JPH10325797A - Measuring apparatus for concentration of fluid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring apparatus by which the concentration of a fluid as a sample can be measured with good accuracy according to the property of the fluid. SOLUTION: A first measuring body 21a, a second measuring body 21b and a third measuring body 21c are connected to a treatment-liquid supply pipe 6 via couplings 20 and intermediation pipes 6a at prescribed intervals in a direction in which a treatment liquid flows. Light transmission parts 22 in which the length of the optical path of light to be transmitted is made different are installed at them. According to a concentration which is set by a concentration setting device, a first optical-path changeover mechanism 15 is changed over, only one out of the light transmission parts 22 at the first, second and third measuring bodies 21a, 21b, 21c is irradiated with light from a light source, and the light which is transmitted through the light transmission part 22 is incident on a photodetector 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid concentration measuring device for measuring the concentration of various kinds of fluids such as a treatment solution obtained by mixing a chemical solution and pure water or a chemical solution for treating a substrate such as a semiconductor wafer.

[0002]

2. Description of the Related Art In a conventional fluid concentration measuring device, for example,
It was configured as shown in JP-A-8-78380.

That is, first, a sample cell having a predetermined optical path length and flowing a processing liquid which is a fluid serving as a sample,
A reference cell filled with pure water is provided, and the sample cell and the reference cell are irradiated with light from a light source through a light branching unit,
Light transmitted through each of the sample cell and the reference cell is incident on a photodetector via an optical path switching unit.

[0004] The photodetector detects light transmitted through the sample cell and the reference cell and outputs a signal corresponding to the transmitted light intensity. And the signal is Lambert-Veil (Lambert-
According to Beer's law, treatment is performed by the following relational expression of absorbance A, and the concentration of the treatment solution is measured.

Absorbance A = log (I _O / I) −log (I _O / I
_S ) = ε · d · C _IO : light intensity before passing through the processing solution, I: light intensity after passing through the processing solution, I _S : light intensity after passing through the solvent (pure water), ε: absorption coefficient (proportional constant), d: length of transmitted light path, C: concentration

[0006]

However, the conventional example has the following problems. That is, the absorbance A is observed as an amount proportional to the concentration, and the absolute value of the absorbance A decreases at a low concentration. On the other hand, at a high concentration, the transmitted light intensity I becomes small, so that it becomes susceptible to disturbances such as mixed bubbles. Thus, depending on the level of the concentration, S /
There is a drawback that the measurable range of the concentration is limited because the N ratio is lowered.

The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to accurately measure a concentration according to the properties of a fluid as a sample.

[0008]

The invention according to claim 1 is
In order to achieve the object as described above, a fluid concentration measurement device that measures the concentration of a fluid, provided in a pipe through which the fluid flows, and a light transmission unit for transmitting light to the fluid in the pipe. A plurality of measurement units, a light source that irradiates the light transmission unit with light, and a light detection unit that detects light transmitted through the light transmission unit, wherein the light transmission unit includes the pipe for each of the measurement units. The optical path of the light passing through the fluid inside is different in length, and the concentration of the fluid is measured based on the light detected by the light detecting means.

The invention according to claim 2 is the fluid concentration measuring device according to claim 1, wherein the pipe has a plurality of branch pipes, and the measuring section is provided for each of the branch pipes. .

According to a third aspect of the present invention, there is provided a fluid concentration measuring device for measuring the concentration of a fluid, wherein the length of the optical path of light passing through the fluid in the piping is provided in a pipe through which the fluid flows. A light source that irradiates light to the light transmitting unit, and a light detecting unit that detects light transmitted through the light transmitting unit, wherein the light detecting unit Is to measure the concentration of the fluid based on the light detected in the step (1).

Further, the invention according to claim 4 is based on claim 1,
4. The fluid concentration measuring device according to claim 2, wherein: a selecting unit that selects a light transmitting unit to transmit light from among the plurality of light transmitting units; and a fluid flowing through the pipe. 5. If the absorbance is large, the selecting means selects a light transmitting portion having a short optical path length, and if the absorbance of the fluid flowing through the pipe is small, the selecting means selects a light transmitting portion having a long optical path length. And rasp control means.

[0012] The invention according to claim 5 is based on claim 1,
4. The fluid concentration measurement device according to claim 2, wherein, when the absorbance of the fluid flowing through the pipe is large, the length of the optical path of the light detected by the light detection unit is reduced. 5. Data of the light transmitted through the short light transmitting portion is selected, and when the absorbance of the fluid flowing through the pipe is small, of the light detected by the light detecting means, the data of the light transmitted through the light transmitting portion having a long optical path. And data concentration means for measuring the concentration of the fluid based on the data of the light selected by the data selection means.

