JP2001242099A - Microwave type concentration meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of concentration measurement on a measurement objective liquid consisting of suspension or solution of a substance with a dielectric constant variable according to a temperature. SOLUTION: In the previous steps to a concentration computing circuit 18, this microwave type concentration meter is provided with a temperature detector 21, a zero point temperature correcting circuit 22, a calibration curve inclination correcting circuit 23, and a calibration curve intercept correcting circuit 24. Therefore, respective factors such as a phase difference Δθ, an inclination (a), an intercept b in the calibration curve of a concentration x are corrected according to a temperature of the measurement liquid, and then, the concentration x is calculated on the basis of the corrected calibration curve.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave densitometer for measuring the concentration of a measurement liquid based on the propagation delay of an incident microwave, and more particularly to a method for correcting the liquid temperature of the measurement liquid. The present invention relates to a microwave type densitometer which can be improved to improve the accuracy of concentration measurement.

[0002]

2. Description of the Related Art Generally, ultrasonic densitometers and optical densitometers are widely used as densitometers for measuring the concentration of a liquid to be measured containing various suspended or soluble substances such as sludge, pulp, and building materials. Used.

[0003] The ultrasonic densitometer is a device that measures the attenuation rate of ultrasonic waves and obtains the concentration of the liquid to be measured. However, when bubbles are mixed in the liquid to be measured, the ultrasonic densitometer tends to increase the measurement error due to the influence of the bubbles.

[0004] An optical densitometer is a device for measuring a transmitted light attenuation rate or a scattered light increase rate using light to obtain a density. However, in the optical densitometer, when dirt adheres to an optical window through which light enters or exits, a measurement error tends to increase due to the influence of the dirt.

On the other hand, recently, a microwave type densitometer has been developed and practically used as a device which hardly causes a measurement error due to such bubbles and dirt.

FIG. 6 is a block diagram showing the configuration of such a microwave type densitometer. In this microwave densitometer, a microwave transmitted from a microwave oscillator 11 is distributed by a power splitter 12 to a reference system path and a measurement system path.

First, the microwave passing through the reference system path is introduced into the phase difference measuring circuit 14 via the transmission cable 13.

On the other hand, the microwave passing through the measurement system path is transmitted to the microwave transmitting antenna 1 attached to the side of the pipe 15.
6 in a direction orthogonal to the longitudinal direction of the pipe 15
5, passes through the liquid to be measured flowing through the pipe 15, is emitted to the microwave receiving antenna 17 disposed opposite to the side surface on the opposite side of the pipe 15, and measures the phase difference from the microwave receiving antenna 17. It is introduced into the circuit 14.

There are two types of liquids to be measured: a liquid for concentration reference having a concentration of zero (or a reference value) and a liquid for measurement having a concentration x.
1, θ2 are measured.

That is, in the phase measuring circuit 14,
As shown in FIG. 7, the microwave directly received from the microwave oscillator 11 via the transmission cable 13 or the like is used as a phase reference. The phase difference θ2 = 360−θs caused by the phase delay θs of the microwave when the
Lag θw when microwaves are filled with a reference liquid (for example, tap water that can be regarded as having a zero concentration) and flowed
Is measured as θ1 = 360−θw, and θ2 is compared with θ1, and the phase difference Δθ = (θ2−θ1) = (θw
−θs) and sends it to the density calculation circuit 18. In addition,
It has been theoretically and experimentally confirmed that there is an excellent linear relationship between the phase difference Δθ and the concentration x of the measurement liquid as shown in a calibration curve in FIG.

The concentration calculation processing section 18 calculates the concentration x of the measuring liquid based on the phase difference Δθ and the calibration curve.
Specifically, the density calculation processing unit 18 calculates the density x = a △ θ +
The density x is calculated by the calculation of b. Here, a is the slope of the calibration curve, and b is the intercept of the calibration curve. Usually, b = 0.

