CN1285904C - Measuring method of electroconductirity of water - Google Patents

Abstract

The present invention discloses a measuring method of conductivity of water. The present invention is characterized in that sine signals of the frequency omega <a> and omega <b> are respectively added on both ends of a conductance cell, wherein omega <b> =2 omega<a>; impedance molds |Z <a>| and |Z<b>| under the two frequency are respectively measured; a conductivity value g needed to be measured is obtained by utilizing a formula which is disclosed in the specification, wherein the K is a constant of the conductance cell, and r=|Z <a> |/|Z<b>|. The present invention does not have theoretical errors and completely eliminates the influence of capacitance effect of a conductance alternate current measuring method. The present invention can accurately measure the conductivity of water.

Description

The measuring method of electrical conductivity of water

Technical field

The present invention relates to a kind ofly know the method for its conductivity, be specifically related to a kind of measuring method of electrical conductivity of water by the test liquid impedance.

Background technology

Conductivity is one of important indicator of generating plant water quality control, for a long time, how accurately to measure electrical conductivity of water, and particularly high-purity electrical conductivity of water is the problem that monitoring water quality personnel and conductivity meter manufacturer extremely pay close attention to and further investigate always.Electrical conductivity of water can be calculated by following formula and obtain in the conductance cell:

g＝K/R (1)

In the formula, K is cell constant of conductometric vessel (claiming electrode constant again).

Thus, the mensuration of conductivity is converted to mensuration to resistance.

At present, the measuring method of conductivity mainly contains DC conductance determination method and conductance for alternating current determination method, and wherein, the DC conductance determination method seldom adopts owing to be difficult to solve " the polarization effect problem " of electrode.It is that two interpolars at conductance cell add sine voltage signal that conductance for alternating current is measured rule, utilizes AC signal to reduce the influence of polarization effect.

After conductance cell two interpolars add sinusoidal voltage, on the two poles of the earth, will produce polarization layer, simultaneously, have capacity effect at polarise layer and two interpolars, like this, conductance cell no longer is a pure resistance, but comprising capacitive reactance in interior impedance, its equivalent physical model is as shown in Figure 1.Among the figure, R _L2, R _L2Be lead resistance, C _DL1And C _DL2Electric capacity on two electrostatic double layers that expression is caused by polarization, C _PBe the interelectrode capacity of conductance cell, Z ₁And Z ₂The impedance that representative is responded on two electrode slices, promptly usually said interpolar polarization resistance, R _SDLRepresent the resistance of water between the two poles of the earth.

Wherein, lead resistance R _L1, R _L2Ignore under normal conditions, when the conductance cell two ends applied an AC power, it will flow through C simultaneously _DL1, C _DL2, R _SDLAnd C _P, because C _DL1And C _DL2For AC signal, provide a low pass path, Z ₁And Z ₂Respectively by C _DL1And C _DL2Short circuit, generally, C _PVery little, C _DL1And C _DL2Very big, the impedance of conductance cell is approximately R _SDLThe method that existing conductance for alternating current determination method that Here it is adopts.Obviously, in measure R _SDLDuring very big high resistance solution (as purer water), C _PInfluence just can not ignore, at this moment, adopt the accuracy of existing interchange determination method not high.

For this reason, people seek the method for testing of electrical conductivity of water more accurately by all means.Liu Kaipei etc. are at " high purity water conductance measurement dynamic pulse production method " (industrial instrument and automation equipment, 1999 the 5th phases) in the literary composition, provided a kind of method of utilizing dynamic pulse to measure conductivity, the influence that it reduces to polarize and produce by the restriction pulse width, but also point out in the literary composition, for different detected solutions, the influence of pulse width is different, this has just caused the difficulty in this method practicality, simultaneously, this method need produce dynamic pulse, and this has also caused the increase of device fabrication difficulty and cost.Disclose a kind of measuring method of electrical conductivity of solution in Chinese patent application CN1459629A, calculated conductivity indirectly by the measurement of active power, this method need be calculated with the time integration, has increased intractability.

