JP3146069B2 - Concentration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for detecting the concentration of a substance to be detected in a mixed solution obtained by dissolving a predetermined substance to be detected in a predetermined solvent.

[0002]

2. Description of the Related Art In brewing and fermentation processes, alcohol concentration is constantly measured for the purpose of process control and quality control. In general, a certain amount of a measurement target is periodically extracted and measured by quantitative analysis. Recently, an alcohol concentration sensor has been used for the purpose of automating this measurement process. The principle of a conventional alcohol concentration sensor is
In this method, the air remaining in the brewing tank or the air forcedly bubbled into the alcohol solution is sucked and brought into contact with the tin oxide semiconductor in a high temperature state, and the change in the electrical conductivity is determined.

[0003]

However, the alcohol concentration sensor based on the above principle requires a suction pump and its peripheral devices, so that miniaturization is difficult.
In addition, since it is difficult to control the amount of suction air quantitatively, high-precision measurement is impossible. In addition, a dilute alcohol aqueous solution such as beer is not practical because the accuracy is significantly reduced. On the other hand, alcohol concentration sensors are often used in the fields of food and medicine and are required to be highly hygienic, but this requirement was one of the factors that hindered the practical use of alcohol concentration sensors. Further, there is a demand for a concentration sensor that can be widely used to detect the concentration of not only alcohol but also other substances.

SUMMARY OF THE INVENTION An object of the present invention is to provide a concentration sensor which has a simple structure, can be easily miniaturized, can measure with high accuracy, and can be used safely from a sanitary point of view. I do.

[0005]

SUMMARY OF THE INVENTION A concentration sensor according to the present invention is a concentration sensor for detecting the concentration of a substance to be detected in a mixed solution obtained by dissolving a predetermined substance to be detected in a predetermined solvent. A crystal oscillator whose natural frequency changes according to the change in the concentration of the crystal, and an oscillation circuit that oscillates the crystal oscillator. The crystal oscillator is immersed in a mixed solution and oscillated. The concentration of the substance to be detected in the mixed solution is obtained by obtaining the frequency, and the crystal oscillator has a temperature coefficient that offsets the temperature coefficient of the specific gravity of the substance to be detected. Is an alcohol solution and the substance to be detected is alcohol, or the mixed solution is urine and the substance to be detected is salt, or the mixed solution is blood and the substance to be detected is lead and iron. That there is It is an butterfly.

[0006]

When the crystal oscillator is oscillated by the oscillation circuit, the natural frequency of the crystal oscillator changes due to the reaction from the mixed solution. This reaction is based on the viscosity of the mixed solution that changes according to the concentration of the substance to be detected. Therefore, since the change in the natural frequency is in accordance with the change in the concentration of the detected substance, the concentration of the detected substance can be obtained by obtaining the natural frequency. In addition, since the quartz oscillator has a temperature coefficient that cancels out the temperature coefficient of the specific gravity of the substance to be detected, errors due to temperature changes are reduced, and the natural frequency is accurately measured.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to these examples. The present embodiment relates to a concentration sensor in which the substance to be detected is alcohol. FIG. 1 is a partial longitudinal sectional view showing a liquid port plug provided with the concentration sensor of the present embodiment, and FIG. 2 is a partially enlarged view of FIG. The lid 51 of the liquid port plug 5 is the same as the conventional liquid port plug, and therefore, the concentration sensor of the present embodiment is provided using the conventional liquid port plug as it is. The concentration sensor according to the present embodiment includes a quartz vibrating plate 10, FIG.
In addition to the oscillation circuit 20 shown in FIG. 4, an interface circuit 30 shown in FIG.

The quartz plate 10 is generally a disc of 8 mm or less. Oscillation circuit 20 and interface circuit 30
Is incorporated in one integrated circuit and is incorporated in the lid portion 51 of the liquid port plug 5. Reference numeral 11 denotes a holding tube that extends vertically from the lid 51, and the quartz vibrating plate 10 is provided horizontally so as to close the lower end opening of the holding tube 11. The quartz vibrating plate 10 is attached to the holding tube 11 with an adhesive 16 such as an ultraviolet curable resin, so that the holding tube 11 is sealed so that the alcohol solution does not enter the inside.

The quartz vibrating plate 10 is provided with electrodes 12 and 13 made of a conductive thin film on both surfaces thereof, thereby forming a quartz vibrator which operates as an electric / mechanical vibrator having a unique vibration form. I have. The electrode 12 is provided on the inner surface of the quartz plate 10, and the electrode 13 is provided from the outer surface to the inner surface. The electrodes 12 and 13 are formed by evaporating gold. One ends of the lead wires 14 and 15 are connected to the electrodes 12 and 13 by a conductive adhesive. The other ends of the lead wires 14 and 15 are connected to the oscillation circuit 20.

