JP2024021533A - Concentration measuring device and method for adjusting the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a concentration measuring device for measuring gas concentration using absorbance and a method for adjusting the same.

Conventionally, there has been known a concentration measuring device that is incorporated into a gas supply line that supplies raw material gas such as an organic metal (MO) gas to semiconductor manufacturing equipment and measures the concentration of gas flowing through the gas supply line (see Patent Document 1, etc.). ).

This type of concentration measuring device measures absorbance by inputting light of a predetermined wavelength from a light source into a measurement cell and using a transmitted light detector to detect the light that is absorbed by the gas as it passes through the measurement cell. The concentration is determined from the absorbance.

A plurality of types of process gases are supplied to semiconductor manufacturing equipment and the like, and the rate of absorption with respect to the wavelength of light differs depending on the type of gas. Therefore, absorbance can be measured using light of a plurality of different wavelengths (ultraviolet light). A plurality of lights of different wavelengths are combined by a multiplexer and then input into a measurement cell. The combined light incident on the measurement cell is absorbed by the gas within the measurement cell, and then received by one transmitted light detector. The analog detection signal output from the transmitted light detector is A/D converted and amplified, then frequency analyzed by fast Fourier transform and converted into an amplitude spectrum of each frequency component, and the amplitude value of the amplitude spectrum is converted into the transmitted light. is output as the intensity. The amplitude of the amplitude spectrum at the wavelength where there is absorption decreases.

Based on the change in the amplitude of the amplitude spectrum, the concentration C is calculated using the following formula (1) for determining the absorbance A _λ based on the Beer-Lambert law.

A _λ = log ₁₀ (I ₀ /I) = αLC (1)
Here, I ₀ is the initial intensity of the incident light that enters the measurement cell, I is the intensity of the transmitted light that has passed through the measurement cell, α is the molar extinction coefficient (m ² /mol), and L is the optical path length of the measurement cell ( m), C is the concentration (mol/m ³ ). The molar extinction coefficient α is a coefficient determined by the substance.

FIG. 1 is a functional block diagram showing a conventional concentration measuring device. This concentration measuring device 1A includes a plurality of light sources 2 and 3, a light emitting circuit 4 for causing each of the light sources 2 and 3 to emit light of a different wavelength, and a combination of light emitted by each of the light sources 2 and 3. A multiplexer 5 that generates a wave, a measurement cell 6 into which the light multiplexed by the multiplexer 5 enters, a transmitted light detector 7 that detects the light that has passed through the measurement cell 6, and a transmitted light detector 7. a light receiving circuit 8 for adjusting the amplification factor and offset voltage of the detection signal of the transmitted light detected by the light receiving circuit 8; and 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. , a processing device 10A configured to collect digital signals converted into digital signals 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. . Although there are two light sources in the illustrated example, three or more light sources may be provided as necessary.

The light sources 2 and 3 are composed of light emitting elements such as light emitting diodes, and the light emitting circuit 4 operates based on a command signal from the processing device 10A in order to flow drive currents of different frequencies to each of the plurality of light sources 2 and 3. , has the function of adjusting and controlling the current value 4a, frequency 4b, and current offset 4c of the drive current, respectively.

The measurement cell 6 includes a gas inlet 6a and a gas outlet 6b through which the gas to be measured flows in and out, a light entrance window 6c, and a light exit window 6d.

The multiplexer 5 includes a half mirror as in FIG. 6 of Patent Document 1, for example, multiplexes light incident from two directions, and outputs the multiplexed light in two directions. One of the two directions of light outputted from the multiplexer 5 enters the measurement cell 6, and the other light does not enter the measurement cell 6 and is detected by the non-incident photodetector 11. A splitter that branches the multiplexed light as a reference light may be provided separately from the multiplexer (FIG. 1 of Patent Document 1).

The detection signal of the non-incident light detector 11 is used as reference light to correct the detection signal of the transmitted light detector 7 (Patent Document 1). The correction may be performed by arithmetic processing based on equation (2) below.

I _cor = I _cell × (I _{ref, 0} /I _ref ) ... (2)
In the above equation (2), I _cor is the light intensity of the transmitted light after correction, I _cell is the intensity of the transmitted light detected by the transmitted light detector at the time of density measurement, and I _ref,0 is the intensity of the transmitted light detected by the transmitted light detector. The initial intensity of the detected non-incident light, I _ref , is the intensity at the time of density measurement of the non-incident light detected by the non-incident light detector.

