Concentration measurement device

Abstract

To provide a concentration measurement device which utilizes light absorption using a light-emitting diode as a light source and which enables accurate concentration measurement even when ambient temperature changes.SOLUTION: A voltage detection circuit 104 detects a forward voltage applied to an LED constituting a light source 111, and a correction circuit 105 corrects transmitted light intensity of a solution measured by an optical measurement device 101 according to a relationship between the forward voltage detected by the voltage detection circuit 104 and a reference forward voltage in a correlation stored in a first storage circuit 102.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a concentration measurement device. [Background technology]

[0002] There is a known technology that uses light absorption to measure the concentration of chemicals such as semiconductor cleaning solutions (Patent Document 1). This measurement technology uses the transmitted light intensity (spectrum) of pure water at around room temperature as a reference, and measures the concentration of the chemical from the amount of change in light intensity (absorbance) of the spectrum of the chemical to be measured from the reference. In addition, this type of measurement device is now using long-life light-emitting diodes (LEDs) as the light source. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-128940 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the environment in which the concentration measuring device described above is used is subject to large temperature changes, and there are cases in which accurate measurements cannot be made because the emission spectrum of the LED used as the light source is highly dependent on the ambient temperature.

[0005] The present invention has been made to solve the above problems, and its object is to provide a concentration measuring device that uses light absorption with a light-emitting diode as a light source, so that the concentration can be measured accurately even if the ambient temperature changes. [Means for solving the problem]

[0006] The concentration measurement device according to the present invention includes an optical measuring instrument that measures the transmitted light intensity of a solution at a measurement wavelength using a light-emitting diode as a light source, the light-emitting diode emitting light including a measurement wavelength corresponding to a solute in the solution whose concentration is to be measured; a first memory circuit configured to store a correlation between a forward voltage applied to the light-emitting diode and the light emission intensity of the light-emitting diode; a second memory circuit configured to store a reference transmitted light intensity obtained by measuring the transmitted light intensity of a reference solution that serves as a reference for measuring the concentration of the solute in the solution with the optical measuring instrument, and a reference forward voltage applied to the light-emitting diode corresponding to the reference transmitted light intensity; a voltage detection circuit configured to detect the forward voltage applied to the light-emitting diode when the transmitted light intensity of the solution is measured with the optical measuring instrument; a correction circuit that corrects the transmitted light intensity 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; an absorbance calculation circuit configured to calculate the absorbance of the solution at the measurement wavelength from the transmitted light intensity of the solution corrected by the correction circuit and the reference transmitted light intensity; and a concentration calculation circuit configured to calculate the concentration of the solute in the solution from the absorbance of the solution.

[0007] In one configuration example of the concentration measurement device, the concentration calculation circuit determines the concentration of the solute 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.

[0008] In one configuration example of the above-mentioned concentration measurement device, the first memory circuit stores correlations corresponding to a plurality of set wavelengths, and the second memory circuit stores reference transmitted light intensities and reference forward voltages corresponding to a plurality of set wavelengths.

[0009] In one configuration example of the above-mentioned concentration measuring device, the first memory circuit stores a correlation corresponding to an arbitrary set reference forward voltage, and the second memory circuit stores a reference transmitted light intensity measured while the light-emitting diode is temperature-controlled to obtain the reference forward voltage. Effect of the Invention

[0010] As described above, according to the present invention, the transmitted light intensity of a solution measured by an optical measuring instrument is corrected using the correlation between the forward voltage applied to the light-emitting diode and the light emission intensity of the light-emitting diode, so that a concentration measurement device that uses light absorption with a light-emitting diode as a light source can accurately measure concentration even if the ambient temperature changes. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the configuration of a concentration measuring device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a partial configuration of the concentration measuring device according to the embodiment of the present invention. [Diagram 3] 3 is a characteristic diagram showing the relationship between the amount of change ΔVf of each forward voltage Vf in the data set relative to the reference forward voltage Vf0 extracted from the data set close to the measurement reference forward voltage Vfm0, and the rate of change Δad(λ) of the emission intensity Iad(λ) in the data set relative to the emission intensity Iad0(λ) corresponding to the reference forward voltage Vf0 extracted from the data set. Here, λ represents the wavelength, and the characteristic diagram in FIG. 3 exists for each wavelength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A concentration measurement device according to an embodiment of the present invention will be described below with reference to Fig. 1. This concentration measurement device includes an optical measurement device 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.

