CN103728498B - A kind of conductivity/freq converting circuit - Google Patents
A kind of conductivity/freq converting circuit Download PDFInfo
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- CN103728498B CN103728498B CN201310518787.6A CN201310518787A CN103728498B CN 103728498 B CN103728498 B CN 103728498B CN 201310518787 A CN201310518787 A CN 201310518787A CN 103728498 B CN103728498 B CN 103728498B
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Abstract
The present invention relates to a kind of conductivity/freq converting circuit, for detecting the conductivity of solution.It is by comparer A1, analog switch IC, resistance R1-R3, electric capacity C, conductance electrode DDJ, form a square-wave generator it is characterized in that, solution resistance between described electric capacity C, conductance electrode DDJ, the RC charge-discharge circuit of composition square-wave generator, the electric current flowing through conductance electrode is made to be alternating current, this circuit structure is simple, the conductivity of solution can be converted to corresponding rate-adaptive pacemaker, and the power frequency of solution resistance can be flow through with the size auto-changing of solution resistance rate, the shunt capacitance effect errors of auto-compensation conductance cell and polarisation error.
Description
Technical field
The present invention relates to a kind of conductivity/freq converting circuit, for detecting the conductivity of solution.
Background technology
The measuring method of existing electrical conductivity of solution is, is inserted in solution by a conductance electrode and forms a conductance cell, and the electric conductivity of solution can with the solution resistance R between conductance electrode
xconductance 1/R reciprocal
xrepresent, by solution resistance R
xafter connecting with a reference resistance R, apply at the two ends of this series circuit to polarize in interface that an alternating voltage U(alternating voltage can not make electrode contact with solution, ensure the accuracy measured), then measure the voltage U on solution resistance
x, according to Ohm law U
x=U × R
x/ (R
x+ R) known, voltage U
xwith solution resistance R
xshould be related in a pair.But this measuring method the structure of measurement mechanism of use comparatively complicated: 1, need to arrange an oscillator device to produce alternating voltage U, an amplifying circuit also will be set to measured signal voltage U
xamplify, to the signal voltage U after amplification
xalso need to carry out rectification and convert thereof into direct-flow signal voltage; 2, the amplitude of the output signal voltage of higher requirement and oscillator is had must to ensure to stablize to oscillator.Moreover need automatically to control the conductivity of solution in many occasions, this needs to convert the direct current simulation signal of conductivity to digital signal, process for computer control system, converting direct current simulation signal to digital signal also needs an A/D conversion equipment.
In addition when measuring highly concentrated solution conductivity, because the current density on conductance electrode is larger, electrostatic double layer can be formed at electrode surface and produce chemical polarization, or the concentration of ate electrode solution is changed generation concentration polarization, make the conductivity of measurement lower than standard value; And measurement low conductivity solutions as during pure water owing to there is an equivalent shunt capacitance in conductance electrode, make the conductivity of measurement higher than standard value; For reducing polarisation error and shunt capacitance effect errors, the frequency of different alternating voltages to be adopted when measuring, making the design of alternating-current voltage source more complicated.
Summary of the invention
The technical problem to be solved in the present invention is to provide a kind of conductivity/freq converting circuit, is exported by the conductivity inversion frequency signal of solution, and this converting circuit structure is simple, and the polarisation error of energy auto-compensation conductance cell and shunt capacitance effect errors.
Technical scheme of the present invention is its new circuit structure, it comprises comparer A1, analog switch IC, resistance R1-R3, electric capacity C, it is characterized in that, resistance R1, R2, one end of R3 is connected with the in-phase input end of comparer A1, another termination power vd D of resistance R1, the output terminal of another termination comparer of resistance R2, the other end ground connection of resistance R3, the inverting input of comparer is by electric capacity C ground connection, conductance electrode DDJ is connected between the inverting input and common port 5 pin of analog switch IC of comparer, normal-closed end 6 pin of analog switch IC meets power vd D, the Chang Kaiduan 4 pin ground connection of analog switch IC, the output terminal of phase inverter exports its frequency of a square-wave signal and becomes a proportionate relationship with solution resistance in conductance electrode.
The resistance of described resistance R1, R2, R3 is 10K ohm, and the capacity of described electric capacity C is 0.1 microfarad, and the electrode constant of described conductance electrode is 1.0.
