JP6878019B2 - Liquid level measurement method - Google Patents

Description

The present invention relates to a liquid level measuring method, and more particularly to a method of measuring a liquid level using a liquid level gauge using an optical fiber.

A liquid level gauge using an optical fiber has a light emitting portion at one end and a light receiving portion at the other end of an optical fiber in which a portion to be a liquid level sensing portion is bent, and a refractive index of a gas phase in contact with the liquid level sensing portion is provided. The liquid level is detected by measuring the change in light intensity caused by the difference between the rate and the refractive index of the liquid phase at the light receiving part and determining whether the liquid phase is in contact with the liquid level sensing part. (See, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2007-71863

In such a liquid level gauge, when a semiconductor element is used for the light emitting part and the light receiving part, the light emitting intensity and the light receiving intensity change greatly due to a change in the environmental temperature, and the liquid level may not be detected reliably. For this reason, an air conditioner for maintaining the environmental temperature in which the liquid level gauge is installed is used, but there is a problem that the installation cost and the operation cost of the air conditioner are required.

In a usage environment where air conditioning is difficult, the light emitting part and the light receiving part may be housed in a constant temperature bath, or the light emitting part and the light receiving part may be adjusted to a constant temperature by using a heater or a cooler. It is done. However, in this case as well, not only the installation cost and operating cost of the constant temperature bath, the heater, the cooler, etc. are required, but also the periphery of the light emitting part and the light receiving part becomes complicated, and the liquid level gauge itself becomes large. There was also.

On the other hand, in some optical sensors that use only the light receiving part without having a light emitting part, the temperature of the light receiving part is measured to correct the light receiving intensity, but in the case of a liquid level gauge, the environment Since the light emitting intensity of the light emitting unit and the light receiving intensity of the light receiving unit change depending on the temperature, accurate liquid level detection cannot be performed only by the temperature of the light receiving unit.

Therefore, an object of the present invention is to provide a liquid level measuring method capable of accurately detecting the liquid level even if the temperature of the light emitting portion or the light receiving portion changes depending on the environmental temperature.

式（１）によって正規化した受光電圧正規化値（Ｖnom）を、下記式（２）を用いて近似し、前記温度測定値と前記基準温度との差（ｔ）から、回帰式係数（α、β）を決定し、

式（２）と、前記受光電圧測定値（Ｖmeas）と前記印加電圧測定値（Ｖout）とに基づいて、前記受光電圧測定値（Ｖmeas）を前記基準温度における受光電圧に補正した受光電圧補正値（Ｖrev）を求めるための下記式（３）

からなる式を補正式としてあらかじめ設定し、
前記印加電圧測定値（Ｖout）、前記受光電圧測定値（Ｖmeas）及び前記温度測定値と前記基準温度との差（ｔ）を、式（３）に導入し、前記温度測定値によって補正した受光電圧補正値（Ｖrev）を求め、求めた受光電圧補正値（Ｖrev）を、あらかじめ基準温度において設定された受光電圧閾値と比較し、受光電圧補正値（Ｖrev）が受光電圧閾値未満のときに液面感知部が液相内にあると判定し、受光電圧補正値（Ｖrev）が受光電圧閾値以上のときに液面感知部が気相内にあると判定することを特徴とする液面測定方法。
In order to achieve the above object, the liquid level measuring method of the present invention is made of an optical fiber in which a liquid level sensing portion is formed by bending and a semiconductor element that introduces measurement light into the optical fiber from one end of the optical fiber. A liquid level that includes a light emitting unit and a light receiving unit made of a semiconductor element that measures the intensity of measurement light derived from the other end of the optical fiber, and detects the liquid level based on the intensity of the measurement light received by the light receiving unit. In the liquid level measurement method using a meter, the temperature measurement value obtained by measuring the temperature inside the housing containing both the light emitting part and the light receiving part and the applied voltage obtained by measuring the voltage applied to the light emitting part for measurement light irradiation. The measured value (Vout) and the measured value of the received voltage (Vmeas) measured by using the intensity of the measured light received by the light receiving unit as the received voltage are obtained, respectively, and the measured value of the received voltage (Vmeas) and the reference temperature obtained in advance are obtained. The received voltage normalized value (Vnom) normalized by using the received voltage reference value (Vsta) in the above and the applied voltage measured value (Vout) was obtained by the following equation (1).

