JP7571482B2 - Infrared gas analyzer and calibration method thereof - Google Patents

Description

The present invention relates to an infrared gas analyzer and a calibration method thereof.

An infrared gas analyzer measures the concentration of a target component contained in a sample gas. For example, an infrared gas analyzer uses a gas that does not contain the target component as a reference gas (which may also be called a comparison gas). An infrared gas analyzer measures the concentration of the target component in the sample gas by detecting the difference in the amount of infrared absorption between the reference gas and the sample gas.

Examples of sample gases to be measured include exhaust gases from combustion facilities such as power plants and incinerators. Such sample gases contain impurities (pollutants), which accumulate in the measurement cell through which the sample gas flows. As a result, a phenomenon known as zero point drift may occur, in which the zero point, which serves as the measurement standard, shifts depending on the amount of accumulated impurities. Conventionally, in order to prevent zero point drift due to contamination of the measurement cell, a drift cancellation method has been proposed that cancels out zero point drift by measuring while alternately switching between a reference gas and a sample gas at a fixed interval (see, for example, Patent Document 1).

Japanese Utility Model Publication No. 57-11251

In some infrared gas analyzers, dry nitrogen is used as the reference gas. However, in this case, the dry nitrogen must be prepared in advance in a cylinder or the like, which increases the running costs. Therefore, in practice, instead of dry nitrogen, air is often sucked in with a pump and dehumidified in a dehumidifier to be used as the reference gas (dry air).

However, even dry air cannot completely remove moisture from the atmosphere. For this reason, when dry air is used as a reference gas, the remaining moisture in the gas will absorb a small amount of infrared light, causing an error that will affect the measurement results.

The present invention has been made in consideration of these points, and one of its objectives is to provide an infrared gas analyzer and a calibration method thereof that can perform highly accurate measurements at low running costs.

An infrared gas analyzer according to one aspect of the present invention is an infrared gas analyzer that measures the concentration of a target component in a sample gas based on the difference between the amount of infrared absorption of a sample gas containing the target component and the amount of infrared absorption of a reference gas, and the infrared gas analyzer includes a measurement cell through which the sample gas and the reference gas flow alternately during measurement, a detector that detects the amount of infrared absorption of the sample gas and the reference gas irradiated with infrared light in the measurement cell, respectively, and a control unit that calculates the concentration of the target component in the sample gas based on the output of the detector, wherein the reference gas includes a first reference gas and a second reference gas that do not contain the target component , the first reference gas is a dehumidified gas containing residual moisture, and the second reference gas is a gas that does not contain moisture, and during the measurement, the first reference gas and the sample gas are alternately circulated as the reference gas within the measurement cell, and the measurement The measurement apparatus further includes a first solenoid valve that switches the flow of the sample gas through a constant cell, a second solenoid valve that switches the flow of the first reference gas through the measurement cell, and a third solenoid valve that switches the flow of the second reference gas through the measurement cell, and the control unit switches the first solenoid valve, the second solenoid valve, and the third solenoid valve , and performs zero calibration based on a difference between a first infrared absorption amount detected by flowing the first reference gas as the reference gas through the measurement cell and a second infrared absorption amount detected by flowing a gas not containing the component to be measured as the sample gas through the measurement cell, and a difference between a third infrared absorption amount detected by flowing the second reference gas as the reference gas through the measurement cell and a fourth infrared absorption amount detected by flowing the gas not containing the component to be measured as the sample gas through the measurement cell .

A method for calibrating an infrared gas analyzer according to one aspect of the present invention is a method for calibrating an infrared gas analyzer that measures the concentration of a component to be measured in a sample gas based on the difference between the infrared absorption amount of the sample gas containing the component to be measured and the infrared absorption amount of a reference gas, the method including: at the time of measurement, the sample gas and the reference gas are alternately circulated through a measurement cell; the reference gas includes a first reference gas not containing the component to be measured and a second reference gas; the first reference gas is a dehumidified gas containing residual moisture, and the second reference gas is a gas not containing moisture; and at the time of measurement, the first reference gas is used as the reference gas. The first reference gas and the sample gas are alternately circulated through the measurement cell, and a control unit of the infrared gas analyzer performs zero calibration based on the difference between a first infrared absorption amount detected by circulating the first reference gas as the reference gas through the measurement cell and a second infrared absorption amount detected by circulating a gas not containing the component to be measured as the sample gas through the measurement cell, and the difference between a third infrared absorption amount detected by circulating the second reference gas as the reference gas through the measurement cell and a fourth infrared absorption amount detected by circulating the gas not containing the component to be measured as the sample gas through the measurement cell .

