CN1300596C - High resolution liquid conductance measuring method and apparatus thereof - Google Patents
High resolution liquid conductance measuring method and apparatus thereof Download PDFInfo
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- CN1300596C CN1300596C CNB2004100248022A CN200410024802A CN1300596C CN 1300596 C CN1300596 C CN 1300596C CN B2004100248022 A CNB2004100248022 A CN B2004100248022A CN 200410024802 A CN200410024802 A CN 200410024802A CN 1300596 C CN1300596 C CN 1300596C
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Abstract
The present invention discloses a high resolution liquid conductance measuring method and a device thereof on the basis of the amplification principle. Under the condition of exerting a stable-amplitude balanced amplitude modulation sine signal excitation on a sensor, relevant calculations are carried out on amplified output signals of the sensor and reference signals of which the frequency of carrier waves is the same as that of the excitation signals of the sensor. The device of the present invention is provided with a conductance measuring circuit board and a conductance probe, wherein the conductance measuring circuit board has the structure that a first oscillation circuit is orderly connected with a balanced modulation circuit, a measuring bridge, a small signal amplification circuit, balanced demodulation circuit, a first low-pass filter circuit, a rectification circuit, a second low-pass filter circuit, an analog-to-digital conversion circuit, a single chip computer and an RS232 interface; the single chip computer is connected with the small signal amplification circuit, a second oscillation circuit is respectively connected with the balanced modulation circuit and a phase shifter, and the phase shifter is connected with a balanced demodulator. The present invention adopts the phase-lock amplification technique, and is suitable for weak conductance measurement; the present invention simplifies the design of the phase-lock amplifier, and realize low-cost high-sensitivity measurement.
Description
Technical field
The present invention relates to a kind of high resolving power method for measuring conductance of liquid and device thereof.
Background technology
It is one of basic physical parameters of liquid that the electricity of liquid is led.The conductance of liquid measuring technology is widely used in containing the scientific research and the production run of industries such as the chemical industry, biology, medical science, environmental protection, water conservancy, metallurgy, electric power of liquid system.
The conductivity test technology at fluid to be measured of a great variety, the conductance property of different liquid is widely different, and common conductivity measuring device is the universal instrument of wide-measuring range, though applicable surface wide measure sensitivity and precision all lower.Because conducting liquid under the DC voltage effect polarization phenomena can take place, conductivity measuring device all applies ac-excited the measurement to fluid to be measured.From the principle, all methods of measuring AC impedance all can be measured electricity and lead, and common have bridge method, branch platen press, amplifier method and an impulse method.Using maximum method for measuring conductance on the engineering is the branch platen press, and its advantage is simple in structure, range easy switching, constitutes the device etc. of wide measurement range easily, but its defective be exactly measuring accuracy and sensitivity (more than 1%) on the low side.Alternating current bridge method is usually used in the laboratory measurement of high request, and its shortcoming is to adjust the measurement range inconvenience.
Though existing conductivity test system has proposed a lot of improvement and optimized Measures to improving system sensitivity, as improve pumping signal amplitude, select for use high-gain low noise amplifier, improve the resolution of A/D converter etc., but because the limitation of its design concept, the measurement that faint electricity is led still is difficult to be competent at.Its basic reason is, when the signal of sensor variation is very faint, interchannel noise becomes significant interference source, can not improve system sensitivity by improving enlargement factor under the close or bigger situation of the amplitude of interchannel noise and the amplitude of useful signal.
Summary of the invention
The purpose of this invention is to provide a kind of high resolving power method for measuring conductance of liquid and device thereof.
The high resolving power method for measuring conductance of liquid adopts phase-locked amplification principle to realize the high resolving power measurement of conductance of liquid, promptly be under the situation of the sinusoidal signal excitation of the balanced amplitude modulation that sensor is applied an amplitude stabilization, carrying out multiplying by the balanced demodulator circuit, realize high-resolution measurement by the gain that improves the sensor signal amplifying circuit through the signal of sensor and a reference signal of amplifying with the carrier wave same frequency of sensor excitation signal.