Such a microwave densitometer is based on the following principle. That is, when the concentration of the suspended substance or the soluble substance in the liquid to be measured changes, the dielectric constant and conductivity of the whole liquid to be measured change. When the dielectric constant and the conductivity change, the speed of the radio wave propagating in the liquid to be measured changes. Here, the microwave densitometer measures the speed change of the radio wave due to such a density change as a phase change, and is based on the principle that the difference Δθ of the phase change is proportional to the density.

[0013] Such a microwave densitometer is not a method of measuring the attenuation rate of microwaves, but a phase difference Δθ.
(Hereinafter referred to as phase difference Δθ) It is not necessary to make the window through which microwaves enter or exit transparent, so it is hardly affected by bubbles and dirt, and the concentration can be measured continuously. It has become.

In the microwave type densitometer as described above, since the dielectric constant of the liquid to be measured generally changes depending on the temperature and affects the phase difference Δθ, the liquid temperature is corrected. .

For example, when the reference liquid is water, the difference Δt (= ts−tw) between the liquid temperature ts of the liquid to be measured and the zero point, that is, the water temperature tw at the time of θ1 measurement, and the phase difference correction value Δθt are shown in FIG. 9
As shown in the above, since the liquid crystal temperature is in a substantially linear relationship via the liquid temperature correction coefficient α, the concentration x is calculated based on the calibration curve using the phase difference Δθ ′ = (Δθ−Δθt) after the liquid temperature correction. ing.

This liquid temperature correction is based on the property that the dielectric constant of water changes substantially linearly according to the water temperature, as shown in FIG. In addition, the liquid temperature correction is a method in which the zero point (θ1) of the phase difference is translated in parallel by a phase difference correction value Δθt obtained by multiplying a previously obtained water temperature difference Δt by a liquid temperature correction coefficient α. ing.

[0017]

However, in the microwave type densitometer as described above, when the substance whose permittivity of the suspended substance changes with temperature is the object to be measured, the concentration measurement result becomes inaccurate. There is.

For example, in the case of a certain polymer or the like, FIG.
As shown in FIGS. 12A and 12A, the dielectric constant of the suspended substance changes according to the temperature, and the slope of the calibration curve changes as shown in FIGS. 11B and 12B. .

For this reason, when the concentration is high or when the liquid temperature difference from the zero point is large, the correction of only the water temperature, that is, the correction of only the parallel movement of the zero point is not sufficient, and the measurement result of the concentration is inaccurate. It may be.

The present invention has been made in view of the above circumstances, and can improve the accuracy of concentration measurement for a liquid to be measured consisting of a suspension or solution of a substance whose dielectric constant changes with temperature. It is intended to realize a microwave densitometer.

[0021]

The gist of the present invention is a micrometer for measuring the concentration of a mixed substance in a liquid to be measured containing mixed substances such as various suspended substances such as sewage sludge, pulp and paint, and soluble substances. In a wave type densitometer, especially when the measurement sensitivity of the liquid to be measured changes with temperature, that is, when the slope or intercept of the calibration curve changes with temperature, the slope and intercept of the calibration curve in addition to the conventional zero point liquid temperature correction Alternatively, there is provided means for correcting the liquid temperature of both of them. This allows
It is possible to realize a microwave densitometer that can accurately measure various substances even when the concentration is high and the liquid temperature greatly changes.

On the basis of the gist of the present invention as described above, the following means are specifically taken. That is,
In order to achieve the above object, the present invention provides a detector pipe for flowing a liquid for measurement, a microwave transmitting antenna and a microwave receiving antenna disposed to face each other with the detector pipe interposed therebetween, and the microwave transmitting antenna. Microwave transmitting means for transmitting microwaves to be supplied to the antenna, and microwaves transmitted from the microwave transmitting antenna, propagated through the liquid for measurement in the pipe, and received by the microwave receiving antenna. Measure the phase delay θ2, and
A phase difference measuring means for comparing the phase delay of a microwave when the pipe is filled with a reference liquid in advance and measuring the same under the same conditions as the measurement liquid, and measuring the phase difference Δθ = (θ2−θ1). And correcting the phase difference Δθ measured by the phase difference measuring means based on a temperature difference Δt (= tw−ts) between the liquid temperature ts of the measuring liquid and the liquid temperature tw of the reference liquid, A phase difference correction unit for obtaining a phase difference Δθ ′, and at least one term on the right side of a calibration curve x = a · Δθ ′ + b corresponding to each of the measurement liquids, based on the liquid temperature ts of the measurement liquid. Calibration curve correcting means for correcting, and concentration calculating means for calculating the concentration x of the measuring liquid based on the phase difference Δθ 'obtained by the phase difference correcting means and the calibration curve corrected by the calibration curve correcting means. It is a microwave type densitometer provided with.

