JP2013205052A - Gas sample chamber and gas concentration measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sample chamber and a gas concentration measuring device obtained at low costs, and improving detection sensitivity of gas concentration.SOLUTION: A gas concentration measuring device comprises a gas cell (2) having an inner peripheral surface formed in a cylindrical shape and with no irregular reflection prevention processing applied, and into which gas to be measured is charged, a light source (8) arranged at one end of the gas cell (2) to emit infrared ray, a sensor holder (6) arranged at the other end of the gas cell (2) and having a housing chamber (6a) having an opening part in contact with the other end of the gas cell (2), and an infrared ray sensor (10) housed at a deep part spaced from the opening part in the housing chamber (6a) of the sensor holder (6) to detect the infrared ray introduced through the inside of the gas cell (2) from the light source (8). Black body processing is applied to the inner surface of the housing chamber (6a) of the sensor holder (6).

Description

  The present invention relates to a gas sample chamber used for measuring the concentration of a gas to be measured such as carbon dioxide, water vapor, carbon monoxide, and the like, and a gas concentration measuring device including the gas sample chamber.

  For example, various gas sample chambers have conventionally been used for gas concentration measuring devices that measure the concentration of a gas to be measured such as carbon dioxide, water vapor, and carbon monoxide. Such a gas sample chamber comprises a hollow tube as a cylindrical gas cell sealed inside, a light source provided at one end of the hollow tube, and an infrared sensor provided at the other end of the hollow tube. I have.

  The hollow tube is formed, for example, by cutting a cylindrical column made of metal such as copper or iron into a cylindrical shape and then performing mechanical polishing (buffing or the like) to smooth the inner peripheral surface thereof. . The hollow tube is provided with a gas introduction hole into which an atmosphere containing a predetermined gas whose concentration is to be measured, and a gas outlet hole through which the atmosphere is discharged.

  The light source is an incandescent lamp and emits infrared rays (that is, infrared light). The infrared sensor includes a light receiving element, and an optical bandpass filter (hereinafter referred to as “filter”) as a transmission member that is disposed between the light receiving element and the light source and transmits only infrared light having a predetermined wavelength. Yes. This infrared sensor outputs a voltage corresponding to the intensity of infrared rays. The wavelength of infrared light that passes through the filter is determined according to the gas whose concentration is to be measured. For example, if the concentration of the gas to be measured is within a relatively low concentration range of 0 ppm to several thousand ppm, the infrared wavelength that is most easily attenuated by the gas to be measured is selected as the wavelength of the infrared light that passes through the filter. The filter is appropriately selected according to the gas to be measured.

  Such a gas sample chamber, that is, a gas concentration measuring device supplies the atmosphere into the hollow tube through the gas introduction hole, and measures the intensity of infrared rays from the light source received by the infrared sensor through the filter. The concentration of the measurement target gas contained in the above was measured.

  However, the filter described above is used in the gas sample chamber described above, which sorts (passes or blocks) infrared rays incident on the filter surface at an angle perpendicular to or close to the vertical according to the wavelength. Since the inner peripheral surface of the hollow tube is smoothed by mechanical polishing, the surface is rough when viewed optically, and infrared rays are irregularly reflected (diffuse reflected) in various directions. Of the irregularly reflected infrared rays, those reflected at an angle close to a right angle with respect to the axial direction of the hollow tube are tanned with respect to the filter surface described above (a direction close to parallel to the filter surface, that is, a direction that is not perpendicular). The filter does not function properly for each infrared wavelength by the filter, and the infrared light with the wavelength that is originally blocked by the filter passes through the filter. The accuracy of the concentration measurement there is a problem that becomes worse.

  In view of this, the applicant has proposed a technique that eliminates irregular reflection by blackening the inner peripheral surface of the gas cell so that the accuracy of concentration measurement does not deteriorate (see Patent Document 1).

JP 2010-060484 A

  However, the black body treatment of the inner peripheral surface of the gas cell eliminates irregular reflection from the inner peripheral surface of the gas cell, but the output of the infrared sensor decreases, the gas concentration detection sensitivity decreases and the cost increases. There was a problem.

  In view of this, an object of the present invention is to provide a gas sample chamber and a gas concentration measuring device that have good gas concentration detection sensitivity and are inexpensive.

  The gas sample chamber of the invention according to claim 1 for solving the above-described problem has an inner peripheral surface which is formed in a cylindrical shape and is not subjected to irregular reflection prevention treatment, and is a gas cell filled with a gas to be measured ( 2), a light source (8) disposed at one end of the gas cell (2) to emit infrared light, and a sensor holder disposed at the other end of the gas cell (2) and having a storage chamber (6a) (6) and is accommodated in the accommodation chamber (6a) of the sensor holder (6) in a depth part spaced from the opening, and is guided from the light source (8) through the inside of the gas cell (2). An infrared sensor (10) for detecting the infrared light, and a black body treatment is performed on an inner surface of the accommodation chamber (6a) of the sensor holder (6).

  The invention according to claim 2 for solving the above problem is that, in the gas sample chamber according to claim 1, the sensor holder is made of aluminum, and black alumite treatment is applied to the inner surface of the storage chamber (6a). It is characterized by being given.

