above-mentioned two voltages one to the measured capacitance charging, another charges to reference capacitance; Make measured capacitance and reference capacitance respectively in said two voltages with that different discharge of self charging voltage, the end that measured capacitance and reference capacitance are linked to each other with the charge measurement circuit is in earth potential when charging, be in virtual ground potential during discharge, measure discharge current poor of measured capacitance and reference capacitance with the electric charge metering circuit.
The present invention utilizes above-mentioned capacitance measurement circuit to design a kind of multirange capacitance meter, by a plurality of semiconductor switchs, and measured capacitance, reference capacitance constitutes and to discharge and recharge bridge circuit, by tested poor with the reference capacitance discharge current of a charge measurement circuit measuring; It is characterized in that said charge measurement circuit has a plurality of different feedback gain resistance; Provide a plurality of different frequencies that discharge and recharge by an oscillator and a plurality of frequency dividers, adopt multi-way switch to select the different frequencies that discharges and recharges, the combination of feedback resistance value and charging voltage changes the range of measuring instrument.
In the enforcement of capacitance measurement circuit of the present invention, often getting above-mentioned two fixed power source voltages is equal and opposite in direction, the voltage of opposite in sign.
The present invention adopts cmos switch to discharge and recharge bridge circuit, and required element seldom and cheaply; Multi-range measurement is by changing frequency and the very easy realization of resistance value; Inhibition ability to stray capacitance influences is strong, its susceptibility to stray capacitance be to ten thousand of the susceptibility of measured capacitance/; Zero point drift test result when the 1MHZ frequency is 0.002pF/12 hour (room temperature change be no more than ± 2 ℃), the survey frequency scope that can provide from about 500HZ to 2MHZ; Can measure differential capacitor and absolute capacitance, be a kind of cheap, measuring accuracy is high, the capacitance meter of good stability.
Brief Description Of Drawings
Fig. 1 is the general structure and the equivalent electrical circuit of industrial capacitive transducer.
Fig. 2 is a kind of circuit more approaching with the present invention in the prior art.
Fig. 3 is for suppressing the schematic diagram that discharges and recharges the differential capacitor metering circuit of stray capacitance influences.
Fig. 4 is the sequential chart of cmos switch among Fig. 3.
Fig. 5 is the basic circuit diagram of multirange capacitance meter.
Wherein: [1], [3] pole plate; [2], [4] lead-in wire; [5] shielding; [6] measured capacitance; [7], [8] stray capacitance; [9] reference capacitance; [10], [11] switch; [12] input capacitance; [13] operational amplifier; [14] resistance; [15] feedback capacity; [16] output voltage; [17], [18], [19] cmos switch; [20] charge measurement circuit; [21] electric capacity; [22], [23] concentric cable; [24], [25] diode; [26] switch; [27] [33] potentiometer; [28], [31] voltage follower; [29], [30], [32], [34] resistance; [35] analog output voltage signal; [36] digital watch; [37] phase inverter; [38], [39] resistance; [40] crystal oscillator; [41], [42] electric capacity; [43] frequency divider; [44] switch; [45] trigger; [46,48,50,52] diode; [47], [49], [51], [53] resistance; [54,55,56,57] phase inverter; [58～71] terminal; [72,73] resistance; [74,75,76,77] gauge tap;
A kind of embodiment of the differential capacitor circuit that can suppress stray capacitance influences of the present invention as shown in Figure 3, mainly by circuit-under-test [6], reference capacitance [9], cmos switch [17], [18], [19] etc. are formed discharges and recharges bridge circuit and charge measurement circuit [20] is formed.Its principle of work is described below: a work period of circuit can be divided into is just charging and two parts of reverse charge.According to sequential shown in Figure 4, in the semiperiod of just charging, switch [17] is thrown to b, switch [18] is thrown to a, switch [19] is thrown to b, make the voltage at measured capacitance [6] two ends be charged to+Vc, the voltage at reference capacitance [9] two ends is+Vc that the electric charge that is stored in [6] and [9] is respectively
CxVc and CyVc
Here Cx and Cy represent the electric capacity of circuit-under-test [6] and reference capacitance [9] respectively.