(Operation) Accordingly, the present invention, by taking the above-described means, can determine the temperature based on the temperature of the measuring liquid.
Each element such as the phase difference Δθ, the slope a, and the intercept b in the calibration curve of the concentration x is corrected, and the concentration x is calculated based on the corrected calibration curve. Therefore, the suspension of a substance whose dielectric constant changes according to the temperature. The accuracy of the concentration measurement can be improved for a liquid to be measured, which is a liquid or a solution.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a microwave densitometer according to one embodiment of the present invention. The same parts as those in the above-mentioned drawings are denoted by the same reference numerals, and detailed description thereof will be omitted. Is mainly described.

That is, in the present embodiment, the accuracy of the concentration measurement is improved even if the slope or intercept of the calibration curve is a substance that changes according to the liquid temperature. Specifically, a temperature detector 21, a zero-point temperature correction circuit 22, a calibration curve inclination correction circuit 23, and a calibration curve intercept correction circuit 24 are provided before the concentration calculation circuit 18.

The temperature detector 21 is attached to the pipe 15, measures the temperature of the liquid to be measured flowing in the pipe 15, and sends a liquid temperature signal indicating the liquid temperature to a zero point temperature correction circuit 22, a calibration curve. It is sent to the inclination correction circuit 23 and the calibration curve intercept correction circuit 24.

The zero-point temperature correction circuit 22 includes a temperature detector 2
As shown in FIG. 9, the function for obtaining a temperature difference (tw−ts) = △ t between the liquid temperature ts indicated by the liquid temperature signal sent from 1 and the water temperature tw at a predetermined zero point, and the temperature difference Δt. Based on the phase difference correction formula △ θt = α · Δt, the phase difference correction value △ θt
And a function of subtracting で θt from the phase difference Δθ measured by the phase difference measurement circuit 14, and calculating the obtained value of the phase difference ゼ ロ θ '= (△ θ- △ θt) after the zero-point temperature correction, for the density calculation. Circuit 1
8 is provided.

The calibration curve slope correction circuit 23 includes a temperature detector 2
Determined based on the slope a _t of the corresponding calibration curve on the liquid temperature ts indicated by the liquid temperature signal sent from the 1 to the function a _{t =} f _(t),
The resulting values a _t is to sent to the concentration calculation circuit 18.

The calibration curve intercept correction circuit 24 includes the temperature detector 2
The intercept b1 of the calibration curve corresponding to the liquid temperature ts indicated by the liquid temperature signal transmitted from 1 is obtained based on the function b _t = g (t),
The resulting value b _t is intended to be sent to the concentration calculation circuit 18.

The concentration arithmetic circuit 18 is having the aforementioned same concentration calculation function, the value used for the calculation is the liquid temperature corrected phase difference [Delta] [theta] ', the slope a _t, and has a section b1. That is,
The concentration calculation circuit 18 receives the zero-point temperature-corrected phase difference 温度 θ ′ received from the zero-point temperature correction circuit 22, the calibration curve slope a _t received from the calibration curve slope correction circuit 23, and the calibration curve intercept correction circuit 24. based on the value of the intercept b _t of the received calibration curve, it has a function of calculating the concentration _{x = a t · △ θ '} + b t, and calculates the concentration x of the analyte solution.

Next, the operation of the microwave densitometer configured as described above will be described. Now, the calibration curve after the zero point temperature correction of the liquid to be measured has the liquid temperature characteristic shown in FIG. 2, and the liquid temperature characteristic of the slope at is the function at = t of the liquid temperature t shown in FIG.
It is assumed that the liquid temperature characteristic of the intercept b is expressed by f (t) and the function bt = g (t) of the liquid temperature t shown in FIG.

