JPH09145617A - Densitometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure concentration with precision by making the constitution wherein to-be-detected material concentration is found based on scattered light intensity. SOLUTION: The densitometer consists of the material transmitting light, and contains a rod 21, to one end of which the first and second optical fibers 151 and 152 are connected, and a probe 11, provided with a protecting tube 22 which covers the side surface of the rod 21 and which is so fixed to the rod 21 that liquid contacts to only a specified part of the tip of rod 21 when the tip of rod 21 is soaked in the liquid. In a light emitting/light-receiving part 12, a light emitting element supplying the light to the rod 21 through the first optical fiber 151 , and a photo-detecting element detecting the light, made incident to the tip of rod 21, through the second optical fiber 152 , are fixed to the same high temperature conductive member. And a temperature control part 13 controls the temperature of the high temperature conductive member constant, and a light emitting element control part makes the light emitting element generate the light, and a concentration measurement part 14 calculates the concentration of to-be-detected material contained in the liquid in which the tip of rod 21 is immersed, based on the level of the signal outputted by the photo-detecting element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concentration measuring device for measuring the concentration of a test substance contained in a liquid by using light, and is used, for example, for measuring the concentration of microbial cells in a fermenter. Concentration measuring device

[0002]

2. Description of the Related Art A device for measuring the concentration of a test substance in a liquid using light is a device for measuring the concentration of a liquid in a container by observing the liquid from the outside, and a probe is immersed in the liquid in the container. It is roughly classified into a device for measuring the concentration.
Among these, the former device cannot be used unless the container is transparent, but the latter device can be used regardless of the shape of the container and is highly versatile. For this reason, various types of concentration measuring devices using probes have been put to practical use or proposed.

For example, Japanese Unexamined Patent Publication No. 56-29146 discloses an immersion photometric sensor having a structure as shown in FIG. As shown in the figure, this immersion type sensor is composed of a probe 51 and a control unit 60,
The probe 51 and the control unit 60 are connected by an optical fiber 52.

The probe 51 is formed mainly of an optical fiber 52 and a concave reflecting mirror 53. The concave reflecting mirror 53 is a reflecting mirror having a radius of curvature substantially equal to the distance between the end face of the optical fiber 52 and the concave reflecting mirror 53,
The optical fiber 52 and the concave reflecting mirror 53 are fixed to each other via a holder 54. That is, this probe 5
In 1, the light emitted from the end surface of the optical fiber 52 passes through the photometric unit 55 and is reflected by the concave reflecting mirror 53. Then, it again passes through the photometric unit 55 and is incident on the end face of the optical fiber 52.

The control section 60 comprises a light source 61, an optical directional coupler 62, photodetectors 63 and 64, a monitor circuit 65, a signal processing circuit 66 and an output section 67. Optical directional coupler 62
Is an optical circuit that splits the light output from the light source 61 in the direction of the photodetector 63 and the direction of the optical fiber 51, and outputs the light input from the optical fiber 51 in the direction of the photodetector 64. The circuit 65 controls the level of the light output from the light source 61 so that the signal level output from the photodetector 63 becomes constant. The signal processing circuit 66 calculates the absorbance based on the signal level output from the photodetector 64, and the output section 67 displays or prints the absorbance.

Thus, in the technique described in this publication,
By providing a reflecting mirror on the photometric path so that light can be supplied and detected from the same direction, the probe is unified and downsized. Similarly, a technique for unifying and miniaturizing the probe by providing a reflecting mirror on the photometric path is disclosed in Japanese Laid-Open Patent Publication No. 56-26245.
It is also disclosed in JP-A-57-61935.

Further, Japanese Patent Laid-Open No. 61-258148 discloses a probe (optical device) as shown in FIG. As shown in the figure, the probe described in this publication has two quartz glass members 7 each having a reflective film 72 formed on a surface forming an angle of 45 degrees with respect to the upper end surface thereof.
0 and a spacer 71. When light is incident from the upper end surface of one of the silica glass members 70, the light is reflected by each reflective film 72 as indicated by the arrow, and the other light is reflected. It is injected from the upper end surface of the quartz glass member 70.

That is, from this probe, the light that has passed through the liquid by the distance between the quartz glass members 70 (the thickness of the spacer 71) is output, and the concentration is measured based on the level of the light. Become. Incidentally, JP-A 1-187
Japanese Unexamined Patent Publication No. 098 discloses a technique that realizes a similar configuration by making the end faces of two optical fibers face each other.

