JP2009180665A - Optical path-length variable cell - Google Patents

Abstract

[PROBLEMS] To adjust a desired optical path length according to the transmittance or refractive index of a sample to be measured with a simple configuration.
A sample measurement space 11 in which a sample M to be measured is accommodated, and an opening hole 14 formed so as to communicate with a substantially middle position of the sample measurement space 11 are provided. A cell main body 10 having a position adjusting female screw portion 15 for adjusting the optical path length according to the transmittance or refractive index of the sample M formed on the inner peripheral surface of the connection portion of the hole 14 to the sample flow path 11; A protective member 20a having a male screw part 23 for position adjustment for screwing with the female screw part 15 for position adjustment on the outer peripheral surface into which the transmission member 20b through which measurement light or transmitted light passes is inserted. The optical path length is adjusted by moving the protective member 20a in the same direction as the optical path by rotation so that the optical path length according to the transmittance or refractive index of the sample M is obtained.
[Selection] Figure 2

Description

  The present invention relates to an optical path length variable cell that is used for optically measuring the transmittance or refractive index of a sample and is capable of adjusting the optical path length of light transmitted through the sample.

Conventionally, when a sample solution is irradiated with light, and the light passes through the sample, the degree of light absorption by the target substance, that is, the absorbance is measured to quantitatively analyze the concentration of the substance. Analytical methods are known. The absorbance of the target substance is determined by the Lambert law indicating that the logarithm of the ratio of the incident light intensity I ₀ to the transmitted light intensity I is proportional to the thickness d of the light absorbing substance, and the light absorption by the solution. The measurement is performed using the Lambert-Beer law (equation 1 below) combined with the Beer law, which indicates that the coefficient depends on the concentration c.

log ₁₀ (I ₀ / I) = εcd (Formula 1)
Here, log ₁₀ (I ₀ / I) is the absorbance, and ε when c is the molar concentration is the molar extinction coefficient.

  When measuring the absorbance of a target substance using this measurement method, the optical path length needs to be changed in order to obtain an appropriate value for the resulting absorbance because it varies depending on the concentration of the sample solution. In order to do this, it was necessary to change the measuring instrument or replace parts, which was cumbersome. Therefore, in order to save such trouble, an optical path length variable cell disclosed in Patent Document 1 below has been developed.

FIG. 8 is a cross-sectional view of a variable optical path length cell used in a COD measurement apparatus that measures COD (chemical oxygen demand) measurement values of wastewater and environmental water. This variable optical path length type cell 201 has a light incident window 202a and a light exit window 202b made of transparent flat plates arranged in parallel with each other, and a cell body 203 in which a liquid to be measured is accommodated or circulated, and a plane pair 204a that makes a pair. , 204b and a transparent optical path length changing block 204 that is detachably inserted into the cell body 203. By selecting a plane pair of any thickness from the plane pairs 204a and 204b of the optical path length changing block 204 and inserting it into the optical path in the cell, the optical path length can be changed in a plurality of stages. In the absorbance measurement method using the variable optical path length cell 201 of the present invention, the cell main body 203 is fixed with respect to the optical path X of the measurement light, and the optical path length changing block 204 is moved in a direction crossing the optical path of the measurement light. It is possible to measure absorbance at multiple optical path lengths. Then, it is determined whether or not the measured absorbance is equal to or lower than the upper limit absorbance, and when it is determined that the measured absorbance is larger than the upper limit absorbance, the optical path length changing block 204 is moved in a direction in which the optical path length is shortened. The optical path length is changed by controlling the motor 205.
JP 2006-194775 A

  However, in the optical path length variable cell disclosed in Patent Document 1, the optical path length is changed by controlling the drive unit (motor 205) for changing the optical path length and moving the optical path length changing block 204. In such a configuration, there are problems that the number of components for changing the optical path length increases and the configuration of the entire apparatus becomes large, and the manufacturing cost increases.

  The present invention has been made in view of the above problems, and an object thereof is to provide an optical path length variable cell that can be adjusted to a desired optical path length with a simple configuration.

