JP2018119896A - Liquid level measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level measuring method for detecting a liquid level accurately even when an environmental temperature changes.SOLUTION: A liquid level gauge includes an optical fiber forming a liquid level sensing part, a light-emitting unit which introduces measurement light from one end of the optical fiber, and a light-receiving unit which measures intensity of the measurement light derived from the other end, to detect a liquid level with the intensity of the measurement light received by the light-receiving unit. A liquid level measuring method using the liquid level gauge includes: determining a measurement temperature value obtained by measuring a temperature in a housing storing the light-emitting unit and the light-receiving unit, a measurement applied voltage value obtained by measuring a voltage applied to the light-emitting unit, and a measurement light-receiving voltage value obtained by measuring intensity of the measurement light received by the light-receiving unit as a light-receiving voltage; determining a light-receiving voltage correction value obtained by introducing the measurement temperature value, measurement applied voltage value, and measurement light-receiving voltage value in a correction expression, to be corrected with the measurement temperature value; comparing the determined light-receiving voltage correction value with a light-receiving voltage threshold; and determining that the liquid level sensing part is located in a liquid phase when the light-receiving voltage correction value is less than the light-receiving voltage threshold, or determines that the liquid level sensing part is located in a gas phase when the value is equal to or larger than the light-receiving voltage threshold.SELECTED DRAWING: Figure 1

Description

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

  A liquid level meter using an optical fiber has a light emitting part at one end of an optical fiber bent at a part that becomes a liquid level sensing part, and a light receiving part at the other end, so that the gas phase refraction is in contact with the liquid level sensing part. The liquid level is detected by measuring the change in light intensity caused by the difference between the refractive index and the refractive index of the liquid phase at the light receiving unit, and determining whether the liquid level sensor is in contact with the gas phase or the liquid phase. (For example, refer to Patent Document 1).

JP 2007-71863 A

  In such a liquid level gauge, when a semiconductor element is used for the light emitting part and the light receiving part, the light emission intensity and the light receiving intensity greatly change due to the change in the environmental temperature, and the liquid level may not be detected reliably. For this reason, although air-conditioning equipment for keeping the environmental temperature at which the liquid level gauge is installed at a constant temperature is used, there is a problem that installation cost and operating cost of the air-conditioning equipment are required.

  In use environments where air conditioning is difficult, the light emitting unit and the light receiving unit may be housed in a thermostatic bath, or the light emitting unit and the light receiving unit may be adjusted to a constant temperature using a heater or a cooler. Has been done. However, in this case as well, not only the installation cost and operation cost of a thermostat, heater, cooler, etc. are required, but also the problem that the periphery of the light emitting unit and the light receiving unit becomes complicated and the liquid level meter itself becomes large. There was also.

  On the other hand, in some optical sensors that do not have a light emitting part and use only the light receiving part, the temperature of the light receiving part is measured to correct the received light intensity. Since the light emission intensity of the light emitting part and the light reception intensity of the light receiving part change in relation to each other, accurate liquid level detection cannot be performed only by the temperature of the light receiving part.

  Therefore, an object of the present invention is to provide a liquid level measurement method capable of detecting a liquid level with high accuracy even if the temperature of a light emitting unit or a light receiving unit changes depending on the environmental temperature.

  In order to achieve the above object, the liquid level measuring method of the present invention includes an optical fiber in which a liquid level sensing unit 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 a 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, a temperature measurement value obtained by measuring the temperature in a housing that houses both the light emitting unit and the light receiving unit, and an applied voltage obtained by measuring a voltage applied to the light emitting unit for measurement light irradiation A measured value and a received voltage measurement value obtained by measuring the intensity of the measurement light received by the light receiving unit as a received voltage are obtained, and the temperature measured value, the applied voltage measured value, and the received voltage measured value are set in advance. The When the received light voltage correction value is less than the received light voltage threshold value, the received light voltage correction value corrected by the temperature measurement value is obtained, and the obtained received light voltage correction value is compared with the preset received light voltage threshold value. It is characterized in that it is determined that the liquid level sensing unit is in the liquid phase, and that the liquid level sensing unit is in the gas phase when the light reception voltage correction value is equal to or greater than the light reception voltage threshold value.