[0013] The optical measuring instrument 101 measures the transmitted light intensity (spectrum) of a solution at a measurement wavelength using a light emitting diode as a light source, which emits light including a measurement wavelength corresponding to a solute in the solution whose concentration is to be measured. The optical measuring instrument 101 includes a light source 111, a spectroscope 112, a light source control circuit 113, a spectrometry control circuit 114, a light receiving control circuit 115, and a controller 116.

[0014] The light source 111 is composed of a light emitting diode (LED) that emits light including a measurement wavelength corresponding to a component (solute) of the solution whose concentration is to be measured. The spectroscope 112 separates the received light. The spectroscope 112 may 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 spectroscope 112.

[0015] The light source control circuit 113 controls the lighting of the light source 111 under control of the controller 116. For example, the light source control circuit 113 controls the light source 111 to emit light in a predetermined wavelength band with a predetermined intensity.

[0016] The spectroscopic control circuit 114 controls the spectrometer 112 under control of the controller 116. For example, the spectroscopic control circuit 114 controls a voltage applied between two mirrors of the Fabry-Perot type spectrometer 112, thereby appropriately controlling the wavelength of light received by the light receiving element.

[0017] The light-receiving control circuit 115 measures the intensity of the dispersed light under control of the controller 116. For example, when the light-receiving control circuit 115 receives an electrical signal indicating the intensity of the light measured by the spectroscope 112, the light-receiving control circuit 115 converts the received electrical signal into a numerical value indicating the intensity of the light, and outputs the converted numerical value.

[0018] The controller 116 is a computer device equipped with a CPU (Central Processing Unit), a main storage device, an external storage device, etc. The CPU operates (executes) a program deployed in the main storage device, thereby realizing each of the above-mentioned functions. The above-mentioned programs are programs for causing a computer to execute each of the above-mentioned control functions. The controller 116 can also be configured with a programmable logic device (PLD) such as an FPGA (field-programmable gate array).

[0019] The controller 116 controls the light source 111 and the spectroscope 112, and acquires the intensity of light at a measurement wavelength that is dispersed by the spectroscope 112 through the solution to be measured.

[0020] For example, the controller 116 acquires the light intensity (transmitted light intensity) of the measurement wavelength corresponding to the measurement target component from the light passing through the solution to be measured. For example, when the measurement target components are ammonia and hydrogen peroxide, the controller 116 selects a measurement wavelength corresponding to ammonia and a measurement wavelength corresponding to hydrogen peroxide, and controls the light source control circuit 113 to turn on the light source 111, thereby emitting light in a wavelength band including the measurement wavelength.

[0021] The controller 116 also controls the spectroscopic control circuit 114 to separate light of a measurement wavelength from the light received by the spectrometer 112 through the solution to be measured. The controller 116 also acquires the intensity of light of the measurement wavelength measured by the spectrometer 112 via the light receiving control circuit 115. For example, the controller 116 causes the spectrometer 112 to measure the light intensity of the measurement wavelength corresponding to ammonia, and then causes the spectrometer 112 to measure the light intensity of the measurement wavelength corresponding to hydrogen peroxide. The controller 116 also acquires the light intensity of each measured measurement wavelength.

[0022] The first storage circuit 102 stores the correlation between the forward voltage applied to the LED and the light emission intensity of the LED. The first storage circuit 102 stores the correlation corresponding to a plurality of set wavelengths. For example, the forward voltage applied to the LED is varied, and the light emission intensity of the LED that changes as a result of this variation is measured. This measurement is performed for each wavelength used for concentration measurement. The change in the LED light emission intensity relative to the change in the forward voltage obtained from each measurement result is prepared as a correlation. The first storage circuit 102 can also store the correlation corresponding to any set reference forward voltage (described later).

