Concentration measuring device and method for adjusting the same

Abstract

To provide a concentration measuring device with which it is possible to prevent abnormal cyclic changes of intensity and appropriately measure a concentration.SOLUTION: The present invention comprises: a plurality of light sources 2, 3 that emit light in respective different wavelengths; a multiplexer 5 that multiplexes rays of light in a plurality of wavelengths that are emitted by the light sources 2, 3; a measurement cell 6 for accommodating a fluid G to be measured which the rays of light multiplexed by the multiplexer 5 pass through; a transmitted light detector 7 for detecting transmitted light having passed through the measurement cell 6; a light reception circuit 8 for adjusting the amplification rate and offset voltage of the analog detection signal outputted by the transmitted light detector 7; a signal converter 9 that converts the analog detection signal having been adjusted by the light reception circuit 8 into a digital signal 9s; a signal detection unit 15 that is configured to detect the behavior of the digital signal 9s; and a concentration computing unit 13 that is configured to calculate the concentration of the fluid G to be measured, by using the amplitude spectrum having been obtained by frequency analyzing the digital signal 9s.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a concentration measuring device and a method for adjusting the same for measuring gas concentration using absorbance. [Background technology]

[0002] Conventionally, concentration measuring devices are known that are incorporated into gas supply lines that supply raw material gases such as organometallic (MO) gases to semiconductor manufacturing equipment, and that measure the concentration of the gas flowing through the gas supply line (Patent Document 1, etc.).

[0003] This type of concentration measuring device measures absorbance by injecting light of a predetermined wavelength from a light source into a measuring cell, detecting the light absorbed by the gas as it passes through the measuring cell with a transmitted light detector, and then determining the concentration from the absorbance.

[0004] In semiconductor manufacturing equipment, multiple types of process gases are supplied, and the absorption rate of light at different wavelengths varies depending on the gas type. Therefore, absorbance can be measured using light of multiple different wavelengths (ultraviolet light). Light of multiple different wavelengths is combined in a multiplexer before being incident on a measurement cell. The combined light incident on the measurement cell is absorbed by the gases within the measurement cell and then received by a single transmitted light detector. The analog detection signal output from the transmitted light detector is A / D converted, amplified, and then frequency-analyzed using a fast Fourier transform to convert it into the amplitude spectrum of each frequency component. The amplitude value of the amplitude spectrum is output as the intensity of the transmitted light. The amplitude of the amplitude spectrum decreases at wavelengths where absorption occurs.

[0005] Based on the change in amplitude of the amplitude spectrum, the absorbance A can be calculated according to Lambert-Beer's law. λ The concentration C is calculated using the following formula (1).

[0006] A λ =log 10 (I0 / I)=αLC ····(1) Here, I0 is the initial intensity of the incident light incident on the measurement cell, I is the intensity of the transmitted light that has passed through the measurement cell, and α is the molar extinction coefficient (m 2 (mol / m³), L is the optical path length of the measurement cell (m), C is the concentration (mol / m³). 3 The molar extinction coefficient α is a coefficient determined by the substance.

[0007] Figure 1 is a functional block diagram showing a conventional concentration measuring device. This concentration measuring device 1A comprises multiple light sources 2 and 3, a light-emitting circuit 4 for emitting light of different wavelengths from each of the light sources 2 and 3, a multiplexer 5 for combining the light emitted from each of the light sources 2 and 3, a measuring cell 6 into which the light combined by the multiplexer 5 is incident, a transmitted light detector 7 for detecting the light that has passed through the measuring cell 6, a light-receiving circuit 8 for adjusting the amplification factor and offset voltage of the detection signal of the transmitted light detected by the transmitted light detector 7, a signal converter 9 for converting the analog signal whose amplification factor and offset voltage have been adjusted by the light-receiving circuit 8 into a digital signal, and a processing device 10A configured to collect the digital signal converted by the signal converter 9 and calculate the concentration of the gas to be measured according to a program recorded in a storage device such as a memory. In the illustrated example there are two light sources, but three or more light sources can be provided as needed.