The light receiving circuit 8 includes a fixed amplification section 8a, an offset adjustment section 8b, and a variable amplification section 8c. They fixedly amplify, adjust the offset voltage, and variably amplify the analog detection signals of the transmitted light and the reference light, respectively. Since the detection signals of the transmitted light and the reference light are minute, the detection signal is fixedly amplified to a large extent by the fixed amplification section 8a, and the detection signal after fixed amplification is finely adjusted by the variable amplification section 8c. The amplification factor of is adjusted. The offset adjustment amount (ie, offset voltage) by the offset adjustment section 8b and the amplification factor of the variable amplification section 8c are determined based on a command signal from the processing device 10A.

The signal converter 9 converts the analog detection signals of the transmitted light and reference light adjusted by the light receiving circuit 8 into digital signals.

The processing device 10A has a data collection function 10a that collects digital signals from the signal converter 9, an analysis function 10b that performs frequency analysis using fast Fourier transform, and an amplitude value of the amplitude spectrum obtained by the frequency analysis as an intensity output 12. It is equipped with an intensity output function 10c. The processing device 10A further includes a concentration calculation unit 13, and the concentration calculation unit 13 uses the intensity output 12 outputted from the intensity output function 10c according to a program stored in a storage device such as an internal memory, and performs the above-described Lambertian The concentration of the gas G to be measured, which is the fluid to be measured, is calculated based on Beer's equation. The processing device 10A uses an MPU (Micro Processor Unit). In the figure, reference numeral 14 indicates a clock generation circuit.

In the concentration measuring device described above, in order to increase the measurement sensitivity, the target value of the intensity output is set so that the output of the amplitude spectrum, that is, the intensity output, is as large as possible. Then, in the light receiving circuit 8, while checking the intensity output so that the intensity output reaches the set target value, the parameters (amplification factor, offset voltage, ) had been adjusted.

International Publication No. WO2017/029791

However, in the conventional concentration measuring device, an abnormal periodic change occurs in the intensity output determined from the amplitude value of a predetermined frequency, and the concentration may not be measured properly.

The main object of the present invention is to provide a concentration measuring device and its adjustment method that can prevent abnormal periodic changes in the intensity output used for absorbance measurement and appropriately measure the concentration.

In order to achieve the above object, a concentration measuring device according to one aspect of the present invention combines a plurality of light sources each emitting light of a different wavelength, and the light of a plurality of different wavelengths emitted by the plurality of light sources. a multiplexer, a measurement cell for containing a fluid to be measured 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, and 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 the analog detection signal outputted by the photodetector; a signal converter for converting the analog detection signal adjusted by the light receiving circuit into a digital signal; and the signal converting section. a signal detection section configured to detect behavior of the digitally converted digital signal; and configured to calculate the concentration of the fluid to be measured using an amplitude spectrum obtained by frequency-analyzing the digital signal. A concentration calculation section.

Further, the multiplexer outputs the multiplexed light in two directions, one light is incident on the measurement cell, and the other light is non-incident light that does not enter the measurement cell. The light receiving circuit further includes a non-incident light detector for detecting incident light as a reference light, and the light receiving circuit further includes an amplification factor and an offset of an analog detection signal of the non-incident light detected by the non-incident light detector. The signal converter may be configured to be able to adjust the voltage, and the signal converter may be further configured to convert an analog detection signal detected by the non-incident photodetector and adjusted by the light receiving circuit into a digital signal.

Further, a splitter for splitting the multiplexed light multiplexed 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 light receiving circuit further includes a non-incident photodetector for detection as a reference light, and the light receiving circuit is further configured to be able to adjust the amplification factor and offset voltage of the detection signal detected by the non-incident photodetector, The signal converter may be further configured to convert an analog detection signal detected by the non-incident photodetector and adjusted by the light receiving circuit into a digital signal.

The signal detection section may be configured to output a signal that displays the waveform of the digital signal on a monitor.

The signal detection unit is configured to determine whether the amplitude value of the digital signal is within a predetermined range, and to output a signal for generating a warning when the amplitude value deviates from the predetermined range. can be done.

