concentration measuring device

Abstract

This concentration measuring device uses light absorption with a light-emitting diode as the light source, enabling accurate concentration measurement even when the ambient temperature changes. [Solution] The first memory circuit 102 stores the correlation between the change in forward voltage ΔVf applied to the LED with respect to a set reference forward voltage Vfx and the change in the amount of light emitted by the LED with respect to the reference amount of light emitted I(Vfx) of the LED at the reference forward voltage Vfx. The correction circuit 105 corrects the amount of transmitted light of the solution measured by the optical measuring instrument 101 based on the relationship between the forward voltage detected by the voltage detection circuit 104 and the reference forward voltage Vfx in the correlation stored in the first memory unit 102.

Description

Technical Field

[0001] The present invention relates to a concentration measuring device.

Background Art

[0002] Techniques for measuring the concentration of chemical solutions such as semiconductor cleaning liquids using light absorption are known (Patent Document 1). This measurement technique measures the chemical solution concentration based on the amount of change in light intensity (absorbance) from the spectrum of the reference of the chemical solution to be measured with respect to the transmitted light intensity (spectrum) of pure water near room temperature. Also, in this type of measuring device, a light-emitting diode (LED) with a long lifespan is used as the light source.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, the concentration measuring device as described above may be used in an environment where the ambient temperature changes. In that case, due to the ambient temperature dependence of the emission spectrum of the LED used as the light source, accurate measurement may not be possible.

[0005] The present invention has been made to solve the above problems, and an object thereof is to enable accurate concentration measurement even when the ambient temperature changes in a concentration measuring device that uses light absorption with a light-emitting diode as the light source.

Means for Solving the Problems

[0006] The concentration measuring device according to the present invention includes an optical measuring instrument that measures the amount of transmitted light in a solution at a measurement wavelength using a light-emitting diode that emits light including a measurement wavelength corresponding to the solute of the solution whose concentration is to be measured as a light source; a first memory circuit configured to store the correlation between the change in the forward voltage applied to the light-emitting diode with respect to a set reference forward voltage and the change in the amount of light emitted by the light-emitting diode with respect to the reference amount of light emitted by the light-emitting diode at the reference forward voltage; and a first memory circuit configured to store a converted reference transmitted light amount obtained by measuring the reference transmitted light amount obtained by measuring the reference solution that serves as a reference for measuring the concentration of the solute in the solution with the optical measuring instrument, based on the correlation. The system comprises a configured second memory circuit, a voltage detection circuit configured to detect the forward voltage applied to a light-emitting diode when measuring the amount of transmitted light in a solution with an optical measuring instrument, a correction circuit configured to correct the amount of transmitted light measured by the optical measuring instrument based on the relationship between the forward voltage detected by the voltage detection circuit and a reference forward voltage in the correlation, and to obtain a corrected amount of transmitted light, an absorbance calculation circuit configured to determine the absorbance of the solution at the measurement wavelength from the corrected amount of transmitted light corrected by the correction circuit and the converted reference amount of transmitted light, and a concentration calculation circuit configured to determine the concentration of the solute in the solution from the absorbance of the solution.

[0007] In one example of the above-described concentration measuring device configuration, the concentration calculation circuit uses a regression equation that determines the concentration of the solute in the solution from the absorbance at the measurement wavelength, thereby determining the concentration of the solute from the absorbance of the solution. [Effects of the Invention]

[0008] As described above, according to the present invention, the transmitted light intensity of a solution measured by an optical measuring instrument is corrected based on the correlation between the change in the forward voltage applied to the LED relative to a set reference forward voltage and the change in the amount of light emitted by the LED relative to the reference amount of light emitted by the LED at the reference forward voltage, and the changes in the LED temperature or the forward current flowing through the LED. As a result, a concentration measuring device that uses light absorption with an LED as a light source can accurately measure the concentration even when the ambient temperature changes. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a diagram showing the configuration of a concentration measuring device according to an embodiment of the present invention. [Figure 2] Figure 2 is a diagram showing a partial configuration of a concentration measuring device according to an embodiment of the present invention. [Figure 3] Figure 3 is a graph showing the correlation between the change in the forward voltage ΔVf applied to the LED with respect to a set reference forward voltage Vfx, and the change in the light output I of the LED with respect to the reference light output I(Vfx) of the LED at the reference forward voltage Vfx, as a result of changes in the LED temperature or the forward current flowing through the LED. [Modes for carrying out the invention]

[0010] Hereinafter, an embodiment of the present invention will be described with reference to Figure 1. This concentration measuring device comprises an optical measuring instrument 101, a first memory circuit 102, a second memory circuit 103, a voltage detection circuit 104, a correction circuit 105, an absorbance calculation circuit 106, and a concentration calculation circuit 107.