The crystal constituting the crystal diaphragm 10 is a single crystal of silicon dioxide having piezoelectricity. The quartz plates cut out at various angles with respect to the crystal axis constitute the above-described quartz resonator, except for those having a plane perpendicular to the Z axis. For example, a plate having a surface perpendicular to the X axis vibrates longitudinally in the thickness direction of the plate, and a plate having a surface perpendicular to the Y axis or an intermediate direction between the Y axis and Z axis vibrates in the thickness direction. Among the sliding vibrations, those having a plane perpendicular to the Y axis have a Y-cut, a plane perpendicular to the Z axis and near 55 degrees in the middle of the -Y axis and the Z axis, and having a small temperature coefficient. Those with features are called AT cuts. Quartz diaphragm 10 of the present invention
Is selected from those that perform a sliding vibration and have an optimum temperature coefficient, that is, a temperature coefficient that cancels out the temperature coefficient of the alcohol specific gravity as described later. In addition, the thickness of the quartz plate 10 is determined in reverse from the required frequency because the natural frequency is related to the thickness of the plate.

The holding tube 11 has a linear expansion coefficient of 1
It is made of glass having a value as close to 0 as possible. This is due to the fact that the coefficient of linear expansion affects the natural frequency of the quartz plate 10 through distortion.

In FIG. 3 showing the oscillation circuit 20, reference numeral 21 denotes an operational amplifier. This circuit has a feature that the oscillation operation can be performed even when the electrode 13 is in the ground state.

The interface circuit divides or subtracts the frequency obtained by the oscillation circuit 20 as described above,
Or to facilitate frequency-to-voltage or frequency-to-current conversion to facilitate transmission to remote locations, to improve the temperature coefficient of measured values, or to adapt to the receiving system at the destination. Yes, and specifically has the circuit configuration shown in FIG. That is, the interface circuit 30
By passing the output frequencies of two different oscillation circuits 20 through a subtraction counting circuit comprising data latches 31 and 32, the temperature coefficient of the natural frequency of the crystal oscillator is canceled out, and at the same time, only the temperature change of the alcohol solution is extracted. , The numerical value of the frequency itself is reduced. The output of the data latch 32 is transmitted through a line driver 33 in order to increase noise resistance during transmission.

Next, the operation will be described. The measurement target was the ethanol concentration in the aqueous ethanol solution. Oscillation circuit 20 oscillates a crystal unit including crystal unit 10 and electrodes 12 and 13 immersed in an aqueous ethanol solution, and the crystal unit excites a transverse wave through its viscosity in the aqueous ethanol solution, thereby causing a reaction. As a result, the aqueous ethanol solution acts as a load on the crystal oscillator, and lowers the natural frequency of the crystal oscillator. It is known that the change in the frequency at this time is theoretically proportional to the square root of the product of the specific gravity of the aqueous ethanol solution and the viscosity coefficient. The change in the frequency is affected by the change in the specific gravity and the viscosity coefficient of the aqueous ethanol solution based on the temperature change. In the present invention, however, the temperature coefficient that cancels out the effect based on the temperature change is determined by the crystal vibrating plate 10, that is, the crystal vibration. Since the child itself has the positive influence, the error based on the temperature change in the measurement of the ethanol concentration is reduced.

FIG. 5 is a graph showing the results of measurement of a plurality of aqueous ethanol solutions having different ethanol concentrations using the concentration sensor having the above-described configuration. In the aqueous ethanol solution, the relationship between the ethanol concentration (% by weight) and the density (g / cm ³ ) is in a linear relationship as shown by a broken line A, and the relationship between the ethanol concentration and the frequency (KHz), that is, the frequency of the quartz oscillator. Are in a substantially linear relationship as shown by the solid line B. That is, the frequency of the quartz oscillator changes monovalently with the change in the ethanol concentration. Therefore, when the frequency of the crystal resonator is determined, the alcohol concentration is determined.

Since the oscillation circuit 20 and the interface circuit 30 are built in the lid 51 and are located very close to the portion to be measured, the influence of electric noise during this period is very small. Moreover, since the data is transmitted by the interface circuit 30 in a signal format resistant to electric noise, even if the data processing device is provided at a distance, the influence of the electric noise during that period is reduced.

[0017]

[Alternative Embodiment] In the above embodiment, the alcohol concentration in the aqueous solution is detected, but the medium in which the alcohol is mixed is not limited to water, but may be another medium such as an organic solvent. Is also good. However, it is necessary that the viscosity of the mixed solution when alcohol is mixed changes in accordance with the alcohol concentration.