[0009]

As described above, the conventional probe is constructed for the purpose of measuring the amount of light attenuation due to passage of the liquid. Therefore, each probe has a problem in that the configuration (shape) of its tip must be complicated, and it is difficult to manufacture. In addition, because the configuration of the tip is complicated, it is difficult to clean it,
Hygiene problems were likely to occur. Therefore, the conventional probe has not been suitable for use in a field in which the fermentation tank is cleaned and sterilized in each batch, such as the fermentation industry.

Further, the conventional concentration measuring device has a problem that an error occurs in the measurement result when the environmental temperature changes. Therefore, an object of the present invention is to provide a concentration measuring device equipped with a probe having a simple structure and capable of measuring the concentration with high accuracy.

[0011]

A concentration measuring device according to the present invention is made of a material that transmits light, and has a rod having one end to which the first and second optical fibers are connected, and a side surface of the rod, A probe provided with a protection tube fixed to the rod so that the liquid touches only a predetermined portion of the tip of the rod when the tip of the rod is immersed in the liquid, and the rod via the first optical fiber. A light-emitting / light-receiving part in which a light-emitting element that supplies light to the front and a light-receiving element that receives the light incident on the tip of the rod through the second optical fiber are fixed to the same high heat-conductive member; A temperature control unit for controlling the temperature of the member to be constant, a light emitting element control unit for generating light to the light emitting element, and a test object contained in the liquid in which the tip of the rod is immersed based on the level of the signal output from the light receiving element. Calculate the concentration of a substance Comprising a that concentration calculation unit.

That is, according to the present invention, by measuring the concentration based on the scattered light intensity, it is possible to make the rod, which is the central constituent element of the probe, into a simple shape. Then, by providing a protective tube that covers the circumference of the rod, it is possible to prevent light other than scattered light from entering the rod and achieve high sensitivity.

Further, by fixing the protective tube and the rod so that the liquid touches only the tip portion of the rod when the tip end of the rod is immersed in the liquid, the liquid is extended to a portion unnecessary for concentration measurement. To prevent intrusion and facilitate cleaning. Note that such a fixed state is realized, for example, by filling the space between the rod and the protective tube with an adhesive.

Further, the light-emitting element for supplying light to the probe having the above-mentioned structure and the light-receiving element for detecting scattered light collected by the probe are the same high thermal conductivity member whose temperature is controlled to be constant. By fixing the light emitting element and the light receiving element, the operating states of the light emitting element and the light receiving element do not change even if the environmental temperature changes. Then, the concentration calculator calculates the concentration of the test substance contained in the liquid based on the level of the signal output by the light receiving element fixed to the high thermal conductivity member. It should be noted that this concentration calculation unit may be one that calculates the concentration by digitally processing the output of the light receiving element, or may be one that calculates the concentration by analog processing using an amplifier or the like.

Thus, in the concentration measuring device of the present invention,
Since the structure is such that the concentration of the test substance is obtained based on the scattered light intensity, the probe is formed with the rod having a simple shape as the main constituent element. For this reason, the probe can be easily manufactured and can be easily washed.

Further, since the temperatures of the light emitting element and the light receiving element are controlled so as to be always constant, changes in the ambient temperature do not affect the operation contents of the light emitting element and the light receiving element. Therefore, a slight change in the scattered light intensity can be surely detected, and as a result, the measurement can be accurately performed from the low concentration region to the high concentration region without switching the range.

In the concentration measuring apparatus of the present invention, a probe having a protective tube having an air vent hole at a portion whose inner surface contacts the liquid when immersed in the liquid can be used. When the concentration measuring device is configured as described above, it is possible to prevent gas from being accumulated in the probe (a portion that comes into contact with the liquid) when the probe is immersed in the liquid. Therefore, the contact state between the tip of the rod and the liquid containing the test substance is always uniform, and it is possible to prevent the difference in the contact state from adversely affecting the measurement result.

Further, when measuring a liquid in which bubbles are generated, it is desirable to provide a bubble vent hole in the protective tube and make the tip of the rod into a conical shape. According to this structure, the bubbles generated in the liquid move upward along the rod surface and are discharged to the outside through the bubble extraction hole, so that the phenomenon that the bubbles stay on the rod surface does not occur. Therefore, it becomes possible to accurately measure the concentration of the test substance in the liquid in which bubbles are generated.