  A gas concentration measuring device according to a third aspect of the invention for solving the above-mentioned problems is the intensity of the infrared light detected by the gas sample chamber (1) according to the first or second aspect and the infrared sensor (10). And a concentration calculating section (23) for calculating the concentration of the gas to be measured in the gas cell.

  The reference numerals in the description of the means for solving the above-described problems correspond to the reference numerals of the constituent elements in the following description of the embodiments for carrying out the invention. The interpretation of is not limited.

  According to the invention described in claims 1, 2, and 3, the gas cell has an inner peripheral surface that is formed in a cylindrical shape and is not subjected to irregular reflection prevention treatment, and the sensor holder that houses the infrared sensor therein Since the black body treatment is applied to the inner surface of the storage chamber, infrared rays can be absorbed on the inner surface to prevent irregular reflection, noise reaching the infrared sensor is reduced, and adverse effects due to irregular reflection are reduced. Since the infrared rays reaching the point increase from the conventional level, the gain and span can be improved, and the detection sensitivity and resolution can be improved. Further, the inner peripheral surface of the long cylindrical gas cell is not subjected to black body treatment (irregular reflection preventing treatment), and only the inner surface of the sensor holder housing chamber is subjected to black body treatment, so that it can be manufactured at low cost.

It is a perspective view which shows the structure of one Embodiment of the gas sample chamber which concerns on this invention. It is a schematic sectional drawing of the gas sample chamber of FIG. It is a schematic sectional drawing which shows the structure of the infrared sensor in the gas sample chamber of FIG. It is a graph which shows the absorption spectrum of a carbon dioxide. It is explanatory drawing which shows the structure of one Embodiment of the gas concentration measuring apparatus which concerns on this invention. It is a block diagram which shows the structure of the light-receiving circuit in the gas concentration measuring apparatus of FIG. It is a typical block diagram for performing the performance measurement experiment of the gas sample chamber of this invention. It is a light source supply voltage used in a performance measurement experiment, and a waveform diagram of a sensor output. It is an output characteristic figure of each wavelength by the presence or absence of black alumite processing as a measurement experiment result. It is each sensor ratio characteristic figure by the presence or absence of the black alumite process as a measurement experiment result. It is a Low output comparison characteristic figure of the infrared sensor for 4.0 micrometers by the presence or absence of the black alumite process as a measurement experiment result. It is a Hi output comparison characteristic figure of the infrared sensor for 4.0 micrometers by the presence or absence of the black alumite process as a measurement experiment result. It is a Low output comparison characteristic figure of the infrared sensor for 4.3 micrometers by the presence or absence of the black alumite process as a measurement experiment result. It is a Hi output comparison characteristic figure of the infrared sensor for 4.3 micrometers by the presence or absence of the black alumite process as a measurement experiment result. It is a comparison characteristic figure of the output ratio of a black alumite / solid aluminum infrared sensor as a measurement experiment result. It is a figure which shows the infrared sensor 0-1000 ppm output difference characteristic for 4.0 micrometers as a measurement experiment result. It is a figure which shows the infrared sensor 0-1000 ppm output difference characteristic for 4.3 micrometers as a measurement experiment result. It is a figure which shows the infrared sensor 0-1000 ppm output difference characteristic for 4.3 / 4.0 micrometers as a measurement experiment result. It is explanatory drawing explaining the law of Beer-Lambert. It is explanatory drawing explaining the property of an optical band pass filter. It is a characteristic view explaining the characteristic of an optical band pass filter.

  (Embodiment of Gas Sample Chamber) Hereinafter, a gas sample chamber according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the gas sample chamber 1 includes a gas cell 2, flanges 3 and 4 fitted and fixed to both ends of the gas cell 2, a light source holder 5 fixed to the flange 3, a flange And a sensor holder 6 fixed to 4.

  The gas cell 2 is a conduit for guiding infrared rays from the light source from one end to the other end through the inside. The gas cell 2 is made of, for example, a metal tube such as aluminum or duralumin, a glass tube, or the like, and is formed in a cylindrical shape. The inner peripheral surface of the gas cell 2 is not subjected to irregular reflection prevention processing such as black body treatment.

  A gas inlet hole (not shown) is provided at one end of the light source holder 5, and a gas outlet hole (not shown) is provided at one end of the sensor holder 6. A gas supply source (not shown) is connected to the gas introduction hole. This gas supply source forcibly sends the atmosphere containing the gas to be measured into the gas cell 2 from the gas introduction hole. And the said atmosphere sent in in the gas cell 2 is discharged | emitted from a gas outlet hole. In addition, although the gas introduction hole and the gas outlet hole are defined, the inlet and the outlet may be reversed.

  A light source unit 7 is accommodated in the light source holder 5. The light source unit 7 includes a light source 8 and a reflector 9. The light source 8 emits infrared light as light from one end portion of the gas cell 2 toward the other end portion when a voltage is applied. As the light source 8, for example, a black body furnace or an incandescent lamp is used. The reflector 9 reflects the light emitted from the light source 8 into parallel light directed toward the other end of the gas cell 2. For example, the light source 8 performs pulse lighting that repeatedly turns on and off at predetermined intervals of a lighting time of 0.6 seconds and a light-off time of 2.4 seconds.