High resolving power conductance of liquid measurement mechanism has the electric waveguide measuring circuit plate and electricity is led probe, the circuit of electric waveguide measuring circuit plate is: oscillatory circuit I successively with equilibrium modulation circuit, measuring bridge, small signal amplification circuit, the balanced demodulator circuit, low-pass filter circuit I, rectification circuit, low-pass filter circuit II, analog to digital conversion circuit, single-chip microcomputer, the RS232 interface joins, single-chip microcomputer and small signal amplification circuit join, oscillatory circuit II joins with equilibrium modulation circuit and phase shifter respectively, phase shifter and balanced demodulator join, said oscillatory circuit: with operational amplifier OP07CP is that core constitutes, the 7th pin and the positive supply of operational amplifier OP07CP join, the 4th pin and the negative supply of operational amplifier OP07CP join, the 2nd pin of operational amplifier OP07CP successively with resistance R 3, resistance R 4 is joined, another termination power ground of resistance R 3, the 2nd pin of the other end of resistance R 4 and adjustable resistance R5 joins, the 3rd pin of adjustable resistance R5 and the 1st pin of adjustable resistance R6 join, the 2nd pin of adjustable resistance R6 joins with the 6th pin of operational amplifier OP07CP and resistance R 1, the other end of resistance R 1 and capacitor C 1 are joined, the other end of capacitor C 1 respectively with capacitor C 2, the 3rd pin of resistance R 2 and operational amplifier OP07CP joins, another termination power ground of the other end of capacitor C 2 and resistance R 2, said phase shifter: with operational amplifier OP07 is core, the one termination signal input of resistance R 1, the 2nd pin of another termination operational amplifier OP07 of resistance R 1, the 2nd pin of one termination operational amplifier OP07 of resistance R 2, another termination operational amplifier OP07 output terminal the 6th pin of resistance R 2, the one termination signal input of capacitor C 1, the 3rd pin of another termination operational amplifier OP07 of capacitor C 1, the 3rd pin of operational amplifier OP07 is by adjustable resistance R3 ground connection, the 7th pin of operational amplifier OP07 connects positive supply, and the 4th pin connects negative supply.
Advantage of the present invention:
1) adopts phase lock amplifying technology, be applicable to faint conductance measurement
This measurement mechanism adopts and is specifically designed to the phase lock amplifying technology that faint small-signal is handled, and has guaranteed that from principle there are higher sensitivity and bigger dynamic range in system.Phase-locked amplifying circuit adopts the alternating-current voltage source of balanced amplitude modulation as the conductivity sensor driving source, insoluble electric polarization problem when having weakened the employing direct current signal as the system incentive source on the one hand, the signal to noise ratio (S/N ratio) of comparing system with the electric waveguide measuring circuit of routine greatly improves;
2) design of simplification lock-in amplifier realizes low-cost, high-sensitivity measurement
Conventional phase-locked amplifying circuit is the design based on digital signal processor (DSP), and system design complexity, cost height are inconvenient integrated with sensing system.This measurement mechanism adopts balance modulating/demodulating special IC to realize the switch lock-in amplifier, and system architecture is simplified, and can realize low cost, the measurement of highly sensitive conductance of liquid;
3) hygienic requirements of the conductance measurement head coincidence detection Chinese medicine industry of process optimal design.
Description of drawings
Fig. 1 is a high resolving power conductance of liquid measurement mechanism structural representation
Fig. 2 is a high resolving power conductance of liquid measurement mechanism circuit block diagram;
Fig. 3 is the input and output oscillogram of equilibrium modulation circuit of the present invention;
Fig. 4 is an oscillatory circuit schematic diagram of the present invention;
Fig. 5 is the schematic diagram of 0-180 of the present invention ° phase shifter;
Fig. 6 is conductance measurement sonde configuration figure of the present invention.
Embodiment
The present invention adopts phase-locked amplification principle to realize the high resolving power measurement of conductance of liquid, promptly be under the situation of the sinusoidal signal excitation of the balanced amplitude modulation that sensor is applied an amplitude stabilization, carrying out related operation through the signal of sensor and a reference signal of amplifying with the carrier wave same frequency of sensor excitation signal, because various noise signals and carrier signal do not have correlativity, the result of related operation only reflects and the relevant part of sensor output that influence is approximately zero to various noise signals to the related operation result.Adopt phase-locked amplification principle can effectively suppress the noise of signal amplification circuit, the interchannel noise that the sensor signal amplifying circuit is introduced can not worsen the signal to noise ratio (S/N ratio) of metering circuit output signal, thereby can realize high-resolution measurement by the gain that improves the sensor signal amplifying circuit.
As shown in Figure 1, high resolution conductance of liquid measurement mechanism has the electric waveguide measuring circuit plate and electricity is led probe, the circuit of electric waveguide measuring circuit plate is: oscillatory circuit I joins with equilibrium modulation circuit, measuring bridge, small signal amplification circuit, balanced demodulator circuit, low-pass filter circuit I, rectification circuit, low-pass filter circuit II, analog to digital conversion circuit, single-chip microcomputer, RS232 interface successively, single-chip microcomputer and small signal amplification circuit join, oscillatory circuit II joins with equilibrium modulation circuit and phase shifter respectively, and phase shifter and balanced demodulator circuit join.