The received voltage normalized value (Vnom) normalized by the equation (1) is approximated by the following equation (2), and the regression equation coefficient (α) is obtained from the difference (t) between the measured temperature value and the reference temperature. , Β)

A received voltage correction value obtained by correcting the received voltage measured value (Vmeas) to the received voltage at the reference temperature based on the equation (2), the received voltage measured value (Vmeas), and the applied voltage measured value (Vout). The following equation (3) for obtaining (Vrev)

The formula consisting of is set in advance as a correction formula,
The applied voltage measured value (Vout), the received voltage measured value (Vmeas), and the difference (t) between the temperature measured value and the reference temperature are introduced into the equation (3) and the received light is corrected by the temperature measured value. The voltage correction value (Vrev) is obtained, the obtained light-receiving voltage correction value (Vrev) is compared with the light-receiving voltage threshold set in advance at the reference temperature, and when the light-receiving voltage correction value (Vrev) is less than the light-receiving voltage threshold, the liquid is liquid. A liquid level measuring method characterized in that the surface sensing unit is determined to be in the liquid phase and the liquid level sensing unit is determined to be in the gas phase when the received voltage correction value (Vrev) is equal to or higher than the received voltage threshold. ..

According to the liquid level measuring method of the present invention, the light receiving voltage measurement value is corrected based on the temperature inside the housing in which both the light emitting part and the light receiving part are housed, thereby preventing the liquid level gauge from malfunctioning due to a temperature change. The liquid level can be measured accurately.

It is explanatory drawing which shows an example of the liquid level gauge to which the liquid level measurement method of this invention can be applied. It is a figure which shows the relationship between the temperature (transistor temperature which constitutes a light emitting part and a light receiving part) in the housing which housed a light emitting part and a light receiving part, and the light receiving voltage in a light receiving part. It is a figure which shows the relationship between the transistor temperature and the received voltage after normalization. It is a figure which shows the relationship between a transistor temperature and a corrected light-receiving voltage.

FIG. 1 is an explanatory diagram showing an example of a liquid level gauge to which the liquid level measuring method of the present invention can be applied. The liquid level gauge 11 detects the position of the liquid level S in the liquid container 12 in three stages of 100%, 75%, and 50%, and the 100% unit 21, 75% unit 31 and 50%. It is provided with three sets of liquid level detection units of the unit 41.

Each unit 21, 31, 41 is bent into the optical fibers 23, 33, 43 forming the liquid level sensing portions 22, 32, 42, and from one end of each optical fiber 23, 33, 43 into each optical fiber. A semiconductor device that measures the intensity of the light emitting units 24, 34, 44 made of a transistor, for example, and the intensity of the measurement light derived from the other ends of the optical fibers 23, 33, 43, respectively, for example. It includes light receiving units 25, 35, and 45 made of transistors.

The light emitting units 24, 34, 44 and the light receiving units 25, 35, 45 are housed in one housing 13, and further, the temperature inside the housing 13 is measured in the housing 13. A thermometer 14 such as a thermistor, a processing device 15 for performing various arithmetic processes, and a storage means 16 for storing various information are housed. Further, a display unit (not shown) for displaying various information is provided on the outside of the housing 13 as needed.

The light emitting units 24, 34, and 44 generate measurement light having a preset wavelength, and for example, a commercially available LED light source or the like is used. Further, the light receiving units 25, 35, 45 are introduced from the light emitting units 24, 34, 44 to one end of the optical fibers 23, 33, 43, propagate in each optical path of the optical fibers 23, 33, 43, and propagate from the other end. It measures the intensity (light intensity) of the derived measurement light, and an appropriate semiconductor element that can measure the light intensity of the measurement light of the wavelength generated by the light emitting units 24, 34, 44 and convert it into a voltage can be used. ..

As the optical fibers 23, 33, 43, those suitable for transmitting the measurement light may be used, and the diameter may be about 1 mm. The bent portions to be the liquid level sensing portions 22, 32, 42 need only be formed so that the amount of light changes according to the refractive index of the fluid in contact with the liquid level sensing portions, and the clad on the outer periphery of the optical fiber is partially removed. It may be.

The processing device 15 has a function of applying a voltage and a current for causing the light emitting units 24, 34 and 44 to emit light, and a function of measuring the intensity of the measurement light received by the light receiving units 25, 35 and 45 as a voltage and a current. It has a function of measuring the temperature inside the housing 13 with a thermometer 14 and a function of determining whether the liquid level sensing units 22, 32, and 42 are in the gas phase or the liquid phase.

The storage means 16 has a function of storing various measured values such as the voltage and current applied to the light emitting units 24, 34 and 44, the voltage and current received by the light receiving units 25, 35 and 45, and the temperature measured by the thermometer 14. It has a function of storing preset formulas and data such as correction formulas and thresholds necessary for determination by the processing device 15.

In the determination unit of the processing device 15, the temperature measurement value obtained by measuring the temperature inside the housing 13 with the thermometer 14 and the applied voltage measurement value obtained by measuring the voltage applied to the light emitting units 24, 34, and 44 for measurement light irradiation, respectively. The liquid level is based on the measured light-receiving voltage values measured by the light-receiving units 25, 35, and 45 as the light-receiving voltage, the preset correction formula, and the preset light-receiving voltage threshold. The position of the liquid level in the liquid container 12 is measured by determining the states of the sensing units 22, 32, and 42, respectively.