  The sensor holder 6 is an aluminum holder having a through hole 6 a having the same inner diameter that is positioned so as to match the inner diameter of the cylindrical gas cell 2. The through hole 6a has an opening in contact with the other end of the gas cell (2). Black body treatment is applied to the inner surface of the through-hole 6a so that infrared rays are not irregularly reflected. The black body treatment is a non-reflection treatment that eliminates reflection of infrared light on the inner surface (that is, makes the emissivity close to 1). The black body processing is performed by, for example, black alumite processing. The black alumite-treated through hole 6 a is used as a storage chamber for storing the infrared sensor 10. The infrared sensor 10 has a back portion spaced from the end (opening) near the gas cell 2 in the through-hole 6a, that is, an end far from the gas cell 2 (on the side far from the gas cell 2). It is accommodated and held in the vicinity of the opening).

  As shown in FIG. 3, the infrared sensor 10 includes a sensor main body 11, a plurality (two in this embodiment) of light receiving elements 12a and 12b, and a plurality (two in this embodiment) of transmissive members 13a and 13b. It is equipped with. The sensor body 11 is formed in a cylindrical shape along the inner peripheral surface of the through hole 6 a of the sensor holder 6.

  The light receiving elements 12a and 12b are made of a thermopile constituting a thermopile infrared sensor. A thermopile is a known heat-voltage energy conversion element in which a plurality of thermocouples are connected in series to increase the output voltage. The thermopile hot junction is disposed to face the transmitting members 13 a and 13 b so as to receive infrared rays from the light source, and the thermopile cold junction is thermally connected to the sensor holder 6. . The light receiving elements 12 a and 12 b are arranged on the same plane at the bottom of the sensor body 11. The transmission members 13a and 13b are arranged on the same plane outside the openings 11a and 11b of the sensor body. The infrared sensor 10 receives infrared rays emitted from the light source 8 and transmitted through the transmission members 13a and 13b, and converts the heat of the infrared rays into electric energy. The infrared sensor 10 converts infrared heat into electric energy, and outputs it as a sensor output to the [mu] com 23 of the gas concentration measuring apparatus 20 described later.

  The transmission members 13 a and 13 b are well-known optical bandpass filters such as interference filters, and are attached to the sensor body 11 and disposed between the infrared sensor 10 and the light source 8. Each of the transmitting members 13 a and 13 b transmits only infrared light having a predetermined wavelength out of infrared light from the light source 8, and guides the transmitted infrared light to the infrared sensor 10. The transmitting members 13a and 13b have different wavelengths of infrared rays to transmit.

  The wavelength of infrared rays transmitted through the transmission members 13a and 13b is determined according to the type of gas to be measured whose concentration is measured by a gas concentration measurement device 20 described later. In this embodiment, the concentration range of the gas to be measured can be detected at a low concentration within the range of 0 ppm to several thousand ppm, and the wavelength of infrared light transmitted through the transmission members 13a and 13b is relative to the gas to be measured. The transmittance is set to a small infrared wavelength. For example, the light receiving element 12a is used as a reference element serving as a measurement reference, and the transmitting member 13a transmits only infrared rays having a wavelength of 4.0 μm that are not attenuated in the atmosphere. The light receiving element 12b is used, for example, to measure the concentration of carbon dioxide (CO2), and the transmission member 13b only transmits infrared light having a wavelength of 4.3 μm, which is easily attenuated in the carbon dioxide (CO2). To Penetrate. The transmitting members 13a and 13b transmit only a predetermined wavelength with high accuracy when the angle of incident infrared rays is close to the incident surface, and when the angle of incident infrared rays is nearly horizontal with respect to the surface. , It has a property of transmitting wavelengths other than the predetermined wavelength.

  FIG. 4 shows the infrared transmittance for carbon dioxide (CO 2). The horizontal axis in FIG. 4 shows the wavelength (μm) of infrared rays, and the vertical axis shows the infrared transmittance (%). FIG. 4 shows that the transmittance of infrared rays with a wavelength of 4.3 μm in carbon dioxide is almost zero, and infrared rays with a wavelength of 4.3 μm hardly pass through carbon dioxide (almost no absorption). It has been shown).

  In the gas sample chamber 1 having the above configuration, when the gas cell 2 is filled with an atmosphere containing, for example, carbon dioxide (CO2) as a gas to be measured, infrared rays emitted from the light source 8 are emitted from the gas cell (2). To the infrared sensor 10. At this time, since the inner peripheral surface of the gas cell 2 is not subjected to the diffuse reflection preventing process, the infrared light guided through the gas cell 2 includes parallel light and irregular reflection light. However, since the inner surface of the through-hole 6a of the sensor holder 6 is anodized, from the end of the through-hole 6a on the side close to the gas cell 2 in the infrared rays that reach the opening of the through-hole 6a from the gas cell 2. The irregularly reflected light striking the inner surface subjected to the alumite treatment at a predetermined interval up to the place where the infrared sensor 6 is held is absorbed by the inner surface. Therefore, only infrared rays that are substantially parallel to the axial direction of the gas cell 2 are guided to the light receiving elements 12a and 12b of the infrared sensor 10 disposed behind the through hole 6a.