[0008] Light sources 2 and 3 are composed of light-emitting elements such as light-emitting diodes, and the light-emitting circuit 4 has the function of adjusting and controlling the current value 4a, frequency 4b, and current offset 4c of the drive current, respectively, based on command signals from the processing unit 10A, in order to supply drive currents of different frequencies to each of the multiple light sources 2 and 3.

[0009] The measurement cell 6 is equipped with a gas inlet 6a and a gas outlet 6b through which the gas to be measured flows in and out, a light incidence window 6c, and a light emission window 6d.

[0010] The multiplexer 5 includes a half mirror, for example, similar to FIG. 6 of Patent Document 1, combines the light incident from two directions, and outputs the combined light in two directions. One of the lights in the two directions output from the multiplexer 5 enters the measurement cell 6, and the other light is detected by the non-incident light detector 11 without entering the measurement cell 6. A splitter that branches the combined light as a reference light may be provided separately from the multiplexer (FIG. 1 of Patent Document 1).

[0011] The detection signal of the non-incident light detector 11 is used as a reference light for correcting the detection signal of the transmitted light detector 7 (Patent Document 1). The correction can be performed by arithmetic processing based on the following formula (2).

[0012] I cor =I cell ×(I ref,0 / I ref ) ···(2) In the above formula (2), I cor is the light intensity of the transmitted light after correction, I cell is the intensity at the time of concentration measurement of the transmitted light detected by the transmitted light detector, I ref,0 is the initial intensity of the non-incident light detected by the non-incident light detector, and I ref is the intensity at the time of concentration measurement of the non-incident light detected by the non-incident light detector.

[0013] The light receiving circuit 8 includes a fixed amplification unit 8a, an offset adjustment unit 8b, and a variable amplification unit 8c. They respectively perform fixed amplification, offset voltage adjustment, and variable amplification on the analog detection signals of the transmitted light and the reference light. Since the detection signals of the transmitted light and the reference light are very small, the detection signals are greatly fixed-amplified by the fixed amplification unit 8a, and the amplification rate of the detection signals is adjusted by finely adjusting the fixed-amplified detection signals by the variable amplification unit 8c. The offset adjustment amount (i.e., the offset voltage) by the offset adjustment unit 8b and the amplification rate of the variable amplification unit 8c are determined based on a command signal from the processing device 10A.

[0014] [[ID=�4]]The signal converter 9 converts the analog detection signals of the transmitted light and the reference light adjusted by the light receiving circuit 8 into digital signals.

[0015] The processing unit 10A includes a data acquisition function 10a for collecting digital signals from the signal converter 9, an analysis function 10b for performing frequency analysis using the Fast Fourier Transform, and an intensity output function 10c for outputting the amplitude value of the amplitude spectrum obtained by the frequency analysis as an intensity output 12. The processing unit 10A further includes a concentration calculation unit 13, which, according to a program stored in a storage device such as internal memory, uses the intensity output 12 output from the intensity output function 10c to calculate the concentration of the gas G to be measured, which is the fluid to be measured, based on the Lambert-Beer equation described above. The processing unit 10A uses an MPU (Micro Processor Unit). In the figure, reference numeral 14 denotes a clock generation circuit.

[0016] In the above concentration measuring device, a target value for the intensity output is set so that the output of the amplitude spectrum, i.e., the intensity output, is as large as possible in order to increase the measurement sensitivity. Then, in the light receiving circuit 8, parameters for amplification and offset of the analog signal input to the light receiving circuit 8 (amplification rate, offset voltage) are adjusted while checking the intensity output so that the intensity output reaches the set target value. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] International Publication No. WO2017 / 029791 [Overview of the project] [Problems that the invention aims to solve]

[0018] However, in the conventional concentration measuring device described above, abnormal periodic changes sometimes occurred in the intensity output, which was obtained from the amplitude value of a predetermined frequency, resulting in an inability to measure the concentration properly.

[0019] The main object of the present invention is to provide a concentration measuring apparatus and an adjustment method thereof that can prevent abnormal periodic changes occurring in the intensity output used for absorbance measurement and appropriately measure the concentration.