In order to achieve the above object, an optical path length variable cell according to claim 1 is provided with a light projecting unit for projecting measurement light onto a sample to be measured, and light transmitted through the sample. An optical path length used in an optical measurement device having an optical measurement unit, and a calculation unit that calculates the transmittance or refractive index of the sample based on the intensity of the transmitted light received by the light reception unit In variable cell,
A sample measuring space formed in an optical path between the light projecting unit and the light receiving unit for measuring the sample, and the light projecting unit so as to communicate with a substantially middle position of the sample measuring space; A cell body having an opening hole formed facing the light receiving portion;
An optical window comprising a transmission member through which the measurement light or the transmission light passes, and a protective member into which the transmission member is inserted;
An optical path length adjusting means is provided for adjusting the optical path length according to the transmittance or refractive index of the sample by moving the protection member in the same direction as the optical path with respect to the cell body.

The optical path length variable cell according to claim 2 is the optical path length variable cell according to claim 1, wherein the optical path length adjusting means is an inner peripheral surface of a connection portion of the cell body with the sample measurement space in the opening hole. A female screw part for position adjustment formed on
It is formed on the outer peripheral surface of the protective member, and consists of a male screw part for position adjustment for screwing with the female screw part for position adjustment,
The protective member is moved in the same direction as the optical path by rotation to be adjusted to an optical path length corresponding to the transmittance or refractive index of the sample.

The variable optical path length cell according to claim 3 is used in the variable optical path length cell according to claim 1 or 2 for an oil circulation rate measuring device for measuring a circulation rate (OCR) of oil mixed in a refrigerant circulating in the heat pump system. And
The transmitting member is formed of an optical material that transmits at least near-infrared light, and at least the cell body and the protective member are formed of a metal material having pressure resistance and corrosion resistance.

  According to the optical path length variable cell of the present invention, the position can be adjusted by moving the protective member in the same direction as the optical path in accordance with the transmittance or refractive index of the sample to be measured. The optimum optical path length can be adjusted.

Also, for example, in optical measurement under high pressure such as OCR measurement in a CO ₂ heat pump system, the transmissive member is a sapphire glass having pressure resistance, and at least the cell body and the protective member are metal materials having pressure resistance and corrosion resistance. Therefore, optical measurement can be performed with high performance even under such a high pressure condition.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is an explanatory diagram for explaining the outline of an optical path length variable cell according to the present invention, FIG. 2 is a cross-sectional view for explaining the configuration of each part in the optical path length variable cell, and FIG. FIG. 4 is a cross-sectional view for explaining an adjustment method when adjusting the optical path length of the variable-length cell, and FIGS. 4 and 5 are cross-sectional views for explaining the mounting procedure of the variable-length cell. FIG. FIG. 7 is a system configuration diagram of a CO ₂ heat pump system employing the same optical path length variable cell, and FIG. 7 is a schematic explanatory diagram for explaining another embodiment of the optical path length adjusting means in the optical path length variable cell.

  In the following description, as the best mode for carrying out the present invention, the case where the sample to be measured flows in the optical path length variable cell is described. However, the sample is transmitted in a state where the sample is accommodated in the cell. It is also possible to measure the refractive index or the refractive index. For convenience, the case where the absorbance is measured from the transmittance is described, but the present invention is not limited to this.

  As shown in FIG. 1, the optical measuring apparatus 2 including the optical path length variable cell 1 of this example includes an optical path length variable cell 1 and an optical measuring unit 3 that optically measures a sample M via optical means 4. Connected and configured. The optical means 4 includes a light-projecting-side optical fiber 4a for guiding light having a wavelength absorbed by the sample M irradiated from the optical measuring section 3 (hereinafter referred to as measurement light) into the cell, and light-projecting-side light. The light receiving side optical fiber 4b for receiving the light (hereinafter referred to as transmitted light) when the measurement light irradiated from the fiber 4a passes through the sample M and guiding it to the optical measuring unit 3 is constituted. Optical lenses 4c and 4d are attached to the ends of the fibers 4a and 4b via fiber connectors, respectively. These optical lenses 4c and 4d (in this example, the optical lens 4c is connected to the light projecting side optical fiber 4a). The optical lens 4d is connected to the light receiving side optical fiber 4b). The optical path length variable cell 1 is connected to a sample introduction tube 5 for allowing the sample M to flow into the cell and a sample discharge tube 6 for discharging the sample M for which the absorbance measurement has been completed from the cell. .