Further, in the method for adjusting a concentration measuring device according to one aspect of the present invention, the concentration measuring device includes a plurality of light sources each of which emits light of a different wavelength, and a plurality of light sources of a plurality of different wavelengths emitted by the plurality of light sources. a multiplexer that multiplexes the multiplexed light and outputs the multiplexed light in two directions; and a measurement cell that contains a fluid to be measured through which one of the two directions of light output from the multiplexer passes. , a transmitted light detector for detecting the transmitted light that has passed through the measurement cell, and a transmitted 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 non-incident photodetector, a light receiving circuit for adjusting the amplification factor and offset voltage of analog detection signals outputted by the transmitted light detector and the non-incident photodetector, and an analog detection adjusted by the light receiving circuit. a signal converter that converts a signal into a digital signal; a signal detection unit that detects the behavior of the digital signal digitally converted by the signal converter; a concentration calculation unit configured to calculate the concentration of the measured fluid, the adjustment method detecting a change in the digital value of the digital signal, and the change in the digital value being within a predetermined range. and if the digital value is outside a predetermined range, changing the amplification factor and/or offset voltage of the analog detection signal of the transmitted light detector and the non-incident light detector. include.

Further, in a method for adjusting a concentration measuring device according to another aspect of the present invention, the concentration measuring device includes a plurality of light sources each emitting light of a different wavelength, and a plurality of light sources emitting light of different wavelengths. A multiplexer for multiplexing the light, a measurement cell for containing a fluid to be measured through which the light multiplexed by the multiplexer passes, and transmitted light for detecting the transmitted light that has passed through the measurement cell. a detector, a splitter for splitting the combined light multiplexed 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 the non-incident light. a non-incident light detector for detecting the light as a reference light; a light receiving circuit for adjusting the amplification factor and offset voltage of analog detection signals outputted by the transmitted light detector and the non-incident 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 converter; a concentration calculation unit configured to calculate concentration using an amplitude spectrum obtained by frequency analysis, and the adjustment method detects a change in a digital value of the digital signal, and detects a change in a digital value of the digital signal. is within a predetermined range, and if the digital value is outside the predetermined range, the amplification factor and/or offset of the analog detection signal of the transmitted light detector and the incident light detector is determined. changing the voltage.

According to the present invention, by detecting the behavior of the digital signal of the multiplexed light that has been digitally converted by the signal converter, it is possible to make adjustments so that abnormal periodic fluctuations do not occur.

FIG. 1 is a functional block diagram showing a conventional concentration measuring device. FIG. 1 is a functional block diagram showing a first embodiment of a concentration measuring device according to the present invention. 3 is a monitor image of digitally converted combined light obtained by the concentration measuring device of FIG. 2. 3 is another monitor image of digitally converted combined light obtained by the concentration measuring device of FIG. 2. FIG. FIG. 2 is a functional block diagram showing a second embodiment of the concentration measuring device according to the present invention.

Embodiments of the concentration measuring device according to the present invention will be described below with reference to FIGS. 2 to 5. Note that the same or similar components as in the prior art are given the same reference numerals.

Referring to FIG. 2, the concentration measuring device 1 according to the first embodiment of the present invention includes a plurality of light sources 2 and 3, each of which emits light of a different wavelength, and a plurality of different light sources emitted by the plurality of light sources 2 and 3. A multiplexer 5 that multiplexes light of different wavelengths, a measurement cell 6 for containing the gas to be measured G through which the light multiplexed by the multiplexer 5 passes, and a transmitted light that has passed through the measurement cell 6 is detected. 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, and an analog signal 8s adjusted by the light receiving circuit 8. A signal converter 9 that converts into a digital signal 9s, a signal detection section 15 configured to detect the behavior of the digital signal 9s digitally converted by the signal converter 9, and a frequency analysis of the digital signal 9s. A concentration calculation section 13 configured to calculate the concentration of the gas to be measured G using the amplitude spectrum is provided.

Although light emitting diodes are used as the light sources 2 and 3 in the illustrated example, other light emitting elements such as laser diodes can also be used. Although the wavelengths of the light sources 2 and 3 are in the ultraviolet region in the illustrated example, it is also possible to use light in wavelength regions other than the ultraviolet region.

The multiplexer 5 includes a half mirror 5a, multiplexes light incident from two directions, and outputs the multiplexed light in two directions. One of the two directions of light outputted from the multiplexer 5 enters the measurement cell 6, and the other light does not enter the measurement cell 6 and is detected by the non-incident photodetector 11.

Although photodiodes are used in the illustrated example as the transmitted light detector 7 and the non-incident light detector 11, other optical sensors such as phototransistors may also be used.

Offset adjustment in the light emitting circuit 4 and the light receiving circuit 8 can be performed by adjusting the offset voltage of an operational amplifier. The variable amplification section 8c in the light receiving circuit 8 can adjust the amplification factor by adjusting the variable resistor provided in the operational amplifier.