[0011] The optical measuring instrument 101 measures the transmitted light intensity (spectrum) of a solution at a measurement wavelength, using a light-emitting diode that emits light containing the measurement wavelength corresponding to the solute of the solution whose concentration is to be measured as a light source. As shown in Figure 2, the optical measuring instrument 101 comprises a light source 111, a spectrometer 112, a light source control circuit 113, a spectroscopic control circuit 114, a light receiving control circuit 115, and a controller 116.

[0012] The light source 111 consists of a light-emitting diode (LED) that emits light containing a measurement wavelength corresponding to the component (solute) of the solution whose concentration is to be measured. The spectrometer 112 spectrally analyzes the received light. The spectrometer 112 can be, for example, a Fabry-Perot type. The light emitted from the light source 111 passes through the solution whose component concentration is to be measured and is received by the spectrometer 112.

[0013] The light source control circuit 113 controls the illumination of the light source 111 according to the control from the controller 116. For example, the light source control circuit 113 controls the light source 111 to emit light in a predetermined wavelength band at a predetermined intensity.

[0014] The spectral control circuit 114 controls the spectrometer 112 according to the control from the controller 116. For example, the spectral control circuit 114 appropriately controls the wavelength of light received by the photodetector by controlling the voltage applied between the two mirrors of the Fabry-Perot type spectrometer 112.

[0015] The light receiving control circuit 115 measures the intensity of the spectrally separated light according to the control from the controller 116. For example, when the light receiving control circuit 115 receives an electrical signal indicating the light intensity measured by the spectrometer 112, it converts the received electrical signal into a numerical value indicating the light intensity and outputs the converted numerical value.

[0016] The controller 116 is a computer device equipped with a CPU (Central Processing Unit), main memory, external memory, etc. The CPU operates (executes the program) based on the program loaded into the main memory, thereby realizing the functions described above. The above program is a program for the computer to execute the control functions described above. The controller 116 can also be configured using a programmable logic device (PLD) such as an FPGA (field-programmable gate array).

[0017] The controller 116 controls the light source 111 and the spectrometer 112, and acquires the intensity of the light of the measurement wavelength spectrally separated by the spectrometer 112 through the solution to be measured.

[0018] For example, the controller 116 obtains the light intensity (transmitted light intensity) of the measurement wavelength corresponding to the component to be measured from the light passing through the solution to be measured. For example, when the component to be measured is ammonia and hydrogen peroxide, the controller 116 selects the measurement wavelength corresponding to ammonia and the measurement wavelength corresponding to hydrogen peroxide, and controls the light source control circuit 113 to light the light source 111, thereby emitting light in the wavelength band including the measurement wavelength.

[0019] In addition, the controller 116 controls the spectroscopic control circuit 114 to spectroscopically separate the light of the measurement wavelength from the light received by the spectroscope 112 through the solution to be measured. Further, the controller 116 obtains the intensity of the light of the measurement wavelength measured by the spectroscope 112 via the light reception control circuit 115. For example, after the controller 116 measures the light intensity of the measurement wavelength corresponding to ammonia, it measures the light intensity of the measurement wavelength corresponding to hydrogen peroxide. Also, the controller 116 obtains the light intensity of each measured measurement wavelength.

[0020] The first storage circuit 102 stores the correlation between the change ΔVf in the forward voltage applied to the LED with respect to the set reference forward voltage Vfx and the change in the light emission amount I of the LED with respect to the reference light emission amount I(Vfx) of the LED at the reference forward voltage Vfx. For example, the forward current flowing through the LED is kept constant, and the ambient temperature of the LED is changed to measure the light amount (I) and the LED forward voltage (Vf). From the data (graph) obtained by this measurement, I / I(Vfx)=f(ΔVf = Vf - Vfx) can be obtained by regression calculation or the like and used as the correlation (Figure 3). In this case, the reference forward voltage Vfx can be any value within the range where I / I(Vfx)=f(ΔVf = Vf - Vfx) holds.

[0021] The second storage circuit 103 stores the converted reference transmitted light amount I'0 obtained by converting the reference transmitted light amount I0 obtained by measuring a reference solution, which is a reference for measuring the concentration of the solute in the solution, with the optical measuring instrument 101, based on the above-described correlation.