  The optical measuring unit 3 is composed of a light source such as a halogen lamp, for example, and a light projecting unit 3a that projects the measurement light transmitted through the sample M in the optical path length variable cell 1 through the light projecting side optical fiber 4a. A light receiving unit 3b configured to receive light irradiated to the sample M, which is composed of a light receiving element such as a photodiode, through the light receiving side optical fiber 4b, and an electric signal based on the intensity of transmitted light received by the light receiving unit 3b. And an arithmetic unit 3c for calculating the absorbance of M. The optical measuring device 3 receives the transmitted light when the measurement light projected on the sample M to be measured passes through the sample M, and measures the absorbance based on the intensity of the transmitted light.

  Next, the configuration of the optical path length variable cell 1 of this example will be described with reference to FIG. The optical path length variable cell 1 includes a cell body 10, an optical window 20, a support member 30, a pressing member 40, and a lid member 50. Hereinafter, each configuration will be described in detail.

  The cell body 10 is made of a material having pressure resistance and / or corrosion resistance such as SUS (preferably SUS316), brass, Teflon (registered trademark), and the like, and has a predetermined diameter for accommodating the sample M to be measured. A measurement space 11 is formed. An introduction side opening 12 for introducing the sample M into the cell body 10 is provided at one end (left side in the figure) of the sample measurement space 11, and the sample M is provided from the cell body 10 at the other end (right side in the figure). A discharge side opening 13 for discharging is provided, the sample introduction pipe 5 for introducing the sample M into the introduction side opening 12, and the sample discharge pipe 6 for discharging the sample M into the discharge side opening 13, respectively. Piping is connected.

  Further, an opening hole 14 having a predetermined diameter so as to communicate with a substantially intermediate position of the sample measurement space 11 (in this example, the upper opening hole 14 in the figure is a light-projecting side opening hole 14a, and the lower opening hole 14 in the figure is shown). Are formed opposite to each other, and the two opening holes 14a and 14b function as an optical path through which the measurement light from the optical measurement unit 3 and the transmitted light transmitted through the sample M pass. Then, the light projecting side opening hole 14a receives a light projecting side optical fiber 4a that projects the measurement light from the optical measuring unit 3, and the light receiving side opening hole 14b receives light transmitted through the sample M. The side optical fibers 4b are connected to each other. An optical path length for adjusting the optical path length according to the absorbance of the sample M to be measured is screwed onto the inner peripheral surface of the connection portion of the opening hole 14 with the sample measurement space 11 and a protective member 20a described later. A position adjusting female screw portion 15 as an adjusting means is formed, and a cap member screw portion 16 for screwing the cap member 50 is formed on the outer peripheral surface of the fiber connecting portion in the opening hole 14. Yes.

  The optical window 20 is made of a material having pressure resistance and / or corrosion resistance, such as SUS (preferably SUS316), brass, Teflon (registered trademark), and the outer diameter is an opening hole as a charging part to be inserted into the opening hole 14. 14, the inner diameter is at least close to the protective member 20a having a substantially cup shape in which a storage portion 21 having the same diameter as that of the transmission member 20b is formed so that the transmission member 20b described later can be inserted. For example, it is made of an optical material such as sapphire glass having pressure resistance and corrosion resistance and quartz glass having corrosion resistance, which transmits infrared light. And a transparent member 20b that is inserted after adjustment of the insertion position of the protection member 20a is completed. A light passage hole 22 for allowing light to pass through is formed on the closed side of the storage portion 21 of the protection member 20a. Further, a position adjusting male screw portion as an optical path length adjusting means for screwing with the position adjusting female screw portion 15 formed in the opening hole 14 is formed on the outer peripheral surface of the protective member 20a on the light passing hole 22 forming side. 23 is formed. In addition, on the outer periphery of the opening end of the storage portion 21 of the protection member 20a, an attachment / detachment hole 24 is formed for inserting / detaching or adjusting the position of the protection member 20a by inserting a pin or a dedicated jig. . That is, the protective member 20 a is mounted by being screwed into the position adjusting female screw portion 15 formed in the opening hole 14 after being inserted into the opening hole 14.

  Here, a method for adjusting the mounting position of the optical window 20 will be described with reference to FIG. Since the absorbance varies depending on the sample M to be measured, it is necessary to adjust the optical path length according to the sample M to be measured. Therefore, as shown in the figure, measurement is performed by rotating at least one of the protective member 20a of the light-projecting-side opening hole 14a or the light-receiving-side opening hole 14b in a predetermined direction and adjusting the loading position in the vertical direction in the figure. It is possible to adjust the optical path length optimal for the sample M.