The processing device 10 has a data collection function 10a that collects data of the digital signal from the signal converter 9, an analysis function 10b that performs frequency analysis using fast Fourier transform, and an amplitude value of the amplitude spectrum obtained by the frequency analysis as an intensity output 12. It includes an intensity output function 10c, a concentration calculation section 13, and a signal detection section 15. The density calculation in the density calculation unit 13 and the density correction calculation using the reference light are well known from the above-mentioned Patent Document 1, etc., so a detailed explanation will be omitted.

The processing device 10 is configured by an MPU (Micro Processor Unit). The data collection function 10a is constituted by a storage device such as a buffer memory, and can record digital data of the combined light sampled from the signal converter 9. The processing device 10 performs fast Fourier transform on the digital signal collected from the signal converter 9 according to a program recorded in a built-in storage device, outputs the intensity of the amplitude value, and calculates the density. The recording device that recorded the program may be externally connected to the processing device 10. The processing device 10 is not limited to an MPU, and may be another computer system such as a microcomputer or an MCU (Micro Controller Unit).

The signal detection unit 15 has a display function that outputs the digital value of the digital waveform signal of the multiplexed light (hereinafter also referred to as "digital multiplexing") digitally converted by the signal converter 9 to the monitor 16. It is possible to detect the behavior of digital signals of wave light. Such a display function can be performed, for example, by constructing a program to display on a monitor using digital data collected by the processing device 10.

A program for executing the display function may be stored in a storage device such as a memory built into the processing device 10. The processing device 10 outputs a signal for displaying the digital value of the digital multiplexing on the monitor 16 in accordance with the recorded program. A storage device that records the program may be externally connected to the processing device 10.

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

FIG. 3 shows an example of an image in which analog data input to the signal converter 9 is displayed on an oscilloscope, and an image in which digital multiplexing output from the multiplexer 5 is displayed on a monitor. . The digital multiplexing monitor image is a graph of digital waveform data retrieved in time series from the storage device that constitutes the data collection function 10a. Note that the image in FIG. 3 is a waveform of a detection signal detected by the transmitted light detector 7.

In the example of FIG. 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, and when 3.3V is input to this A/D converter, the output is The maximum value (quantization number) of 16 bits is 65535 digits, which is the upper limit of normal output.

In the example of FIG. 3, the analog input signal to the A/D converter constituting the signal converter 9 is within the rated range, and the digital value of the digital combination obtained by digitally converting the analog input signal is also sampled normally. A 16-bit value is output, which is within the range of the maximum value (65535 digits) of the output value (sampled value) after A/D conversion.

If the digital value of the digital combination output from the A/D converter is below the maximum output value corresponding to the input rating of the A/D converter (in the case of Fig. 3), fast Fourier transform Even when frequency analysis was performed, no abnormal periodic changes occurred in the intensity output 12, and a substantially constant intensity output was obtained.

FIG. 4 shows that the analog input signal to the A/D converter constituting the signal converter 9 deviates from the rating (0 to 3.3 V) of the A/D converter, and the analog input signal is converted into a digital signal. The combined digital value has reached the upper limit and is saturated. When frequency analysis was performed using fast Fourier transform in such a state, an abnormal periodic change occurred in the intensity output 12, and an appropriate density calculation could not be performed.

Therefore, the maximum value of the 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 the upper limit reference value. In the example of FIG. 3, the reference value is set to 62259 digits. Note that this reference value can be changed, for example, by making it several percent smaller, taking into account intensity fluctuations due to long-term use of the light sources 2 and 3.

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

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

In another embodiment, the signal detection unit 15 determines whether the digital value of the detected combined digital signal is within a predetermined range (0 to a reference value), and determines whether the digital value is outside the predetermined range. Outputs a signal to generate a warning when The warning may be, for example, an alarm display on the monitor 16 or the generation of an alarm sound from a speaker (not shown). Such a warning issuing function uses, for example, digital data of the combined light collected and stored in the data collection function 10a of the processing device 10 to determine whether the amplitude value of the combined light is within a predetermined range. This can be done by constructing a program that generates a predetermined signal when the value falls outside of a predetermined range.

A program for executing the warning issuing function may be stored in a storage device such as a memory built into the processing device 10. The processing device 10 determines whether the digital value (amplitude value) of the digital multiplexing is within a predetermined range in accordance with the recorded program, and outputs a signal for generating the warning when it deviates from the predetermined range. do. A storage device that records a program for executing the warning issuing function may be externally connected to the processing device 10.

