JP2017058221A - Gas analyzing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas analyzing device capable of measuring information on a specific gas amount in a gas to be measured whose pressure varies greatly.SOLUTION: The present invention relates to a gas analyzing device 1 comprising: an arithmetic part 41g which calculates specific gas amount information in an n-th cycle; a gas pressure variation amount calculation part 41d which calculates a gas pressure variation amount ΔP(t) in each time t; and a correction signal generation part 41f which generates time variation i(t) in corrected light intensity at each wavelength ν by performing fitting processing using time variation I(t) in a long time section in a time zone in which the gas pressure variation amount ΔP(t) is small, and performing fitting processing using time variation I(t) in a short time section in a time zone in which the gas pressure variation amount ΔP(t) is large. The arithmetic part 41g generates light intensity variation i(ν) of measurement light within a predetermined wavelength range ν-νin the n-th cycle using time variation i(t) in corrected light intensity at each wavelength ν, and thus calculates specific gas amount information in the n-th cycle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas analyzer that measures specific gas amount information (density / partial pressure / concentration) in a gas to be measured using laser absorption spectroscopy, and more particularly, in a vacuum region or in a heat treatment furnace in a semiconductor manufacturing apparatus. The present invention relates to a gas analyzer that measures specific gas amount information such as in a flue, in a combustion process, in a measurement target gas (intake and exhaust) of an internal combustion engine (engine), in a flow path of a fuel cell, and a global warming gas.

  As one of the methods for measuring the oxygen concentration in the measurement target gas, absorption spectroscopy using the fact that oxygen molecules absorb only light in a specific wavelength region (for example, 761 nm) is known. This absorption spectroscopy allows non-contact measurement to the measurement target gas, so it can not only measure the oxygen concentration in the measurement target gas without disturbing the measurement target gas field, but also has an extremely short response. It can be measured in time.

  Among such absorption spectroscopy, in particular, “tunable wavelength semiconductor laser absorption spectroscopy” using a tunable semiconductor laser (laser element) as a light source can be realized with a simple apparatus configuration. For example, in a gas analyzer using “wavelength tunable semiconductor laser absorption spectroscopy”, an incident optical window and an output optical window formed in a pipe are connected to a pipe in which a measurement target gas flows in a predetermined direction. In general, it is common to add a wavelength tunable semiconductor laser and a light detection sensor (light receiving unit) provided to face each other so that an optical path (optical distance) 1 is formed across the pipe (for example, Patent Document 1).

According to such a gas analyzer, laser light (measurement light) having a predetermined wavelength ν oscillated from a wavelength tunable semiconductor laser is shielded by oxygen molecules present in the measurement target gas in the process of passing through the pipe. Utilizing the fact that the amount of light incident on the light detection sensor is reduced corresponding to the concentration of oxygen molecules in the measurement target gas, the progress of the laser light is obstructed, and the amount of laser light emitted from the wavelength tunable semiconductor laser is reduced. The concentration of oxygen molecules is calculated by measuring the light amount I of the laser light incident on the light detection sensor. FIG. 4 is a graph showing an example of an absorption spectrum obtained by the gas analyzer described above. The vertical axis represents the received light intensity I, and the horizontal axis represents the wavelength ν. Note that I ₀ (ν) (reference line) is a light receiving intensity when oxygen molecules are not absorbed at the wavelength ν, and is derived by creating an approximate expression based on the light receiving intensity I of the non-absorbing wavelength. .

  And from the Lambert-Beer law, the following formula (1) is established.

Here, I ₀ (ν) is the light intensity when oxygen molecules are not absorbed at the wavelength ν, I (ν) is the transmitted light intensity at the wavelength ν, c (mol / cm ³ ) is the number density of oxygen molecules, l (cm) is the length (optical distance) of the optical path passing through the measurement target gas, S (T) (cm ⁻¹ / (mol / cm ⁻² )) is a function of temperature T at a predetermined absorption line intensity, K (Ν) is an absorption profile function.