The present invention makes it possible to perform highly accurate measurements at low running costs.

1 is an overall configuration diagram of an infrared gas analyzer according to an embodiment of the present invention; 1 is a time chart showing a zero calibration method according to a conventional example. 4 is a time chart showing an example of a zero calibration method according to the present embodiment. 4 is a time chart showing an example of a span calibration method according to the present embodiment. 4 is an explanatory diagram of the operation of the infrared gas analyzer according to the present embodiment. FIG. 4 is an explanatory diagram of the operation of the infrared gas analyzer according to the present embodiment. FIG.

The following describes an infrared gas analyzer to which the present invention can be applied. Figure 1 is a diagram showing the overall configuration of an infrared gas analyzer according to this embodiment. Note that the infrared gas analyzer shown below is merely an example, and is not limited to this example and can be modified as appropriate. Note that this embodiment naturally includes the basic components that an infrared gas analyzer normally includes, and explanations will be omitted as appropriate.

As shown in FIG. 1, the infrared gas analyzer 100 according to the present embodiment measures the concentration of the component to be measured in the sample gas by irradiating infrared rays to the sample gas containing the component to be measured and detecting the amount of absorption of the infrared rays. The infrared gas analyzer 100 is broadly divided into three parts according to their roles: an optical system, a gas supply system, and a control system. Specifically, the optical system includes a measurement cell 10, a light source 11, a chopper 12, a motor 13, and a detector 14. The gas supply system includes a sample gas supply source, two reference gas supply sources described later, and a gas switching mechanism (multiple solenoid valves described later) that switches the gas introduced from each gas supply source to the measurement cell. The gas supply system will be described in detail later. The control system includes an A/D conversion unit 20, a control unit 21, and a semiconductor relay 22.

The measurement cell 10 is formed as a cylinder having a gas inlet 15 at one end and a gas outlet 16 at the other end. A predetermined gas (such as a sample gas or a reference gas, which will be described later) flows through the measurement cell 10. An infrared light source 11, a chopper 12, and a motor 13 are provided at one end of the measurement cell 10. A detector 14 is provided at the other end of the measurement cell 10.

The light source 11 irradiates infrared light of a predetermined wavelength from one end to the other end within the measurement cell 10. The chopper 12 is provided between the measurement cell 10 and the light source 11, and is rotated by the motor 13. The chopper 12 intermittently blocks the optical path between the light source 11 and the detector 14. In other words, the chopper 12 is rotated by the motor 13, thereby intermittently controlling the incidence of infrared light on the measurement cell 10 at a constant cycle. The drive of the motor 13 is controlled by the control unit 21.

The detector 14 detects the infrared intensity in the same wavelength range as the infrared absorption wavelength absorbed by the component to be measured in the gas. The detector 14 detects the change in the amount of infrared absorption according to the concentration of the component to be measured in the gas in the measurement cell 10 (hereinafter, sometimes simply referred to as the gas concentration), and outputs an electrical signal according to the change.

The A/D conversion unit 20 converts the electrical signal from an analog signal to a digital signal. An amplifier (not shown) that amplifies the electrical signal from the detector 14 may be provided between the detector 14 and the A/D conversion unit 20. The digital signal converted by the A/D conversion unit 20 is input to the control unit 21.

The control unit 21 controls the specified components within the device and is composed of hardware such as a microprocessor and memory that execute various processes, and software that is read from the memory and executed by the microprocessor. The memory is composed of one or more storage media such as ROM (Read Only Memory) and RAM (Random Access Memory) depending on the application.