Means for Solving the Problems

[0020] To achieve the above object, a concentration measuring apparatus according to one aspect of the present invention includes a plurality of light sources each emitting light of a different wavelength, a multiplexer that multiplexes the lights of the plurality of different wavelengths emitted by the plurality of light sources, a measurement cell for containing a measurement fluid through which the light multiplexed by the multiplexer passes, a transmitted light detector for detecting the transmitted light that has passed through the measurement cell, a light receiving circuit for adjusting the amplification factor and offset voltage of an analog detection signal output by the transmitted light detector, a signal converter that converts the analog detection signal adjusted by the light receiving circuit into a digital signal, a signal detection unit configured to detect the behavior of the digital signal digitally converted by the signal conversion, and a concentration calculation unit configured to calculate the concentration of the measurement fluid using an amplitude spectrum obtained by frequency analyzing the digital signal. vessel Further, the multiplexer outputs the multiplexed combined light in two directions, one of the lights is incident on the measurement cell, the other light is non-incident light that is not incident on the measurement cell, and the non-incident light detector for detecting the non-incident light as reference light is further provided, the light receiving circuit is further configured to be able to adjust the amplification factor and offset voltage of the analog detection signal of the non-incident light detected by the non-incident light detector, and the signal converter can be further configured to convert the analog detection signal detected by the non-incident light detector and adjusted by the light receiving circuit into a digital signal.

[0021]

[0022] ​Furthermore, the light receiving circuit may further include a splitter for splitting the combined light obtained by the multiplexer into transmitted light that passes through the measurement cell and non-incident light that does not pass through the measurement cell, and a non-incident light detector for detecting the non-incident light as a reference light, wherein the light receiving circuit is further configured to adjust the amplification factor and offset voltage of the detection signal detected by the non-incident light detector, and the signal converter may further be configured to convert the analog detection signal detected by the non-incident light detector and adjusted by the light receiving circuit into a digital signal.

[0023] The signal detection unit may be configured to output a signal that displays the waveform of the digital signal on a monitor.

[0024] The signal detection unit may be configured to determine whether the amplitude value of the digital signal is within a predetermined range, and to output a signal to generate a warning if the amplitude value falls outside the predetermined range.

[0025] Furthermore, a method for adjusting a concentration measuring device according to one aspect of the present invention comprises: a plurality of light sources each emitting light of a different wavelength; a multiplexer that combines the light of a plurality of different wavelengths emitted by the plurality of light sources and outputs the combined light in two directions; a measuring cell for containing a fluid to be measured through which one of the two beams of light output from the multiplexer passes; a transmitted light detector for detecting the transmitted light that has passed through the measuring cell; a non-incident light detector for detecting the other beam of light output from the multiplexer as a reference light that does not enter the measuring cell; and a receiver for adjusting the amplification factor and offset voltage of the analog detection signals output by the transmitted light detector and the non-incident light detector. The optical circuit includes a signal converter that converts an analog detection signal adjusted by the light receiving circuit into a digital signal, a signal detection unit that detects the behavior of the digital signal converted by the signal converter, and a concentration calculation unit configured to calculate the concentration of the fluid to be measured using the amplitude spectrum obtained by frequency analysis of the digital signal, wherein the adjustment method includes the steps of detecting a change in the digital value of the digital signal and determining that the change in the digital value is within a predetermined range, and, if the digital value is outside the predetermined range, changing the amplification factor and / or offset voltage of the analog detection signals of the transmitted light detector and the non-incident light detector.