The liquid temperature characteristics of the calibration curve may be obtained by a theoretical calculation formula based on the temperature change characteristics of the permittivity, conductivity, density and permittivity of the suspended substance. When the characteristics are unknown, etc., it may be obtained from the measurement results of the temperature change characteristics of the sample liquid of the substance to be measured.

Here, the phase difference measuring circuit 14 measures the phase difference Δθ and sends the phase difference Δθ to the zero point temperature correction circuit 22 as described above.

On the other hand, the liquid temperature signal measured by the temperature detector 21 is sent to a zero point correction circuit 22, a calibration curve inclination correction circuit 23, and a calibration curve intercept correction circuit 24.

The zero point temperature correction circuit 22 calculates a temperature difference (t) between the liquid temperature ts indicated by the liquid temperature signal and a predetermined zero point water temperature tw.
(w−ts) = △ t, the phase difference correction value △ θt is obtained from Δt based on the phase difference correction formula △ θt = α · △ t as shown in FIG. Then, △ θt is subtracted from the phase difference Δθ measured in step (1), and the obtained value of the phase difference △ θ ′ = (△ θ- △ θt) after the zero point temperature correction is sent to the density calculation circuit 18.

On the other hand, a calibration curve inclination correction circuit 23 obtains based on the slope a _t of calibration curve corresponding to the liquid temperature ts indicated by the liquid temperature signal to the function a _{t =} f (t) such as shown in FIG. 3, the resulting values a _t is sent to the concentration calculation circuit 18.

On the other hand, the calibration curve intercept correction circuit 24 obtains the intercept b1 of the calibration curve corresponding to the liquid temperature ts indicated by the liquid temperature signal based on the function b _t = g (t) as shown in FIG. the resulting value b _t is sent to the concentration calculation circuit 18.

[0038] In the concentration arithmetic circuit 18, a phase difference after these zero-point temperature compensation △ theta ', the slope a _t of calibration curve corresponding to the liquid temperature _ts, the value of the intercept b _t of the calibration curve corresponding to the liquid temperature ts based on, calculates the concentration _{x = a t · △ θ '} + b t, and calculates the concentration x of the analyte solution.

As described above, according to the present embodiment, based on the liquid temperature ts of the measuring liquid, each element such as the phase difference Δθ, the slope a, and the intercept b in the calibration curve of the concentration x is corrected.
Since the concentration x is calculated based on the calibration curve after the correction, the accuracy of the concentration measurement can be improved for a measurement target liquid composed of a suspension or solution of a substance whose dielectric constant changes according to the temperature. . In addition, the concentration can be accurately measured even when the concentration is high or the liquid temperature difference from the zero point is large.

In the above embodiment, FIG.
Although the case where the change characteristic of the dielectric constant depending on the temperature of the suspended substance shows a simple characteristic such as a linear relationship as shown in FIG. 12A has been described as an example, the present invention is not limited to this. In the case of a functional polymer or the like, even when the complex characteristic shown in FIG. 5 is shown (when the calibration curves corresponding to FIG. 11B and FIG. 12B also have a complicated curve relationship), The zero point correction circuit 22, the calibration curve slope correction circuit 23, and the calibration curve intercept correction circuit 24 each approximate (linear line approximation) the curve of the calibration curve in a linear relationship that is divided for each temperature band having a certain width to perform the liquid temperature correction. By doing so, the present invention can be implemented in the same manner and the same effect can be obtained.

In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0042]

As described above, according to the present invention, it is possible to improve the accuracy of concentration measurement for a liquid to be measured consisting of a suspension or solution of a substance whose dielectric constant changes with temperature. An expression densitometer can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a microwave densitometer according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an example of a liquid temperature characteristic of a calibration curve in the embodiment.

FIG. 3 is a characteristic diagram showing an example of a liquid temperature characteristic of a slope of a calibration curve in the embodiment.

