JP2002071646A - Liquid concentration measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of needing to be careful about the accuracy evaluation of the divided position of a concentration region, an interpolation point and an extrapolation point, and the like other than data used for fitting when expressing concentration by a relational expression to a specific material property value. SOLUTION: In this concentration measuring method for measuring the concentration C of a solution from two kinds of specific material property quantities αand β, the relational expression β=fi(α) is stored for each of a plurality of different concentrations Ci and the liquid concentration C is obtained from the measured material property quantity α, a new relational expression C=g(β) obtained at real time from the stored β=fi(α), and the measured material property quantity β. In this case, the temperature of the liquid is used as the material property quantity α to compensate the temperature of the measured liquid concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a concentration, and more particularly to a method for measuring a concentration of a liquid exhibiting a concentration corresponding to two physical properties.

[0002]

2. Description of the Related Art The concentration of a liquid is expressed as a function of density and refractive index, a function of conductivity and pressure, a function of ultrasonic velocity and temperature, and the like. For example, from the density D and the refractive index R, the density C
Is determined beforehand by experimentally determining a relational expression C = F (D, R) using the density D and the refractive index R as variables, and obtaining the concentration C from the measured values of the density D and the refractive index R. There is. In addition, C = F (P, ρ) using the pressure P and the conductivity ρ as variables is experimentally determined, and the concentration C is determined from the measured values of the pressure P and the conductivity ρ.
Further, as shown in Japanese Patent Publication No. 04-008746, the relational expression C = T between the temperature T, the velocity V of the ultrasonic wave, and the concentration C
There is a method in which F (T, V) is experimentally determined, and a concentration C is obtained from a measured value of the temperature T and the velocity V of the ultrasonic wave.

[0003]

When these methods are used, it is important to evaluate the accuracy of the relational expression F. That is, as shown in FIG. 4, the relational expression F = (α, β) represents a curved surface in a three-dimensional space having two variables, and may exhibit a complicated curved surface depending on the solution. In this case, even if a term having a higher order is used, the term may be different from the actually measured value. In this case, a plurality of relational expressions may be used by dividing the density region into several parts.

In particular, when a change in a physical property value due to a change in density is large, it is necessary to pay attention to the accuracy of evaluation of a division position of a density region, an interpolation point and an extrapolation point other than data used for fitting. Become.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a concentration measuring method which can easily perform fitting and can easily evaluate the accuracy of an empirical formula. .

[0006]

The present invention employs the following means to achieve the above object. That is, an object of the present invention is to provide a concentration measuring method for measuring the concentration C of a solution from two physical quantities α and β of a solution. For each of a plurality of different concentrations Ci, a relational expression β = fi (α) is obtained. The measured physical property α and the stored β
= Fi (α), the liquid concentration C is obtained from a new relational expression C = g (β) obtained in real time and the measured physical property β.

Here, the temperature of the measured liquid concentration can be compensated by adopting the temperature of the liquid as the physical quantity α.

[0008]

1 and 2 are conceptual diagrams showing an embodiment of the present invention when the concentration C depends on the temperature T and the sound velocity V of the ultrasonic wave, and FIG. 3 shows an apparatus used in the present invention. It is a block diagram showing an example.

First, while the concentration of a specific type of solution is kept constant, the temperature is changed, and the sound speed V of the ultrasonic wave in the solution at each temperature is actually measured by the measuring means 3. This operation is performed for solutions having different concentrations, and for each concentration,
As shown in FIG. 1, the relational expression V = fi (T) is stored in the storage unit 1.
To memorize it.

Next, the temperature T of the solution having the unknown concentration C and the sound velocity V of the ultrasonic wave are actually measured by the measuring means 3, and as shown in FIG. The relational expression C = g (V) between the sound velocity V and the density C at the time is calculated in real time by the calculating means 2, and the density C is obtained from the sound velocity V obtained by actual measurement.

As described above, in addition to the temperature T (= α) and the sound speed V (= β) of the ultrasonic wave, the relational expression D = fi (R) is stored by using the refractive index R as α and the density D as β. 1 to calculate the relationship C = g (D), or
Using the pressure P as α and the conductivity ρ as β, the relational expression ρ =
fi (P) is stored in the storage means 1, and the relation C = g
A method of calculating (ρ) can be considered.

As is clear from the above description, the present invention reduces the number of orders to be handled, simplifies the curve shape, and facilitates fitting without dividing the density region and setting an equation. In addition, accuracy evaluation of the empirical formula can be simplified. Basically, a relational expression relating only to a necessary area (for example, a specific temperature, a specific refractive index, and a specific pressure) is calculated in real time.
The present invention can be applied to a case where more than one kind of specific physical quantity is used.

[Brief description of the drawings]

FIG. 1 is a graph showing actually measured values of the temperature and the sound speed of an ultrasonic wave used in the present invention.

FIG. 2 shows sound velocity V and density C obtained from FIG. 1 at a specific temperature.
6 is a graph showing a relationship with the graph.

FIG. 3 is a block diagram showing an apparatus for implementing the present invention.

FIG. 4 is a graph for calculating a density according to a conventional method.

Claims (2)

[Claims] 1. A concentration measuring method for measuring a concentration C of a solution from two physical quantities α and β of a solution, wherein a relational expression β = fi (α) is stored for each of a plurality of different concentrations Ci. In advance, from the measured physical property α and the stored β = fi (α), a new relational expression C = g (β) obtained in real time and the liquid concentration C from the measured physical property β
A liquid concentration measuring method, wherein 2. The method according to claim 1, wherein the physical quantity α is a temperature of the liquid.