Summary of the invention

The object of the invention provides a kind of influence that can avoid polarization effect and distributed capacitance, obtains the measuring method of the electrical conductivity of water of conductivity value accurately.

For achieving the above object, the technical solution used in the present invention is: a kind of measuring method of electrical conductivity of water, adding upper frequency at the two poles of the earth of conductance cell respectively is ω _aAnd ω _bSinusoidal signal, wherein, ω _b=2 ω _a, measure the mould of the impedance of conductance cell under two kinds of frequencies respectively | Z _a| and | Z _b|, utilize following formula to obtain the conductivity value g of required mensuration,

$g=K/\left(\right|Z_a|\&CenterDot;\sqrt{1+\frac{r^2-1}{4-r^2}})$

In the formula, K is a cell constant of conductometric vessel, r=|Z _a|/| Z _b|.

In the technique scheme, the measuring method of the mould of described impedance is, the circuit that adopts the output terminal of conductance cell to be connected with the operational amplifier end of oppisite phase adds the sinusoidal signal of an amplitude stability to conductance cell, by the output voltage V of measuring operational amplifier _oInput voltage V with conductance cell _i, the mould of acquisition impedance | Z|=R _fV _i/ V _o, in the formula, R _fBe the operational amplifier end of oppisite phase with output terminal between the feedback resistance that is connected.Adding upper frequency respectively is ω _aSinusoidal signal and frequency be ω _b=2 ω _aSinusoidal signal, can record the mould of two impedances under the frequency.

Certainly, also can adopt another kind of technical scheme to measure the mould of impedance, that is, add frequencies omega earlier _aSinusoidal signal, measure voltage U _aAnd electric current I _a, the mould of acquisition impedance | Z _a|=U _a/ I _aAdd frequencies omega _b=2 ω _aSinusoidal signal, measure voltage U _bAnd electric current I _b, the mould of acquisition impedance | Z _b|=U _b/ I _b

Principle of the present invention is:

In accompanying drawing 1, because C _DL1And C _DL2Very big, and C _PVery little, therefore, Fig. 1 can be reduced to the equivalent physical model of accompanying drawing 2, wherein R ≈ R _SDL, C ≈ C _P

In frequency is ω _aThe sinusoidal signal effect under, the RC parallel impedance is

$Z_a=\frac{R(1-j{\mathrm{\&omega;}}_a\mathrm{RC})}{1+{{\mathrm{\&omega;}}_a}^2{R}^2{C}^2}$

The mould of impedance

$\left|Z_a\right|=\frac{R}{\sqrt{1+{\mathrm{\&omega;}}_a^2{R}^2{C}^2}}$

Lead the amplitude (as long as promptly knowing the mould of impedance) of knowing sine wave as long as measure electricity, there is no need to be concerned about phase place, when the frequencies omega of excitation sine wave signal _b=2 ω _aThe time, the mould of impedance is

$\left|Z_b\right|=\frac{R}{\sqrt{1+4{\mathrm{\&omega;}}_a^2{R}^2{C}^2}}$

Order $t={\mathrm{\&omega;}}_a^2{R}^2{C}^2,$ R=|Z _a|/| Z _b|, have

$r=\sqrt{\frac{1+4\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="C20041006614700073.png"\; state="\{\{state\}\}">t</figure-callout>}}{1+t}}$

Can solve

$t=\frac{r^2-1}{4-r^2}$

Thereby,

$g=K/\left(\right|Z_a|\&CenterDot;\sqrt{1+\frac{r^2-1}{4-r^2}})$

When measuring impedance, shown in accompanying drawing 3, wherein, conductance cell is equivalent to the mould of its impedance | and Z| then has

V _o＝V _iR _f/|Z|

As can be known, | Z|=R _fV _i/ V _o

Because the technique scheme utilization, the present invention compared with prior art has following advantage:

1. because the present invention utilizes the sinusoidal signal of two frequencys multiplication to measure, can obtain the actual resistance of water, not have theoretical error, lead the influence of the capacity effect that exchanges determination method thereby eliminated electricity fully;

2. the present invention is by the mould value of two impedances of twice mensuration acquisition, can obtain conductivity through simple operation, it is convenient to realize, can utilize existing AC conductivity measurement mechanism, increase double frequency sinusoidal signal generator, can realize measuring by changing control program.