The invention has the beneficial effects as follows: 1, adopt simple circuit structure, the resistivity of solution between conductance electrode is converted to corresponding frequency signal; 2, this circuit can flow through the power frequency of solution resistance with the size auto-changing of solution resistance rate, the shunt capacitance effect errors of auto-compensation conductance cell and polarisation error.
Accompanying drawing explanation
Fig. 1 is circuit theory diagrams of the present invention.
Fig. 2 is the working waveform figure of Fig. 1.
Embodiment
Now contrast accompanying drawing and the specific embodiment of the present invention is described.
Circuit structure of the present invention is shown in Fig. 1, it comprises comparer A1, analog switch IC, resistance R1-R3, electric capacity C, conductance electrode DDJ, its interconnected relationship is, resistance R1, R2, one end of R3 is connected with the in-phase input end of comparer A1, another termination power vd D of resistance R1, the output terminal of another termination comparer of resistance R2, the other end ground connection of resistance R3, the inverting input of comparer is by electric capacity C ground connection, conductance electrode DDJ is connected between the inverting input and common port 5 pin of analog switch IC of comparer, normal-closed end 6 pin of analog switch IC meets power vd D, the Chang Kaiduan 4 pin ground connection of analog switch IC, control end 1 pin of analog switch IC is connected with the output terminal of comparer, this circuit forms a square-wave generator, the output terminal of phase inverter exports a square-wave signal, its frequency becomes a proportionate relationship with solution resistance in conductance electrode.
The model of described comparer is LM311 or other intimate models, and the model of described analog switch is MAX4729, and be hilted broadsword/double throw switch, its conducting resistance is less than 3 ohm.
Described resistance R1, R2, R3 form a positive-feedback circuit, level signal on comparator output terminal is fed back to the in-phase input end of comparer, the resistance of resistance R1, R2, R3 is 10K ohm, when comparator output terminal is high level, the voltage of comparer in-phase input end is about 2/3 of supply voltage, when comparator output terminal is low level, the voltage of comparer in-phase input end is about 1/3 of supply voltage; Change the resistance of resistance R1, R2, R3, the voltage of comparer in-phase input end can be changed.
Described electric capacity C is the tantalum electric capacity of 0.1 microfarad, and the voltage of power vd D is+5V, for comparer, analog switch provide working power.
The electrode constant (also claiming cell constant of conductometric vessel) of described conductance electrode DDJ is 1.0.
Principle of work of the present invention is, conductance electrode inserts in solution, solution resistance Rx between conductance electrode and electric capacity C and analog switch form a RC charge-discharge circuit, terminal voltage Uc on electric capacity C is input to the inverting input of comparer, when the voltage of inverting input is greater than the voltage of in-phase input end, comparator output terminal is low level " 0 ", and when the voltage of inverting input is less than the voltage of in-phase input end, comparator output terminal is high level " 1 "; Described charge-discharge circuit is controlled by the level state of inverter output, when comparator output terminal is high level " 1 ", 5 pin of analog switch communicate with 6 pin, electric capacity C is charged by solution resistance Rx, when comparator output terminal is low level " 0 ", 5 pin of analog switch communicate with 4 pin, and electric capacity C is discharged by solution resistance Rx, in solution resistance Rx, form alternating current thus, the frequency of this alternating current becomes a proportionate relationship with the size of solution resistance Rx.
When after power on circuitry of the present invention, because the voltage uc of electric capacity C can not suddenly change, voltage uc is 0, and the voltage of comparer inverting input is less than the voltage of in-phase input end, comparator output terminal is high level " 1 ", 5 pin of analog switch communicate with 6 pin, and electric capacity C is charged by solution resistance Rx, and the terminal voltage of electric capacity C exponentially rises, see 0-t1 section waveform in Fig. 2, in Fig. 2, Vo is the waveform of comparator output terminal, and uc is the waveform of electric capacity C terminal voltage, and I is the current waveform in solution resistance Rx.