In cycle, switch [19] is thrown to a at reverse charge, connects the charge measurement circuit, and switch [17] is thrown to a simultaneously, and electric capacity [6] is charged to-Vc; Switch [18] is thrown to b, and electric capacity [9] is charged to-Vc.The electric charge that flows out from [6] in this process is:
2VcCx
The electric charge that flows out from [9] is
2VcCy
The net charge amount that flows out charge measurement circuit [20] by switch [19] is:
2Vc（Cx-Cy）
Charge measurement circuit among Fig. 3 is by a low drifting operating amplifier (as LF355 356 etc.) [13], an input capacitance [12], and feedback capacity [15], feedback resistance [14] is formed.Input capacitance [12] is generally 0.1 μ F, to 1 μ F, is used for absorbing any voltage fluctuation of amp.in, is in stable virtual ground potential to guarantee this point.Feedback capacity [15], resistance [14] decision low pass filter band width.Resistance [14] also determines the gain of charge measurement circuit [20].
In specific implementation, each has all adopted two switches on the CMOS 4066 stamen sheets switch [17], [18], [19].
The process of above-mentioned positive reverse charge repeats with frequency f, the output of metering circuit [16] can by under show expression:
V＝2VcfRf（Cx-Cy） （1）
Here V is an output voltage, and Rf is the resistance of feedback resistance [14].
In above-mentioned measuring process, switch [17] and [18] all the time+Vc and-switch between Vc, and stray capacitance [7] just discharges and recharges by these two power supplys, therefore its discharge current does not influence measurement by the charge measurement circuit.Switch [19] just switches between ground and the virtual earth that formed by the amplifier inverting input in measuring process.Because the potential difference (PD) between ground and virtual earth can be ignored compared with charging voltage Vc, therefore the charge variation in the stray capacitance [8] is inappreciable when switch [19] switches, thereby the variation of electric capacity [8] is inappreciable for the influence of measuring.Experiment shows that metering circuit is about 10,000 times to the susceptibility of electric capacity [7] and [8] to the susceptibility of measured capacitance [6].
According to formula (1), if change charge frequency f, or feed back resistance Rf, then can change the range of metering circuit.
Multirange capacitance meter according to this principle design.
As shown in Figure 5, owing to be absolute capacitive measurement, so the reference capacitance among Fig. 3 [9] and switch [18] have been removed; Switch among Fig. 3 [17] is realized that by cmos switch [74] and [75] switch [19] is realized by [76] and [77].The measuring lead wire of measuring instrument has adopted concentric cable [22] and [23].Resistance [72] and [73] are used for increasing the damping of charging.Electric capacity [21] is used for being absorbed in to bigger measured capacitance [6] when discharging and recharging, and A is ordered the due to voltage spikes that is produced.Diode [24] and [25] are used for protecting cmos switch [74] and [75].
The clock signal of gauge tap [74-77] is produced by a crystal oscillator square-wave generator.This oscillator is by phase inverter [37], resistance [38] [39], and crystal oscillator [40] and two electric capacity [41,42] are formed.The square wave of output produces the signal of several different frequencies through 14 grades of frequency dividers [43], and these signals are drawn by terminal [65-71] respectively.When selecting the range of instrument, select different clock frequencies with switch [44], use switch [26] between terminal [58-64], to select a corresponding feedback resistance value (be to guarantee that the frequency band of metering circuit is no more than the scope of requirement, different feedback resistances generally is furnished with different feedback capacities) simultaneously.Clock frequency after the selection becomes the anti-phase square wave of two-way through a trigger [45], and one the tunnel through phase inverter [54], and [55] driving switch [76] and [75], another road are through phase inverter [56], [57] driving switch [77] and [74].4 diodes, the one resistance parallel circuit of forming with diode [46,48,50,52] and resistance [47,49,51,53] provides negative edge to delay, thereby guarantees when several switches move simultaneously, and the switch of disconnection always moves prior to the switch of closure slightly.