Description of drawings

Accompanying drawing 1 is the equivalent physical model of conductance cell;

Accompanying drawing 2 is the simplification equivalent physical model of conductance cell;

Accompanying drawing 3 is the metering circuit principle schematic that the method for the embodiment of the invention one adopts.

Wherein: [1], conductance cell.

Embodiment

Below in conjunction with drawings and Examples the present invention is further described:

Embodiment one: a kind of measuring method of electrical conductivity of water, adding upper frequency at the two poles of the earth of conductance cell respectively is ω _aAnd ω _bSinusoidal signal, wherein, ω _b=2 ω _a, measure the mould of the impedance under two kinds of frequencies respectively | Z _a| and | Z _b|, utilize following formula to obtain the conductivity value g of required mensuration,

$g=K/\left(\right|Z_a|\&CenterDot;\sqrt{1+\frac{r^2-1}{4-r^2}})$

In the formula, K is a cell constant of conductometric vessel, r=|Z _a|/| Z _b|.

In the present embodiment, the metering circuit of the mould of described impedance is referring to shown in the accompanying drawing 3, and an electrode of conductance cell 1 is connected with the end of oppisite phase of operational amplifier A, is connected with resistance R between the end of oppisite phase of operational amplifier A and the output terminal _f, add the sinusoidal signal V of an amplitude stability for conductance cell 1 _i, by the output voltage V of measuring operational amplifier A _oInput voltage V with conductance cell 1 _i, the mould of the impedance of acquisition conductance cell 1 | Z|=R _fV _i/ V _o, in the formula, R _fBe the operational amplifier end of oppisite phase with output terminal between the feedback resistance that is connected.During measurement, add the sinusoidal signal of two kinds of frequencies respectively, measure the mould of the impedance of corresponding conductance cell, draw the conductivity value of required mensuration again.

Embodiment two: a kind of measuring method of electrical conductivity of water, adding upper frequency at the two poles of the earth of conductance cell respectively is ω _aAnd ω _bSinusoidal signal, wherein, ω _b=2 ω _a, measure the mould of the impedance under two kinds of frequencies respectively | Z _a| and | Z _b|, utilize following formula to obtain the conductivity value g of required mensuration,

$g=K/\left(\right|Z_a|\&CenterDot;\sqrt{1+\frac{r^2-1}{4-r^2}})$

In the formula, K is a cell constant of conductometric vessel, r=|Z _a|/| Z _b|.

In the present embodiment, the measuring method of the mould of described impedance can be to add frequencies omega earlier _aSinusoidal signal, measure voltage U _aAnd electric current I _a, the mould of acquisition impedance | Z _a|=U _a/ I _aAdd frequencies omega _b=2 ω _aSinusoidal signal, measure voltage U _bAnd electric current I _b, the mould of acquisition impedance | Z _b|=U _b/ I _b

Claims (2)

1. A method for measuring the conductivity of water, characterized in that: adding frequency ω _a and ω _b sinusoidal signals at the two poles of the conductance cell, wherein, ω _b = 2ω _a , measured at two frequencies The modulus |Z _a | and |Z _b | of the impedance of the lower conductivity cell, use the following formula to obtain the required measured conductivity value g, $\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; K</span>}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; \&Center\; Dot;</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; )</span>$ In the formula, K is the conductivity cell constant, r=|Z _a |/|Z _b |. 2. the measuring method of the conductivity of water according to claim 1, is characterized in that: the measuring method of the mold of described impedance is, adopts the circuit that the output end of conductance cell is connected with the inverting end of operational amplifier, gives conductance cell Add a sinusoidal signal with stable amplitude, and measure the output voltage V _o of the operational amplifier and the input voltage V _i of the conductivity cell to obtain the modulus of impedance |Z|=R _f V _i /V _o , where R _f is Feedback resistor connected between the inverting terminal of the operational amplifier and the output terminal.

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