  The position of the protective member 20a is adjusted so that the flow of the sample M is not interrupted so as to be positioned closer to the opening hole 14 than the center position of the sample measurement space 11 (the one-dot chain line in FIG. 2). In order to suppress the error as much as possible, it is desirable to make the movement distances from the light projecting side opening hole 14a and the light receiving side opening hole 14b uniform. Further, since the moving distance of the protective member 20a varies depending on the pitch of the formed male screw portion 23 for position adjustment, by calculating the moving distance per rotation from the pitch of the male screw portion 23 for position adjustment in advance, It is possible to precisely adjust the optical path length.

  The support member 30 is made of a material having pressure resistance and / or corrosion resistance such as SUS (preferably SUS316), brass, Teflon (registered trademark), and the outer diameter is an opening hole as a charging part to be inserted into the opening hole 14. 14, the inner diameter has a cylindrical shape in which a through hole 31 for accommodating the optical lenses 4c and 4d connected to the light projecting side optical fiber 4a and the light receiving side optical fiber 4b is formed. Yes. The support member 30 is inserted so as to support the optical window 20 inserted in the opening hole 14. Further, on the outer peripheral surface at a predetermined location of the support member 30, there are formed groove portions 34 and 35 in which an O-ring 32 for sealing and ensuring airtightness and a backup ring 33 which is normally used under high pressure are mounted. The O-ring 32 is attached to the groove 34 formed in the contact portion with the transmitting member 20b, and the O-ring 32 and the backup ring 33 are attached to the other groove 35 in this order.

  The holding member 40 is made of a material having pressure resistance and / or corrosion resistance such as SUS (preferably SUS316), brass, Teflon (registered trademark), and the outer diameter is an opening hole as a charging part to be inserted into the opening hole 14. 14 has a cylindrical shape in which a through hole 41 having the same diameter as the through hole 31 is formed so as to communicate with the through hole 31. The through hole 31 of the support member 30 and the through hole 41 of the pressing member 40 constitute a lens storage hole for storing the optical lenses 4c and 4d connected to the light projecting side optical fiber 4a and the light receiving side optical fiber 4b. is doing. The pressing member 40 is inserted into the opening hole 14 so as to be pressed so that the supporting member 30 is not detached from the cell body 10 after the supporting member 30 is inserted. A threaded portion 42 for screwing the fiber connector is formed on the inner surface of the through hole 41.

  The lid member 50 is made of a material having pressure resistance and / or corrosion resistance such as SUS (preferably SUS316), brass, Teflon (registered trademark), and has a concave lid shape. In addition, a screw portion 51 is formed on the inner peripheral surface of the lid member 50 so as to be screwed with the screw portion 16 for the lid member formed in the cell body 10, and an optical end is provided on the closed end side of the lid member 50. An insertion hole 52 for inserting the lenses 4c and 4d is formed. After the optical window 20, the support member 30, and the pressing member 40 are sequentially inserted, the lid member 50 is screwed and attached so as to close the opening hole 14 in order to fix them.

  Next, an attachment procedure of the optical path length variable cell 1 described above will be described with reference to FIGS. The light projecting side opening hole 14a and the light receiving side opening hole 14b in the optical path length variable cell 1 of this example have the same structure, parts to be loaded, and the order of loading. Description of the attachment procedure to 14b is abbreviate | omitted, and only the attachment procedure of the light emission side opening hole 14a is demonstrated.

  As shown in FIG. 4A, first, the protection member 20a is inserted into the light projecting side opening hole 14a. At this time, the protective member 20a screwed to the cell body 10 is moved up and down while rotating in a predetermined direction so that the optimum optical path length according to the absorbance of the sample M to be measured is reached, until the optimum optical path length is reached. Adjust. Next, when the insertion position of the protection member 20a is determined, the transmission member 20b is inserted as shown in FIG. Then, as shown in FIG. 4C, the support member 30 having the O-ring 32 in the groove 34, the O-ring 32 and the backup ring 33 in the groove 35 is inserted into the light projecting side opening hole 14a.