For example, the control unit 21 calculates the gas concentration based on the digital signal input from the A/D conversion unit 20 described above. The control unit 21 also controls the driving of the motor 13. Furthermore, the control unit 21 performs opening and closing control of the multiple solenoid valves 40 that constitute the gas switching mechanism via the semiconductor relay 22. The semiconductor relay 22 relays the opening and closing signals of each solenoid valve from the control unit 21 to each solenoid valve. Also, as will be described in detail later, various calculation processes are performed based on the electrical signal corresponding to the specified gas during measurement, zero calibration, or span calibration.

Next, the gas supply system will be described. In FIG. 1, one sample gas and two reference gases (a first reference gas and a second reference gas) are shown as gases circulating in the measurement cell 10. Although the source of each gas is not specifically shown, each gas is configured to be able to circulate in the measurement cell 10 via a predetermined gas passage and solenoid valve. Note that the gases circulating in the measurement cell 10 are not limited to these, and can be changed as appropriate. For example, a supply system for dry span gas (not shown) for span calibration, which will be described later, may be provided. In this case, it is preferable to provide a solenoid valve for each type of gas.

The sample gas is a gas that contains a component to be measured that can be detected by the detector 14, and absorbs infrared rays according to the concentration of the component to be measured in the gas. The sample gas is, for example, exhaust gas from a combustion facility such as a power plant or an incinerator. In this embodiment, the reference gas is composed of a first reference gas and a second reference gas. Basically, a gas that does not absorb infrared rays is used as the reference gas.

Specifically, the first reference gas is dehumidified air (hereinafter referred to as dry air) cooled to a predetermined temperature (for example, 2°C to 5°C). Dry air contains a small amount of moisture. The second reference gas is dry nitrogen (hereinafter referred to as dry nitrogen) that does not contain the measurement target component that absorbs infrared rays. Dry nitrogen does not contain moisture. Note that in this embodiment, a case will be described in which dry air is used as the first reference gas and dry nitrogen is used as the second reference gas, but this configuration is not limiting. The types of the first and second reference gases can be changed as appropriate. Details of these gases will be described later.

The flow paths of each gas will now be described. As shown in FIG. 1, the sample gas can flow from the sample gas flow path 30 to the measurement cell 10 via the solenoid valve 40 (first solenoid valve) and the introduction gas flow path 31. The first reference gas can flow from the reference gas flow path 32 to the measurement cell 10 via the solenoid valve 41 (second solenoid valve) and the introduction gas flow path 33. The second reference gas can flow from the reference gas flow path 34 to the measurement cell 10 via the solenoid valve 42 (third solenoid valve) and the introduction gas flow path 35.

The three solenoid valves 40-42 described above can be configured, for example, as three-way solenoid valves. The three-way solenoid valves are configured with a common inlet port (Common: com), a normally closed outlet port (Normally Close: NC), and a normally open outlet port (Normally Open: NO). The switching between NC and NO is controlled by the control unit 21 described above.

The downstream end of the sample gas flow path 30 is connected to the common inlet port of the solenoid valve 40. The upstream end of the introduction gas flow path 31 is connected to the normally open outlet port of the solenoid valve 40. The downstream end of the introduction gas flow path 31 is connected to the inlet 15 of the measurement cell 10. The upstream end of the exhaust gas flow path 36 is connected to the outlet 16 of the measurement cell 10. The downstream end of the exhaust gas flow path 36 is open to the outside. The upstream end of the exhaust gas flow path 37 is connected to the normally closed inlet port of the solenoid valve 40. The sample gas flows into the measurement cell 10 or is exhausted to the outside depending on the open/closed state of the solenoid valve 40.

The downstream end of the reference gas flow path 32 is connected to the common inlet port of the solenoid valve 41. The upstream end of the introduction gas flow path 33 is connected to the normally closed outlet port of the solenoid valve 41. The downstream end of the introduction gas flow path 33 is connected to the middle of the introduction gas flow path 31. The upstream end of the exhaust gas flow path 38 is connected to the normally open inlet port of the solenoid valve 41. The downstream end of the exhaust gas flow path 38 is open to the outside. The downstream end of the exhaust gas flow path 37 is connected to the middle of the exhaust gas flow path 38. The first reference gas is circulated to the measurement cell 10 or discharged to the outside depending on the open/close state of the solenoid valve 41.