  As described above, according to the gas sample chamber according to the present invention, the infrared rays can be absorbed by the inner surface of the through-hole 6 a that is the accommodation chamber of the infrared sensor 10 in the sensor holder 6, and irregular reflection can be prevented. Noise light is reduced and adverse effects caused by the noise are reduced, and infrared rays reaching the infrared sensor 10 are increased as compared with the prior art. Therefore, gain and span can be improved, and detection sensitivity and resolution can be improved. Further, since the inner peripheral surface of the long cylindrical gas cell 2 is not subjected to black body processing (irregular reflection prevention processing), only the inner surface of the through hole 6a (accommodating chamber) of the sensor holder 6 is subjected to black alumite processing, so that the cost is low. Can be produced.

  (Embodiment of Gas Concentration Measuring Device) Next, an embodiment of the gas concentration measuring device of the present invention will be described with reference to FIG. The gas concentration measuring device 20 includes a gas sample chamber 1 filled with an atmosphere containing a gas to be measured, a control circuit unit 21, a light receiving circuit unit 22, and a microcomputer (hereinafter referred to as μcom) as a concentration calculation unit. 23).

  The control circuit unit 21 includes an oscillator 21a, a clock frequency dividing circuit 21b, and a constant voltage circuit 21c, and blinks (pulses light) the light source 8 at a predetermined frequency in accordance with a command of μcom23.

  As shown in FIG. 6, the light receiving circuit unit 22 includes amplifiers 221 a and 221 b, a switch 222, and an A / D converter (ADC) 223. The amplifier 221 a amplifies an analog output signal as a sensor output from the corresponding light receiving element 12 a of the infrared sensor 10 and outputs the amplified signal to the A / D converter 223 via the switch 222. The amplifier 221 b amplifies an analog output signal as a sensor output from the corresponding light receiving element 12 b of the infrared sensor 10 and outputs the amplified signal to the A / D converter 223 via the switch 222. The A / D converter (ADC) 223 converts an analog output signal from the light receiving element 12 a or 12 b of the infrared sensor 10 into a digital signal and inputs the digital signal to the μcom 23.

  The μcom 23 is connected to the control circuit unit 21 and the light receiving circuit unit 22 and controls these operations, thereby controlling the overall operation of the gas concentration measuring apparatus 20. The μcom 23 is a computer that operates according to a predetermined program. As is well known, the μcom 23 includes a central processing unit (CPU) that performs various processes and controls according to a predetermined program, a ROM that is a read-only memory storing a program for the CPU, and various data. And a RAM that is a readable / writable memory having an area necessary for processing operations of the CPU.

  In addition, a non-volatile memory (not shown) (for example, EEPROM) is connected to μcom 23. The nonvolatile memory stores various data such as an extinction coefficient, a measurement distance, and a concentration conversion coefficient, which will be described later, necessary for calculating the concentration, and stores the calculated concentration in a time series so that it can be read from the outside. .

  The gas concentration measuring apparatus 20 having the above-described configuration supplies an atmosphere containing a gas to be measured in the gas cell 2 and fills the gas cell 2 with the atmosphere. Then, the gas concentration measuring device 20 blinks the light source 8 (pulse lighting), and the infrared light from the light source 8 is received by the infrared sensor 10 through the inside of the gas cell 2. The μcom 23 of the gas concentration measuring device 20 determines the intensity of infrared rays received by the infrared sensor 10 (that is, the output voltage (Hi output) of the infrared sensor 10 when the light source 8 is turned on) and the output of the infrared sensor 10 when the light source 8 is turned off. Based on the voltage (potential difference with the Low output), the concentration of the gas to be measured (for example, carbon dioxide, water vapor, carbon monoxide, etc.) in the gas sample chamber 1 is measured. Specifically, the μcom 23 of the gas concentration measuring apparatus 20 receives light from the light receiving element 12b for measuring the intensity of infrared light received by the light receiving element 12a used as a reference element and the gas to be measured (for example, carbon dioxide). The concentration of the gas to be measured (for example, carbon dioxide) is measured by comparing with the intensity of infrared rays.

  As described above, the gas sample chamber 1 of the gas concentration measuring device 20 holds the infrared light from the light source 8 in the through-hole 6a (accommodating chamber) of the sensor holder 6 through the gas cell 2 that has not been subjected to the irregular reflection prevention treatment. The inner surface of the through-hole 6a (accommodating chamber) is black anodized, so that the infrared rays from the light source 8 are not diffusely reflected in the through-hole 6a. Only infrared rays substantially parallel to the axial direction of the gas cell 2 can be guided to the light receiving elements 12a and 12b.

  As described above, according to the gas concentration measuring apparatus of the present invention, the black alumite treatment is applied to the inner surface of the through hole 6a (accommodating chamber) of the sensor holder 6 that holds the infrared sensor 10 therein, so Can be absorbed to prevent irregular reflection, so that infrared rays can be prevented from entering the transmissive members 13a and 13b from the licking direction, gain and span can be improved, and detection sensitivity and resolution can be improved. .