That is, the temperature measurement value, the applied voltage measurement value, and the light reception voltage measurement value are introduced into a preset correction formula to obtain a light reception voltage correction value corrected by the temperature measurement value, and the obtained light reception voltage correction value is obtained. Is compared with a preset light receiving voltage threshold, and when the light receiving voltage correction value is less than the light receiving voltage threshold, it is determined that the liquid level sensing unit is in the liquid phase, and when the light receiving voltage correction value is equal to or higher than the light receiving voltage threshold. It is determined that the liquid level sensing unit is in the gas phase.

For example, it is determined that the liquid level sensing unit 22 of the 100% unit 21 is in the gas phase, and both the liquid level sensing unit 32 of the 75% unit 31 and the liquid level sensing unit 42 of the 50% unit 41 are in the liquid phase. If it is determined to be inside, the measurement position of the liquid level in the liquid container 12 is 75% or more and less than 100%.

Here, the procedure for deriving the correction formula will be described. First, the combination of the light emitting unit 24, the light receiving unit 25, and the optical fiber 23 in the 100% unit 21 (hereinafter referred to as sample 1) and the combination of the light emitting unit 34, the light receiving unit 35, and the optical fiber 33 in the 75% unit 31. (Hereinafter referred to as sample 2) and the combination of the light emitting unit 44, the light receiving unit 45 and the optical fiber 43 (hereinafter referred to as sample 3) in the 50% unit 41, the light emitting units 24 and 34, respectively. With the injection current (applied voltage) to 44 constant and each liquid level sensing unit arranged in the gas phase, the light receiving units 25, 35, and 45 receive light when the temperature inside the housing 13 is changed. Experiments were conducted to measure the received voltage with respect to the amount of light. The result is shown in FIG.

From the results shown in FIG. 2, the light-receiving voltage has a large temperature dependence, and the light-receiving voltage also rises as the temperature rises. For example, when the threshold value of the light-receiving voltage for determining the liquid level is set to 2.0 V. In each sample, when the temperature is high, it is determined that the liquid level sensing unit is in the gas phase, and when the temperature is low, it is determined that the liquid level sensing unit is in the liquid phase. Therefore, the liquid level position cannot be accurately measured due to the temperature change. Further, when each sample shown in FIG. 2 is compared, it can be seen that the tendency of the received light voltage rise is also different for each sample, and it cannot be dealt with by a simple inclination correction.

Therefore, the relationship between the temperature and the received voltage in each sample is normalized. In this normalization, the light receiving voltage when the reference temperature inside the housing is first set to 25 ° C. as the reference temperature, for example, about room temperature, and the temperature of the light emitting part and the light receiving part (transistor temperature) is set to the reference temperature. Is obtained in advance as the received voltage reference value (Vsta). Then, in each experiment, the received voltage measured by each light receiving unit is defined as the received voltage measured value (Vmeas), the applied voltage to each light emitting unit is defined as the applied voltage measured value (Vout), and the received voltage measured value (Vmeas) is applied. The received voltage normalized value (Vnom) obtained by normalizing the received voltage is obtained by the following equation (1) using the measured voltage value (Vout) and the received voltage reference value (Vsta).

As a result, as shown in FIG. 3, the relationship between the normalized light-receiving voltage normalized value (Vnom) and the temperature inside the housing (transistor temperature) can be obtained, and the light-receiving voltage of each sample having a different tendency for the light-receiving voltage to rise. Can be matched. This makes it possible to curve-fit the relationship between the received voltage normalized value (Vnom) shown in FIG. 3 and the temperature inside the housing with a single equation, and the normalized received voltage normalized value (Vnom) is expressed by the following equation. Approximate using (2), the regression equation coefficients (α, β) arbitrarily determined can be determined from the difference (t) between the temperature measurement value in the housing and the reference temperature.

For example, in the case of the relationship shown in FIG.
Vnom = f (t) = 0.00048 × t ² + 0.05442 × t
It can be expressed by the quadratic expression.

Based on the mathematical expression (f (t)) in the determined equation (2), the received voltage measured value (Vmeas), and the applied voltage measured value (Vout), the received voltage measured value (Vmeas) is received at the reference temperature. The correction formula for obtaining the received voltage correction value (Vrev) corrected to the voltage can be derived as the following formula (3).

The light-receiving voltage correction value (Vrev) is obtained by substituting the temperature measurement value, the applied voltage measurement value, and the light-receiving voltage measurement value measured at the time of liquid level measurement into the correction formula derived in this manner. As shown in 4, the relationship between the measured housing temperature (transistor temperature) and the received voltage corrected to the reference temperature (received voltage corrected value) can be obtained for each sample.