The downstream end of the reference gas flow path 34 is connected to the common inlet port of the solenoid valve 42. The upstream end of the introduction gas flow path 35 is connected to the normally closed outlet port of the solenoid valve 42. The downstream end of the introduction gas flow path 35 is connected to the middle of the introduction gas flow path 31. The upstream end of the exhaust gas flow path 39 is connected to the normally open inlet port of the solenoid valve 42. The downstream end of the exhaust gas flow path 39 is open to the outside. The second reference gas is circulated to the measurement cell 10 or exhausted to the outside depending on the open/close state of the solenoid valve 42.

In the infrared gas analyzer 100 configured in this manner, when a specific gas flows through the measurement cell 10, the gas is irradiated with infrared light to detect its absorption amount. For example, when measuring a sample gas, as shown in FIG. 1, the normally open outlet port of the solenoid valve 40 is opened, and the sample gas flows from the inlet 15 through the sample gas flow path 30 and the inlet gas flow path 31 into the measurement cell 10.

In the measurement cell 10, the infrared light emitted from the light source 11 is chopped by the chopper 12 and reflected from the inner surface of the measurement cell 10 as it enters the detector 14. At that time, the amount of infrared light absorbed in the measurement cell 10 changes depending on the concentration of the component to be measured present in the measurement cell 10. The detector 14 detects the change in the amount of infrared light absorbed and outputs it as a predetermined electrical signal (which may be called a concentration signal). The sample gas is then discharged to the outside from the exhaust port 16 through the exhaust gas flow path 36.

As mentioned above, the sample gas to be measured includes exhaust gas from combustion facilities such as power plants and incinerators. Such exhaust gas contains impurities, and so there is a risk that impurities will accumulate in the measurement cell 10 if measurements are repeated. As a result, a phenomenon known as zero point drift may occur, in which the zero point, which serves as the measurement standard, shifts depending on the amount of accumulated impurities.

Therefore, in this embodiment, including the conventional method, the sample gas and the reference gas are alternately passed through the measurement cell 10 at predetermined time intervals, and the components to be measured in the sample gas are calculated from the difference in the infrared absorption of the two gases, thereby performing the measurement. By alternately passing the sample gas and the reference gas through the measurement cell 10 multiple times, it is possible to alternately obtain a zero point signal due to the reference gas and a sample gas measurement signal due to the sample gas. Therefore, by performing a calculation process to subtract the zero point signal from the sample gas measurement signal, it is possible to obtain a concentration signal that is not affected by the zero point drift as described above. This type of measurement method is called, for example, a drift cancellation method.

Even in an infrared gas analyzer 100 that employs such a method, zero calibration and span calibration, which serve as the measurement reference, are periodically performed prior to measuring the sample gas. Zero calibration refers to determining the zero point, which is the lower limit of the measurement range, and span calibration refers to determining the span point, which is the reference point of a predetermined measurement range, using a gas for span calibration.

When performing calibration, dry nitrogen is often used as the reference gas or sample gas. For example, when dry nitrogen is used as the reference gas during zero calibration, dry nitrogen is also used as the sample gas. Since dry nitrogen does not contain any components to be measured, the levels of the electrical signals of the sample gas and reference gas are equal, and the difference between the two electrical signals is zero. This allows for proper zero calibration. Also, during span calibration, dry nitrogen is used as the reference gas, and a dry span gas that shows a predetermined concentration signal is used as the sample gas.

However, when using dry nitrogen as the reference gas, a special cylinder must be prepared, which tends to increase the running costs of the device. For this reason, dehumidified air (dry air) is often used as the reference gas. Dry air is dehumidified by drawing in the air with a pump and cooling it to about 2 degrees using an electronic cooler or similar device.

However, even when using dry air, it is not possible to completely remove moisture from the air, and a small amount of moisture remains mixed in the dry air. In this case, the moisture remaining in the dry air absorbs infrared rays. As a result, the detection signal levels of the sample gas and reference gas during zero calibration differ, and the difference between the two electrical signals does not become zero, resulting in an error.

Now, referring to Figure 2, we will explain the zero calibration method when dry air is used as the reference gas. Figure 2 is a time chart showing a conventional zero calibration method. The horizontal axis of Figure 2 indicates time, and the vertical axis indicates the magnitude (level) of the electrical signal.