Here, FIG. 5 is a schematic configuration diagram showing an example of a gas analyzer using wavelength tunable semiconductor laser absorption spectroscopy. One direction horizontal to the ground is defined as an X direction, a direction horizontal to the ground and perpendicular to the X direction is defined as a Y direction, and a direction perpendicular to the X direction and the Y direction is defined as a Z direction.
The gas analyzer 101 includes a light source unit 10, a light receiving unit 20, a gas temperature sensor (not shown) that measures a temperature T, and a control unit 140 that includes a microcomputer and a PC.

The gas analyzer 101 shall be used to measure the oxygen concentration c _n of the measurement object gas flowing through the sample channel 70 connected to each line of the supply and exhaust of the fuel cell system. The sample channel 70 extends in the Z direction, and on the side wall of the sample channel 70, a lens 35 serving as an incident optical window, and an exiting beam disposed opposite to the lens 35 with a distance 1 in the −X direction. A lens 36 serving as an optical window is formed. The measurement target gas flows in the Z direction in the sample flow path 70.

  The light source unit 10 includes a semiconductor laser (for example, a distributed feedback (DFB) semiconductor laser diode for optical communication) 11, a lens 13, and a D / A converter 12. The laser light from the semiconductor laser 11 enters the sample channel 70 in the −X direction from the lens 35 via the optical fiber 33 and the lens 13, and exists in the sample channel 70. The gas to be measured is irradiated.

Further, such a light source unit 10 changes the drive current value applied to the semiconductor laser 11 at a predetermined period n, and more specifically, by applying a drive current value having a sawtooth shape, a predetermined wavelength range. (Sweep Width) Laser light of ν _{1 to} ν ₂ is oscillated from the semiconductor laser 11 with a predetermined period n. FIG. 6 is a conceptual diagram showing the relationship between the drive current value and the oscillation wavelength ν of the laser beam, and FIG. 6A is a waveform diagram of the drive current value applied to the semiconductor laser 11, and FIG. ) Is a waveform diagram of the oscillation wavelength ν of the laser light oscillated from the semiconductor laser 11 to which the drive current value is applied.

  The light receiving unit 20 may be any unit that can convert the light intensity I into an electric signal. For example, a photodiode 21 is used. The photodiode 21 is arranged so as to receive the laser light emitted from the lens 36 to the outside of the sample flow path 70 in the −X direction via the optical fiber 34 and the lens 23, and passes through the measurement target gas. The laser beam intensity I is received.

By the way, it is known that laser light having multiple reflections by the lenses 35 and 36 and the like having different optical distances 1 is received by the photodiode 21 and causes interference noise (fringe noise). This interference noise cannot be completely eliminated even if a low-reflective material is used for the lenses 35 and 36 or the like.
Therefore, it can measure only the interference noise in the photodiode 21 before measuring the oxygen concentration c _n, and or extract interference noise than the light receiving intensity I by the photodiode 21 before measuring the oxygen concentration c _n Place, by subtracting the interference noise measured or previously extracted from the light receiving intensity I in measuring the oxygen concentration c _n, are creating a correction light intensity i removing the interference noise. Alternatively, the time change I _v (t) of the light intensity at the wavelength ν is created, and the fitting process is performed using a signal (secondary function) that matches the physical phenomenon with respect to the time change I _v (t). The time change i _ν (t) of the corrected light intensity from which the interference noise is removed is created.

Then, the control unit 140 acquires the intensity I _n (ν ₁ ) to I _n (ν ₂ ) of the laser light from the photodiode 21 via the A / D converter 22 in each period n, and the corrected light intensity i _n. ([nu ₁₎ through i _n ([nu ₂₎ by creating, and calculates the oxygen concentration _{c n} based on equation (1).

On the other hand, in the current automobile industry, it is required to measure the concentration of hydrocarbon (Hydro Carbon) contained in exhaust gas from an internal combustion engine such as an engine. Therefore, the gas analyzer 101, later the number density (specific gas amount information) c _n elaborating in FIG engine oxygen molecule (specific gas) of a measurement target gas present in the combustion chamber of the (internal combustion engine) 50 It can be used for measurement.