[0026] Furthermore, a method for adjusting a concentration measuring device according to another aspect of the present invention comprises: a plurality of light sources each emitting light of a different wavelength; a multiplexer for combining the light of a plurality of different wavelengths emitted by the plurality of light sources; a measuring cell for containing a fluid to be measured through which the light combined by the multiplexer passes; a transmitted light detector for detecting the transmitted light that has passed through the measuring cell; a splitter for splitting the combined light combined by the multiplexer into transmitted light that passes through the measuring cell and non-incident light that does not pass through the measuring cell; a non-incident light detector for detecting the non-incident light as a reference light; and adjusting the amplification factor and offset voltage of the analog detection signals output by the transmitted light detector and the non-incident light detector. The adjustment method includes a light receiving circuit for adjustment, a signal converter that converts the analog detection signal adjusted by the light receiving circuit into a digital signal, a signal detection unit configured to detect the behavior of the digital signal converted by the signal converter, and a concentration calculation unit configured to calculate the concentration using the amplitude spectrum obtained by frequency analysis of the digital signal, wherein the adjustment method includes the steps of detecting a change in the digital value of the digital signal and determining that the change in the digital value is within a predetermined range, and, if the digital value is outside the predetermined range, changing the amplification factor and / or offset voltage of the analog detection signals of the transmitted light detector and the incident light detector. [Effects of the Invention]

[0027] According to the present invention, by detecting the behavior of the digital signal of the combined light converted digitally by the signal converter, it becomes possible to adjust the signal so that abnormal periodic fluctuations do not occur. [Brief explanation of the drawing]

[0028] [Figure 1] This is a functional block diagram showing a conventional concentration measuring device. [Figure 2] This is a functional block diagram showing a first embodiment of the concentration measuring device according to the present invention. [Figure 3] Figure 2 shows a monitor image of the digitally converted multiplexed light obtained by the concentration measuring device. [Figure 4] Figure 2 shows another monitor image of the digitally converted multiplexed light obtained by the concentration measuring device. [Figure 5] This is a functional block diagram showing a second embodiment of the concentration measuring device according to the present invention. [Modes for carrying out the invention]

[0029] Embodiments of the concentration measuring device according to the present invention will be described below with reference to Figures 2 to 5. Note that components identical or similar to those in the prior art are denoted by the same reference numerals.

[0030] Referring to Figure 2, the concentration measuring device 1 according to the first embodiment of the present invention comprises a plurality of light sources 2, 3 each emitting light of different wavelengths, a multiplexer 5 that combines the light of multiple different wavelengths emitted by the plurality of light sources 2, 3, a measuring cell 6 for containing the gas to be measured G through which the light combined by the multiplexer 5 passes, a transmitted light detector 7 for detecting the transmitted light that has passed through the measuring cell 6, a light receiving circuit 8 for adjusting the amplification factor and offset voltage of the transmitted light signal of the transmitted light detected by the transmitted light detector 7, a signal converter 9 that converts the analog signal 8s adjusted by the light receiving circuit 8 into a digital signal 9s, a signal detection unit 15 configured to detect the behavior of the digital signal 9s converted by the signal converter 9, and a concentration calculation unit 13 configured to calculate the concentration of the gas to be measured using the amplitude spectrum obtained by frequency analysis of the digital signal 9s.

[0031] In the illustrated example, light-emitting diodes are used as light sources 2 and 3, but other light-emitting elements such as laser diodes can also be used. In the illustrated example, wavelengths in the ultraviolet region are used for light sources 2 and 3, but light in wavelength regions other than the ultraviolet region can also be used.

[0032] The multiplexer 5 includes a half-mirror 5a and combines light incident from two directions, outputting the combined light in two directions. Of the two beams of light output from the multiplexer 5, one beam is incident on the measurement cell 6, while the other beam of light does not incident on the measurement cell 6 and is detected by the non-incident photodetector 11.

[0033] In the illustrated example, photodiodes are used for the transmitted light detector 7 and the non-incident light detector 11, but other light sensors such as phototransistors can also be used.

[0034] The offset adjustment in the light-emitting circuit 4 and the light-receiving circuit 8 can be performed by adjusting the offset voltage of the operational amplifier. The variable amplification section 8c in the light-receiving circuit 8 can have its amplification factor adjusted by adjusting the variable resistor provided in the operational amplifier.