As shown in Figure 2, measurements are performed by alternating between the reference gas and the sample gas at regular intervals. In this case, dry air is used as the reference gas, and dry nitrogen is used as the sample gas. As mentioned above, dry air contains residual moisture, so the amount of infrared light absorbed by the residual moisture is output as an electrical signal. On the other hand, dry nitrogen does not contain any components to be measured, so the level of the electrical signal is zero. If the level difference between the two electrical signals is ΔS, zero calibration is performed based on the level of this dry air. Furthermore, if span calibration is performed under these conditions, the level of the span signal will be a value that includes the above-mentioned error.

In this way, there is a trade-off between running costs and measurement accuracy when it comes to infrared gas analyzers.

The inventors of the present invention have therefore come up with the idea of achieving both low running costs and high measurement accuracy. In this embodiment, two types of gas (dry air and dry nitrogen) are prepared as reference gases, and a third solenoid valve 42 is provided that can selectively circulate dry air or dry nitrogen through the measurement cell 10. During zero calibration, the difference between the electrical signal based on dry air and the electrical signal based on dry nitrogen is calculated, thereby eliminating the calibration error that occurs when dry air is used as the reference gas. During span calibration, the error in the zero calibration using dry air is corrected, making it possible to perform a calibration equivalent to that performed when span calibration is performed using dry nitrogen.

Now, referring to Figures 3 to 6, a method for configuring an infrared gas analyzer according to this embodiment will be described. Figure 3 is a time chart showing an example of a zero calibration method according to this embodiment. Figure 4 is a time chart showing an example of a span calibration method according to this embodiment. The horizontal axis of Figures 3 and 4 indicates time, and the vertical axis indicates the magnitude (level) of the electrical signal. Figures 5 and 6 are diagrams explaining the operation of the infrared gas analyzer according to this embodiment. In the following description, the main entity that controls the opening and closing of each solenoid valve and the main entity that performs the calculation processing for various calibrations is the control unit 21.

As shown in FIG. 3, during zero calibration, dry air is first used as the first reference gas, and the first reference gas is circulated inside the measurement cell 10. Specifically, as shown in FIG. 5, the normally closed outflow port of the solenoid valve 41 is opened, and the first reference gas is circulated from the inlet 15 into the measurement cell 10 through the reference gas flow path 32 and the introduced gas flow path 33. The first reference gas is then exhausted to the outside from the exhaust port 16 through the exhaust gas flow path 36. The level of the electrical signal at this time is Srz1.

After a predetermined time has elapsed, the solenoid valves are switched, dry nitrogen is used as the sample gas, and the sample gas is circulated through the measurement cell 10. The flow of the sample gas is the same as in FIG. 1, so a description thereof is omitted. The level of the electrical signal at this time is Ssz1. The control unit 21 calculates Ssz1-Srz1=Sz1 as the zero point signal level based on the first reference gas.

After a further predetermined time has elapsed, the solenoid valves are switched, and then dry nitrogen is used as the second reference gas, and the second reference gas is circulated within the measurement cell 10. Specifically, as shown in FIG. 6, the normally closed outflow port of the solenoid valve 42 is opened, and the second reference gas is circulated from the inlet 15 through the reference gas flow path 34 and the introduced gas flow path 35 into the measurement cell 10. The second reference gas is then exhausted to the outside through the exhaust gas flow path 36 from the exhaust port 16. The level of the electrical signal at this time is Srz2.

After a predetermined time has elapsed, each solenoid valve is switched, dry nitrogen is used as the sample gas, and the sample gas is circulated through the measurement cell 10. The flow of the sample gas is the same as in FIG. 1, so a description is omitted. The level of the electrical signal at this time is Ssz2. The control unit 21 calculates Ssz2-Srz2=Sz2 as the zero point signal level based on the second reference gas. In this way, since the level based on zero calibration using the first reference gas and the level based on zero calibration using the second reference gas are different, the control unit 21 calculates and stores the difference, Sz1-Sz2=Sz3. This Sz3 may be called a correction value.

In this way, by calculating the difference Sz3 between Sz1 and Sz2 calculated using two types of reference gas, it is possible to eliminate the calibration error that occurs when dry air is used as the reference gas. Note that the zero calibration can be performed by repeating the above procedure multiple times and taking the average.