In the concentration measuring apparatus of the present invention, the light emitting element control unit uses a circuit that causes the light emitting element to generate stable peak level light at a predetermined period, and the concentration calculation unit uses a signal output from the light receiving element. It is also possible to use a circuit that extracts a signal component that changes in the cycle of, and calculates the concentration of the test substance contained in the liquid in which the tip of the rod is immersed based on the level of the extracted signal component. The light emitting element control unit may be a circuit that causes the light emitting element to output pulsed light, or may be a circuit that outputs light whose level continuously changes.

When the concentration measuring device is constructed in this way, the concentration of the test substance is calculated based on the level of only scattered light. Therefore, it is possible to obtain a highly accurate concentration measuring device in which the influence of the difference in the measurement environment on the measurement result is extremely small.

Further, a light receiving element for monitoring for monitoring the light output from the light emitting element is added to the light emitting / receiving section, and the level of the signal output from the light receiving element for monitoring serves as a target level as the light emitting element control section. Therefore, a circuit for changing the level of the control signal given to the light emitting element can be used. In this way, when the concentration measuring device is configured, the level of light irradiated on the liquid is stabilized,
A concentration measuring device with the same accuracy as the above can be obtained.

Further, when constructing the concentration measuring apparatus of the present invention, an optical filter, which is directly or indirectly fixed to the high thermal conductivity member and which passes light of a wavelength output by the light emitting element, is provided, The element can also use a light emitting / light receiving unit that receives light from the second optical fiber via the optical filter.

In general, the peak transmittance wavelength of the optical filter fluctuates depending on the temperature, but since the optical filter is fixed directly or indirectly to the high thermal conductivity member in this configuration, its temperature Is always constant and the peak transmittance wavelength does not change. Therefore, in the case where the concentration measuring device has such a configuration, only scattered light is always introduced into the light receiving element, which enables highly accurate concentration measurement.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows the configuration of a concentration measuring device according to an embodiment of the present invention. As shown in the figure, the concentration measuring apparatus according to the present embodiment includes a probe 11 and a light emitting / receiving unit 12.
, Temperature control unit 13, concentration measuring unit 14, optical fiber 1
It is composed of 5 ₁ and 15 ₂ .

The present concentration measuring device is a device for measuring the concentration of the test substance contained in the liquid by measuring the scattered light intensity of the liquid. When performing the measurement, the probe 11 is attached to the tip of the probe 11. It is fixed to the container of the liquid so that is immersed in the liquid to be measured.

The probe 11 comprises a quartz rod 21, a protective tube 22, a silicon processing section 23 and a connector 24. One end of the quartz rod 21 is processed into a conical shape with an apex angle of 60 degrees, and two connectors 24 are provided at the other end. At the time of measurement, the optical fibers 15 ₁ and 15 ₂ are connected to these connectors 24, and the light from the optical fiber 15 ₁ is irradiated into the liquid from the tip of the quartz rod 21. Further, scattered light generated in response to the irradiation is transmitted through the quartz rod 21 to the optical fiber 15 ₂
Has been introduced.

The tip of the quartz rod 21 is processed into a conical shape so that when the probe 11 is used for a sample in which bubbles are generated, the bubbles stay on the surface of the quartz rod 21. This is to prevent the quartz rod 21
Bubbles attached to the surface move upward along the conical surface,
It is discharged to the outside through a bubble vent hole described later. In addition,
When using only for samples that do not generate bubbles,
The tip of the quartz rod 21 may be flat or hemispherical.

The silicon processing section 23 is formed by filling the space between the quartz rod 21 and the protective tube 22 with a silicon adhesive. In the probe 11, the protection tube 22 and the quartz rod 21 are fixed by the silicon processing section 23, and when the probe 11 is immersed in the liquid, the liquid does not enter above the silicon processing section 23. It is like this.

At the lower part of the protective tube 22, there is provided a bubble vent hole 25 for preventing gas from accumulating at the tip portion when the tip of the probe 11 is immersed in the liquid. As described above, the bubble vent hole 25 also has a function of removing bubbles generated in the liquid to be measured from the tip portion of the probe. A screw (not shown) is cut on the upper portion of the protective tube 22 so that a blind plug can be fixed when the optical fiber 15 is detached from the connector 24.

The main role of the protective tube 22 is to prevent light other than scattered light from entering the quartz rod 21, but the outer wall of the protective tube 22 fixes the probe 11 to the container. Also used to do. Further, when the blind plug is performed, it also plays a role of protecting the end surface of the rod 21 and the connector 24, and the probe 11 with the blind plug is provided.
It is also possible to perform autoclave with the container.