  (Performance measurement experiment of gas sample chamber) Next, a performance measurement experiment of the gas sample chamber of the present invention will be described. In this experiment, the sensor output of the infrared sensor 10 when the black alumite treatment was applied to the inner surface of the through hole 6a of the sensor holder 6 was confirmed by measurement. In addition, as a comparison, the sensor output in a solid aluminum state not subjected to black alumite treatment (without black alumite) was used to measure the sensor output, and the sensor holder 6 with black alumite treated (with black alumite) The comparison was made with the sensor output. The only difference in the configuration in the experiment is the presence or absence of black alumite in the sensor holder 6.

  FIG. 7 is a schematic configuration diagram for conducting a performance measurement experiment of the gas sample chamber of the present invention. In FIG. 7, first, a constant concentration of CO 2 gas is switched from a gas container 31 by an electromagnetic valve 32 controlled by a PC (personal computer) 35 and then sent to the gas sample chamber 1 of the present invention disposed in a thermostatic chamber 34. . The sensor output of the infrared sensor 10 in the gas sample chamber 1 (the sensor output of the 4.0 μm (reference) light receiving element 12 a and the sensor output of the 4.3 μm (CO2 gas absorption) light receiving element 12 b) is sent to the PC 35. Sensor output data for 0.0 μm and 4.3 μm, and temperature output data of a temperature sensor (not shown) installed in the thermostat 34 are collected. The gas flow rate supplied to the infrared sensor 10 is controlled and quantified by the mass flow controller 33. Moreover, the temperature in the thermostat 34 is monitored by the PC 35 and is controlled so that the temperature in the thermostat 34 is constant.

The measurement conditions in the performance measurement experiment with the above configuration are as follows.
(Measurement condition)
CO2 gas supply: 3-stage switching between 0 ppm, 400 ppm and 1000 ppm Temperature inside the thermostatic chamber: 3 stages: 0 ° C, 30 ° C and 50 ° C Temperature transition time: 20 minutes Temperature stabilization time in the constant temperature bath: 40 minutes Gas temperature stabilization time: 4 Minute Concentration measurement time: 4 minutes Light source: IR light source made by INTEX Infrared sensor: IR sensor made by Perkin Elma

(Data processing)
As shown in FIG. 8, a pulse voltage of L (Low) = 0 V and H (Hi) = 6.75 V was applied to the light source 8. The infrared sensor output was subjected to data processing by calculating a potential difference between L (minimum output value of the waveform) and H (maximum output value of the waveform) in the figure and using it as a sensor output value of the infrared sensor.

  The measurement experiment results in the performance measurement experiment with the above configuration are as follows.

(Measurement experiment result 1)
FIG. 9 is a diagram showing output characteristics of each wavelength depending on the presence or absence of black alumite as a measurement experiment result. In FIG. 9, the ADC value on the vertical axis is a value after the sensor output is converted into a digital signal by the ADC. Output characteristics A to M are as follows:
A: 4.0 μm wavelength, 0 ° C., sensor without alumite (12a) output characteristics B: 4.0 μm wavelength, 30 ° C., sensor without black alumite (12a) output characteristics C: 4.0 μm wavelength, 50 ° C. Sensor with black alumite (12a) Output characteristics D: 4.0μm wavelength, 0 ° C, sensor with black alumite (12a) Output characteristics E; 4.0μm wavelength, 30 ° C, sensor with black alumite (12a) Output characteristics F: 4.0 μm wavelength, 50 ° C., sensor with black anodized (12a) output characteristics G: 4.3 μm wavelength, 0 ° C., sensor without black anodized (12b) Output characteristics H: 4.3 μm wavelength, 30 ° C. Black anodized sensor (12b) output characteristics I: 4.3 μm wavelength, 50 ° C., black anodized sensor (12b) output characteristics J: 4.3 μm wavelength, 0 ° C., sensor with black anodized (12b) Force characteristics K: 4.3 μm wavelength, 30 ° C., sensor with black anodized (12b) output characteristics M; 4.3 μm wavelength, 50 ° C., sensor with black anodized (12b) output characteristics・ ・ Although there is a change in the sensor output regardless of the presence or absence of black alumite treatment, the tendency of the characteristic curve is similar regardless of the presence or absence of black alumite and there is no significant change.

(Measurement experiment result 2)
FIG. 10 is a diagram showing sensor ratio characteristics depending on the presence or absence of black alumite as a measurement experiment result. In FIG. 10, the 4.3 / 4.0 value on the vertical axis is a value obtained by dividing the output of the 4.3 μm sensor (12b) by the output of the 4.0 μm sensor (12a). The output ratio characteristics A to F are as follows:
A: Output ratio characteristic of 4.3 μm sensor (12b) output without black alumite at 0 ° C./output of 4.0 μm sensor (12a) B: Output at 4.3 μm sensor without black alumite (12b) / 4. Output ratio characteristic of output of 0 μm sensor (12a) C: Output ratio characteristic of output of 4.3 μm sensor (12b) without black anodized / 4.0 μm sensor (12a) D: 0 ° C., 4 with black anodized Output ratio characteristics of output of 3 μm sensor (12b) /4.0 μm sensor (12a) E: Output ratio characteristics of 4.3 μm sensor (12b) output with black alumite / 4.0 μm sensor (12a) output F: Output ratio characteristic of 4.3 μm sensor (12b) output / 4.0 μm sensor (12a) output with black anodized at 50 ° C. ○ What was found from FIG. 10: In the value of 4.3 / 4.0 , About 5-7% larger than the state of no better of anodized aluminum there.