When performing span calibration, as shown in FIG. 4, dry air is first used as the first reference gas, and the first reference gas is circulated through the measurement cell 10. The flow of the first reference gas is the same as that shown in FIG. 5, so a description thereof will be omitted. The level of the electrical signal at this time is designated as Srs1.

After a predetermined time has passed, the solenoid valves are switched, and the dry span gas is used as the sample gas, and the sample gas is circulated through the measurement cell 10. The flow of the sample gas is the same as in FIG. 1, so the description is omitted. The level of the electrical signal at this time is Sss1. The control unit 21 calculates Sss1-Srs1=Ss1 as the span point signal level by the first reference gas. Furthermore, the control unit 21 calculates Ss1-Sz3 as the span signal level using the zero calibration correction value Sz3 calculated in the previous zero calibration. In this case, both Ss1 and Sz3 contain the error amount when dry air is used. Therefore, the difference Ss1-Sz3 is offset by the error amount, and it is possible to perform a calibration equivalent to the calibration when dry nitrogen is used as described above. The span calibration may be performed by repeating the above procedure multiple times and taking the average.

In this way, according to this embodiment, by alternately switching between the first and second reference gases (dry air and dry nitrogen) as the reference gas during zero calibration, it is possible to correct the error when dry air is used as the reference gas by taking into account the difference between the two. In addition, by using this difference (correction value) during span calibration, it is possible to perform appropriate calibration without worrying about the error of dry air. Note that expensive dry nitrogen is only used for a part of the zero calibration, and it is possible to use dry air, which is the first reference gas, as the reference gas during span calibration and normal measurement. Therefore, it is possible to realize an infrared gas analyzer 100 that balances running costs and measurement accuracy.

Furthermore, the present embodiment is not limited to the above-mentioned embodiment and modifications, and may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way due to technological advances or derived other technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea.

The features of the above embodiment are summarized below.
The infrared gas analyzer according to the above embodiment is an infrared gas analyzer that measures the concentration of a target component in a sample gas based on the difference between the infrared absorption amount of a sample gas containing the target component and the infrared absorption amount of a reference gas, and includes a measurement cell through which the sample gas and the reference gas flow alternately during measurement, a detector that detects the infrared absorption amounts of the sample gas and the reference gas irradiated with infrared light in the measurement cell, respectively, and a control unit that calculates the concentration of the sample gas based on the output of the detector, wherein the reference gas is composed of a first reference gas and a second reference gas that do not contain the target component, and further includes a first solenoid valve that switches the flow of the sample gas to the measurement cell, a second solenoid valve that switches the flow of the first reference gas to the measurement cell, and a third solenoid valve that switches the flow of the second reference gas to the measurement cell, and the control unit performs zero-point calibration by switching the second solenoid valve and the third solenoid valve.

In the infrared gas analyzer according to the above embodiment, the first reference gas is dry air, and the second reference gas is dry nitrogen.

In addition, in the infrared gas analyzer according to the above embodiment, the control unit calculates the difference between the electrical signal based on the first reference gas and the electrical signal based on the second reference gas during zero calibration.

In addition, in the infrared gas analyzer according to the above embodiment, the control unit switches the first solenoid valve and the second solenoid valve, and measures the sample gas using the first reference gas.

In addition, in the infrared gas analyzer according to the above embodiment, the control unit performs span calibration based on the difference calculated during the zero calibration.

The calibration method for the infrared gas analyzer according to the above embodiment is a calibration method for an infrared gas analyzer that measures the concentration of a component to be measured in a sample gas based on the difference between the amount of infrared absorption of the sample gas containing the component to be measured and the amount of infrared absorption of a reference gas, in which the sample gas and the reference gas are alternately circulated through a measurement cell during measurement, and the reference gas is composed of a first reference gas that does not contain the component to be measured and a second reference gas, and in zero calibration, the first reference gas and the reference gas are switched to correct the error.

As described above, the present invention has the effect of enabling highly accurate measurements at low running costs, and is particularly useful for infrared gas analyzers and methods for constructing the same.

