JP5481154B2 - Electromagnetic applied densitometer - Google Patents

Description

  The present invention relates to a capacitance type concentration meter that measures the concentration of a liquid to be measured based on a change in capacitance and a microwave concentration meter that measures the concentration of a liquid to be measured based on a propagation time delay of the microwave. In particular, the present invention relates to an electromagnetic application densitometer improved so as to reduce a measurement error of concentration when bubbles are mixed in a liquid to be measured.

  Conventionally, as a method of measuring the concentration of a liquid to be measured including suspended substances and soluble substances in the liquid by applying electromagnetic, the concentration of the liquid to be measured is determined based on the transmitted light attenuation rate, the scattered light increase rate, etc. An optical densitometer to measure has been devised.

  In addition, a capacitance type densitometer that measures the concentration of the liquid to be measured based on the change in capacitance and a microwave type densitometer that measures the concentration of the liquid to be measured based on the propagation time delay of the microwave have been devised. ing.

  FIG. 6 is a configuration diagram of a conventional capacitance densitometer. In FIG. 6, an electrode pair composed of an electrode 2 and an electrode 3 disposed opposite to the electrode 2 is attached inside the pipe 1 along the longitudinal direction of the pipe 1. The capacitance measuring circuit 6 generates an electric field between the electrodes of the electrode 2 and the electrode 3 via the transmission cable 4 and the transmission cable 5, and charges accumulated between the electrodes of the electrode 2 and the electrode 3. Is measured to obtain a capacitance according to the concentration of the fluid to be measured. The capacitance signal obtained by the capacitance measurement circuit 6 is input to the concentration calculation circuit 7 and converted into a concentration.

  This capacitance type densitometer is based on the following measurement principle. When the concentration of the suspended substance or soluble substance in the liquid to be measured changes, the dielectric constant of the entire liquid to be measured changes. When the dielectric constant of the liquid to be measured passing between the electrodes 2 and 3 changes, the capacitance between the electrodes 2 and 3 changes. Based on this change in capacitance, the capacitance densitometer can measure the concentration.

  FIG. 7 is a configuration diagram of a conventional microwave densitometer (Patent Document 1). In the microwave densitometer, the microwave oscillated from the microwave oscillator 8 is distributed by the power splitter 9 to the reference system path and the measurement system path.

  First, the microwave passing through the reference system path is input to the phase difference measurement circuit 14 via the transmission cable 10. On the other hand, the microwave passing through the measurement system path is incident via a microwave transmission antenna 12 mounted in the pipe 11. The microwaves that have passed through the liquid to be measured flowing in the pipe 11 are received by the microwave receiving antenna 13 that is mounted facing the pipe 11, and the received signal is transmitted from the receiving antenna 13 to the phase difference measuring circuit 14. Is input.

  There are two types of liquids to be measured: a concentration reference liquid having a zero concentration (or reference value) and a liquid to be measured having a concentration x, and the liquids are individually flowed through the pipes, and phase delays θ1 and θ2 are generated. Measured.

  That is, the phase difference measurement circuit 14 uses the microwave directly received from the microwave oscillator 8 via the transmission cable 10 or the like as a phase reference, and fills the pipe 11 with a liquid to be measured with a concentration. The phase delay θ2 of the microwave when measured by measuring the phase delay θ2 of the microwave when flowing and filling the pipe 11 with a concentration reference liquid (for example, tap water that can be regarded as zero concentration). θ1 is measured, θ2 and θ1 are compared, and a phase difference Δθ = (θ2-θ1) is obtained and sent to the concentration calculation circuit 15.

  The concentration calculation circuit 15 calculates the concentration of the liquid to be measured based on the phase difference Δθ and a calibration curve calibrated in advance.

  This microwave densitometer is based on the following principle. That is, when the concentration of the suspended substance or soluble substance in the liquid to be measured changes, the dielectric constant and conductivity of the entire liquid to be measured change. When the dielectric constant and conductivity change, the speed of the microwave propagating through the liquid to be measured changes.

  Here, the microwave densitometer measures the change in the microwave velocity due to the change in concentration as a change in phase, and the concentration of the liquid to be measured based on the principle that the phase difference Δθ of the change in phase is proportional to the concentration. Is measuring.