The range of capacitance meter can be finely tuned by potentiometer [27].Can be adjusted zero point by potentiometer [33], and [32], [34] are two fixed resistances, is used to reduce the voltage drop at potentiometer [33] two ends.[28] and [31] be two voltage followers, be that zeroing is adjusted circuits needed with range.[29] be two resistance that resistance is identical with [30].The output of metering circuit can be used as an analog voltage signal [35] and uses for other instrument, also can locate to connect a digital watch in [36], directly reads capacitance.
Claims (2)
1, a kind of differential capacitor metering circuit that can suppress stray capacitance influences, by two above semiconductor switchs and measured capacitance, one of forming together of reference capacitance discharges and recharges bridge circuit and the charge measurement circuit constitutes, it is characterized in that first pole plate of measured capacitance in the said bridge circuit and the contact mutually of first pole plate of reference capacitance, link to each other with this charge measurement circuit by said first semiconductor switch, second pole plate of measured capacitance is by above-mentioned second semiconductor switch, link to each other with two mutually different supply voltages, second pole plate of reference capacitance links to each other with above-mentioned two supply voltages by the 3rd semiconductor switch, in above-mentioned two voltages one is charged to measured capacitance, another charges to reference capacitance, make measured capacitance and reference capacitance respectively in said two voltages with that different discharge of self charging voltage, the end that measured capacitance and reference capacitance are linked to each other with the charge measurement circuit is in earth potential when charging, be in virtual ground potential during discharge, measure discharge current poor of measured capacitance and reference capacitance with the electric charge metering circuit.
2, a kind of multirange capacitance meter that utilizes the described capacitance measurement circuit of claim 1, by a plurality of semiconductor switchs, measured capacitance, reference capacitance constitutes and to discharge and recharge bridge circuit, by tested poor with the reference capacitance discharge current of a charge measurement circuit measuring; It is characterized in that said charge measurement circuit has a plurality of different feedback gain resistance; Provide a plurality of different frequencies that discharge and recharge by an oscillator and a plurality of frequency dividers, adopt multi-way switch to select the different frequencies that discharges and recharges, the combination of feedback resistance value and charging voltage changes the range of measuring instrument.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 88106571 CN1009031B (en) | 1988-10-06 | 1988-10-06 | Differential capacitor metering circuit and multirange capacitance meter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 88106571 CN1009031B (en) | 1988-10-06 | 1988-10-06 | Differential capacitor metering circuit and multirange capacitance meter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN1031428A true CN1031428A (en) | 1989-03-01 |
| CN1009031B CN1009031B (en) | 1990-08-01 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN 88106571 Expired CN1009031B (en) | 1988-10-06 | 1988-10-06 | Differential capacitor metering circuit and multirange capacitance meter |
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| CN (1) | CN1009031B (en) |
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101975893A (en) * | 2010-10-20 | 2011-02-16 | 沈阳工业大学 | Differential capacitance detection circuit based on instrument amplifier and detection method thereof |