[0013]

According to the first aspect of the present invention, the plurality of measuring sections provided on the pipe through which the fluid flows have light transmitting sections having different optical paths of light passing through the fluid in the pipe. Therefore, the concentration of the fluid is measured based on the light detected by the light detection means while changing the measurement unit used according to the properties of the fluid.

According to the second aspect of the present invention, since the measuring unit is provided for each of the plurality of branch pipes provided in the pipe, the fluid concentration measuring device is short and compact in the direction in which the fluid flows. .

According to the third aspect of the present invention, the measuring section provided in the pipe through which the fluid flows has a plurality of light transmitting sections having different optical paths of light passing through the fluid in the pipe. Therefore, the concentration of the fluid is measured based on the light detected by the light detecting means while changing the light transmitting portion used according to the properties of the fluid.

According to the fourth aspect of the present invention, the control means controls the selection means, so that when the absorbance of the fluid flowing through the pipe is large, the selection means is provided with a light transmitting portion having a short optical path length. When the absorbance of the fluid flowing through the pipe is small, the selection unit selects the light transmission unit having a long optical path, so that the light transmission unit corresponding to the absorbance of the fluid is selected.

According to the fifth aspect of the present invention, when the absorbance of the fluid flowing through the pipe is large, the data selecting means transmits light having a short optical path length out of the light detected by the light detecting means. When data of light transmitted through the portion is selected, and when the absorbance of the fluid flowing through the pipe is small, data of light transmitted through the light transmitting portion having a long optical path is selected from among the light detected by the light detecting means. Therefore, the concentration of the fluid according to the absorbance of the fluid is measured. Note that the light data here refers to transmitted light intensity and the like.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a substrate processing apparatus using a fluid concentration measuring apparatus according to a first embodiment of the present invention. In this substrate processing apparatus, a plurality of substrates such as semiconductor wafers are stored. An overflow tank 2 for retaining the processing liquid overflowing from the processing tank 1 is provided around the processing tank 1 in which a wafer carrier not to be immersed is immersed.

A pure water supply source (not shown) is supplied to the processing tank 1 via a pure water supply pipe 3 provided with a first flow control valve V1.
Is connected, and pure water is supplied into the processing tank 1 at a predetermined pressure. On the other hand, a chemical liquid tank 5 is connected to the overflow tank 2 via a chemical liquid supply pipe 4 provided with a second flow control valve V2, and a predetermined amount of the chemical liquid is supplied from the chemical liquid tank 5 into the overflow tank 2. .

The bottom of the processing tank 1 and the overflow tank 2 are connected via a processing liquid supply pipe 6 for circulating the remaining processing liquid. The processing liquid supply pipe 6 includes a pump 7 for circulating a processing liquid which is a sample fluid, a heater 8 for heating the circulating processing liquid, and a temperature sensor 9 for measuring the temperature of the processing liquid. And a filter 10 for removing particles and the like in the circulating treatment liquid.

With the above structure, a substrate such as a semiconductor wafer is cleaned by immersing a substrate such as a semiconductor wafer in a processing solution having a predetermined concentration by mixing and adjusting a chemical solution and pure water according to a purpose at a predetermined ratio. You.

Next, the fluid concentration measuring device will be described. That is, a light transmission mechanism 11 for transmitting light to the flowing processing liquid is interposed between the filter 10 and the processing tank 1 in the processing liquid supply pipe 6.
In the vicinity of 1, a reference cell 12 filled with pure water is arranged.

Irradiation light from a light source 13 such as a halogen lamp is branched via a light branching means 14, and the branched irradiation light is referred to the light transmission mechanism 11 by first and second optical path switching mechanisms 15 and 16. The cell 12 is selectively irradiated.

The light transmitted through the light transmission mechanism 11 and the reference cell 12 enters a light detector 18 as light detecting means via a light guide 17, and the light detector 18 outputs a signal corresponding to the light intensity of the incident light. Is output to the microcomputer 19.

FIG. 2 is a developed configuration diagram of the light transmission mechanism. The first, second, and third measurement bodies 21 serving as measurement units are provided at the processing liquid supply pipe 6 via the joint 20 and the relay pipe 6a at predetermined intervals in the direction in which the processing liquid flows.
a, 21b and 21c are connected.