FIG. 4 is a characteristic diagram showing an example of a liquid temperature characteristic of a section of a calibration curve in the embodiment.

FIG. 5 is a characteristic diagram showing the temperature dependence of the dielectric constant of a substance having complicated characteristics in a modification of the embodiment.

FIG. 6 is a block diagram showing the configuration of a conventional microwave densitometer.

FIG. 7 is a relationship θ1 between a general phase difference θ1 and a phase delay θw.
= 360-θw, relation θ2 between phase difference θ2 and phase delay θs =
Waveform diagram for explaining 360-θs

FIG. 8 is a characteristic diagram for explaining a general calibration curve.

FIG. 9 is a characteristic diagram for explaining a general relationship between a liquid temperature difference and a phase difference correction value.

FIG. 10 is a characteristic diagram for explaining a change in dielectric constant of water depending on a general water temperature.

FIG. 11 is a characteristic diagram showing an example of a change in temperature and dielectric constant of a general substance, and a characteristic diagram for explaining an example of a change in a calibration curve when the dielectric constant of a suspended substance changes according to temperature.

FIG. 12 is a characteristic diagram showing an example of the temperature dependency of a general permittivity and the temperature dependency of a calibration curve.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Microwave oscillator 12 ... Power splitter 13 ... Transmission cable 14 ... Phase difference measurement circuit 15 ... Piping 16 ... Microwave transmission antenna 17 ... Microwave reception antenna 18 ... Concentration calculation circuit 21 ... Temperature detector 22 ... Zero point temperature correction Circuit 23: Calibration curve inclination correction circuit 24: Calibration curve intercept correction circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Takemura 1 Toshiba-cho, Fuchu-shi, Tokyo Toshiba Fuchu Plant

Claims (5)

[Claims] 1. A detector pipe for flowing a liquid for measurement, a microwave transmitting antenna and a microwave receiving antenna which are arranged to face each other with the detector pipe interposed therebetween, and a power supply for supplying the microwave transmitting antenna to the microwave transmitting antenna. Microwave transmitting means for transmitting microwaves, and measuring the phase delay θ2 of microwaves transmitted from the microwave transmitting antenna, propagated through the liquid for measurement in the pipe, and received by the microwave receiving antenna. Further, the phase difference of the microwave when the pipe is filled with the reference liquid in advance and measured under the same conditions as the measurement liquid is compared, and the phase difference Δθ = (θ2−θ1) is measured. A phase difference measuring means, and a phase difference Δθ measured by the phase difference measuring means, a temperature difference Δt (= tw−ts) between the liquid temperature ts of the measuring liquid and the liquid temperature tw of the reference liquid. Based corrected, 'and the phase difference correction means for obtaining a calibration curve x = a · Δθ corresponding to each liquid for the measurement' phase difference [Delta] [theta] + b
Calibration curve correction means for correcting at least one term on the right side based on the liquid temperature ts of the measurement liquid; and a phase difference Δθ 'obtained by the phase difference correction means and correction by the calibration curve correction means. Based on the calibration curve
And a concentration calculating means for calculating a concentration x of the measuring liquid. 2. The microwave densitometer according to claim 1, wherein the calibration curve correction means includes a calibration curve x = a · Δθ ′ + b based on a temperature characteristic of a slope a of the calibration curve. A microwave densitometer characterized in that the inclination a is corrected. 3. The microwave densitometer according to claim 1, wherein the calibration curve correction unit is configured to calculate the calibration curve x = a · Δθ ′ + b based on a temperature characteristic of an intercept b of the calibration curve. A microwave densitometer, wherein the intercept b is corrected. 4. The microwave densitometer according to claim 1, wherein said calibration curve correcting means comprises a slope a and an intercept b of said calibration curve.
The calibration curve x = a · Δ based on each temperature characteristic of
A microwave densitometer characterized in that the inclination a and the intercept b of θ ′ + b are corrected. 5. The microwave densitometer according to claim 1, wherein the phase difference correction means and the calibration curve correction means correct based on a liquid temperature ts of the measurement liquid. Is performed for each temperature band having a predetermined width.