JP2017090310A - Liquid concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable stable liquid concentration measurement even when a volume of a liquid under measurement is large.SOLUTION: A liquid concentration sensor 10 of the present invention comprises an oscillator 13 and a capacitor unit 16 serially connected with the oscillator 13, the capacitor unit 16 comprising a first capacitor 11 and a second capacitor 12 connected to the first capacitor 11 in parallel. A liquid under measurement is placed between electrodes of the second capacitor 12.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid concentration sensor.

  Various types of sensors are known as sensors for measuring the liquid concentration. For example, a sensor that measures the concentration of a liquid such as an etchant using a coil is known (see Patent Document 1).

  A liquid concentration sensor using a coil is generally highly sensitive. However, a liquid concentration sensor using a coil has problems such as being expensive, limited in size and shape of a measurement target, and difficult to be made to order.

  As a liquid concentration sensor that can solve the above-mentioned problems, a liquid concentration sensor that is configured by connecting a vibrator such as a crystal vibrator and a capacitor in series is known. The liquid concentration sensor having this configuration can be configured using only an inexpensive general-purpose product, and has a high degree of freedom with respect to what shape it is configured.

  A liquid concentration sensor configured by connecting a vibrator and a capacitor in series places a liquid to be measured between electrodes of the capacitor. Since the capacitance of the capacitor changes according to the concentration of the liquid between the electrodes, the oscillation frequency of the vibrator connected in series with the capacitor changes according to the concentration of the liquid. Therefore, the liquid concentration can be measured by measuring the oscillation frequency of the vibrator.

Japanese Patent Laid-Open No. 11-200074

  The liquid concentration sensor configured by connecting the vibrator and the capacitor in series as described above is good when the distance between the electrodes of the capacitor is short, for example, when the distance between the electrodes is about several mm. The measurement characteristics are shown.

  However, if the distance between the electrodes of the capacitor increases, it becomes sensitive to the parasitic capacitance caused by the measurement environment and the oscillation of the vibrator becomes unstable. There was a problem that the change could not be measured stably. For this reason, for example, liquids in pipes and tanks used in factories and the like are in great demand, but pipes and tanks are large in size, so the distance between the capacitor electrodes is increased. Therefore, there is a problem that stable measurement cannot be performed even if the liquid concentration is measured.

  An object of the present invention made in view of such a point is to provide a liquid concentration sensor that can stably measure a liquid concentration even when the size of a liquid to be measured is large.

  In order to solve the above problems, a liquid concentration sensor of the present invention includes a vibrator and a capacitor unit connected in series to the vibrator, the capacitor unit being in parallel with the first capacitor and the first capacitor. A second capacitor to be connected, and a liquid to be measured is disposed between electrodes of the second capacitor.

  In the liquid concentration sensor of the present invention, the second capacitor is configured such that the distance between the electrodes is adjusted according to the size of the liquid to be measured.

  In the liquid concentration sensor of the present invention, the vibrator can oscillate in an overtone mode in addition to a basic mode by changing a driving voltage applied to the vibrator.

  In the liquid concentration sensor of the present invention, the liquid concentration sensor oscillates the vibrator in a basic mode and an overtone mode, and measures the oscillation frequency in each mode, thereby measuring the concentration of the liquid to be measured. And the conductivity can be measured.

  The liquid concentration sensor according to the present invention can stably measure the liquid concentration even when the size of the liquid to be measured is large.

It is an equivalent circuit diagram of the liquid concentration sensor which concerns on one Embodiment of this invention. It is a figure which shows a mode that the liquid in a pipe is measured with the circuit of FIG. It is a figure which shows a mode that soil and concrete are measured with the circuit of FIG. It is a figure which shows the response | compatibility with the relative permittivity at the time of measuring the various liquids from which a dielectric constant differs in the circuit of FIG. It is a figure which shows the result of having oscillated the circuit of FIG. 1 in two modes, a fundamental mode and an overtone mode, and measuring two types of liquids.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an equivalent circuit diagram of a liquid concentration sensor 10 according to an embodiment of the present invention. The liquid concentration sensor 10 includes a first capacitor 11, a second capacitor 12, and a vibrator 13 between the first terminal 14 and the second terminal 15.

  The first capacitor 11 and the second capacitor 12 are connected in parallel to constitute a capacitor unit 16.

  The vibrator 13 is connected to the capacitor unit 16 in series. The side of the vibrator 13 that is not connected to the capacitor unit 16 is connected to the first terminal 14. The side of the capacitor unit 16 that is not connected to the vibrator 13 is connected to the second terminal 15.