JP 2000-258362 A

  In the conventional capacitance type densitometer shown in FIG. 6, the electrode pair for measuring the change in the dielectric constant of the fluid to be measured is a rod-like or parallel plate-like electrode pair as shown by the electrode 2 and the electrode 3. It was configured to be inserted into a measurement tube through which the liquid to be measured flows. However, in such a configuration, there is a problem that when the liquid to be measured passes through the electrode pair, the flow of the liquid to be measured is hindered by the electrode pair.

  In addition, although the influence of bubbles in the capacitance type densitometer is less than that of, for example, an optical type or an ultrasonic type, there is a problem that a change in dielectric constant due to mixing of bubbles directly affects the concentration indication value.

  Furthermore, in the microwave densitometer, the increase in propagation time due to refraction and scattering of microwaves at the interface between the bubble and the liquid to be measured is smaller than the decrease in propagation time of the microwave due to the decrease in the dielectric constant due to bubble mixing. Since they are canceled out, the influence of air bubbles is less than that of the capacitance type, but there is a problem of affecting the density instruction value.

  An object of the present invention is to provide an electromagnetic application densitometer that can reduce the influence on the concentration measurement value due to mixing of bubbles without obstructing the flow of the liquid to be measured by the electrode pair.

  In order to solve the above-mentioned problem, the first invention relates to an annular pair of electrodes and a change in dielectric constant accompanying a change in concentration of a fluid to be measured passing through the annular portion of the pair of electrodes. A capacitance measurement circuit for measuring the capacitance change of the microwave, and a microwave phase delay when the fluid to be measured is filled in the pipe and flowed with the microwave directly received from the microwave oscillator as a phase reference A phase difference measuring circuit for measuring a phase difference from a phase delay of the microwave when the pipe is filled with a concentration reference fluid, and a static electricity between the electrodes of the electrode pair from the capacitance measuring circuit; The measured fluid is determined by a difference between a measured concentration value of the measured fluid measured based on a change in capacitance and a measured concentration value of the measured fluid measured based on the phase difference of the microwave from the phase difference measuring circuit. To correct the effect of air bubbles inside Characterized in that it comprises a calculation circuit.

  According to the first aspect of the present invention, it is possible to provide a highly accurate electromagnetic applied densitometer that can reduce the influence of the concentration measurement value due to mixing of bubbles without hindering the flow of the liquid to be measured by the electrode pair.

It is a block diagram of the electromagnetic application densitometer of Example 1 of this invention. It is a figure explaining the annular electrode pair of Example 1 of this invention. It is a figure explaining the effect | action of the annular electrode pair of Example 1 of this invention. It is a comparison graph of the density | concentration instruction | indication value based on the dielectric constant change at the time of bubble mixing of Example 1 of this invention, and the density | concentration instruction | indication value of a microwave densitometer. It is a block diagram of the electromagnetic application densitometer of Example 2 of this invention. It is a block diagram of the conventional electrostatic capacitance type densitometer. It is a block diagram of the conventional microwave densitometer.

  Hereinafter, embodiments of an electromagnetic application densitometer of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of an electromagnetic application densitometer according to Embodiment 1 of the present invention. The electromagnetic application densitometer includes an annular electrode 21, an annular electrode 22, a capacitance measuring circuit 6, a microwave oscillator 17, a power splitter 18, a transmission cable 19, a transmitting antenna 23, a receiving antenna 24, a phase difference measuring circuit 29, and a concentration calculation. A circuit 30 is included.

  First, capacitance type concentration measurement will be described. Inside the pipe 16, an electrode pair (first electrode pair) including an annular electrode 21 and an annular electrode 22 disposed so as to face the annular electrode 21 is attached substantially perpendicularly to the longitudinal direction of the pipe 16. ing.

  The capacitance measuring circuit 6 generates an electric field between the electrodes of the annular electrode 21 and the annular electrode 22 via the transmission cable 25 and the transmission cable 27, and the electrode pair of the annular electrode 21 and the annular electrode 22. By measuring the charge accumulated between the electrodes, a capacitance corresponding to the concentration of the fluid to be measured is obtained. The capacitance signal obtained by the capacitance measurement circuit 28 is input to the concentration calculation circuit 30 and converted into a concentration.