The present invention adopts the phase lock amplifying technology of the small-signal extraction that is specifically designed under the strong noise background that system signal noise ratio is improved more than the 80dB.The Core Feature of phase-locked amplifying circuit is that sensor output signal is carried out phase demodulation, and phase demodulation can be realized by on-off circuit, mlultiplying circuit and digital information processing system.The present invention adopts on-off circuit to realize demodulation, is that the phase-locked amplifying circuit that core constitutes has improved the sensitivity of conductivity measuring device effectively with balance modulating/demodulating integrated circuit AD630, and makes simplified, more practical.
Two Wien bridge circuit oscillatory circuits generated frequency respectively are the sinusoidal signal of 10Hz and 1KHz, the sinusoidal signal of 10Hz offers the balanced modulator that is made of integrated circuit AD630 and imports as modulation, and the sinusoidal signal of 1KHz is connected to the carrier wave input end of balanced modulator as carrier signal.
The output signal of balanced modulator is the balanced amplitude modulation signal, and its oscillogram as shown in Figure 3.This balanced amplitude modulation signal provides excitation for measuring bridge after by a voltage follower.
The structure of conductivity sensor circuit is for exchanging unbalanced bridge, leads comprehensive impedance that equiva lent impedance that probe connects lead, electrode, detected solution a constitutes arm as electric bridge by electricity.The output of conductivity sensor is a faint balanced amplitude modulation signal, and this signal amplifies 50 times through the differential amplifier that is made of AD620, and the output terminal of AD620 is connected to the signal input part of balanced demodulator.
For guaranteeing that balanced demodulator can carry out correct demodulation to the balanced amplitude modulation signal of sensor output, must guarantee to offer the reference signal of detuner and carrier wave same frequency, the same-phase of input signal.Phase shift obtains to the 1KHz sinusoidal signal by 0-180 ° of phase shifter to meet the reference signal of above-mentioned condition.
As shown in Figure 4, oscillatory circuit is to be that core constitutes with operational amplifier OP07CP, the 7th pin and the positive supply of operational amplifier OP07CP join, the 4th pin and the negative supply of operational amplifier OP07CP join, the 2nd pin of operational amplifier OP07CP successively with resistance R 3, resistance R 4 is joined, another termination power ground of resistance R 3, the 2nd pin of the other end of resistance R 4 and adjustable resistance R5 joins, the 3rd pin of adjustable resistance R5 and the 1st pin of adjustable resistance R6 join, the 2nd pin of adjustable resistance R6 joins with the 6th pin of operational amplifier OP07CP and resistance R 1, the other end of resistance R 1 and capacitor C 1 are joined, the other end of capacitor C 1 respectively with capacitor C 2, the 3rd pin of resistance R 2 and operational amplifier OP07CP joins, another termination power ground of the other end of capacitor C 2 and resistance R 2.
As shown in Figure 5, phase shifter is to be core with operational amplifier OP07, the one termination signal input of resistance R 1, the 2nd pin of another termination operational amplifier OP07 of R1, the 2nd pin of one termination operational amplifier OP07 of resistance R 2, another termination operational amplifier OP07 output terminal the 6th pin of resistance R 2, the one termination signal input of capacitor C 1, the 3rd pin of another termination operational amplifier OP07 of capacitor C 1, the 3rd pin of operational amplifier OP07 is by adjustable resistance R3 ground connection, the 7th pin of operational amplifier OP07 connects positive supply, and the 4th pin connects negative supply.
By adjusting the resistance value of R3 in the phase shifter, can make the output of phase shifter that 0-180 ° phase pushing figure is arranged with respect to its input signal.During concrete the adjustment, the output waveform that must observe the balanced demodulator circuit with oscillograph simultaneously can realize that with the balanced demodulator circuit demodulation is made as standard completely, and this moment, the output of balanced demodulator should be the 10Hz simple alternating current waveform of rule.
Balanced demodulator is output as the sinusoidal ac signal of frequency 10Hz, its amplitude and conductivity sensor electric bridge be output into linear relationship.This sinusoidal ac signal generates a d. c. voltage signal after through the ideal rectifier circuit that is made of AD630 and low-pass filter filtering, and the size of this d. c. voltage signal has reflected the size that the fluid to be measured electricity is led.This direct current signal is sampled by analog to digital conversion circuit, and the digital quantity of the output of analog to digital conversion circuit is sent to host computer by single-chip microcomputer storage, digital filtering and by the RS232 interface.