| CN103714330A (en) * | 2014-01-06 | 2014-04-09 | 李扬渊 | Capacitive fingerprint sensor |
| CN104169728A (en) * | 2011-12-23 | 2014-11-26 | Imec公司 | Method and system for measuring capacitance difference between capacitive elements |
| CN104871019A (en) * | 2012-09-17 | 2015-08-26 | Sem技术公司 | Capacitance measurement of high voltage device |
| CN105652099A (en) * | 2016-02-22 | 2016-06-08 | 西安电子科技大学 | Micro capacitance difference detection method based on switching circuit |
| CN105807142A (en) * | 2016-03-15 | 2016-07-27 | 四川理工学院 | Sensor detection circuit |
| CN108333434A (en) * | 2018-01-31 | 2018-07-27 | 北京航空航天大学 | One kind dividing formula parallel organization capacitor array measuring circuit |
| CN108957144A (en) * | 2018-07-06 | 2018-12-07 | 安徽贝昂科技有限公司 | A kind of capacitance testing device |
| CN112014647A (en) * | 2020-08-10 | 2020-12-01 | 南京天易合芯电子有限公司 | Capacitance detection method capable of restraining temperature drift |
| CN113075459A (en) * | 2021-03-18 | 2021-07-06 | 合肥恒钧检测技术有限公司 | Electrostatic capacity detection device |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2299284A1 (en) * | 2009-09-18 | 2011-03-23 | ABB Technology AG | Method, capacitance meter, and computer program product for improved capacitance measurement |
-
1988
- 1988-10-06 CN CN 88106571 patent/CN1009031B/en not_active Expired
Cited By (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101975893B (en) * | 2010-10-20 | 2013-03-20 | 沈阳工业大学 | Differential capacitance detection circuit based on instrument amplifier and detection method thereof |
| CN101975893A (en) * | 2010-10-20 | 2011-02-16 | 沈阳工业大学 | Differential capacitance detection circuit based on instrument amplifier and detection method thereof |
| CN104169728B (en) * | 2011-12-23 | 2016-11-23 | Imec公司 | Method and system for measuring capacitance difference between capacitive elements |
| CN104169728A (en) * | 2011-12-23 | 2014-11-26 | Imec公司 | Method and system for measuring capacitance difference between capacitive elements |
| CN104871019B (en) * | 2012-09-17 | 2017-06-23 | Sem技术公司 | The capacitance measurement of high voltage device |
| CN104871019A (en) * | 2012-09-17 | 2015-08-26 | Sem技术公司 | Capacitance measurement of high voltage device |
| CN103714330A (en) * | 2014-01-06 | 2014-04-09 | 李扬渊 | Capacitive fingerprint sensor |
| CN103714330B (en) * | 2014-01-06 | 2017-12-19 | 苏州迈瑞微电子有限公司 | Capacitive fingerprint sensor |
| CN105652099B (en) * | 2016-02-22 | 2018-10-12 | 西安电子科技大学 | A kind of micro- capacitance difference detection method based on switching circuit |
| CN105652099A (en) * | 2016-02-22 | 2016-06-08 | 西安电子科技大学 | Micro capacitance difference detection method based on switching circuit |
| CN105807142A (en) * | 2016-03-15 | 2016-07-27 | 四川理工学院 | Sensor detection circuit |
| CN105807142B (en) * | 2016-03-15 | 2018-06-12 | 四川理工学院 | A kind of sensor detection circuit |
| CN108333434A (en) * | 2018-01-31 | 2018-07-27 | 北京航空航天大学 | One kind dividing formula parallel organization capacitor array measuring circuit |
| CN108333434B (en) * | 2018-01-31 | 2020-08-18 | 北京航空航天大学 | A Split-Program Parallel Structure Capacitance Array Measuring Circuit |
| CN108957144A (en) * | 2018-07-06 | 2018-12-07 | 安徽贝昂科技有限公司 | A kind of capacitance testing device |
| CN112014647A (en) * | 2020-08-10 | 2020-12-01 | 南京天易合芯电子有限公司 | Capacitance detection method capable of restraining temperature drift |
| CN112014647B (en) * | 2020-08-10 | 2023-04-28 | 南京天易合芯电子有限公司 | Capacitance detection method capable of inhibiting temperature drift |
| CN113075459A (en) * | 2021-03-18 | 2021-07-06 | 合肥恒钧检测技术有限公司 | Electrostatic capacity detection device |
Also Published As
| Publication number | Publication date |
|---|---|
| CN1009031B (en) | 1990-08-01 |
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