When the terminal voltage of electric capacity C rises to the voltage being more than or equal to comparer in-phase input end, comparator output terminal is low level " 0 ", and 5 pin of analog switch communicate with 4 pin, and electric capacity C is discharged by solution resistance Rx, the terminal voltage of electric capacity C exponentially declines, see t1-t2 section waveform in Fig. 2; When the terminal voltage of electric capacity C drops to the voltage being less than or equal to comparer in-phase input end, comparator output terminal is high level " 1 ", and 5 pin of analog switch communicate with 6 pin, and electric capacity C is charged by solution resistance Rx, see t2-t3 section waveform in Fig. 2; So go round and begin again and form vibration, comparer exports a square-wave signal, and the frequency of square-wave signal is
f=1.443／（2Ro’＋2Rx’）C’(1)
The resistance of the conducting resistance that Ro ' is analog switch in formula 1, Rx ' is the resistance of the solution resistance between conductance electrode, the electric capacity that C ' is electric capacity;
Due to the conducting resistance of analog switch resistance Relative electro-conductivity electrode between the resistance of solution resistance very little (resistance of solution resistance can convert by selecting the conductance electrode of Different electrodes constant), can ignore, therefore formula 1 can be rewritten as
f=0.72／Rx’C’(2)
The inverse of solution resistance is solution conductivity, can find out the signal frequency that comparer exports and electrical conductivity of solution direct proportionality from formula 2.
In circuit of the present invention, be analog switch → solution resistance → electric capacity to the path of electric capacity C charge circuit, the path in capacitor discharge loop is electric capacity → solution resistance → analog switch, therefore the electric current flowing through solution resistance is the alternating current of positive and negative half cycle symmetry, not containing DC component, when measuring electrical conductivity of solution, polarization phenomena are smaller.
Another feature of the present invention is, can flow through the power frequency of solution resistance, the shunt capacitance effect errors of auto-compensation conductance cell and polarisation error with the size auto-changing of electrical conductivity of solution.Compensation principle is described as follows:
The electric capacity of described shunt capacitance for being formed for the migration of electrode because of the mutual migration of electric charge and electric charge, two pole pieces of it and conductance electrode are in parallel, and its capacity is about tens picofarads.(as distilled water, pure water) its resistance comparatively large (being greater than 100K ohm) when electrolysis of solutions matter concentration is lower, due to the impact of shunt capacitance, measured conductivity can be made to be greater than standard value, for reducing the impact of shunt capacitance, usually to adopt lower power frequency (lower than 100HZ);
Its resistance less (being less than 100 ohm) when the electrolyte concentration of solution is higher, current density on conductance electrode is crossed conference and is caused polarization, show as at electrode surface formation electrostatic double layer or the concentration of the electrolytic solution near conductance electrode is changed, this just makes the solution resistance of equivalence increase, and produces measuring error.According to electrochemical theory, can release due to the Wu Cha ⊿ R caused that polarizes, namely
⊿R＝E
2/fRx
2(3)
In formula 3, E is that polarization potential is relevant with the voltage swing being applied to the alternating current on solution resistance with the electrolyte concentration of solution, and f is alternating current voltage frequency, and Rx is the solution resistance between conductance electrode;
Can find out from formula 3 adopts high ac power frequency to reduce polarisation error.
The present invention can with the automatic change frequency of the size of solution resistance when measuring conductivity, and can find out from formula 2, the power frequency flow through when solution resistance is less is wherein higher, and the power frequency flow through when solution resistance is larger is wherein higher.It is 0.1 microfarad that the capacity of C is held in power taking, and when solution resistance is 100 ohm of-100K ohm, the power frequency flowing through solution resistance is 72KHZ-72HZ, therefore can the shunt capacitance effect errors of auto-compensation conductance cell and polarisation error.
Output frequency signal of the present invention is equivalent to a digital signal, can save A/D conversion equipment and directly be connected with the input end of single-chip microcomputer or other data processing chips, for controlling or display after data processing.
Claims (2)
1. conductivity/freq converting circuit, it comprises comparer A1, analog switch IC, resistance R1, R2, R3, electric capacity C, it is characterized in that, resistance R1, R2, one end of R3 is connected with the in-phase input end of comparer A1, another termination power vd D of resistance R1, the output terminal of another termination comparer of resistance R2, the other end ground connection of resistance R3, the inverting input of comparer is by electric capacity C ground connection, conductance electrode DDJ is connected between the inverting input and common port (5) pin of analog switch IC of comparer, normal-closed end (6) pin of analog switch IC meets power vd D, Chang Kaiduan (4) the pin ground connection of analog switch IC, the output terminal of comparer exports its frequency of a square-wave signal and becomes a proportionate relationship with solution resistance in conductance electrode.