The light emitting / receiving unit 12 includes a semiconductor laser 31, a photodiode 32, and a Peltier element 33 as main constituent elements. The semiconductor laser 31 and the photodiode 32 are embedded in a copper block 34, and a Peltier element 33 having a heat dissipation plate 35 is fixed to one surface of the copper block 34.

A case 36 made of a heat insulating material is provided around the copper block 34.
A connector 37 ₁ for introducing the output light of the semiconductor laser 31 into the optical fiber 15 ₁ and a connector 37 ₂ for introducing the light from the optical fiber 15 ₂ into the photodiode 32.
Is provided. An interference filter 39 is inserted between the connector 37 ₂ and the light-receiving surface of the light-receiving element 32 to transmit the light of the wavelength output by the semiconductor laser 31. Also,
A temperature sensor 38 for measuring the temperature is attached to the copper block 34.

The output of the temperature sensor 38 is the output of the temperature control unit 13.
Has been entered. The temperature control unit 13 is a so-called PI.
It is a D controller and the Peltier element 3 is adjusted so that the temperature observed by the temperature sensor 38 matches the target temperature.
3 is driven. In the concentration measuring device of this embodiment, when the target temperature is set to 25 ° C., the temperature of the copper block 36 is controlled to 25 ° C. ± 0.04 ° C. by the temperature control unit 13.

The semiconductor laser 31 provided in the light emitting / receiving unit 12 is a device incorporating a monitor light receiving element for monitoring the output light intensity, and the semiconductor laser 31 and the photodiode 32 are controlled by Concentration measurement unit 1
4 is performed.

FIG. 2 shows the structure of the concentration measuring unit. As shown in the figure, the concentration measuring unit 14 includes an oscillator 40, a laser drive circuit 41, a photoamplifier 42, and an auto-zero circuit 43.
Switching circuit 44, amplifier 45, bandpass filter 46
And an effective value conversion circuit 47, an amplifier 48 and a display 49.

When the concentration is measured by this concentration measuring apparatus, the oscillator 40 outputs a signal of a predetermined frequency. The laser drive circuit 41 receives a signal from the oscillator 40 and causes the semiconductor laser 31 to periodically output pulsed light having a level corresponding to the signal level. On this occasion,
The laser drive circuit 41 monitors the signal level from the light receiving element in the semiconductor laser 31 so that the level of the output light becomes a level that exactly corresponds to the signal level from the oscillator 40. To control.

The signal from the photodiode 32 is input to the photoamplifier 42, and the signal amplified by the photoamplifier 42 is sent to the amplifier 4 via the switching circuit 44.
5 is input and amplified. The auto zero circuit 43
Is a circuit for canceling the influence of ambient light from the output of the photodiode 32.
It works when is OFF.

The bandpass filter 46 supplies a signal in a predetermined frequency range centered on the oscillation frequency of the oscillator 40 from the signal output from the amplifier 45 to the RMS conversion circuit 47. The effective value conversion circuit 47 is a circuit provided to avoid the influence of the voltage drift of the amplifier 45 and the bandpass filter 46. The output of the effective value conversion circuit 47 is input to the amplifier 48. A zero position determination volume 50 ₁ and a span determination volume 50 ₂ are connected to the amplifier 48, and the amplifier 48 sets an offset according to the set value of the zero position determination volume 50 ₁ to an effective value conversion circuit 47. After being applied to the signal from, the amplification according to the set value of the span determination volume 50 ₂ is performed. The output of the amplifier 48 is input to the display 49, and the display 49 numerically displays the level of the input signal.

As described above, in the concentration measuring unit 14, a process of causing the semiconductor laser 31 to output pulsed light whose level changes periodically and a process of detecting the output of the photodiode 32 at that period. Is being done. That is, in the concentration measuring unit 14, of the light from the rod 21,
The density is calculated only for the light generated according to the light supplied to the rod 21.

Further, as already described, the semiconductor laser 31 and the photodiode 32 are fixed to the copper block 34 whose temperature is controlled to be constant, so that their operating temperatures are changed even if the environmental temperature changes. , Always constant.
Therefore, in the present concentration measuring apparatus, the relationship between the input and the output in each of the semiconductor laser 31 and the photodiode 32 does not change even if the ambient temperature changes.