(Measurement experiment result 3)
FIG. 11 is a comparative characteristic diagram of the Low output (absolute value) of the 4.0 μm sensor (12a) with or without black alumite as a measurement experiment result. Characteristics A and B are as follows:
A: Low output characteristic of 4.0 μm sensor (12a) without black anodized B: Low output characteristic of 4.0 μm sensor (12a) with black anodized

(Measurement experiment result 4)
FIG. 12 is a comparative characteristic diagram of the Hi output (absolute value) of the 4.0 μm sensor (12a) depending on the presence or absence of black alumite as a measurement experiment result. Characteristics A and B are as follows:
A: Hi output characteristic of 4.0 μm sensor (12a) without black anodized B: Hi output characteristic of 4.0 μm sensor (12a) with black anodized

(Measurement experiment result 5)
FIG. 13 is a comparative characteristic diagram of the Low output (absolute value) of the 4.3 μm sensor (12b) depending on the presence or absence of black alumite as a measurement experiment result. Characteristics A and B are as follows:
A: Low output characteristic of 4.3 μm sensor (12b) without black anodized B: Low output characteristic of 4.3 μm sensor with black anodized (12b)

(Measurement experiment result 6)
FIG. 14 is a comparative characteristic diagram of the Hi output (absolute value) of the 4.3 μm sensor (12b) depending on the presence or absence of black alumite as a measurement experiment result. Characteristics A and B are as follows:
A: Hi output characteristic of 4.3 μm sensor (12b) without black anodized B: Hi output characteristic of 4.3 μm sensor with black anodized (12b)

(Measurement experiment result 7)
FIG. 15 is a comparative characteristic diagram of values obtained by dividing the absolute value of black alumite with the absolute value of black anodized by the 4.0 μm sensor (12a) and the 4.3 μm sensor (12b) depending on the presence or absence of black anodized as a measurement experiment result. It is. Characteristics A to D are as follows:
A: Low output black anodized absolute value / black anodized absolute value characteristic of 4.0 μm sensor (12a) B; Hi output black anodized absolute value / black anodized value of 4.0 μm sensor (12a) Absolute value characteristics C: Low output black anodized absolute value / black anodized absolute value characteristic of 4.3 μm sensor (12b) D: High output black anodized of 4.3 μm sensor (12b) Characteristics of absolute value / black anodized absolute value

  ○ What is understood from FIG. 11 to FIG. 15... When the light source 8 is turned off, the output of each sensor varies greatly depending on the presence or absence of black anodized processing. There is a 40-60% reduction in absolute value output. Further, when the light source 8 is turned on, the output of each sensor is less changed than when the light source is turned off, and the output with black alumite is about 10 to 15% lower than that without.

(Measurement experiment result 8)
FIG. 16 is a characteristic diagram showing an output difference between a concentration of 0 ppm and a concentration of 1000 ppm in the 4.0 μm sensor (12a) as a measurement experiment result, and a horizontal axis: temperature. Characteristics A and B are as follows:
A: 0-1000 ppm output characteristics of 4.0 μm sensor (12a) without black anodized B: 0-1000 ppm output characteristics of 4.0 μm sensor with black anodized (12a)

(Measurement experiment result 9)
FIG. 17 is a characteristic diagram showing an output difference between a concentration of 0 ppm and a concentration of 1000 ppm in the 4.3 μm sensor (12B) as a measurement experiment result, and a horizontal axis: temperature. Characteristics A and B are as follows:
A: 0-1000 ppm output characteristics of 4.3 μm sensor (12b) without black anodized B: 0-1000 ppm output characteristics of 4.3 μm sensor with black anodized (12b)

(Measurement experiment result 10)
FIG. 18 shows the vertical axis as a measurement experiment result: the output difference between the concentration at 0 ppm and the concentration at 1000 ppm in the 4.3 μm sensor (12B) is the output difference at the concentration of 0 ppm and the concentration at 1000 ppm in the 4.0 μm sensor (12a). It is a characteristic figure which shows the ADC value of the value divided by the difference, and a horizontal axis: temperature. Characteristics A and B are as follows:
A: Ratio of 0-1000 ppm output difference of 4.3 / 4.0 with no black anodized B: Ratio of 0-1000 ppm output difference of 4.3 / 4.0 with black anodized ○ From FIG. 16 to FIG. The range ability of each sensor is about 12% larger with black anodized depending on the presence or absence of black anodized.