FIG. 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 is different from the first embodiment in that it includes a branching device 17 that branches the combined light as a reference light separately from the multiplexer 5, and other points. The configuration is the same as that of the first embodiment, so detailed explanation will be omitted.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, two light sources are provided, but a configuration may also be adopted in which three or more light sources are provided, and each light source emits light of a different wavelength. Alternatively, a configuration may be adopted in which no correction processing using the reference light is performed.

1 Concentration measuring device 2, 3 Light source 4 Light emitting circuit 5 Multiplexer 6 Measuring cell 7 Transmitted light detector 8 Light receiving circuit 9 Signal converter 10 Processing device 11 Non-incident light detector 13 Concentration calculating section 15 Signal detecting section

Claims (7)

multiple light sources each emitting light of a different wavelength,
a multiplexer that multiplexes the light of a plurality of different wavelengths emitted by the plurality of light sources;
a measurement cell for containing a fluid to be measured through which the light multiplexed by the multiplexer passes;
a transmitted light detector for detecting transmitted light passing 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 behavior of the digital signal digitally converted by the signal conversion unit;
a concentration calculation unit configured to calculate the concentration of the fluid to be measured using an amplitude spectrum obtained by frequency analysis of the digital signal;
A concentration measuring device comprising: The multiplexer outputs the multiplexed light in two directions, one light is incident on the measurement cell, and the other light is non-incident light that does not enter the measurement cell,
further comprising a non-incident light detector for detecting the non-incident light as a reference light,
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,
The signal converter is further configured to convert an analog detection signal detected by the non-incident photodetector and adjusted by the light receiving circuit into a digital signal.
The concentration measuring device according to claim 1. a splitter for splitting the multiplexed light multiplexed by the multiplexer into transmitted light that passes through the measurement cell and non-incident light that does not pass through the measurement cell;
further comprising a non-incident light detector for detecting the non-incident light as a reference light,
The light receiving circuit is further configured to be able to adjust the amplification factor and offset voltage of the detection signal detected by the non-incident photodetector,
The signal converter is further configured to convert an analog detection signal detected by the non-incident photodetector 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 claim 1, wherein the signal detection section is configured to output a signal for displaying a waveform of the digital signal on a monitor. The signal detection unit is configured to determine whether the amplitude value of the digital signal is within a predetermined range, and to output a signal for generating a warning when the amplitude value deviates from the predetermined range. The concentration measuring device according to any one of claims 1 to 3, wherein: A method for adjusting a concentration measuring device, the method comprising:
The concentration measuring device includes:
multiple light sources each emitting light of a different wavelength,
a multiplexer that multiplexes the light of a plurality of different wavelengths emitted by the plurality of light sources and outputs the multiplexed light in two directions;
a measurement cell for containing a fluid to be measured through which one of the two directions of light outputted from the multiplexer passes;
a transmitted light detector for detecting transmitted light passing through the measurement cell;
a non-incident photodetector for detecting the other 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 analog detection signals output by the transmitted light detector and the non-incident 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 that detects the behavior of the digital signal converted by the signal converter;
a concentration calculation unit configured to calculate the concentration of the fluid to be measured using an amplitude spectrum obtained by frequency analysis of the digital signal,
The adjustment method is
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;
If the digital value is outside a predetermined range, changing the amplification factor and/or offset voltage of the analog detection signal of the transmitted light detector and the non-incident light detector;
A method for adjusting the concentration measuring device. A method for adjusting a concentration measuring device, the method comprising:
The concentration measuring device includes:
multiple light sources each emitting light of a different wavelength;
a multiplexer that multiplexes the light of a plurality of different wavelengths emitted by the plurality of light sources;
a measurement cell for containing a fluid to be measured through which the light multiplexed by the multiplexer passes;
a transmitted light detector for detecting transmitted light passing through the measurement cell;
a splitter for splitting the multiplexed light multiplexed 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 analog detection signals output by the transmitted light detector and the non-incident 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 behavior of the digital signal digitally converted by the signal converter;
a concentration calculation unit configured to calculate concentration using an amplitude spectrum obtained by frequency analysis of the digital signal,
The adjustment method is
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;
If the digital value is out of a predetermined range, changing the amplification factor and/or offset voltage of the analog detection signal of the transmitted light detector and the non-incident light detector;
A method for adjusting the concentration measuring device.