[0023] The second memory circuit 103 stores a reference transmitted light intensity obtained by measuring the transmitted light intensity of a reference solution, which is a reference for measuring the concentration of a solute in a solution to be measured, using an optical measuring device. The second memory circuit 103 also stores a reference forward voltage applied to the light-emitting diode corresponding to the reference transmitted light intensity. The reference forward voltage can be the forward voltage of the LED when the light emission intensity of the LED is the reference transmitted light intensity. The second memory circuit 103 stores the reference transmitted light intensity and the reference forward voltage corresponding to a plurality of wavelengths that have been set. The second memory circuit 103 can also store the reference transmitted light intensity measured in a state in which the light-emitting diode is temperature-controlled so as to become the reference forward voltage.

[0024] For example, when the concentration of an aqueous solution is to be measured, the reference liquid serving as the reference for the concentration measurement can be water (pure water) which is a medium. In this case, the transmitted light intensity of the pure water is measured in advance by the optical measuring instrument 101 and used as the reference transmitted light intensity. Also, for example, the forward voltage applied to the LED at the time when the transmitted light intensity of the pure water is measured can be measured and used as the reference forward voltage. Also, for example, a solution with a known concentration can be used as the reference liquid. 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 used as the reference transmitted light intensity.

[0025] The voltage detection circuit 104 detects a forward voltage applied to the LED constituting the light source 111. 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. The correction circuit 105 corrects the transmitted light intensity 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 a reference forward voltage in the correlation stored in the first storage circuit 102.

[0026] The absorbance calculation circuit 106 calculates the absorbance of the solution at the measurement wavelength from the transmitted light intensity of the solution corrected by the correction circuit 105 and the reference transmitted light intensity. The concentration calculation circuit 107 calculates the concentration of the solute in the solution from the absorbance of the solution. The concentration calculation circuit 107 can calculate the concentration of the solute from the absorbance of the solution using a regression equation that calculates the concentration of the solute in the solution from the absorbance at the measurement wavelength.

[0027] Each of the above-mentioned circuits can be a computer device equipped with a CPU, a main memory device, an external memory device, etc. Each of the above-mentioned functions is realized by the CPU operating (executing) a program deployed in the main memory device. The above-mentioned program is a program for causing a computer to execute each of the above-mentioned control functions. Also, each of the above-mentioned circuits can be configured by a programmable logic device (PLD) such as an FPGA (field-programmable gate array).

[0028] As described above, according to the embodiment, the transmitted light intensity of the solution measured by the optical measuring device 101 is corrected based on the correlation between the forward voltage applied to the LED constituting the light source 111 and the light emission intensity of the LED. As a result, the concentration measurement device using the LED as the light source and light absorption can accurately measure the concentration even if the ambient temperature changes.

[0029] The following will explain in more detail. The forward voltage Vf of the LED is changed, and the luminous intensity I of the LED corresponding to the changed Vf is calculated. ad A set of measured values ​​(data set) of (λ) is acquired in advance and stored (see Table 1), where λ represents the wavelength. It is desirable for the measurement resolution of Vf to be 0.1 mV or less.

[0030] [Table 1]

[0031] Also, measure the reference transmitted light intensity (reference spectrum) I0(λ). Furthermore, measure the reference forward voltage Vf of the LED during this measurement. m0 Measure.

[0032] Next, the measurement reference forward voltage Vf m0 The forward voltage Vf closest to the reference voltage Vf0 is extracted from the data set, and the corresponding light emission intensity I ad0 (λ) is extracted from the data set. For example, the measured reference forward voltage Vf m0 = 1000.1 mV, the reference forward voltage Vf0 = 1000.0 mV, and the I ad0 (λ) = 11000, 20000, . . . , 15000 are extracted from the data set. Note that linear interpolation is performed between the rows of each measurement data example in Table 1 to set the reference forward voltage Vf0 = 1000.1 mV, and the corresponding I ad0 The reference forward voltage Vf0 can be set to (λ)=11333, 20333, . . . , 15333. The determined reference forward voltage Vf0 can be stored in the second memory circuit 103.