JP 2010-237075 A

By the way, it is known that the refractive index of gas changes with temperature and density (pressure), and density (pressure) is mainly dominant. Therefore, when measuring the oxygen concentration c _n of the measurement target gas as the pressure P greatly changes, the refractive index changes greatly in the measurement target gas, even optical distance l of the laser light passing through the measurement object gas refraction It changes in proportion to the rate. As a result, the optical distance l of the laser beam passing through the measurement target gas is changed by the change of the pressure P, and interference noise is generated. At the same time, the transmittance and the absorption spectrum of the measurement target gas are changed by the change of the pressure P.

Therefore, when measuring the oxygen concentration c _n of the measurement target gas as the pressure P greatly changes, the interference noise is changed, it can not be left to determine the fitting parameters and noise filter in advance, and obtains It is very difficult to remove interference noise from the intensity I _n (ν ₁ ) to I _n (ν ₂ ) of the laser beam.

Applicant has investigated a method of measuring the oxygen concentration c _n of the measurement target gas as the pressure P greatly changes. It was found that when the pressure change is large, the interference noise changes rapidly, while when the pressure change is small, the interference noise changes slowly. Therefore, in a time zone in which the gas pressure change amount ΔP (t) is small, the fitting process is performed using the time change I (t) in a long time interval, while the gas pressure change amount ΔP (t) is large. Have found that the fitting process is performed using the time change I (t) in a short time interval.

That is, the gas analyzer of the present invention has passed through the measurement target gas and the light source unit that irradiates the measurement target gas in the measurement target with the measurement light in the predetermined wavelength range ν _{1 to} ν ₂ at predetermined time intervals. Using the light receiving unit that receives the light intensity I of the measurement light and the light intensity change I _n (ν) of the measurement light in the predetermined wavelength range ν _{1 to} ν ₂ of the nth period, specific gas amount information in the nth period is obtained. A gas analyzer including a calculation unit that calculates a pressure sensor that detects a gas pressure P of the measurement target gas and a time change P (t) of the gas pressure P, and gas at each time t A gas pressure change amount calculating unit for calculating the pressure change amount ΔP (t), an acquisition signal generating unit for generating a temporal change I _ν (t) of the light intensity at each wavelength ν, and the gas pressure change amount ΔP (t ) is the small time period, using the time variation I _[nu (t) at a long time interval fit Performs Ingu process, whereas, the the greater the time period the gas pressure variation [Delta] P (t) is to perform the fitting process by using the time variation I _ν (t) in a short time interval, at each wavelength [nu A correction signal generating unit that generates a time change i _v (t) of the correction light intensity of the correction light intensity, and the arithmetic unit uses the time change i _v (t) of the correction light intensity at each wavelength ν and The light intensity change i _n (ν) of the measurement light in the predetermined wavelength range ν _{1 to} ν ₂ of the period is created, and the specific gas amount information in the nth period is calculated.

Here, the “predetermined time interval” is an arbitrary time interval (period) determined by a measurer or the like. For example, in order to oscillate measurement light in the predetermined wavelength range ν _{1 to} ν ₂ from the laser element, for example, several 10 Hz to several tens kHz, and more specifically 1 kHz or the like.
The “specific gas” is an arbitrary component determined by a measurer or the like, and is, for example, oxygen, water vapor, carbon dioxide, carbon monoxide, or the like.

  As described above, according to the gas analyzer of the present invention, by setting the fitting range using the gas pressure change amount ΔP (t) for counting, the fitting range corresponding to the periodic change of the influence due to the interference noise is appropriately set. Can be selected. As a result, it is possible to accurately calculate the specific gas amount information in the measurement target gas that greatly changes the pressure.

(Means and effects for solving other problems)
In the above invention, the light source unit may include a laser element and a laser control unit that oscillates measurement light in a predetermined wavelength range ν _{1 to} ν ₂ from the laser element at a predetermined period n.

Furthermore, in the above invention, the measurement object may be an internal combustion engine that executes an intake process, a compression process, a combustion process, and an exhaust process in this order in a predetermined cycle.
Here, the “predetermined cycle” is an arbitrary time determined by a measurer or the like, and is a time longer than the predetermined time interval.