First, second and third measuring objects 21a, 21a
Each of 1b and 21c has a different optical path length of light passing through the processing liquid (for example, 1 mm, 1.5 mm, 2 mm).
Etc.) A light transmitting portion 22 is provided, and connection portions 23 for screwing the joint 20 are formed at both ends in the direction in which the processing liquid flows. Note that, in FIG.
2 is exaggerated for easy understanding of the difference in optical path length.

FIG. 3 is a structural view of a main part of the optical branching unit, and FIG. 4 is a side view of a main part of the optical branching unit.
As shown in FIGS. 3 and 4, the light branching unit 14 includes a first collimator lens 24 that converts the irradiation light from the light source 13 into parallel light, and the irradiation light from the first collimator lens 24 into four. There are provided first, second, third and fourth condensing lenses 25a, 25b, 25c and 26 which are branched.

The light split by the first, second, third and fourth condenser lenses 25a, 25b, 25c and 26 is shown in FIG.
As shown in the figure, first, second, third and fourth optical fibers 27a, 27b, 27c and 28, and second, third, fourth and fifth collimator lenses 29a, 29b and 29 are provided.
c, 30 and the first, second and third measuring objects 21
Irradiation is performed on the light transmitting portions 22 and the reference cells 12 of the respective a, 21b, and 21c.

The first, second and third measuring bodies 21
The light transmitted through the respective light transmitting portions 22 and the reference cells 12 of the a, 21b, and 21c is transmitted to the fifth, sixth, seventh, and eighth condenser lenses 31a, 31b, 31c, and 32, and the fifth and fifth condenser lenses. 6, seventh and eighth optical fibers 33a, 33
b, 33c, and 34, and is incident on the light guide 17.

The first optical path switching mechanism 15 includes first, second and third condenser lenses 25a, 25b and 25c, and first, second and third optical fibers 27a, 27b and 2
7c are provided between each of the light-receiving ends 7c and 7c. The first optical path switching mechanism 15 switches between a transmitting state and a light blocking state by first, second, and third air cylinders 36a, 36b, 36c.
Shutters 37a, 37b and 37c.

The second optical path switching mechanism 16 is provided between the fourth condenser lens 26 and the incident end to the fourth optical fiber 28. This second optical path switching mechanism 1
Reference numeral 6 includes a fourth shutter 39 which is switched between a transmitting state and a light shielding state by a fourth air cylinder 38.

Each of the first, second, third, and fourth air cylinders 36a, 36b, 36c, and 38 is constituted by a single-acting air cylinder. Built-in compression coil spring (not shown) in a natural state where the on-off valve is closed and air is not supplied under pressure
, The light-shielding state is achieved. On the other hand, the electromagnetic switching valve is opened and the air is pressurized and supplied to shorten the light-shielding state.

As shown in FIG. 1, in order to alternatively select the light transmitting portion 22 for transmitting light, a signal to the electromagnetic on-off valves of the first, second and third air cylinders 36a, 36b, 36c is provided. The line is connected to an optical path switching control unit 44 in the microcomputer 19 via the switching means 40.
A density setting device 41 is connected to the switching device 40, and the switching device 40 is switched according to the density range set by the density setting device 41.
Is automatically switched.

For example, in the maximum set density range (60 to 80%), the light transmitting portion 22 of the first measuring object 21a having a short optical path is selected, and in the intermediate set density range (45 to 60%), the optical path length is selected. Selects the light transmitting portion 22 of the intermediate second measuring object 21b, and selects the light transmitting portion 22 of the third measuring object 21c having a long optical path in the minimum set density range (30 to 45%). The switching means 40 is switched. The selection means of the present invention includes a first optical path switching mechanism 15 and a second optical path switching mechanism 16.
And switching means 40.

The microcomputer 19 includes a transmitted light intensity measuring section 42, a density calculating section 43, and an optical path switching control section 44.
, A temperature control unit 45, a feedback control unit 46, and a supply amount control unit 47. Transmitted light intensity measurement unit 4
In 2, the signal from the photodetector 18 is input at a predetermined timing in response to the switching signal from the optical path switching control unit 44,
Based on the signal, the intensity of light transmitted through each of the selected light transmitting unit 22 and reference cell 12 is measured.

The density calculator 43 calculates the transmittance based on the ratio of the transmitted light intensity to the processing liquid and the transmitted light intensity of the reference cell 12, and calculates and measures the density of the processing liquid based on the transmittance.