Since the interference filter 39 that passes only the light of the wavelength output by the semiconductor laser 31 is provided on the front surface of the photodiode 32, the light other than the wavelength of
That is, light whose level does not depend on the concentration of the test substance does not enter the photodiode 32. Moreover, the interference filter 39 is provided in the copper block 34, and the temperature thereof is always controlled to be constant like the semiconductor laser 31 and the photodiode 32. Therefore, the peak transmittance wavelength of the interference filter 39 is It does not change depending on the ambient temperature. Therefore, only light having the same wavelength as the light output from the semiconductor laser 31 is input to the photodiode 32 and converted into an electric signal.

As described above, in the present concentration measuring device, the scattered light intensity is measured in such a manner that the influence due to the change of the environmental temperature and the influence due to the ambient light can be excluded, so that the concentration measured by the present concentration measuring device is , Will be extremely accurate.

FIG. 3 shows the result of actually monitoring the growth of yeast using the concentration measuring apparatus according to this embodiment.
This figure shows 28 yeasts in a Jafamentor with an internal volume of 2L.
The yeast concentration (bacterial cell concentration) grown at 0 ° C. was simultaneously measured by a temperature measuring concentration measuring device and a temperature controlling non-concentrating concentration measuring device. It is the figure plotted against L). In the figure, the data indicated by ● are the measurement results obtained by the concentration measuring device that controls the temperature, and the data indicated by ○ are the measurement results obtained by the concentration measuring device that does not perform the temperature control. Further, the temperature measurement result in the vicinity of the light emitting / receiving unit 12 of each concentration measuring device is shown as the environmental temperature.

As is clear from the figure, the output of the temperature-controlled concentration measuring device shows a high linearity (correlation coefficient R = 0.99944) with the bacterial cell concentration. It can be seen that the cell concentration can be accurately measured.

Also, when the temperature control is not performed,
A certain degree of linearity (correlation coefficient R = 0.98748) is recognized between the output and the bacterial cell concentration, but this linearity is only obtained because the environmental temperature changes gently. Absent. For example, consider a case where the environmental temperature is 23 ° C. when the cell concentration is about 4 g / L and the environmental temperature is 25 ° C. when the cell concentration is about 8 g / L. In this case, when the bacterial cell concentration is about 4 g / L, the data indicated by ◯ is measured, but when measured at 8 g / L, the data indicated by ● is measured (when temperature control is performed). Each measurement result corresponds to the measurement result when the ambient temperature is 25 ° C.), and the phenomenon in which the output increases despite the increase in the concentration occurs.

As described above, when the temperature control is not performed, the output fluctuates when the environmental temperature fluctuates.
The concentration cannot be uniquely determined. In contrast,
Since the concentration measuring device of the embodiment that controls the temperature is configured not to be affected by the fluctuation of the environmental temperature, it is possible to always measure the concentration with high accuracy.

<Modification of Embodiment> In the concentration measuring device of this embodiment, the optical fiber and the quartz rod are connected via a connector, but the quartz rod and the optical fiber may be directly connected. It is natural.

Further, in the concentration measuring apparatus of this embodiment, the probe is formed by using the quartz rod, but for example, the light transmittance of BK7 (borosilicate crown glass), sapphire, Pyrex, silicon, etc. is high. Even if the probe is formed using the rod made of the material, the concentration measuring device of the embodiment and the concentration measuring device having the same function can be configured. When high-pressure steam sterilization is not performed, a rod formed of vinyl chloride, acrylic, polycarbonate, etc. can be used.

Further, as the concentration measuring section, the semiconductor laser outputs light whose level continuously changes at a predetermined cycle, and the output of the photodiode is synchronously detected at the cycle to measure the density. Even if the measuring unit is used, a concentration measuring device having the same effect can be configured.

Further, the control temperature of the semiconductor laser and the photodiode does not have to be 25 ° C., and the temperature at which the semiconductor laser and the photodiode operate, for example, −10.
It may be -50 ° C.

[0051]

As described in detail above, according to the present invention, since the concentration of the test substance is obtained based on the scattered light intensity, the probe having a simple shape as a central element is used. Can be configured. For this reason, the probe is easy to fabricate and is easy to wash. Further, since the temperatures of the light emitting element and the light receiving element are controlled so as to be always constant, the change in environmental temperature does not affect the measurement result, and accurate concentration measurement can always be performed.

If a probe having a protective tube provided with a bubble vent is used in the concentration measuring device of the present invention, the difference in contact state between the tip of the rod and the liquid containing the substance to be tested is reflected in the measurement result. It will be possible to prevent adverse effects.