(Summary of findings from measurement experiment results)
a) Regardless of the presence or absence of the black alumite treatment, there is a change in the magnitude of the output, but there is no significant change in the curve characteristics, only a relative change.
b) The ratio of the output value for the 4.3 μm sensor (12b) and the output value for the 4.0 μm sensor (12a) is about 5 to 7% greater with and without black alumite than the ratio used for concentration conversion. The detection sensitivity is improved due to the increase in the.
c) In the absolute value output of each sensor, when the light source is turned off, it is about 40% smaller than when there is no black anodized, but when the light source is turned on, it is 10 to 15% when there is no black anodized. There is only a decrease in the degree.
d) Depending on the presence or absence of black alumite, the range ability of each sensor was increased by about 12% when black anodize was present, and it can be said that the resolution of the gas concentration was improved.

(Discussion)
The principle of detecting the CO2 concentration is that when infrared rays are passed through a medium layer (detection gas or the like), Beer-Lambert's law is applied to the infrared rays that have passed. When incident light I ₀ λ having a wavelength λ is incident on a medium layer having a thickness l (el), a gas concentration C, and an absorption coefficient αλ shown in FIG. 19, the transmittance of the incident light I ₀ λ and the transmitted light Iλ When the ratio Dλ is expressed in natural logarithm, the following formula (1) is established.
Dλ = log _n (I ₀ λ / Iλ) = log _n (4.0 μm sensor output / 4.3 μm sensor output) = αλ · Cl (1)

In the CO2 absorption spectrum of FIG. 4 described above, it can be seen that there is absorption around 4.3 μm. Therefore, by measuring the absorption spectrum of 4.3 μm, the gas concentration can be determined if the transmittances of the incident light I ₀ λ and the transmitted light Iλ are known in the above formula (1).

  A structural diagram of the infrared sensor used in the present invention is shown in FIG. The structure is such that one package has a median 4.0 μm band-pass filter having a certain half width (a transmission member 13a and a thermopile sensor (light receiving element 12a) paired with the filter, and a center having a certain half width). Value 4.3μm band pass filter (transmission member 13b) and thermopile sensor (light receiving element 12b) paired with the filter.4.0 μm band pass filter (transmission member 13a) absorbs infrared rays in the general atmosphere. The 4.3 μm band-pass filter (transmission member 13b) absorbs infrared rays by CO2 gas and heat changes in response to changes in gas concentration.

  When attention is paid only to one side of the filter having the structure shown in FIG. 3 (for example, the transmissive member 13a), FIG. The characteristic of the optical bandpass filter (transmission member 13a) in the figure shows the bandpass specification for the case where infrared light enters perpendicularly to the filter surface like A light. For infrared light other than vertical light, for example, infrared light having an angle with respect to the filter surface, such as B light, the thickness of the bandpass filter increases and the characteristics of the bandpass filter change.

  For example, as shown in FIG. 21A, the center wavelength A of the filter shifts to the shorter wavelength (A ′) or the longer wavelength (A ″), or as shown in FIG. In addition, there are several phenomena in which the bandpass filter characteristics change, such as a phenomenon in which the half-value width of the filter widens (D1 → D2).

  As a result, the characteristics of the 4.0 μm optical filter (transmission member 13a) change, and even a wavelength that is not required is detected, resulting in noise. Also, the characteristics of the 4.3 μm optical filter (transmission member 13b) are the same, and an unnecessary wavelength becomes noise and is output from the infrared sensor.

As a countermeasure against this, as shown in FIG. 2, a black alumite treatment that does not reflect infrared rays is performed on the inner surface of the through-hole 6 a that is a storage chamber of the sensor holder 6 to eliminate irregular reflection in the sensor holder 6. Thus, by making the inner surface of the sensor holder 6 not reflect infrared, the excess noise is eliminated, and the output ratio (sensor) of the 4.3 μm sensor (light receiving element 12b) and 4.0 μm sensor (light receiving element 12a) is eliminated. The ratio is an element used to calculate the CO2 concentration). The value of the following equation (2) is α: an output noise coefficient due to infrared light incident from other than perpendicular to the surface of the filter (transmission member 13a). , Β: If the output noise coefficient by infrared light incident from other than perpendicular to the surface of the filter (transmission member 13b) is used, the terms α and β are set to 1 by performing infrared non-reflection (black anodized treatment). Since it becomes close, the value of Formula (2) becomes large.
4.3 μm sensor (light receiving element 12b) output × β / 4.0 μm sensor (light receiving element 12a) output × α (2)
The value of this equation (2) is shown in FIG. 10 in the performance measurement experiment.

Moreover, the range ability between gas concentrations 0-5000 ppm is represented by following formula (3).
4.3 μm sensor (light receiving element 12b) output × β / 4.0 μm sensor (12a) output × α-4.3 μm sensor output (light receiving element 12b) × γ × β / 4.0 μm sensor output (light receiving element 12a) × α
= 4.3 sensor (light-receiving element 12b) output × (β−γ · β) /4.0 μm sensor (12a) output × α (3)
(However, 4.3 μm sensor (12b) output: sensor output at a gas concentration of 0 ppm, γ: sensor output attenuation at 5000 ppm when compared with a CO2 gas concentration of 0 ppm.)
The α and β terms in Equation (3) become close to 1 when the noise becomes small, and become Equation (4).
4.3 μm sensor (12b) output / 4.0 μm sensor (12a) output−4.3 μm sensor (12b) output × γ / 4.0 μm sensor (12a) output = 4.3 μm sensor (12a) output × (1− γ) /4.0 μm sensor (12a) output (4)
From equation (4), it can be seen that excess noise is eliminated and the range ability is widened. The value of this equation (4) is shown in FIG. 18 in the performance measurement experiment.