As shown in Figure 6, the design that the present invention leads probe to electricity does not have special requirement, can cooperate with most of common conductance measurement probes to constitute complete conductance of liquid measuring system.At the traditional Chinese medicine industry in the Chinese medicine manufacture process to containing the demand that Chinese crude drug solution carries out state-detection, the present invention leads probe through the electricity of optimal design, that this probe has is anticorrosion, pollution-free, not with characteristics such as fluid to be measured generation electrochemical reaction, cooperate the complete conductivity test system of formation with said conductivity measuring device, realize the on-line monitoring of solution conductivity characteristic in the Chinese medicine manufacture process, for the status monitoring in the Chinese medicine manufacture process provides a kind of quantification, easy, low cost solution.
Custom-designed electricity is led probe at containing the conductance measurement of Chinese crude drug solution in the Chinese medicine manufacture process: electricity is led probe and is had the cork 1 that is connected with vial; the centre perforate of cork also closely is connected with glass bar 2; there is a radome 4 glass bar inside; have the contact conductor 3 and the potential electrode 5 that connect the conductance measurement electrode in the radome; rectangular channel is opened in the glass bar bottom; on relative two walls of a pair of rectangle potential electrode attached to rectangular channel; there is conductivity ceramics protection thin layer 7 on the potential electrode surface; the embedded temperature survey sleeve pipe of glass bar; the sealing of temperature survey sleeve bottom; outstanding glass bar is outer and concordant with the conductance measurement electrode; the temperature survey inside pipe casing has thermometric thermal resistance 6, and thermal resistance wiring and conductance electrode lead-in wire are drawn by the glass bar top.
Electricity is led in the brachium pontis of the temperature sensor PT100 cut-in temperature measuring bridge circuit on the probe.The temperature survey electric bridge is powered by a 2.5V constant-voltage DC source, the output of electric bridge through programmable amplifier amplify, after the analog to digital conversion by the Single Chip Microcomputer (SCM) system collection.
Claims (3)
1. high resolving power method for measuring conductance of liquid, it is characterized in that it adopts phase-locked amplification principle to realize that the high resolving power of conductance of liquid measures, promptly be under the situation of the sinusoidal signal excitation of the balanced amplitude modulation that sensor is applied an amplitude stabilization, carrying out multiplying by the balanced demodulator circuit, realize high-resolution measurement by the gain that improves the sensor signal amplifying circuit through the signal of sensor and a reference signal of amplifying with the carrier wave same frequency of sensor excitation signal.
2. high resolving power conductance of liquid measurement mechanism, it is characterized in that it has the electric waveguide measuring circuit plate and electricity is led probe, the circuit of electric waveguide measuring circuit plate is: oscillatory circuit I successively with equilibrium modulation circuit, measuring bridge, small signal amplification circuit, the balanced demodulator circuit, low-pass filter circuit I, rectification circuit, low-pass filter circuit II, analog to digital conversion circuit, single-chip microcomputer and RS232 interface join, single-chip microcomputer and small signal amplification circuit join, oscillatory circuit II joins with equilibrium modulation circuit and phase shifter respectively, phase shifter and balanced demodulator circuit join, said oscillatory circuit: with operational amplifier OP07CP is that core constitutes, the 7th pin and the positive supply of operational amplifier OP07CP join, the 4th pin and the negative supply of operational amplifier OP07CP join, the 2nd pin of operational amplifier OP07CP successively with resistance R 3, resistance R 4 is joined, another termination power ground of resistance R 3, the 2nd pin of the other end of resistance R 4 and adjustable resistance R5 joins, the 3rd pin of adjustable resistance R5 and the 1st pin of adjustable resistance R6 join, the 2nd pin of adjustable resistance R6 joins with the 6th pin of operational amplifier OP07CP and resistance R 1, the other end of resistance R 1 and capacitor C 1 are joined, the other end of capacitor C 1 respectively with capacitor C 2, the 3rd pin of resistance R 2 and operational amplifier OP07CP joins, another termination power ground of the other end of capacitor C 2 and resistance R 2, said phase shifter: with operational amplifier OP07 is core, the one termination signal input of resistance R 1, the 2nd pin of another termination operational amplifier OP07 of resistance R 1, the 2nd pin of one termination operational amplifier OP07 of resistance R 2, another termination operational amplifier OP07 output terminal the 6th pin of resistance R 2, the one termination signal input of capacitor C 1, the 3rd pin of another termination operational amplifier OP07 of capacitor C 1, the 3rd pin of operational amplifier OP07 is by adjustable resistance R3 ground connection, the 7th pin of operational amplifier OP07 connects positive supply, and the 4th pin connects negative supply.