  Then, as shown in FIGS. 5A to 5C, first, after the pressing member 40 serving as a pressing member for the loaded support member 30 is loaded on the support member 30, the lid member 50 is attached to the cell body 10. Screw together. Next, the optical lens 4c is inserted into the through hole 41, and finally a fiber connector (not shown) is screwed into the screw portion 42 provided in the through hole 41, whereby the light projecting side optical fiber 4a is connected to the optical lens 4c. After connecting, the attachment of the optical path length variable cell 1 is completed.

Next, an example in which the above-described optical path length variable cell 1 is employed will be specifically described with reference to FIG. Here, in the CO ₂ heat pump system 101 using CO ₂ as a natural refrigerant, it is an example used for measuring an oil circulation rate (OCR) that is an index of the amount of oil mixed in CO _{2 as the} sample M.
In the optical path length variable cell used below, in order to enable OCR measurement even under high pressure conditions such as a CO ₂ heat pump system, the transmission member 20b is formed of sapphire glass having pressure resistance and corrosion resistance, Of the cell body 10, the protection member 20a, the support member 30, the pressing member 40, and the lid member 50, at least the cell body 10 and the protection member 20a are formed of SUS316, which is a metal material having pressure resistance and corrosion resistance.

First, the CO ₂ heat pump system 101 will be described. The compressor 102, which uses CO ₂ as a refrigerant, converts the refrigerant (CO ₂ ) vaporized by heat exchange into a high-pressure vapor refrigerant (CO ₂ ), a high-pressure high-temperature refrigerant ( A gas cooler 103 that cools CO ₂ ) to a high-pressure low-temperature refrigerant (CO ₂ ), and squeezes and expands the cooled refrigerant liquid (CO ₂ ) to form a low-pressure / low-temperature liquid mixture (evaporated refrigerant (CO ₂ )). An expansion valve 104 and an evaporator 105 for evaporating wet vapor refrigerant (CO ₂ ) partially evaporated by expansion through heat exchange are arranged in one circulation system so that oil-mixed refrigerant (CO ₂ ) flows in this order. It is the structure formed and connected by piping. The variable optical path length cell 1 of this example is connected by piping between the gas cooler 103 and the expansion valve 104.

  When a calibration curve was created from the result of OCR measurement using the optical path length variable cell 1 connected by piping as described above, N = 32, R = 0.99, and σ = 0.05%. This shows that high-performance measurement can be performed without inferiority to a calibration curve created from measurement results measured using a conventional optical path length fixed cell. Here, N represents the number of measurements, R represents a correlation coefficient, and σ represents a standard deviation.

  Thus, in the optical path length variable cell 1 described above, the position adjusting male screw portion 23 for adjusting the optical path length based on the sample M to be measured is formed in the protective member 20a in which the transmitting member 20b is inserted, By adjusting the position by moving the protective member 20a in a predetermined direction based on the sample M to be measured, the optical path length can be adjusted to the optimum.

In addition, even when optical measurement is performed under high pressure (about 20 Mpa) such as OCR measurement in a CO ₂ heat pump system, the transmission member 20b is formed of sapphire glass having pressure resistance and corrosion resistance, and the cell body 10, at least the cell body 10 and the protection member 20a among the protection member 20a, the support member 30, the pressing member 40, and the lid member 50 are formed of SUS316, which is a metal material having pressure resistance and corrosion resistance. Even under conditions, optical measurement can be performed with high performance.

  By the way, in the form mentioned above, in FIGS. 1 and 2, the introduction side opening 12 is the left side in the drawing, the discharge side opening 13 is the right side in the drawing, the light projecting side opening hole 14a is the upper side in the drawing, and the light receiving side opening hole 14b is. Although described as the lower side in the figure, the formation position of each part is not particularly limited as long as the opening hole 14 is formed in the cell body 10 so as to face the sample measurement space 11.

Further, the optical path length adjusting means for adjusting the optical path length according to the transmittance or refractive index of the sample is formed in the position adjusting female screw portion 15 formed in the opening hole 14 of the cell body 10 and the protective member 20a. The position adjusting male screw portion 23 is used, and the structure in which the protective member 20a is screwed into the opening hole 14 and screwed into the optical path length according to the transmittance or refractive index of the sample has been described.
However, in this optical path length adjusting means, for example, as shown in FIG. 7A, a locking groove 25 is cut at a predetermined interval on the outer peripheral surface of the protective member 20a, and this locking groove 25 is provided on the inner surface of the opening hole 14. A structure that is fixed at an arbitrary insertion position by a convex locking member 26, or as shown in FIG. 7B, a locking groove 28 is cut at a predetermined interval on the inner surface of the opening hole 14, and this locking is performed. It is also possible to adopt a configuration in which a convex locking member 27 provided on the outer surface of the protective member 20a is locked in the groove 28.
Thus, there is no particular limitation as long as the protection member 20a can be moved in the same direction as the optical path so as to adjust the optical path length.