  A predetermined voltage is applied between the first terminal 14 and the second terminal 15.

  The liquid to be measured is disposed between the electrodes of the second capacitor 12. The liquid is disposed between the electrodes of the second capacitor 12 in a state where the liquid is contained in a container such as a pipe or a tank used in a factory. The second capacitor 12 has a long inter-electrode distance of about several centimeters to several meters so that a large-sized object such as a pipe can be disposed between the electrodes. The electrode of the 2nd capacitor | condenser 12 is comprised by adjusting the distance between electrodes so that it may become an appropriate distance between electrodes according to the size of the liquid of a measuring object. In FIG. 1, the symbol with the distance between the electrodes separated as the symbol of the second capacitor 12 is emphasized that the distance between the electrodes of the second capacitor 12 is large.

  The first capacitor 11 is connected in parallel to the second capacitor 12 and is strongly capacitively coupled to the second capacitor 12.

  The vibrator 13 is, for example, a crystal vibrator. The vibrator 13 oscillates at a frequency depending on the capacity of the capacitor unit 16. Here, when the liquid concentration of the liquid arranged as a measurement target between the electrodes of the second capacitor 12 changes, the dielectric constant of the liquid changes. Therefore, the capacity of the capacitor unit 16 changes depending on the liquid concentration of the liquid disposed as a measurement object between the electrodes of the second capacitor 12. Therefore, by measuring the oscillation frequency of the vibrator 13, the liquid concentration of the liquid disposed between the electrodes of the second capacitor 12 can be detected.

  The vibrator 13 can also oscillate in the overtone mode instead of the basic mode by changing the drive voltage applied to the vibrator 13. Here, the oscillation in the overtone mode is, for example, in the case of an AT cut crystal resonator, oscillation at a frequency that is an odd multiple of the frequency when oscillating in the basic mode.

  In the present embodiment, the liquid concentration sensor 10 includes a first capacitor 11 connected in parallel to the second capacitor 12. Thereby, even if the distance between the electrodes of the second capacitor 12 is large, the oscillation of the vibrator 13 can be stabilized.

  Specific measurement examples by the liquid concentration sensor 10 are shown in FIGS. FIG. 2 is a diagram illustrating a state in which a pipe 21 (for example, glass) is arranged between the electrodes of the second capacitor 12 and the liquid concentration of the liquid 22 flowing through the pipe 21 is measured.

  As a modification, FIG. 3 shows an example in which a solid 31 (for example, soil or concrete) is arranged between the electrodes of the second capacitor 12 instead of a liquid. Since the vibrator 13 has the first capacitor 11 connected in parallel to the second capacitor 12, it is stable regardless of the distance between the electrodes of the second capacitor 12 and the characteristics of the substance disposed between the electrodes. Therefore, the liquid concentration sensor 10 can measure not the liquid but the solid 31 as shown in FIG.

  FIG. 4 shows the result of measuring the oscillation frequency of the vibrator 13 by flowing various liquids having different dielectric constants into the pipe 21 in the configuration of FIG.

  In the measurement shown in FIG. 4, the distance between the electrodes of the second capacitor 12 was about 8 cm. The horizontal axis of FIG. 4 is the relative dielectric constant, and the vertical axis is the normalized frequency that is normalized so that the oscillation frequency of the vibrator 13 becomes 1 when the liquid 22 is water.

  In the measurement shown in FIG. 4, four liquids such as methylcyclohexane, chloroform, propanol, and water were measured as the liquid 22. For reference, the measurement was also performed when the pipe 21 was air.

  As shown in FIG. 4, as the relative dielectric constant (that is, the dielectric constant) increases, the oscillation frequency change of the vibrator 13 increases. By referring to the relationship as shown in FIG. 4, the liquid concentration sensor 10 can measure the relative dielectric constant (dielectric constant) of the liquid 22 by measuring the oscillation frequency of the vibrator 13. Therefore, the liquid concentration sensor 10 can measure the liquid concentration of the liquid 22 to be measured by setting the liquid whose concentration can be determined from the value of the dielectric constant as the measurement target.

  As described above, the vibrator 13 can oscillate in the overtone mode by changing the drive voltage to be applied. Therefore, for example, in the configuration shown in FIG. 2, by changing the voltage applied between the first terminal 14 and the second terminal 15, the vibrator 13 is oscillated in the basic mode or in the overtone mode. Can be.