With the above configuration, the light transmitting section 22 having the optical path of the most suitable length is automatically selected according to the initial setting of the density by the density setting device 41, and the light transmitting section 22 and the reference cell 12 are selected. The light is alternately irradiated with the light, and the concentration of the processing liquid can be accurately calculated and measured based on the transmitted light intensity with respect to the processing liquid and the transmitted light intensity of the reference cell 12.

The temperature control section 45 compares the temperature measured by the temperature sensor 9 with the target temperature while circulating the processing liquid, and turns ON / OFF the heater 8 based on the comparison result.
Then, the temperature of the processing liquid is maintained at the target temperature.

After the transmitted light intensity measuring section 42 confirms that the temperature of the processing liquid has reached the predetermined temperature, the optical path switching control section 44
The optical path switching control section 44 outputs an opening signal and a closing signal to the first and second optical path switching means 15 and 16 at the above-described timing.

The feedback control section 46 stores the target concentration set by the concentration setting device 41 and circulates the processing liquid from the overflow tank 2 to the processing tank 1 through the processing liquid supply pipe 6 by the pump 7. Then, the target density is compared with the density calculated by the density calculator 43, and a control signal corresponding to the difference is output to the supply amount controller 47.

In the supply amount control unit 47, the first pure water supply pipe 3 is controlled in accordance with a control signal from the feedback control unit 46.
Or the second flow control valve V2 of the chemical liquid supply pipe 4 is adjusted to adjust the concentration of the processing liquid in the processing layer 1. By repeating these operations, the concentration of the processing solution can be adjusted to the target concentration.

FIG. 5 is a sectional view of a main part of a light transmission mechanism according to a second embodiment. The light transmission mechanism 11 includes three measurement bodies 51 each serving as a measurement unit, each having a different optical path length of light passing through the processing liquid while being spaced apart in the flow direction of the processing liquid. First, second and third light transmitting portions 52
a, 52b, 52c are provided, and
A processing liquid supply pipe 6 is provided at each end of the processing liquid in the flow direction.
Is provided with a connecting portion 53 connected to the joint via the joint 20. Other configurations, such as a configuration for irradiating light from a light source and a configuration for transmitting transmitted light to a photodetector, are the same as those in the first embodiment, and will not be described.

FIG. 6 is a cross-sectional view of a main part of a light transmission mechanism showing a third embodiment. , And each of the first, second, and third branch pipes 63a, 63b, 63c is provided with one first, second, and third measurement body 64a, 64b, 64
c is provided.

First, second and third measuring bodies 64a, 6
4b and 64c have first, second and third light transmitting portions 65a and 65 each having a different optical path length.
b, 65c, and first, second and third branch pipes 63 at both ends in the flow direction of the processing liquid.
A connecting portion is connected to each of the connectors a, 63b, and 63c through the joint 20. Other configurations, such as a configuration for irradiating light from a light source and a configuration for transmitting transmitted light to a photodetector, are the same as those in the first embodiment, and a description thereof will be omitted.

FIG. 7 is a schematic diagram showing a fourth embodiment of the fluid concentration measuring device according to the present invention. In this fluid concentration measuring device, the same light transmission mechanism 11 as in the first embodiment is used, and the first, second and third measuring bodies 21a, 21b, 2
The three light sources 71 for each of the light transmitting portions 22 of 1c
Is irradiated through a collimator lens 72, and the transmitted light is incident on three photodetectors 74 via a condenser lens 73. Also, the reference cell 12 is irradiated with light from a light source 75 having the same performance as the light source 71 through a collimator lens 76, and transmits the transmitted light through a condenser lens 77 to an individual photodetector. At 78.

Each of the three photodetectors 74 is connected to the data selecting means 79, and the data setting means 79 is connected to the density setting device 41a. The data of the light transmitted through all the light transmitting portions 22 is collected by the data selecting means 79, and the light transmitting portion 22 having the most suitable length of the optical path is selected according to the initial setting of the density by the density setting device 41a. Automatically selects the data of transmitted light (transmitted light intensity).

The data selecting means 79 and the photodetector 78 are connected to the concentration calculating section 80, and the transmitted light intensity for the treatment liquid selected by the data selecting means 79 and the transmitted light intensity of the reference cell 12 are calculated by the density calculating section 80. To calculate the transmittance based on the ratio of the transmitted light intensities, and calculate and measure the concentration of the processing liquid based on the transmittance.