3. a kind of high resolving power conductance of liquid measurement mechanism according to claim 2; it is characterized in that said electricity leads probe and have a cork (1) that is connected with vial; the centre perforate of cork also closely is connected with glass bar (2); there is a radome (4) glass bar inside; have the contact conductor (3) and the potential electrode (5) that connect the conductance measurement electrode in the radome; rectangular channel is opened in the glass bar bottom; on relative two walls of a pair of rectangle potential electrode attached to rectangular channel; there is conductivity ceramics protection thin layer (7) on the potential electrode surface; the embedded temperature survey sleeve pipe of glass bar; the sealing of temperature survey sleeve bottom; outstanding glass bar is outer and concordant with the conductance measurement electrode; the temperature survey inside pipe casing has thermometric thermal resistance (6), and thermal resistance wiring and conductance electrode lead-in wire are drawn by the glass bar top.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB2004100248022A CN1300596C (en) | 2004-05-26 | 2004-05-26 | High resolution liquid conductance measuring method and apparatus thereof |
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| Application Number | Priority Date | Filing Date | Title |
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| CNB2004100248022A CN1300596C (en) | 2004-05-26 | 2004-05-26 | High resolution liquid conductance measuring method and apparatus thereof |
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| CN1584611A CN1584611A (en) | 2005-02-23 |
| CN1300596C true CN1300596C (en) | 2007-02-14 |
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| CNB2004100248022A Expired - Fee Related CN1300596C (en) | 2004-05-26 | 2004-05-26 | High resolution liquid conductance measuring method and apparatus thereof |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101696994B (en) * | 2009-10-15 | 2012-09-05 | 杭州电子科技大学 | Online conductivity detector for seawater desalting |
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| CN100339718C (en) * | 2005-06-24 | 2007-09-26 | 浙江大学 | Operation frequency adjustable method for measuring conductance of liquid, and equipment |
| CN101609113B (en) * | 2009-06-11 | 2011-05-18 | 浙江大学 | Non-contact conductivity measuring device based on double shield structure and acceptor resonance and method thereof |
| CN104897970B (en) * | 2015-06-05 | 2017-12-01 | 中国海洋大学 | Liquid electric conductivity measuring method and system based on complement digital electric bridge |
| CN110320244B (en) * | 2019-07-29 | 2021-08-24 | 山东省科学院海洋仪器仪表研究所 | Seawater salinity measuring system and method based on quadrature phase-locked amplification technology |
| CN111289806A (en) * | 2020-03-27 | 2020-06-16 | 北京先通康桥医药科技有限公司 | Dynamic measurement circuit of array type capacitive sensor |
| CN112630268A (en) * | 2020-11-26 | 2021-04-09 | 燕山大学 | Bipolar miniature ion concentration sensor and measurement system thereof |
| CN113984839A (en) * | 2021-11-02 | 2022-01-28 | 上海交通大学 | Novel capacitive silk screen sensor for high-conductivity fluid measurement |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN2069567U (en) * | 1990-04-03 | 1991-01-16 | 常州市佳乐电子仪器厂 | Liquid dielectric resistivity/resistance tester |
| JPH06112290A (en) * | 1993-03-31 | 1994-04-22 | Agency Of Ind Science & Technol | Semiconductor evaluation device |
| CN1092870A (en) * | 1993-03-24 | 1994-09-28 | 中国兵器工业第五三研究所 | A kind of non-polar low-conductivity auto-measuring method |
| US6011400A (en) * | 1995-11-09 | 2000-01-04 | Krohne A.G. | Bushing for an electrical high-frequency signal and a measuring instrument containing same |
-
2004
- 2004-05-26 CN CNB2004100248022A patent/CN1300596C/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN2069567U (en) * | 1990-04-03 | 1991-01-16 | 常州市佳乐电子仪器厂 | Liquid dielectric resistivity/resistance tester |
| CN1092870A (en) * | 1993-03-24 | 1994-09-28 | 中国兵器工业第五三研究所 | A kind of non-polar low-conductivity auto-measuring method |
| JPH06112290A (en) * | 1993-03-31 | 1994-04-22 | Agency Of Ind Science & Technol | Semiconductor evaluation device |
| US6011400A (en) * | 1995-11-09 | 2000-01-04 | Krohne A.G. | Bushing for an electrical high-frequency signal and a measuring instrument containing same |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101696994B (en) * | 2009-10-15 | 2012-09-05 | 杭州电子科技大学 | Online conductivity detector for seawater desalting |
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