As is clear from FIG. 4, since the light-receiving voltage correction value that eliminates the temperature dependence in each sample can be obtained, an appropriate light-receiving voltage threshold value is set for each sample, and the set light-receiving voltage threshold value and light-receiving voltage correction are obtained. By comparing with the value, it is possible to determine whether the liquid level sensing unit is in the liquid phase or in the gas phase.

Based on the results shown in FIG. 4, for example, in Sample 1, by setting the light-receiving voltage threshold value to 2.0 V, the liquid is liquid when the light-received voltage correction value is 2.0 V or more regardless of the temperature inside the housing (transistor temperature). When the surface sensing unit is in the gas phase and the received voltage correction value is less than 2.0V, it can be determined that the liquid level sensing unit is in the liquid phase. Therefore, in the 100% unit 21 used as the sample 1, the liquid level in the liquid container 12 is 100% when the received voltage correction value falls below 2.0 V during the liquid injection work into the liquid container 12. It can be determined that the above is achieved, and the liquid injection work can be completed.

Similarly, by setting the light-receiving voltage threshold value to 1.5 V in sample 2 and the light-receiving voltage threshold value to 1.0 V in sample 3, the liquid level in the liquid container 12 can be accurately adjusted regardless of the temperature inside the housing. Can be measured. As a result, the liquid injection operation into the liquid container 12 can be reliably started.

Therefore, the correction formula is derived for the combination of the light emitting unit, the light receiving unit, and the optical fiber, and the correction formula and the light receiving voltage threshold are stored in the storage means, respectively, so that the liquid level can be measured with a thermometer. The liquid level in the liquid container can be accurately obtained from the temperature inside the housing (transistor temperature), the voltage applied to the light emitting unit, and the light receiving voltage measured by the light receiving unit.

11 ... Liquid level gauge, 12 ... Liquid container, 13 ... Housing, 14 ... Thermometer, 15 ... Processing device, 16 ... Storage means, 21 ... 100% unit, 22 ... Liquid level sensing unit, 23 ... Optical fiber, 24 ... light emitting unit, 25 ... light receiving unit, 31 ... 75% unit, 32 ... liquid level sensing unit, 33 ... optical fiber, 34 ... light emitting unit, 35 ... light receiving unit, 41 ... 50% unit, 42 ... liquid level Sensing unit, 43 ... Optical fiber, 44 ... Light emitting unit, 45 ... Light receiving unit, S ... Liquid level

Claims (1)

An optical fiber having a liquid level sensing portion formed by bending, a light emitting portion made of a semiconductor element that introduces measurement light into the optical fiber from one end of the optical fiber, and a measurement light derived from the other end of the optical fiber. In a liquid level measuring method using a liquid level gauge which includes a light receiving unit made of a semiconductor element for measuring the intensity and detects the liquid level based on the intensity of the measured light received by the light receiving unit, the light emitting unit and the light receiving portion. A temperature measurement value that measures the temperature inside the housing in which the unit is housed, an applied voltage measurement value (Vout) that measures the voltage applied to the light emitting unit for measurement light irradiation, and a measurement light received by the light receiving unit. The light-receiving voltage measurement value (Vmeas) measured with the intensity as the light-receiving voltage is obtained, and the light-receiving voltage measurement value (Vmeas), the light-receiving voltage reference value (Vsta) at the reference temperature obtained in advance, and the applied voltage measurement value ( The received voltage normalized value (Vnom) normalized using Vout) is obtained by the following equation (1).

The received voltage normalized value (Vnom) normalized by the equation (1) is approximated by the following equation (2), and the regression equation coefficient (α) is obtained from the difference (t) between the measured temperature value and the reference temperature. , Β)

A received voltage correction value obtained by correcting the received voltage measured value (Vmeas) to the received voltage at the reference temperature based on the equation (2), the received voltage measured value (Vmeas), and the applied voltage measured value (Vout). The following equation (3) for obtaining (Vrev)

The formula consisting of is set in advance as a correction formula,
The applied voltage measured value (Vout), the received voltage measured value (Vmeas), and the difference (t) between the temperature measured value and the reference temperature are introduced into the equation (3) and the received light is corrected by the temperature measured value. The voltage correction value (Vrev) is obtained, the obtained light-receiving voltage correction value (Vrev) is compared with the light-receiving voltage threshold set in advance at the reference temperature, and when the light-receiving voltage correction value (Vrev) is less than the light-receiving voltage threshold, the liquid is liquid. A liquid level measuring method characterized in that the surface sensing unit is determined to be in the liquid phase and the liquid level sensing unit is determined to be in the gas phase when the received voltage correction value (Vrev) is equal to or higher than the received voltage threshold. ..

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