FIG. 8 is a schematic configuration diagram showing a schematic configuration of another substrate processing apparatus to which the fluid concentration measuring apparatus according to the present invention is applied. The difference from the previous substrate processing apparatus is as follows. .

That is, a pure water supply source (not shown) is connected to the processing liquid supply pipe 81 via a pure water supply pipe 82 provided with a third flow control valve V3, and pure water is supplied at a predetermined pressure. Supplied. Further, a plurality of chemical liquid tanks 83a, 83b, 83c are provided in the processing liquid supply pipe 81 with a chemical liquid pipe 8 having fourth, fifth and sixth flow rate regulating valves V4, V5, V6 interposed therebetween.
4a, 84b, and 84c are connected, and a predetermined chemical solution is selected and mixed with pure water, and a processing solution adjusted to a predetermined temperature and a predetermined concentration is supplied to the processing tank 1. Note that a drain pipe 85 is connected to the overflow tank 2.

From the supply amount control unit 47, the third flow control valve V3 and the fourth, fifth, and sixth flow control valves V4, V
A signal is output to a predetermined one of V5 and V6 to adjust the concentration of the processing solution to a target concentration. The configuration of the fluid concentration measuring device and other configurations are the same as those of the above-described substrate processing device, and the same reference numerals are assigned and the description is omitted.

In the case where the first, second and third embodiments are applied to this another substrate processing apparatus, when the extinction coefficient is relatively significantly different depending on the chemical, a chemical selecting means for selecting the chemical to be supplied is provided. When the liquid medicine is connected to the switching means 40 and a chemical solution having a large absorption coefficient is selected, that is, when the absorbance of the sample fluid is large, the light from the light source 13 is transmitted through the light transmission portion having a short optical path. On the other hand, when a chemical solution having a small absorption coefficient is selected, that is, when the absorbance is small, the light from the light source 13 may be transmitted through the light transmission portion having a long optical path. In short, the configuration may be such that, in accordance with the absorbance of the chemical solution, switching is performed so as to select a light transmitting portion having a longer optical path as the absorbance is smaller.

In the case where the fourth embodiment is applied to the above-mentioned another substrate processing apparatus, the data of the light transmitted through the light transmitting portion having a longer transmission optical path as the absorbance is smaller is determined in accordance with the absorbance of the processing solution. What is necessary is just to comprise so that it may be switched so that it may be selected.

According to the present invention, in the first, second and third embodiments, the density setting device 41 is not provided.
For example, first, one light transmitting part is irradiated with light from a light source, thereby measuring the concentration of the processing solution, comparing the measured concentration with a preset concentration range, and determining which concentration range the concentration range falls in. May be automatically switched to irradiate light to the light transmitting portion corresponding to the corresponding density range.

In the first, second and third embodiments, the first optical path switching means 1 is provided between the light source 13 and the light transmitting mechanism 11.
However, the present invention may be configured such that the first optical path switching means 15 is provided between the light transmission mechanism 11 and the photodetector 18.

The light source 13 is not limited to a halogen lamp that emits infrared rays, but may be a deuterium lamp or a xenon lamp that emits ultraviolet rays.

Further, the present invention is not limited to the case of measuring the concentration of a treatment liquid consisting of pure water and a chemical solution, that is, a liquid such as a gas such as nitrogen oxides NOx and sulfur oxides SOx. Can be applied when measuring the concentration of

In the above-described embodiment, the reference cell 12 filled with pure water is used. However, the reference cell 12 may be any one having a constant light absorption coefficient, for example, using an optical filter having a predetermined light absorption coefficient.

[0058]

As is apparent from the above description, according to the first aspect of the present invention, a plurality of measuring units provided in a pipe through which a fluid flows are provided with a plurality of measuring sections for transmitting light through the fluid in the pipe. Since it has light transmitting portions having different lengths, for example, by changing the measuring portion used in accordance with the properties of the fluid such as the absorbance of the fluid, the fluid is detected based on the light detected by the light detecting means. The concentration can be measured accurately.

According to the second aspect of the present invention, since the measuring section is provided for each of the plurality of branch pipes provided in the pipe, a fluid concentration measuring apparatus which is short and compact in the direction in which the fluid flows can be provided. Can be provided.

Further, according to the third aspect of the present invention, the measuring section provided in the pipe through which the fluid flows has a plurality of light transmitting sections having different optical paths of light passing through the fluid in the pipe. For example, the concentration of the fluid can be accurately measured based on the light detected by the light detection unit by changing the used light transmitting portion according to the properties of the fluid such as the absorbance of the fluid.