式１によって正規化した受光電圧正規化値（Ｖnom）を、前記温度測定値と前記基準温度との差（ｔ）と、回帰式係数（α、β）とを使用して数式化することにより下記式（２）を決定し、

式２における数式（ｆ(t)）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）を求めるための前記補正式となる下記式（３）

からなる前記補正式を導き出すことを特徴としている。 Furthermore, the liquid level measuring method of the present invention is normalized using the light reception voltage measurement value (Vmeas), the light reception voltage reference value (Vsta) at a reference temperature determined in advance, and the applied voltage measurement value (Vout). The received light voltage normalized value (Vnom) is obtained by the following formula (1),

By formulating the light reception voltage normalized value (Vnom) normalized by Equation 1 using the difference (t) between the measured temperature value and the reference temperature and the regression equation coefficients (α, β). Determine the following formula (2),

Based on the equation (f (t)) in Equation 2, the light reception voltage measurement value (Vmeas), and the applied voltage measurement value (Vout), the light reception voltage measurement value (Vmeas) is converted into the light reception voltage at the reference temperature. The following formula (3) which is the correction formula for obtaining the corrected received light voltage correction value (Vrev)

It is characterized by deriving the correction formula consisting of:

  According to the liquid level measurement method of the present invention, by correcting the light reception voltage measurement value based on the temperature in the housing that houses both the light emitting unit and the light receiving unit, malfunction of the liquid level gauge due to temperature change can be prevented. The liquid level can be accurately measured.

It is explanatory drawing which shows an example of the liquid level meter which can apply the liquid level measuring method of this invention. It is a figure which shows the relationship between the temperature (transistor temperature which comprises a light emission part and a light-receiving part) in the housing | casing which accommodated the light emission part and the light-receiving part, and the light reception voltage in a light reception part. It is a figure which shows the relationship between transistor temperature and the received light voltage after normalization. It is a figure which shows the relationship between transistor temperature and the correct | amended received light 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%. The 100% unit 21, 75% unit 31 and 50% 3 units of the liquid level detection unit of the unit 41 are provided.

  Each unit 21, 31, 41 is bent into an optical fiber 23, 33, 43 in which the liquid level sensing units 22, 32, 42 are formed, and from one end of each optical fiber 23, 33, 43 into each optical fiber. For example, a semiconductor element made of a semiconductor element that introduces measurement light, for example, a light emitting section 24, 34, 44 made of a transistor, and a semiconductor element that measures the intensity of the measurement light derived from the other end of each optical fiber 23, 33, 43, for example And light receiving portions 25, 35, 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 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. In addition, a display unit (not shown) for displaying various types of information is provided outside the housing 13 as necessary.

  The light emitting units 24, 34, and 44 generate measurement light having a preset wavelength. For example, a commercially available LED light source is used. The light receiving parts 25, 35, 45 are introduced from the light emitting parts 24, 34, 44 to one end of the optical fibers 23, 33, 43, propagated through the respective optical paths of the optical fibers 23, 33, 43 and from the other end. An intensity of the derived measurement light (light quantity) is measured, and an appropriate semiconductor element capable of measuring the light quantity of the measurement light having the wavelength generated by the light emitting units 24, 34, and 44 and converting it into a voltage can be used. .

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

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

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

  In the determination unit in the processing device 15, a temperature measurement value obtained by measuring the temperature in the housing 13 with the thermometer 14, and an applied voltage measurement value obtained by measuring the voltage applied to the light emitting units 24, 34, 44 for measuring light irradiation, respectively. And the received light voltage measurement value measured by using the intensity of the measurement light received by the light receiving sections 25, 35, and 45 as the received light voltage, the preset correction equation, and the preset received light voltage threshold value, respectively. 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 received light voltage correction value obtained by introducing the measured temperature value, the applied voltage measured value, and the received light voltage measured value into a correction equation set in advance and corrected by the measured temperature value is obtained. Is compared with a preset light reception voltage threshold, and when the light reception voltage correction value is less than the light reception voltage threshold, it is determined that the liquid level sensor is in the liquid phase, and the light reception voltage correction value is greater than or equal to the light reception voltage threshold. It is determined that the liquid level sensor 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 the liquid level sensing unit 32 of the 75% unit 31 and the liquid level sensing unit 42 of the 50% unit 41 are both in the liquid phase. If it is determined that the liquid level is in the liquid container 12, the measurement position of the liquid level in the liquid container 12 is 75% or more and less than 100%.

  Here, a procedure for deriving the correction formula will be described. First, a 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 a 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 three combinations of the light emitting part 44, the light receiving part 45 and the optical fiber 43 (hereinafter referred to as sample 3) in the unit 41 for 50%, each light emitting part 24, 34, The light receiving portions 25, 35, and 45 receive light when the temperature in the casing 13 is changed with the injection current (applied voltage) to 44 constant and the liquid level sensing portions arranged in the gas phase. Each experiment was conducted to measure the received light voltage with respect to the light quantity. The result is shown in FIG.