If the protective tube is provided with a bubble vent hole and the tip of the rod is conical, the concentration of the test substance in the liquid in which bubbles are generated can be measured accurately.

Then, the light emitting element is made to generate periodically stable peak level light, and the concentration of the test substance is calculated from the signal component corresponding to the change in the signal output from the light receiving element. In this case, it is possible to obtain the concentration measuring device in which the influence of the difference in the measurement environment on the measurement result is extremely reduced.

Further, when the concentration measuring device is constructed by using the light emitting element having the monitor light receiving element, the concentration measuring device capable of highly accurately measuring the concentration in a stable state for a long period of time can be obtained. .

In the case where an optical filter that transmits only the light of the wavelength output by the light emitting element is provided on the front surface of the light receiving element and the temperature of the optical filter is controlled to be constant, the concentration measurement is performed. Since disturbing ambient light can be prevented from being input to the light receiving element, accurate concentration measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an outline of a concentration measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a concentration measuring unit used in the concentration measuring device according to the embodiment.

FIG. 3 is a diagram showing an example of a measurement result by the concentration measuring device according to the embodiment.

FIG. 4 is a configuration diagram showing an outline of a sensor described in JP-A-56-29146.

FIG. 5 is a configuration diagram showing an outline of a probe described in JP-A-61-258148.

[Explanation of symbols]

 11 Probe 12 Light Emitting / Receiving Section 13 Temperature Control Section 14 Concentration Measuring Section 15 Optical Fiber 21 Quartz Rod 22 Protective Tube 23 Silicon Processing Section 24, 37 Connector 25 Bubble Extraction Hole 31 Semiconductor Laser 32 Photodiode 33 Peltier Element 34 Copper Block 35 Heat Dissipation Plate 36 Case 38 Thermometer 39 Interference filter 40 Oscillator 41 Laser drive circuit 42 Photoamplifier 43 Auto-zero circuit 44 Switching circuit 45, 48 Amplifier 46 Bandpass filter 47 Effective value conversion circuit 49 Indicator 50 Volume

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Sakamoto, 17 Nishinishiyama, Nishinasuno-machi, Nasu-gun, Tochigi Prefecture Kagome Co., Ltd. (72) Inventor Yoshiya Furuta, 17 Nishinishiyama, Nishinasuno-cho, Nasu-gun, Tochigi Prefecture Inside Kagome Research Institute

Claims (6)

[Claims] 1. A rod which is made of a material that transmits light and has one end to which the first and second optical fibers are connected, and a rod which covers the side surface of the rod and when the tip of the rod is immersed in a liquid. A probe provided with a protection tube fixed to the rod so that the liquid touches only a predetermined portion of the tip of the rod; and a light emitting element that supplies light to the rod via the first optical fiber. A light-emitting / light-receiving part in which a light-receiving element that receives the light incident on the tip of the rod through the second optical fiber is fixed to the same high thermal-conductive member; and the temperature of the high-thermal-conductive member is constant. A temperature control unit that controls the light emitting element, a light emitting element control unit that generates light in the light emitting element, and a tip of the rod based on the level of a signal output by the light receiving element Calculate concentration Concentration measuring apparatus comprising a that concentration calculation unit. 2. The protective tube constituting the probe is provided with a bubble vent hole at a portion whose inner surface comes into contact with the liquid when the probe is immersed in the liquid. Concentration measuring device. 3. The concentration measuring apparatus according to claim 2, wherein a tip of the rod forming the probe has a conical shape. 4. The light emitting element control unit causes the light emitting element to generate light having a stable peak level in a predetermined cycle, and the concentration calculation unit changes in a predetermined cycle from a signal output from the light receiving element. 4. The concentration of the test substance contained in the liquid in which the tip of the rod is immersed is calculated based on the level of the extracted signal component, and the concentration of the test substance is calculated. The concentration measuring device according to claim 2. 5. The light-emitting / light-receiving unit further includes a monitor light-receiving element that monitors light output from the light-emitting element, and the light-emitting element control unit includes a level of a signal output from the monitor light-receiving element. 5. The concentration measuring device according to claim 1, wherein the level of the control signal given to the light emitting element is changed so as to reach a target level. 6. The light emitting / receiving unit is further fixed directly or indirectly to the high thermal conductivity member,
The light emitting element includes an optical filter that passes light having a wavelength output, and the light emitting element receives the light from the second optical fiber via the optical filter. 5. The concentration measuring device according to any one of 5.