FIG. 5 shows the measurement results obtained by oscillating the vibrator 13 in the two modes of the basic mode and the overtone mode with the configuration of FIG. In the measurement shown in FIG. 5, an electrolyte aqueous solution was used as the liquid 22 to be measured. Specifically, an aqueous solution of sodium chloride (NaCl) and sodium bicarbonate (NaHCO ₃ ) is used, and the weight percent concentration of each aqueous solution is 0 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%. By changing the dielectric constant and conductivity of the aqueous solution by changing the ratio to 1% and 1% by weight, the oscillation frequency of the vibrator 13 was measured.

  The horizontal axis in FIG. 5 is the normalized oscillation frequency of the vibrator 13 in the overtone mode, and the vertical axis is the normalized oscillation frequency of the vibrator 13 in the basic mode.

  As shown in FIG. 5, as the sample concentration (liquid concentration) increases, the oscillation frequency change of the vibrator 13 increases in both the basic mode and the overtone mode. Only the change in the dielectric constant changes on the dotted line where the ratio between the fundamental mode and the overtone mode is constant, but when the change is accompanied by a change in conductivity, it deviates from the dotted line depending on the mass percent concentration. If the difference in dependence is examined and used in advance, the liquid concentration sensor 10 oscillates the vibrator 13 in two types of modes and measures the oscillation frequency in each mode, so that only the dielectric constant of the liquid 22 is obtained. In addition, the conductivity of the liquid 22 can also be measured.

  Thus, according to the present embodiment, the second capacitor 12 in which the liquid to be measured is disposed between the electrodes is connected in parallel to the first capacitor 11. As a result, even if the distance between the electrodes of the second capacitor 12 is increased, the oscillation frequency of the vibrator 13 is not easily affected by parasitic capacitance or the like caused by the measurement environment. Even when the liquid in the pipe or tank is a large liquid to be measured, the liquid concentration can be measured stably.

  In addition, according to the present embodiment, inexpensive general-purpose products can be adopted for the first capacitor 11 and the vibrator 13, and the distance between the electrodes of the second capacitor 12 can be easily adjusted. Therefore, the liquid concentration sensor 10 can be configured at a low cost and can be easily made to order.

  Further, according to the present embodiment, the vibrator 13 can oscillate in the overtone mode in addition to the basic mode by changing the drive voltage applied to the vibrator 13. By oscillating and measuring at different frequencies in this way, the liquid concentration sensor 10 can measure not only the liquid concentration (dielectric constant) but also the conductivity of the liquid.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each component can be rearranged so as not to be logically contradictory, and the measurement object can also be diverted to other purposes that can be detected by capacity detection.

  The present invention can be applied to evaluation of deterioration of cutting oil and lubricating oil in a machine factory, and can contribute to automation of control in the factory based on this deterioration evaluation.

  Further, the present invention can be applied to a system for evaluating the quality and concentration of water circulating in a fuel cell.

  The present invention can also be applied to a system that automatically evaluates the mixing of reaction solutions used in printing manufacturers, semiconductor process manufacturers, chemical manufacturers, and the like.

  Further, the present invention can be applied to a system that automatically evaluates a culture solution or the like.

  In addition, the present invention can be applied to a system that detects the presence of contaminants and foreign substances in waste liquid, raw material water.

DESCRIPTION OF SYMBOLS 10 Liquid concentration sensor 11 1st capacitor | condenser 12 2nd capacitor | condenser 13 Oscillator 14 1st terminal 15 2nd terminal 16 Capacitor unit 21 Pipe 22 Liquid 31 Solid

Claims (4)

A vibrator,
A capacitor unit connected in series to the vibrator,
The capacitor unit has a first capacitor and a second capacitor connected in parallel to the first capacitor;
A liquid concentration sensor in which a liquid to be measured is disposed between electrodes of the second capacitor.   2. The liquid concentration sensor according to claim 1, wherein the second capacitor is configured such that a distance between the electrodes is adjusted in accordance with a size of a liquid to be measured. 3.   3. The liquid concentration sensor according to claim 1, wherein the vibrator can oscillate in an overtone mode in addition to a basic mode by changing a drive voltage applied to the vibrator. Liquid concentration sensor.   4. The liquid concentration sensor according to claim 3, wherein the liquid concentration sensor oscillates the vibrator in a fundamental mode and an overtone mode, and measures an oscillation frequency in each mode, thereby measuring the liquid to be measured. A liquid concentration sensor capable of measuring concentration and conductivity.

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