  From the results shown in FIG. 2, the light reception voltage has a large temperature dependency, and the light reception voltage increases as the temperature rises. For example, when the threshold value of the light reception voltage for determining the liquid level is set to 2.0V In each sample, when the temperature is high, it is determined that the liquid level sensor is in the gas phase, and when the temperature is low, it is determined that the liquid level sensor is in the liquid phase. For this reason, it becomes impossible to accurately measure the liquid surface position due to a temperature change. Furthermore, when the samples shown in FIG. 2 are compared, it can be seen that the tendency of the received light voltage to rise is different for each sample and cannot be handled by simple inclination correction.

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

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

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

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

  By substituting the measured temperature value, the applied voltage measured value, and the received light voltage measured value measured during the liquid level measurement into the correction formula derived in this way, the received light voltage correction value (Vrev) is obtained, respectively. As shown in FIG. 4, the relationship between the measured temperature in the casing (transistor temperature) and the received light voltage (received voltage correction value) corrected to the reference temperature can be obtained for each sample.

  As can be seen from FIG. 4, a light reception voltage correction value that eliminates the temperature dependence of each sample can be obtained. Therefore, an appropriate light reception voltage threshold value is set for each sample, and the set light reception voltage threshold value and light reception voltage correction are set. By comparing the values, it can be determined 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, the light reception voltage threshold value is set to 2.0 V, so that the light reception voltage correction value is 2.0 V or more regardless of the temperature in the housing (transistor temperature). When the surface sensing unit is in the gas phase and the light-receiving voltage correction value is below 2.0 V, it can be determined that the liquid level sensing unit is in the liquid phase. Therefore, in the unit for 100% used as the sample 1, the liquid level in the liquid container 12 is 100% when the light receiving voltage correction value is less than 2.0V during the liquid injection operation into the liquid container 12. It can be determined that the above has been reached, and the liquid injection operation can be completed.

  Similarly, by setting the light reception voltage threshold value to 1.5 V in sample 2 and to 1.0 V in sample 3, the liquid level in the liquid container 12 can be accurately adjusted regardless of the temperature in the housing. Can be measured. Thereby, the liquid injection | pouring operation | work in the liquid container 12 can be started reliably.

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

  DESCRIPTION OF SYMBOLS 11 ... Liquid level meter, 12 ... Liquid container, 13 ... Housing, 14 ... Thermometer, 15 ... Processing device, 16 ... Memory | storage means, 21 ... Unit for 100%, 22 ... Liquid level sensing part, 23 ... Optical fiber, 24 ... Light emitting part, 25 ... Light receiving part, 31 ... 75% unit, 32 ... Liquid level sensing part, 33 ... Optical fiber, 34 ... Light emitting part, 35 ... Light receiving part, 41 ... Unit for 50%, 42 ... Liquid level Sensing part 43 ... Optical fiber 44 ... Light emitting part 45 ... Light receiving part S ... Liquid level

Claims (2)

  An optical fiber in which a liquid level sensing part is formed by bending, a light emitting part made of a semiconductor element for introducing measuring light into the optical fiber from one end of the optical fiber, and a measuring light derived from the other end of the optical fiber. A light receiving unit made of a semiconductor element for measuring the intensity, and in a liquid level measuring method using a liquid level meter that detects a liquid level based on the intensity of measurement light received by the light receiving unit, the light emitting unit and the light receiving unit A temperature measurement value obtained by measuring the temperature in the housing housing the part together, an applied voltage measurement value obtained by measuring a voltage applied to the light emitting part for measurement light irradiation, and an intensity of the measurement light received by the light receiving part. A received light voltage measurement value measured as a voltage is obtained, and the temperature measured value, the applied voltage measured value, and the received light voltage measured value are introduced into a preset correction equation and corrected by the temperature measured value. A voltage correction value is obtained, and the obtained light reception voltage correction value is compared with a preset light reception voltage threshold value.When the light reception voltage correction value is less than the light reception voltage threshold value, it is determined that the liquid level sensor is in the liquid phase. A liquid level measurement method comprising: determining that the liquid level sensing unit is in a gas phase when the light reception voltage correction value is equal to or greater than a light reception voltage threshold value. The light reception voltage normalized value (Vnom) normalized using the light reception voltage measurement value (Vmeas), the light reception voltage reference value (Vsta) at the reference temperature obtained in advance, and the applied voltage measurement value (Vout) is as follows: Obtained by equation (1),

The received light voltage normalized value (Vnom) normalized by the equation (1) is formulated using the difference (t) between the temperature measurement value and the reference temperature and the regression equation coefficients (α, β). The following formula (2) is determined by

Based on the equation (f (t)) in equation (2), the light reception voltage measurement value (Vmeas), and the applied voltage measurement value (Vout), the light reception voltage measurement value (Vmeas) is received at the reference temperature. The following equation (3) for obtaining the received light voltage correction value (Vrev) corrected to the voltage

The liquid level measurement method according to claim 1, wherein the correction formula is derived.

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