The schematic block diagram which shows an example of the gas analyzer of this invention. The graph which shows an example of a time change of gas pressure and light intensity. The graph which superimposes and shows an example of the time change of correction | amendment light intensity on the graph of FIG. The graph which shows an example of the absorption spectrum obtained with the conventional gas analyzer. The schematic block diagram which shows an example of the gas analyzer using a wavelength-tunable semiconductor laser absorption spectroscopy. The conceptual diagram which shows the relationship between a drive current value and the oscillation wavelength of a laser beam.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and it goes without saying that various aspects are included without departing from the spirit of the present invention.

FIG. 1 is a schematic configuration diagram showing an example of a gas analyzer of the present invention. In addition, the same code | symbol is attached | subjected about the thing similar to the conventional gas analyzer 101 mentioned above.
The gas analyzer 1 includes a light source unit 10, a light receiving unit 20, a gas temperature sensor (not shown) that measures a temperature T, a pressure sensor 32 that measures a pressure P, and a control unit that includes a microcomputer and a PC. 40.

Gas analyzer 1 of the present invention is used to measure the number density (specific gas amount information) c _n of the engine oxygen molecules of the measuring object gas present in the combustion chamber of the (internal combustion engine) 50 (specific gas) Shall. The engine 50 includes a cylinder 51, a piston 52 slidable in the Z direction and the −Z direction within the cylinder 51, a crankshaft (not shown) connected to the piston 52 via a connecting rod 53, And an ECU 60 for controlling the fuel injection amount and the ignition timing.

The intake port and the exhaust port are formed in the head of the cylinder 51, and the intake port and the exhaust port communicate with the combustion chamber. The intake port is connected to the intake passage 54, and an intake valve 56 for opening and closing the intake port with respect to the combustion chamber is provided between the intake port and the combustion chamber. The exhaust port is connected to the exhaust passage 55, and an exhaust valve 57 for opening and closing the exhaust port with respect to the combustion chamber is provided between the exhaust port and the combustion chamber.
Although not shown, the combustion chamber is provided with an injector for injecting fuel into the combustion chamber, an ignition plug for igniting the air-fuel mixture in the combustion chamber, and the like.

  According to such an engine 50, an intake process is performed in which intake gas from the intake passage 54 is drawn into the combustion chamber via the intake valve 56 as the piston 52 descends. After the intake process, the intake valve 56 is closed, and a compression process is performed in which the air-fuel mixture in which fuel is injected into the intake air is compressed in the combustion chamber by the rise of the piston 52 that has reached bottom dead center. When the piston 52 rises to near the top dead center, a combustion process is performed by ignition of the air-fuel mixture at a predetermined timing. Then, when the piston 52 lowered by the combustion pressure rises again, the exhaust valve 57 is opened, and an exhaust process is performed in which the combustion gas in the combustion chamber is discharged as exhaust gas through the exhaust valve 57 to the exhaust passage 55. Is called. A series of four processes including the intake process, the compression process, the combustion process, and the exhaust process constitute one cycle.

On the side wall of the cylinder 51, a lens 35 serving as an incident optical window and a lens 36 serving as an outgoing optical window disposed facing the lens 35 with a distance l in the −X direction are formed. .
Further, a pressure sensor 32 is installed in the combustion chamber, and the pressure P of the measurement target gas is measured at predetermined time intervals and output to the control unit 40 via the A / D converter 31.

The control unit 40 includes a CPU 41 and a memory (data storage unit) 42. Further, the functions processed by the CPU 41 will be described as a block. A laser control unit 41a that controls the light source unit 10, a light intensity acquisition unit 41b that acquires the intensity I of the laser light, and a pressure acquisition unit 41c that acquires the pressure P. A gas pressure change amount calculating unit 41d that calculates the gas pressure change amount ΔP (t), an acquisition signal generating unit 41e that generates a time change I _ν (t) of the light intensity at the wavelength ν, and correction light at the wavelength ν. a correction signal generating unit 41f to create a time variation i ν _(t) of intensity, and a computing unit 41g for calculating the number density c _n in the n periods.