[0033] Next, the reference forward voltage Vf0, I ad0 Using (λ) and the data set (Table 1), ΔVf = Vf - Vf0 and ΔI ad (λ)=I ad (λ) / I ad0 (λ) and calculate ΔVf and ΔI shown in Figure 3. ad From the characteristics showing the relationship between ΔVf and ΔI ad (λ) is determined. ΔVf is the measurement reference forward voltage Vf m0 The change in each forward voltage Vf in the data set relative to the reference forward voltage Vf0 extracted from the data set close to ΔI (=Vf-Vf0). ad (λ) is the light emission intensity I corresponding to the reference forward voltage Vf0 extracted from the data set. ad0 Each emission intensity I in the data set based on (λ) ad (λ) change rate (=I ad (λ) / I ad0 (λ)). ΔI ad (λ) is (Vf0,Iad0 (λ)) is (Vf,I ad The relationship can also be expressed as the rate of change in LED light intensity when the temperature changes from 100 to 150°C (λ). The relationship is expressed as "ΔI ad (λ)=a×ΔVf 2 +b×ΔVf+1 (1)”. The constants a and b exist for each wavelength. This relation can be expressed as a quadratic equation or higher.

[0034] The obtained relational expression is stored in the first storage circuit 102 as the correlation between the forward voltage applied to the LED and the light emission intensity of the LED.

[0035] With the correlation between the forward voltage applied to the LED and the light emission intensity of the LED obtained as described above, the concentration of the solution to be measured is measured. In measuring the concentration of the solution to be measured, the transmitted light intensity Ic(λ) is measured (optical measuring device 101), and the forward voltage Vfc applied to the LED is detected (voltage detection circuit 104).

[0036] Once Ic(λ) and Vfc have been obtained by measurement, in order to unify the effect of the temperature characteristics of the LED light intensity on the light intensity change when measuring the reference transmitted light intensity (reference spectrum) I0(λ) and when measuring the transmitted light intensity Ic(λ) of the target solution, calculate the LED light intensity Ic0(λ) (=Ic(λ) / ΔIc(λ)) when Vfc is the reference forward voltage Vf0. Here, ΔIc(λ) is the rate of change of the LED light intensity when (Vf0, Ic0(λ)) changes to (Vfc, Ic(λ)), and is expressed as "ΔIc(λ)=a×ΔVf 2 +b×ΔVf+1···(2)" where ΔVf=Vfc−Vf0, and the constants a and b have the same values ​​as in equation (1) (correction circuit 105).

[0037] Next, using I0(λ) and Ic0(λ) from (Vf0,I0(λ)) and (Vf0,Ic0(λ)), we can calculate A(λ) = -log 10 The absorbance A(λ) of the wavelength is calculated by (Ic0(λ) / I0(λ)) (3) (the absorbance calculation circuit 106).

[0038] Next, the concentration C is calculated using the calculated absorbance A(λ) and the regression equation "C=b1·A(λ1)+b2·A(λ2)+b3·A(λ3)+b0" (concentration calculation circuit 107). Note that this equation is an example of a case where three wavelengths λ1, λ2, and λ3 are used, and the coefficients b0, b1, b2, and b3 of the regression equation are calculated in advance by multivariate analysis or the like. The wavelengths used in the measurement are not limited to three.

[0039] It can also be shown as follows. For the measured values ​​in Table 1 above, when each Vf is Vf0, Vf0 and the LED light emission intensity I corresponding to this Vf0 ad0 (λ) and the measured values ​​in Table 1, the temperature characteristic correction formula (ΔVf and ΔI ad (relationship between a and λ) is calculated in advance, and a set of coefficients (a, b) of this correction equation (coefficient data set) is calculated in advance and stored (Table 2).