2. conductivity/freq converting circuit according to claim 1, is characterized in that, the resistance of described resistance R1, R2, R3 is 10K ohm, and the capacity of described electric capacity C is 0.1 microfarad, and the electrode constant of described conductance electrode is 1.0.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310518787.6A CN103728498B (en) | 2013-10-29 | 2013-10-29 | A kind of conductivity/freq converting circuit |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310518787.6A CN103728498B (en) | 2013-10-29 | 2013-10-29 | A kind of conductivity/freq converting circuit |
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| CN103728498A CN103728498A (en) | 2014-04-16 |
| CN103728498B true CN103728498B (en) | 2015-12-02 |
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Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109188099B (en) * | 2018-09-12 | 2021-03-26 | 湖南宝德机电设备有限公司 | Liquid conductivity detection system |
| CN113484370A (en) * | 2021-05-26 | 2021-10-08 | 浙江探芯科技有限公司 | Conductivity measurement method and equipment |
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| US3906353A (en) * | 1973-10-09 | 1975-09-16 | Westinghouse Electric Corp | Oscillator circuit for providing a conductivity ratio of sea water |
| US4160946A (en) * | 1975-10-13 | 1979-07-10 | Sandoz Ltd. | Device for measuring conductivity of a solution |
| CN2669202Y (en) * | 2003-12-31 | 2005-01-05 | 北京联合大学生物化学工程学院 | Conductivity Pulse Measuring Device |
| CN1619318A (en) * | 2004-12-07 | 2005-05-25 | 苏州大学 | How to measure the conductivity of water |
| CN1821764A (en) * | 2006-01-24 | 2006-08-23 | 南京师范大学 | Concentration Online Measurement Method of High Concentration Acid |
| CN101135705A (en) * | 2006-08-30 | 2008-03-05 | 梅特勒-托利多仪器（上海）有限公司 | Measurement method of solution electric conductivity |
| CN202008592U (en) * | 2011-01-07 | 2011-10-12 | 肖斌 | Water yield and water quality monitoring alarm for water purifier |
| CN202948067U (en) * | 2012-09-19 | 2013-05-22 | 福建师范大学 | Key solution conductivity measuring circuit adopting triangular waves for excitation and integration processing |
| CN203572885U (en) * | 2013-10-29 | 2014-04-30 | 高玉琴 | Conductivity/frequency converting circuit |
-
2013
- 2013-10-29 CN CN201310518787.6A patent/CN103728498B/en active Active
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3906353A (en) * | 1973-10-09 | 1975-09-16 | Westinghouse Electric Corp | Oscillator circuit for providing a conductivity ratio of sea water |
| US4160946A (en) * | 1975-10-13 | 1979-07-10 | Sandoz Ltd. | Device for measuring conductivity of a solution |
| CN2669202Y (en) * | 2003-12-31 | 2005-01-05 | 北京联合大学生物化学工程学院 | Conductivity Pulse Measuring Device |
| CN1619318A (en) * | 2004-12-07 | 2005-05-25 | 苏州大学 | How to measure the conductivity of water |
| CN1821764A (en) * | 2006-01-24 | 2006-08-23 | 南京师范大学 | Concentration Online Measurement Method of High Concentration Acid |
| CN101135705A (en) * | 2006-08-30 | 2008-03-05 | 梅特勒-托利多仪器（上海）有限公司 | Measurement method of solution electric conductivity |
| CN202008592U (en) * | 2011-01-07 | 2011-10-12 | 肖斌 | Water yield and water quality monitoring alarm for water purifier |
| CN202948067U (en) * | 2012-09-19 | 2013-05-22 | 福建师范大学 | Key solution conductivity measuring circuit adopting triangular waves for excitation and integration processing |
| CN203572885U (en) * | 2013-10-29 | 2014-04-30 | 高玉琴 | Conductivity/frequency converting circuit |
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Effective date of registration: 20211117 Address after: 276700 Zhongchuang space, Xingye street, economic development zone, Linshu County, Linyi City, Shandong Province Patentee after: Linshu Yixing steam supply maintenance service Co.,Ltd. Address before: 225500 C2-304 room, Kam do international garden, Jiangyan Town, Jiangyan District, Taizhou, Jiangsu. Patentee before: Gao Yuqin |
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