Further, in the above embodiment, the substance to be detected is alcohol, and the medium of the mixed solution is water. However, the concentration sensor of the above embodiment has, for example, (1) a mixed solution of urine, When the substance to be detected is a salt, (2) it can be used also when the mixed solution is blood and the substance to be detected is lead and iron. It is well known that the specific gravity and viscosity of urine change according to salt content, and that the specific gravity and viscosity of blood change according to lead and iron content.

The oscillation circuit 20 having the configuration shown in FIG. 6 may be used. 22 and 23 are inverters.

The shape of the lower end portion of the holding tube 11 may be changed, and the quartz plate 10 may be provided obliquely. According to this, the bubbles in the alcohol solution are prevented from adhering to the quartz plate 10, and the attachment of the bubbles is prevented from hindering the operation of the quartz plate 10.

The lead wires 14 and 15 are connected to the holding tube 11.
May be printed on the inner surface with conductive ink or the like, deposited by a vapor deposition method, a sputtering method, or the like, or may be configured by fixing a conductive foil with an adhesive. According to this, productivity and vibration resistance can be improved.

[0022]

As described above, according to the concentration sensor of the present invention, the concentration of the substance to be detected can be obtained by obtaining the natural frequency of the crystal oscillator oscillated in the mixed solution. Specifically, the concentration of alcohol in an alcohol solution, the concentration of salt in urine, or the concentration of lead and iron in blood can be determined. And, for example, by determining the concentration of alcohol in the alcohol solution,
It is possible to improve the efficiency of alcohol brewing work.

In the present invention, since the concentration sensor is constituted by the oscillation circuit and the quartz oscillator immersed in the mixed solution, the constitution is simple. In addition, since the crystal unit can be composed of a small crystal plate and electrodes on both sides, the size can be reduced. For example, the crystal unit can be provided using a conventional liquid port plug, and the productivity is good and the cost is low. . In addition, it can be easily applied to conventional alcohol reaction vessels and the like.

Since the quartz oscillator has a temperature coefficient that cancels out the temperature coefficient of the specific gravity of the substance to be detected, errors due to temperature changes can be reduced, and the natural frequency can be measured accurately. The concentration of a substance can be determined accurately.

The holding tube 11 is made of glass.
3 is made of gold, and the quartz vibrating plate 10 is of course made of quartz. These materials can be safely used in hygiene due to their chemical properties. In addition, only the portion composed of these is brought into contact with the mixed solution. Therefore, it can be preferably used also in the fields of food and medicine which are required to be highly hygienic.

[Brief description of the drawings]

FIG. 1 is a partial vertical sectional view showing a liquid port plug provided with a concentration sensor of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a circuit diagram illustrating an oscillation circuit.

FIG. 4 is a circuit diagram showing an interface circuit.

FIG. 5 is a diagram showing a result of measuring a plurality of alcohol solutions having different alcohol concentrations using the concentration sensor of the present invention.

FIG. 6 is a circuit diagram showing another example of the oscillation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Crystal vibrating plate 11 Holding tube 12, 13 Electrode 20 Oscillation circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-163640 (JP, A) WO 93/6452 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 9/00 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. A concentration sensor for detecting a concentration of a substance to be detected in a mixed solution obtained by dissolving a predetermined substance to be detected in a predetermined solvent, wherein a natural frequency changes according to a change in the concentration of the substance to be detected. A crystal oscillator that oscillates the crystal oscillator and a crystal oscillator that oscillates the crystal oscillator, oscillates by immersing the crystal oscillator in the mixed solution, and detects the natural frequency of the crystal oscillator at that time to detect the crystal oscillator. The concentration of the substance is determined.The quartz oscillator has a temperature coefficient that offsets the temperature coefficient of the specific gravity of the substance to be detected.The mixed solution is an alcohol solution and the substance to be detected is alcohol. A concentration sensor, wherein the mixed solution is urine and the substance to be detected is salt, or the mixed solution is blood and the substance to be detected is lead and iron. 2. A crystal unit is provided with electrodes provided on both sides of a crystal plate. Each electrode is electrically connected to an oscillation circuit, and only one side of the crystal plate is in a mixed solution. The concentration sensor according to claim 1, wherein the concentration sensor is provided to be in contact with the sensor. 3. An immersion part to be immersed in the mixed solution is formed of a cylindrical body, and the crystal unit is provided with electrodes provided on both sides of the crystal plate, respectively. It is provided so as to close the opening and seal the cylinder, each electrode is electrically connected to an oscillation circuit through a lead wire passing through the cylinder, the cylinder is made of glass, The concentration sensor according to claim 1, wherein the electrode is made of gold.