  Next, microwave concentration measurement will be described. The microwave oscillated from the microwave oscillator 17 is distributed by the power splitter 18 to the reference system path and the measurement system path.

  First, the microwave passing through the reference system path is input to the phase difference measurement circuit 29 via the transmission cable 19. On the other hand, the microwave passing through the measurement system path enters through a microwave transmission antenna 23 attached in the pipe 16. The microwave that has passed through the liquid to be measured flowing in the pipe 16 is received by the microwave receiving antenna 24 that is mounted facing the pipe 16, and the received signal is received from the receiving antenna 24 by the phase difference measuring circuit 29. Is input.

  There are two types of liquids to be measured: a concentration reference liquid having a zero concentration (or reference value) and a liquid to be measured having a concentration x, and the liquids are individually flowed through the pipes, and phase delays θ1 and θ2 are generated. Measured.

  That is, the phase difference measuring circuit 29 uses the microwave directly received from the microwave oscillator 17 via the transmission cable 19 or the like as a phase reference, and fills the pipe 16 with a liquid to be measured with a concentration. The phase delay θ2 of the microwave when measured by measuring the phase delay θ2 of the microwave when flowing and filling the pipe 16 with a concentration reference liquid (for example, tap water that can be regarded as zero concentration). θ1 is measured, θ2 and θ1 are compared, and a phase difference Δθ = (θ2-θ1) is obtained and sent to the concentration calculation circuit 30.

  The concentration calculation circuit 30 calculates the concentration of the liquid to be measured based on the phase difference Δθ and a calibration curve calibrated in advance. When there is a difference between the concentration instruction value calculated based on the capacitance change and the concentration instruction value calculated based on the phase difference of the microwave, the concentration calculation circuit 30 determines that bubbles are mixed and Calculate the concentration without the influence.

  Next, the operation of the electromagnetic applied densitometer of Example 1 configured as described above will be described. First, there is a problem that the electrode pair of the capacitance type densitometer obstructs the flow of the liquid to be measured when the liquid to be measured passes through the ring of the annular electrode pair constituted by the annular electrodes 21 and 22 shown in FIG. Can be solved.

  When an electric field is applied between the electrodes of the annular electrode pair 21, 22, the flow of the electric field in the cross section of the annular electrode pair 21, 22 is as shown in FIG. When a dielectric is filled in the ring of the electrodes of the annular electrode pair 21 and 22, dielectric polarization occurs along the flow of the electric field, so that the capacitance between the electrodes of the annular electrode pair 21 and 22 changes. become. That is, a change in dielectric constant can be detected even in the annular electrodes 21 and 22.

  The capacitance between the electrodes when the dielectric is filled in the ring of the electrodes of the annular electrode pairs 21 and 22 is estimated as follows.

A capacitance C ₀ per unit length between parallel conductors having a diameter a and a distance d between the centers of conductors in a dielectric body having a relative dielectric constant ε _s is expressed by the following equation.

In the case of D >> d >> a, the capacitance Cr between the electrodes of the parallel annular electrode pair having a diameter D is expressed by the following equation.

When D >> d >> a and the electrode ring of the parallel ring electrode pair is filled with a dielectric having a relative dielectric constant ε _sri and outside the electrode ring is filled with a dielectric having a relative dielectric constant ε _sro , the diameter D is parallel. The capacitance Cr between the electrodes of the annular electrode pair is expressed by the following equation.

From Equation 3, for example, when D = 100 mm, d = 3 mm, and a = 0.3 mm,
The electrostatic capacity Cr when the outside of the electrode ring is filled with air and the inside of the electrode ring is filled with water is about 160 pF.

In addition, when the outside of the electrode ring is filled with air to be measured and the liquid to be measured is filled with a measured liquid having an ethanol concentration of 10% (weight) with respect to water, the relative dielectric constant ε _sri of the measured liquid in the electrode ring is about Since 74.6, the capacitance Cr is about 150 pF. This indicates that the concentration can be measured by a change in capacitance between the electrodes of the annular electrode pair 21 and 22 having the above-described shape.

  Moreover, the influence on the measurement value by mixing of bubbles can be reduced by the following method. As described above, when bubbles are mixed into the liquid to be measured, the microwave densitometer measures the microwave at the interface between the bubble and the liquid to be measured against the decrease in the propagation time of the microwave due to the decrease in the dielectric constant due to the mixing of bubbles. The increase in propagation time due to the refraction scattering of is canceled out.