[0035] The processing unit 10 includes a data acquisition function 10a for collecting digital signal data from the signal converter 9, an analysis function 10b for performing frequency analysis using a fast Fourier transform, an intensity output function 10c for outputting the amplitude value of the amplitude spectrum obtained by the frequency analysis as an intensity output 12, a density calculation unit 13, and a signal detection unit 15. The density calculation and density correction calculation using reference light in the density calculation unit 13 are known from the above-mentioned Patent Document 1, etc., so a detailed explanation is omitted.

[0036] The processing unit 10 is composed of an MPU (Micro Processor Unit). The data acquisition function 10a is composed of a storage device such as a buffer memory and can record digital data of the multiplexed light sampled from the signal converter 9. The processing unit 10 performs a Fast Fourier Transform on the digital signal collected from the signal converter 9 according to a program recorded in its built-in storage device, outputs the intensity of the amplitude value, and calculates the density. The recording device on which the program is recorded may be externally connected to the processing unit 10. The processing unit 10 is not limited to an MPU, but may also be other computer systems such as a microcomputer or an MCU (Micro Controller Unit).

[0037] The signal detection unit 15 is equipped with a display function that outputs the digital value of the digital waveform signal of the combined light (hereinafter also referred to as "digital combined light") digitally converted by the signal converter 9 to the monitor 16, thereby enabling detection of the behavior of the digital signal of the combined light. Such a display function can be implemented, for example, by constructing a program that displays the digital data collected by the processing unit 10 on the monitor.

[0038] The program for executing the display function can be stored in a memory or other storage device built into the processing unit 10. The processing unit 10 outputs a signal to display the digital value of the digital multiplexer on the monitor 16 according to the recorded program. The storage device for recording the program may be externally connected to the processing unit 10.

[0039] The signal detection unit 15 outputs a signal that displays the digital waveform signal of the multiplexed light detected by the transmitted light detector 7 on the monitor. The signal detection unit 15 can also be configured to output a signal that displays the digital waveform of the multiplexed light detected by the non-incident light detector 11 on the monitor.

[0040] Figure 3 shows an example of juxtaposing an image of the analog data input to the signal converter 9 displayed on an oscilloscope with an image of the digital multiplex output from the multiplexer 5 displayed on a monitor. The monitor image of the digital multiplex is a graph of digital waveform data extracted in time series from the storage device constituting the data acquisition function 10a. Note that the image in Figure 3 is the waveform of the detection signal detected by the transmitted light detector 7.

[0041] In the example shown in Figure 3, the signal converter 9 is an A / D converter with an input rating of 0 to 3.3V and a resolution of 16 bits. When 3.3V is input to this A / D converter, the maximum value of the 16 bits (quantization number) output is 65,535 digits, which is the upper limit of normal output.

[0042] In the example shown in Figure 3, the analog input signal to the A / D converter that constitutes the signal converter 9 is within the rated range, and the digital value of the digital combined signal obtained by digitally converting that analog input signal is also sampled normally, outputting a 16-bit value that is within the range of the maximum value (65535 digits) of the output value (sampling value) after A / D conversion.

[0043] When the digital value of the digital combined wave output from the A / D converter is below the maximum output value corresponding to the input rating of the A / D converter (as in Figure 3), frequency analysis using the Fast Fourier Transform shows no abnormal periodic changes in the intensity output 12, and a nearly constant intensity output is obtained.

[0044] Figure 4 shows a state where the analog input signal to the A / D converter constituting the signal converter 9 deviates from the A / D converter's rating (0-3.3V), and the digital value of the digital combined signal obtained by A / D conversion of that analog input signal reaches its upper limit and saturates. In this state, frequency analysis using the Fast Fourier Transform shows that an abnormal periodic change occurs in the intensity output 12, and the appropriate intensity calculation could not be performed.

[0045] Therefore, the maximum resolution of the A / D converter that is output when the rated voltage is input to the A / D converter constituting the signal converter 9 can be set as an upper limit reference value. In the example in Figure 3, the reference value is set to 62259 digits. Note that this reference value can be changed to a value several percent smaller to account for intensity fluctuations due to long-term use of light sources 2 and 3.