According to the fourth aspect of the present invention, the control means controls the selection means so that when the absorbance of the fluid flowing through the pipe is large, the selection means is provided with a light transmitting portion having a short optical path length. When the absorbance of the fluid flowing through the pipe is small, the selection unit selects the light transmission unit having a long optical path, so that the light transmission unit according to the absorbance of the fluid can be selected. Can be accurately measured.

According to the fifth aspect of the present invention, when the absorbance of the fluid flowing through the pipe is large, the data selection means transmits light having a short optical path length out of the light detected by the light detection means. When data of light transmitted through the portion is selected, and when the absorbance of the fluid flowing through the pipe is small, data of light transmitted through the light transmitting portion having a long optical path is selected from among the light detected by the light detecting means. Therefore, light data according to the absorbance of the fluid can be selected, and as a result, the concentration of the fluid can be accurately measured.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a substrate processing apparatus using a fluid concentration measuring device of a first embodiment according to the present invention.

FIG. 2 is a developed configuration diagram of a light transmission mechanism.

FIG. 3 is a configuration diagram of a main part of an optical branching unit.

FIG. 4 is a side view of a main part of the optical branching unit of FIG. 3;

FIG. 5 is a sectional view of a main part of a light transmission mechanism according to a second embodiment.

FIG. 6 is a sectional view of a main part of a light transmission mechanism according to a third embodiment.

FIG. 7 is a schematic configuration diagram showing a fourth embodiment of the fluid concentration measuring device according to the present invention.

FIG. 8 is a schematic configuration diagram of another substrate processing apparatus to which the fluid concentration measuring device according to the present invention is applied.

[Explanation of symbols]

 6 Processing liquid supply pipe 13 Light source 15 First optical path switching mechanism 16 Second optical path switching mechanism 18 Photodetector 21a First measuring body 21b Second measuring body 21c Third measurement Body 22 ... Light transmitting part 23 ... Connecting part 40 ... Switching means 41 ... Density setting device 51 ... Measuring body 52 ... Light transmitting part 53 ... Connecting part 64a ... First measuring body 64b ... Second measuring body 64c ... Third Measurement body 65a: first light transmitting portion 65b: second light transmitting portion 65c: third light transmitting portion 66: connecting portion 71: light source 74: photodetector 79: data selection means 81: processing liquid supply pipe

Claims (5)

[Claims] 1. A fluid concentration measuring device for measuring the concentration of a fluid, comprising: a plurality of measuring units provided on a pipe through which the fluid flows, and having a light transmitting unit for transmitting light to the fluid in the pipe; A light source that irradiates light to the light transmitting unit; and a light detection unit that detects light transmitted through the light transmitting unit, wherein the light transmitting unit transmits a fluid in the pipe for each of the measuring units. A fluid concentration measuring device, wherein the optical path of light is different, and the concentration of the fluid is measured based on the light detected by the light detecting means. 2. The fluid concentration measurement device according to claim 1, wherein the pipe includes a plurality of branch pipes, and the measurement unit is provided for each of the branch pipes. apparatus. 3. A fluid concentration measuring device for measuring a concentration of a fluid, wherein the plurality of lights are provided on a pipe through which the fluid flows, and have different optical path lengths of the light passing through the fluid in the pipe. A measurement unit having a transmission unit, a light source that irradiates the light transmission unit with light, and a light detection unit that detects light transmitted through the light transmission unit, based on the light detected by the light detection unit. A fluid concentration measuring device for measuring the concentration of a fluid. 4. The fluid concentration measurement device according to claim 1, wherein the light transmitting unit that transmits light is selected from the plurality of light transmitting units. Means, when the absorbance of the fluid flowing through the pipe is large, the selecting means selects a light transmitting portion having a short optical path length, and when the absorbance of the fluid flowing through the pipe is small, the selecting means Control means for selecting a light transmitting portion having a long length,
A fluid concentration measurement device, further comprising: 5. The fluid concentration measurement device according to claim 1, wherein the light detected by the light detection unit is large when the absorbance of the fluid flowing through the pipe is large. Of the light, data of light transmitted through the light transmitting portion having a short optical path length is selected, and when the absorbance of the fluid flowing through the pipe is small, of the light detected by the light detection unit, the light path having a long optical path is selected. A fluid concentration measurement device, further comprising data selection means for selecting data of light transmitted through the light transmission part, wherein the concentration of the fluid is measured based on the data of light selected by the data selection means.