Reference Signs List 100 Infrared gas analyzer 10 Measurement cell 11 Light source 12 Chopper 13 Motor 14 Detector 15 Inlet 16 Outlet 20 A/D converter 21 Control unit 22 Semiconductor relay 30 Sample gas flow path 31 Inlet gas flow path 32 Reference gas flow path 33 Inlet gas flow path 34 Reference gas flow path 35 Inlet gas flow path 36 Exhaust gas flow path 37 Exhaust gas flow path 38 Exhaust gas flow path 39 Exhaust gas flow path 40 Solenoid valve (first solenoid valve)
41 Solenoid valve (second solenoid valve)
42 Solenoid valve (third solenoid valve)

Claims (6)

An infrared gas analyzer for measuring a concentration of a target component in a sample gas based on a difference between an amount of infrared absorption of the sample gas containing the target component and an amount of infrared absorption of a reference gas, comprising:
a measurement cell through which the sample gas and the reference gas are alternately passed during measurement;
a detector for detecting the amount of infrared absorption of the sample gas and the reference gas irradiated with infrared rays in the measurement cell;
a control unit that calculates a concentration of a measurement target component in the sample gas based on an output of the detector,
The reference gas includes a first reference gas and a second reference gas that do not contain the component to be measured,
the first reference gas is a dehumidified gas containing residual moisture,
the second reference gas is a gas that does not contain moisture;
During the measurement, the first reference gas is alternately circulated as the reference gas and the sample gas through the measurement cell;
a first solenoid valve that switches the flow of the sample gas to the measurement cell;
a second solenoid valve for switching the flow of the first reference gas to the measurement cell;
a third solenoid valve that switches the flow of the second reference gas to the measurement cell;
The control unit switches the first solenoid valve, the second solenoid valve, and the third solenoid valve ,
a difference between a first infrared absorption amount detected by passing the first reference gas through the measurement cell as the reference gas and a second infrared absorption amount detected by passing a gas not containing the component to be measured through the measurement cell as the sample gas;
an infrared gas analyzer that performs zero calibration based on a difference between a third infrared absorption amount detected by flowing the second reference gas through the measurement cell as the reference gas and a fourth infrared absorption amount detected by flowing the gas not containing the component to be measured through the measurement cell as the sample gas . The infrared gas analyzer of claim 1, wherein the first reference gas is dry air and the second reference gas is dry nitrogen. the detector outputs an electrical signal corresponding to a change in the amount of infrared absorption of the sample gas and the reference gas;
3. The infrared gas analyzer according to claim 1, wherein the control unit calculates, during the zero calibration, a difference between an electrical signal corresponding to a difference between the first infrared absorption amount and the second infrared absorption amount and an electrical signal corresponding to a difference between the third infrared absorption amount and the fourth infrared absorption amount . 4. The infrared gas analyzer according to claim 3, wherein the control unit switches the first solenoid valve and the second solenoid valve after the zero calibration , and measures the concentration of the measurement target component in the sample gas using the first reference gas as the reference gas . The infrared gas analyzer according to claim 3 or claim 4, wherein the control unit performs span calibration based on the difference calculated during the zero calibration. 1. A method for calibrating an infrared gas analyzer that measures the concentration of a component to be measured in a sample gas based on a difference between an amount of infrared absorption of the sample gas containing the component to be measured and an amount of infrared absorption of a reference gas, comprising:
During measurement, the sample gas and the reference gas are alternately passed through a measurement cell,
The reference gas includes a first reference gas and a second reference gas that do not contain the component to be measured,
the first reference gas is a dehumidified gas containing residual moisture,
the second reference gas is a gas that does not contain moisture;
During the measurement, the first reference gas is alternately circulated as the reference gas and the sample gas through the measurement cell;
A control unit of the infrared gas analyzer
a difference between a first infrared absorption amount detected by passing the first reference gas through the measurement cell as the reference gas and a second infrared absorption amount detected by passing a gas not containing the component to be measured through the measurement cell as the sample gas;
Zero calibration is performed based on the difference between a third infrared absorption amount detected by passing the second reference gas through the measurement cell as the reference gas and a fourth infrared absorption amount detected by passing the gas not containing the component to be measured through the measurement cell as the sample gas.
How to calibrate an infrared gas analyzer.

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