[0046] If the digital value of the combined light exceeds the reference value, or falls outside a predetermined range (0 to reference value), the offset voltage by the offset adjustment unit 8b and / or the amplification factor by the variable amplification unit 8c in the light receiving circuit 8 are readjusted so that the digital value of the combined light falls below the reference value or within the predetermined range.

[0047] The offset voltage and amplification factor in the light receiving circuit 8 are readjusted using the same parameters, i.e., the same offset voltage and the same amplification factor, for both the analog detection signal of the non-incident light detector 11 and the analog detection signal of the transmitted light detector 7. Furthermore, the offset voltage and amplification factor in the light receiving circuit 8 are readjusted while checking the intensity output so that the intensity output reaches the set target value.

[0048] In another embodiment, the signal detection unit 15 determines whether the digital value of the detected multiplexed light digital signal is within a predetermined range (0 to a reference value), and outputs a signal to generate a warning if the digital value falls outside the predetermined range. The warning may be, for example, an alarm displayed on the monitor 16, or an alarm sound generated from a speaker (not shown). Such a warning generation function can be implemented, for example, by constructing a program that uses the digital data of the multiplexed light collected and stored in the data acquisition function 10a of the processing unit 10 to determine whether the amplitude value of the multiplexed light is within a predetermined range, and generates a predetermined signal if it falls outside the predetermined range.

[0049] The program for executing the warning function can be stored in a memory or other storage device built into the processing unit 10. The processing unit 10 determines, according to the recorded program, whether the digital value (amplitude value) of the digital multiplexer is within a predetermined range, and outputs a signal to generate the warning if it falls outside the predetermined range. The storage device for recording the program for executing the warning function may be externally connected to the processing unit 10.

[0050] Figure 5 shows a functional block diagram of a concentration measuring device according to a second embodiment of the present invention. The concentration measuring device 1 of the second embodiment differs from the first embodiment in that it includes a splitter 17, which splits the combined light into reference light, as a separate component from the multiplexer 5. The other configurations are the same as those of the first embodiment, so a detailed explanation is omitted.

[0051] The present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, although the above embodiments include two light sources, it is also possible to have a configuration with three or more light sources, each emitting light of a different wavelength. Furthermore, it is also possible to have a configuration without correction processing using a reference light. [Explanation of Symbols]

[0052] 1 Concentration measuring device 2, 3 Light source 4. Light-emitting circuit 5 Multiplexer 6 Measurement Cells 7. Transmitted light detector 8. Light receiving circuit 9. Signal Converter 10 Processing Unit 11 Non-incident light detector 13 Concentration calculation section 15 Signal detection unit

Claims

1. Multiple light sources, each emitting light of a different wavelength, A multiplexer that combines the light of multiple different wavelengths emitted by the multiple light sources, A measuring cell for containing the fluid to be measured through which the light combined by the aforementioned multiplexer passes, A transmitted light detector for detecting transmitted light that has passed through the measurement cell, A light receiving circuit for adjusting the amplification factor and offset voltage of the analog detection signal output by the transmitted light detector, A signal converter that converts the analog detection signal adjusted by the light receiving circuit into a digital signal, A signal detection unit configured to detect the behavior of the digital signal converted digitally by the signal converter, A concentration calculation unit configured to calculate the concentration of the fluid to be measured using the amplitude spectrum obtained by frequency analysis of the digital signal, Equipped with, The aforementioned signal converter includes an A / D converter, A value smaller than the maximum value of the digital data output from the A / D converter is set as the reference value. A density measuring device in which, upon receiving the analog detection signal input to the A / D converter and detecting that the digital signal output from the A / D converter exceeds the reference value, the light receiving circuit adjusts at least one of the amplification factor and the offset voltage so that the digital signal output from the A / D converter does not exceed the reference value.

2. The multiplexer outputs the combined light in two directions, with one beam of light incident on the measurement cell and the other beam of light not incident on the measurement cell as non-incident light. The system further includes a non-incident light detector for detecting the non-incident light as a reference light, The light receiving circuit is further configured to allow adjustment of the amplification factor and offset voltage of the analog detection signal of the non-incident light detected by the non-incident light detector. The signal converter is further configured to convert the analog detection signal, which is detected by the non-incident light detector and adjusted by the light receiving circuit, into a digital signal. The concentration measuring device according to claim 1.