[0022] For example, when the object to be measured for concentration is an aqueous solution, the reference solution for concentration measurement can be water (pure water) as the medium. In this case, the transmitted light intensity of pure water is measured in advance by the optical measuring instrument 101 and taken as the reference transmitted light quantity I0. Also, for example, a solution with a known concentration can be used as the reference solution. In this case, the transmitted light intensity of the solution with a known concentration can be measured in advance by the optical measuring instrument 101 and taken as the reference transmitted light quantity I0.

[0023] The voltage detection circuit 104 detects the forward voltage applied to the LED when the optical measuring instrument 101 measures the transmitted light quantity of the solution. The voltage detection circuit 104 detects the forward voltage applied to the LED when the optical measuring instrument 101 measures the transmitted light intensity of the solution.

[0024] The correction circuit 105 corrects the measured transmitted light quantity Im of the solution measured by the optical measuring instrument 101 based on the relationship between the forward voltage detected by the voltage detection circuit 104 and the reference forward voltage Vfx in the correlation stored in the first storage unit 102, and obtains the corrected measured transmitted light quantity I’m.

[0025] The absorbance calculation circuit 106 obtains the absorbance of the solution at the measurement wavelength from the corrected measured transmitted light quantity I’m corrected by the correction circuit 105 and the conversion reference transmitted light quantity I’0. The concentration calculation circuit 107 obtains the concentration of the solute in the solution from the absorbance of the solution. The concentration calculation circuit 107 can obtain the concentration of the solute from the absorbance of the solution using a regression formula for obtaining the concentration of the solute in the solution from the absorbance at the measurement wavelength.

[0026] Each of the circuits described above can be a computer device including a CPU, a main memory device, an external memory device, etc. By the CPU operating (executing a program) according to a program developed in the main memory device, each of the functions described above is realized. The above program is a program for a computer to execute each of the control functions described above. Also, each of the circuits described above can be configured by a programmable logic device (PLD) such as an FPGA (Field Programmable Gate Array).

[0027] As described above, according to the embodiment of the present invention, the transmitted light intensity of the solution measured by the optical measuring instrument 101 is corrected based on the correlation between the change in forward voltage ΔVf applied to the LED with respect to a set reference forward voltage Vfx and the change in the amount of light emitted by the LED with respect to the reference amount of light emitted by the LED I(Vfx) at the reference forward voltage Vfx, in the condition of the LED temperature or the forward current flowing through the LED. As a result, the concentration measuring device that uses light absorption with an LED as a light source can accurately measure the concentration even when the ambient temperature changes.

[0028] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be implemented within the technical concept of the present invention by those with ordinary skill in the art. [Explanation of Symbols]

[0029] 101...Optical measuring instrument, 102...First memory circuit, 103...Second memory circuit, 104...Voltage detection circuit, 105...Correction circuit, 106...Absorbance calculation circuit, 107...Concentration calculation circuit.

Claims

1. An optical measuring instrument that measures the amount of transmitted light in a solution at a measurement wavelength, using a light-emitting diode that emits light including a measurement wavelength corresponding to the solute of the solution whose concentration is to be measured as a light source, A first storage circuit configured to store the correlation between the change in the forward voltage applied to the light-emitting diode with respect to a set reference forward voltage and the change in the amount of light emitted by the light-emitting diode with respect to a reference amount of light emitted by the light-emitting diode at the reference forward voltage, A second memory circuit is configured to store a converted reference transmitted light amount obtained by measuring a reference solution, which serves as a standard for measuring the concentration of the solute in the aforementioned solution, using the optical measuring instrument, and converting that reference transmitted light amount based on the correlation. A voltage detection circuit configured to detect the forward voltage applied to the light-emitting diode when measuring the amount of transmitted light of the solution using the optical measuring instrument, A correction circuit is configured to correct the measured transmitted light amount of the solution measured by the optical measuring instrument based on the relationship between the forward voltage detected by the voltage detection circuit and the reference forward voltage in the correlation, and to obtain a corrected measured transmitted light amount. An absorbance calculation circuit is configured to determine the absorbance of the solution at the measurement wavelength from the corrected measured transmitted light amount corrected by the correction circuit and the converted reference transmitted light amount, A concentration calculation circuit configured to determine the concentration of the solute in the solution from the absorbance of the solution. A concentration measuring device equipped with the following features.

2. In the concentration measuring device according to claim 1, The concentration calculation circuit is a concentration measuring device that determines the concentration of the solute in the solution from the absorbance of the solution using a regression equation that determines the concentration of the solute in the solution from the absorbance at the measurement wavelength.

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