[0040] [Table 2]

[0041] Once the coefficient data set is prepared as described above, measure the reference spectrum I0(λ). In addition, measure the reference forward voltage Vf of the LED during this measurement. m0 Next, measure the measurement reference forward voltage Vf m0 The reference forward voltage Vf0 and the corresponding light intensity I ad0 (λ), and the temperature characteristic correction formula (ΔVf and ΔI ad (λ)) from the coefficient data set, and extract the coefficients a and b of "ΔI ad (λ)=a×ΔVf 2 +b×ΔVf+1···(1)” is the LED light emission intensity I ad The obtained relational expression is stored in the first storage circuit 102 as a correlation between the forward voltage applied to the LED and the light emission intensity of the LED.

[0042] If the concentration of the solution to be measured is measured while the correlation between the forward voltage applied to the LED and the LED's light emission intensity has been obtained as above, it is possible to find the absorbance A(λ) and therefore the concentration C, as described above.

[0043] It is also possible to set an arbitrary reference forward voltage Vf0 in advance for the measurement value group in Table 1 described above, and calculate the LED light emission intensity I corresponding to the arbitrary reference forward voltage Vf0 that has been set. ad (λ) temperature characteristic correction formula (ΔVf and ΔI ad The relational expression with respect to (λ) is obtained in advance. The method for obtaining the relational expression is the same as that described above. The obtained relational expression is stored in the first memory circuit 102.

[0044] Next, in the measurement of the reference spectrum I0(λ), the forward voltage measured in the measurement of this spectrum (measurement reference forward voltage Vf m0 The LED temperature is adjusted using a heater or the like so that the reference forward voltage Vf0 matches the arbitrary reference forward voltage Vf0 that has been set in advance. In this state, if the reference spectrum I0(λ) is measured, the relationship between ΔVf and ΔI ad The relation between the reference spectrum I0(λ) and the forward voltage Vf0 can be applied to measure the concentration of the solution to be measured. Note that the LED temperature only needs to be controlled so that the forward voltage becomes the predetermined reference forward voltage Vf0 when measuring the reference spectrum I0(λ), and there is no need to constantly control the temperature during operation.

[0045] As described above, according to the present invention, the transmitted light intensity of a solution measured by an optical measuring instrument is corrected using the correlation between the forward voltage applied to the light-emitting diode and the light emission intensity of the light-emitting diode, so that a concentration measurement device that uses light absorption with a light-emitting diode as a light source can accurately measure concentration even if the ambient temperature changes.

[0046] It should be noted that the present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0047] 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 for measuring the intensity of light transmitted through the solution at a measurement wavelength corresponding to a solute in the solution to be measured; and a first storage circuit configured to store a correlation between a forward voltage applied to the light emitting diode and a light emission intensity of the light emitting diode; a second memory circuit configured to store a reference transmitted light intensity obtained by measuring a transmitted light intensity of a reference solution serving as a reference for measuring a concentration of the solute in the solution by the optical measuring device, and a reference forward voltage applied to the light emitting diode corresponding to the reference transmitted light intensity; a voltage detection circuit configured to detect a forward voltage applied to the light emitting diode when the optical measuring device measures the transmitted light intensity of the solution; a correction circuit that corrects the transmitted light intensity of the solution measured by the optical measuring device based on a relationship between the forward voltage detected by the voltage detection circuit and the reference forward voltage in the correlation; an absorbance calculation circuit configured to calculate an absorbance of the solution at the measurement wavelength from the transmitted light intensity of the solution corrected by the correction circuit and the reference transmitted light intensity; a concentration calculation circuit configured to calculate a concentration of the solute in the solution from the absorbance of the solution; A concentration measuring device comprising:

2. 2. The concentration measuring device according to claim 1, The concentration calculation circuit is a concentration measurement device that determines the concentration of the solute 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.

3. 3. The concentration measuring device according to claim 1, the first storage circuit stores the correlation corresponding to a plurality of set wavelengths; The second memory circuit stores the reference transmitted light intensity and the reference forward voltage corresponding to a plurality of wavelengths that have been set.

4. 3. The concentration measuring device according to claim 1, the first storage circuit stores the correlation corresponding to any one of the reference forward voltages that is set; The second memory circuit is a concentration measuring device that stores the reference transmitted light intensity measured in a state where the light emitting diode is temperature controlled so as to have the reference forward voltage.

Images