  For this reason, a change in dielectric constant due to bubble mixing directly indicates a concentration instruction value different from that of a capacitance type densitometer that directly affects the concentration instruction value. That is, if the shape of the bubble is the same, the bubble mixing amount is uniquely determined from the difference in the concentration instruction value between the capacitance densitometer and the microwave densitometer.

  Thus, according to the electromagnetic application densitometer of Example 1, concentration measurement is performed by capacitance measurement without interfering with the flow of the liquid to be measured by the annular electrode pair constituted by the annular electrode 21 and the annular electrode 22. At the same time, the concentration measurement using microwaves is performed, and the concentration measurement value obtained by capacitance measurement is compared with the concentration measurement value obtained by microwave detection to detect bubble contamination and correct the influence of the concentration indication value due to bubble contamination. Even if bubbles are mixed in the measurement liquid, the influence of measurement errors can be reduced.

  FIG. 4 is a comparison graph between a concentration indication value (theoretical value) based on a change in relative permittivity when bubbles are mixed in Example 1 of the present invention and a concentration indication value (actual measurement value) of a microwave densitometer, and the horizontal axis is the horizontal axis. The bubble content (volume%) is shown, and the vertical axis shows the concentration indication value.

  In an actual experiment, as shown in FIG. 4, the fluctuation of the concentration indication value when air bubbles of 1% in volume ratio with respect to water are mixed is about 0.96% from the theoretical value to about 0.58% actually measured value. Therefore, the result that the microwave densitometer is 30 to 40% less than the capacitance densitometer is obtained. Thereby, it is shown that the influence of mixing of bubbles can be corrected based on the difference between the concentration instruction values of the microwave densitometer and the capacitance densitometer.

  FIG. 5 is a configuration diagram of an electromagnetic application densitometer according to Example 2 of the present invention. The electromagnetic applied densitometer of Example 2 shown in FIG. 5 is obtained by adding an annular electrode 20 to the electromagnetic applied densitometer of Example 1 shown in FIG.

  An annular electrode 20 is disposed inside the pipe 16 so as to face the annular electrode 21, and the annular electrode 20 and the annular electrode 21 constitute a second electrode pair. An interval d1 between the annular electrode 20 and the annular electrode 21 and an interval d2 between the annular electrode 21 and the annular electrode 22 are different. By changing the distance d1 and the distance d2 to share the annular electrode 21, two annular electrode pairs having different capacitances are formed.

  The lengths and electrical properties of the transmission cables 25, 26, and 27 are all identical. In this case, the influence of the capacitance change due to temperature can be eliminated by obtaining the difference between the capacitances measured by the two pairs of annular electrodes having different capacitances. As a result, it is possible to perform capacitance-type concentration measurement that is less susceptible to temperature fluctuations.

  The present invention is applicable to a densitometer.

2,3 electrode 20,21,22 annular electrode 4,5,25,26,27 transmission cable 8,17 microwave oscillator 9,18 power splitter 10,19 microwave transmission cable 1,11,16 pipe 12,23 transmission Antennas 13, 24 Receiving antennas 14, 29 Phase difference measuring circuits 6, 28 Capacitance measuring circuits 7, 15, 30 Density calculation circuit

Claims (1)

An annular pair of electrodes;
A capacitance measuring circuit for measuring a change in dielectric constant accompanying a change in concentration of a fluid to be measured passing through the ring of the electrode pair as a capacitance change between the electrodes of the electrode pair;
When the microwave received directly from the microwave oscillator is used as the phase reference, the phase delay of the microwave when the fluid to be measured is filled in and flowed in the pipe, and the concentration reference fluid is filled and flowed in the pipe A phase difference measuring circuit for measuring a phase difference from the phase delay of the microwave of
Measured based on the measured concentration of the fluid to be measured measured based on the capacitance change between the electrodes of the electrode pair from the capacitance measuring circuit and the phase difference of the microwave from the phase difference measuring circuit. A concentration calculation circuit for correcting the influence of bubbles in the measured fluid by the difference from the measured concentration value of the measured fluid;
An electromagnetic application densitometer characterized by comprising:

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