(result)
As a result of comparing non-reflective treatment (black alumite treatment) on the inner surface of the through-hole 6a which is the accommodation chamber of the sensor holder 6 with non-reflective treatment (solid aluminum), the following was found. It was.
a) Regarding the ratio between the output value of the 4.3 μm sensor (12b) and the output value of the 4.0 μm sensor (12a), the output (gain) was larger with the black anodized by about 5 to 7% than the state without the black anodized.
b) Depending on the presence or absence of black anodized, the range ability of each sensor increased with the span of about 12% when black anodized was present.

  Thus, it can be said that the infrared non-reflection process (black alumite process) reduces noise, improves the span, and improves the detection sensitivity and resolution.

  As described above, one embodiment of the present invention has been described. However, the present invention is not limited to this, and various modifications and applications are possible. Of course, such modifications and applications are included in the scope of the present invention as long as the configuration of the present invention is provided.

  For example, although the sensor holder 6 is made of aluminum in the above-described embodiment, it may be made of another metal or glass instead of aluminum. In this case, an appropriate black body process suitable for the material of the sensor holder 6 is performed. The black body treatment is performed, for example, by applying a general black body coating carbon black paint or the like. As a black body treatment paint, a black body paint or the like containing carbon black as a pigment and ceramic alumina as a binder is used. A black body paint may be used, or a method other than applying a black body paint may be used.

  Alternatively, the entire inner surface of the through-hole 6a, which is a storage chamber, may not be black anodized, but only the inner surface at a predetermined interval from the opening to the holding position of the infrared sensor 10 may be black anodized. Further, the black alumite treatment may be performed not only on the inner surface of the through-hole 6a but also on the entire sensor holder 6 including the inner surface and the outer surface. In this case, the treatment becomes easy.

  The diameter of the through hole 6a of the sensor holder is the same as the inner diameter of the gas cell 2 in the above-described embodiment, but may be larger than the inner diameter of the gas cell 2. Further, the accommodation chamber of the sensor holder 6 may be a hole with a bottom instead of the through hole 6a. In this case, the sensor holder 6 is inserted from the opening of the hole and held at the bottom.

  Further, in the above-described embodiment, the wavelength of infrared light transmitted through the transmission members 13a and 13b when the concentration of the gas to be measured is low is shown. However, in the present invention, the gas to be measured is changed from low concentration to high concentration. When the concentration is within the range of 0 ppm to several percent, the length of the gas cell 2 is changed, or only the infrared rays having wavelengths with which the transmitting members 13a and 13b absorb less infrared rays in the gas to be measured. It may be made transparent.

  Furthermore, in the above-described embodiment, the gas concentration measuring device 20 measures the concentration of carbon dioxide. However, the gas concentration measuring device 20 of the present invention can measure carbon monoxide, water vapor, NOx, SOx, H2S, O3, CH4. The concentration of various gases such as NO can also be measured. Moreover, in this invention, the gas cell 2 may be formed in various cylinder shapes other than cylindrical shape.

  In the above-described embodiment, the thermoelectric infrared sensor is provided as the infrared sensor. However, the present invention is not limited to this. For example, the well-known quantum infrared using the photoconductive effect as the infrared sensor. Other types of infrared sensors such as sensors may be used. Even in such a quantum infrared sensor, measurement errors and the like can be eliminated by quickly adjusting itself to the ambient temperature by the heat control member. This type of quantum infrared sensor is suitable for measurement at room temperature, uses PbSe as the material for the photoconductive element, and is suitable for measurement at a low temperature, and uses PbS as the material for the photoconductive element. There are things used.

1 Gas Sample Chamber 2 Gas Cell 6 Sensor Holder 6a Through Hole (Housing Chamber)
8 Light source 10 Infrared sensor 23 μcom (concentration calculator)

Claims (3)

A gas cell having an inner peripheral surface that is formed in a cylindrical shape and not subjected to irregular reflection prevention treatment, and is filled with a gas to be measured;
A light source arranged at one end of the gas cell to emit infrared rays;
A sensor holder having a storage chamber disposed at the other end of the gas cell and having an opening in contact with the other end of the gas cell;
An infrared sensor that is housed in the housing chamber of the sensor holder at a depth spaced from the opening and detects the infrared light that is guided from the light source through the interior of the gas cell;
With
A gas sample chamber, wherein a black body treatment is applied to an inner surface of the storage chamber of the sensor holder. The gas sample chamber of claim 1,
The sensor holder is made of aluminum,
A gas sample chamber, wherein the inner surface of the storage chamber is subjected to black alumite treatment. A gas sample chamber according to claim 1 or 2,
A concentration calculator that calculates the concentration of the gas to be measured in the gas cell based on the intensity of the infrared rays detected by the infrared sensor;
A gas concentration measuring device comprising:

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