  As mentioned above, although the best form in this invention was demonstrated, this invention is not limited with the description and drawing by this form. That is, it is a matter of course that all other forms, examples, operation techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

It is explanatory drawing for demonstrating the outline of the optical path length variable cell which concerns on this invention. It is sectional drawing for demonstrating the structure of each part in the same optical path length variable cell. It is sectional drawing for demonstrating the adjustment method at the time of adjusting the optical path length of the same optical path length variable cell. (A)-(c) It is sectional drawing for demonstrating the attachment procedure of the optical path length variable cell. (A)-(c) It is sectional drawing for demonstrating the attachment procedure of the optical path length variable cell. It is a system configuration diagram of a CO ₂ heat pump system the optical path length varying cell is employed. (A)-(b) It is a schematic explanatory drawing for demonstrating the other Example of the optical path length adjustment means in the same optical path length variable cell. It is a schematic block diagram for demonstrating the conventional optical path length variable cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical path length variable cell 2 Optical measuring apparatus 3 Optical measuring part (3a light projection part, 3b light receiving part, 3c calculating part)
4 Optical means (4a light emitting side optical fiber, 4b light receiving side optical fiber, 4c, 4d optical lens)
5 Sample introduction tube 6 Sample discharge tube 10 Cell body 11 Sample measurement space 12 Introduction side opening 13 Discharge side opening 14 Opening hole (14a light emitting side opening hole, 14b light receiving side opening hole)
15 Female screw part for position adjustment 16 Screw part for lid member 20 Optical window (20a protection member, 20b transmission member)
DESCRIPTION OF SYMBOLS 21 Storage part 22 Light passage hole 23 Position adjustment male screw part 24 Detachment hole 25 Locking groove 26 Locking member 27 Locking member 28 Locking groove 30 Support member 31 Through-hole 32 O-ring 33 Backup ring 34, 35 Groove part 40 Holding member 41 Through hole 42 Screw part 50 Lid member 51 Screw part 52 Insertion hole 101 CO ₂ heat pump system 102 Compressor 103 Gas cooler 104 Expansion valve 105 Evaporator

Claims (3)

A light projecting unit for projecting measurement light onto a sample to be measured, a light receiving unit for receiving transmitted light transmitted through the sample by the measurement light, and the sample based on the intensity of the transmitted light received by the light receiving unit In an optical path length variable cell used in an optical measurement device having an optical measurement unit with a calculation unit that calculates the transmittance or refractive index of
A sample measuring space formed in an optical path between the light projecting unit and the light receiving unit for measuring the sample, and the light projecting unit so as to communicate with a substantially middle position of the sample measuring space; A cell body having an opening hole formed facing the light receiving portion;
An optical window comprising a transmission member through which the measurement light or the transmission light passes, and a protective member into which the transmission member is inserted;
An optical path length comprising an optical path length adjusting means for adjusting the optical path length according to the transmittance or refractive index of the sample by moving the protective member in the same direction as the optical path with respect to the cell body. Variable cell. The optical path length adjusting means includes a position adjusting female thread portion formed on an inner peripheral surface of a connection portion with the sample measurement space in the opening hole of the cell body,
It is formed on the outer peripheral surface of the protective member, and consists of a male screw part for position adjustment for screwing with the female screw part for position adjustment,
2. The optical path length variable cell according to claim 1, wherein the protective member is moved in the same direction as the optical path by rotation to adjust the optical path length according to the transmittance or refractive index of the sample. Used in an oil circulation rate measuring device that measures the circulation rate of oil mixed in the refrigerant circulating in the heat pump system,
2. The transmissive member is formed of an optical material that transmits at least near-infrared light, and at least the cell body and the protective member are formed of a metal material having pressure resistance and corrosion resistance. Or the optical path length variable cell of 2.

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