3. A splitter for splitting the combined light obtained by the multiplexer into transmitted light that passes through the measurement cell and non-incident light that does not pass through the measurement cell, The system further comprises a non-incident light detector for detecting the non-incident light as a reference light, The light receiving circuit is further configured to allow adjustment of the amplification factor and offset voltage of the detection signal detected by the non-incident light detector. The signal converter is further configured to convert the analog detection signal, which is detected by the non-incident light detector and adjusted by the light receiving circuit, into a digital signal. The concentration measuring device according to claim 1.

4. The concentration measuring device according to any one of claims 1 to 3, wherein the signal detection unit is configured to output a signal that displays the waveform of the digital signal on a monitor.

5. The concentration measuring device according to any one of claims 1 to 3, wherein the signal detection unit is configured to determine whether the amplitude value of the digital signal is less than or equal to the reference value, and to output a signal for generating a warning when the amplitude value exceeds the reference value.

6. A method for adjusting a concentration measuring device, The aforementioned concentration measuring device, Multiple light sources, each emitting light of a different wavelength, A multiplexer that combines the light of multiple different wavelengths emitted by the multiple light sources and outputs the combined light in two directions, A measuring cell for containing the fluid to be measured, through which one of the two beams of light output from the multiplexer passes; A transmitted light detector for detecting transmitted light that has passed through the measurement cell, A non-incident light detector for detecting the other light of the two directions of light output from the multiplexer as a reference light that does not enter the measurement cell, A light receiving circuit for adjusting the amplification factor and offset voltage of the analog detection signals output by the transmitted light detector and the non-incident light detector, A signal converter including an A / D converter, which converts an analog detection signal adjusted by the light receiving circuit into a digital signal using the A / D converter, A signal detection unit that detects the behavior of the digital signal converted digitally by the signal converter, The system includes a concentration calculation unit configured to calculate the concentration of the fluid to be measured using the amplitude spectrum obtained by frequency analysis of the digital signal, The adjustment method described above is: The steps include setting a reference value that is smaller than the maximum value of the digital data output from the A / D converter, The steps include detecting a change in the digital value of the digital signal and determining that the digital value is less than or equal to the reference value, If the digital value exceeds the reference value, the step of changing the amplification factor and / or offset voltage of the analog detection signals of the transmitted light detector and the non-incident light detector so that the digital value does not exceed the reference value, A method for adjusting the concentration measuring device, including the above.

7. A method for adjusting a concentration measuring device, The aforementioned concentration measuring device, Multiple light sources, each emitting light of a different wavelength, A multiplexer that combines the light of multiple different wavelengths emitted by the multiple light sources, A measuring cell for containing the fluid to be measured through which the light combined by the aforementioned multiplexer passes, A transmitted light detector for detecting transmitted light that has passed through the measurement cell, A splitter for splitting the combined light obtained by the multiplexer into transmitted light that passes through the measurement cell and non-incident light that does not pass through the measurement cell, A non-incident light detector for detecting the non-incident light as a reference light, A light receiving circuit for adjusting the amplification factor and offset voltage of the analog detection signals output by the transmitted light detector and the non-incident light detector, A signal converter including an A / D converter, which converts an analog detection signal adjusted by the light receiving circuit into a digital signal using the A / D converter, A signal detection unit configured to detect the behavior of the digital signal converted digitally by the signal converter, The system includes a concentration calculation unit configured to calculate the concentration using the amplitude spectrum obtained by frequency analysis of the digital signal, The adjustment method described above is: The steps include setting a reference value that is smaller than the maximum value of the digital data output from the A / D converter, The steps include detecting a change in the digital value of the digital signal and determining that the digital value is less than or equal to the reference value, If the digital value exceeds the reference value, the step of changing the amplification factor and / or offset voltage of the analog detection signals of the transmitted light detector and the non-incident light detector so that the digital value does not exceed the reference value, A method for adjusting the concentration measuring device, including the above.

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