  The gas pressure change amount calculation unit 41d performs control to create a time change P (t) of the gas pressure based on the pressure P acquired by the pressure acquisition unit 41c. The gas pressure change amount calculation unit 41d performs control to calculate the gas pressure change amount ΔP (t) at each time t by differentiating the time change P (t) of the gas pressure.

The acquisition signal creation unit 41e performs control to create a time change I _ν (t) of light intensity at each wavelength ν in a predetermined wavelength range ν _{1 to} ν ₂ . For example, a time change I _ν1 (t) of the light intensity at the wavelength ν ₁ is created, and a time change I _νA (t) of the light intensity at the wavelength ν _A is created. to create a time variation _I ν2 (t) of the light intensity at _2.

Here, FIG. 2 shows an example of the time change P (t) of the gas pressure created by the gas pressure change amount calculation unit 41d and the time change I _v (t) of the light intensity created by the acquisition signal creation unit 41e. It is a graph which writes and shows. The time change I _νA (t) of the light intensity at the wavelength ν _A is indicated by a solid line, and the time change P (t) of the gas pressure is indicated by a dotted line.

The correction signal generation unit 41f determines the fitting range W based on the gas pressure change amount ΔP (t) at each time t, and performs the fitting process using the time change I _v (t) of the light intensity in the fitting range W. By performing this, control is performed to create a temporal change i _ν (t) of the corrected light intensity at each wavelength ν.
For example, by substituting the gas pressure variation ΔP (t) to the following equation (2), to determine the fitting range W ₁ at time period t _1, then determines the fitting range W ₂ at time period t ₂ Thus, the fitting range W in each time zone is determined.
W = α / (ΔP (t)) + β (2)
Α and β are constants.

Then, with respect to the temporal change I _ν1 (t) of the light intensity at the wavelength ν ₁ , a fitting process is performed using a quadratic function in the fitting range W ₁ in the time zone t ₁ , and the fitting range W in the time zone t _{2. The} fitting process is performed using the quadratic function in each fitting range W in each time zone t, such as performing the fitting process using the quadratic function in 2. Thereby, a time change i _ν1 (t) of the correction light intensity is created.
Further, for the time change I _νA (t) of the light intensity at the wavelength ν _A , the fitting process is performed using a quadratic function in the fitting range W ₁ in the time zone t ₁ , and the fitting range W in the time zone t _{2. The} fitting process is performed using the quadratic function in each fitting range W in each time zone t, such as performing the fitting process using the quadratic function in 2. Thereby, a time change i _νA (t) of the correction light intensity is created. FIG. 3 is a graph in which an example (broken line) of the temporal change i _νA (t) of the correction light intensity at the wavelength ν _A is superimposed on the graph of FIG.

In this way, in a time zone in which the gas pressure change amount ΔP (t) is small, the fitting process is performed with the time change I _v (t) of the fitting range W that is a long time interval, while the gas pressure change amount ΔP ( In a time zone where t) is large, the fitting process is performed with a time change I _v (t) of the fitting range W, which is a short time interval, so that the correction light at each wavelength v in the predetermined wavelength range v _{1 to} v ₂ . An intensity time change i _v (t) is created.

The computing unit 41g creates an approximate expression based on the intensity i _n (ν) of the laser light having a non-absorption wavelength in each period n, thereby creating an intensity change i _0n (ν), and using the formula (1) control is performed to calculate the number density c _n in the n period Te.

As described above, according to the gas analyzer 1 of the present invention, by setting the fitting range W using the gas pressure change amount ΔP (t) for counting, the fitting range according to the periodic change of the influence due to the interference noise. W can be selected appropriately. As a result, it is possible to accurately calculate the number density c _n of the measurement target gas as the pressure P greatly changes.

<Other embodiments>
(1) In the gas analyzer 1 described above, the light source unit 10 is configured to include the DFB semiconductor laser diode 11, but as a configuration including a short wavelength laser, a white light source, a superluminescent diode light source, and the like. Also good.

(2) In the gas analyzer 1 described above, the configuration in which the fitting range W is determined by substituting the gas pressure change amount ΔP (t) into the equation (2) is shown, but the gas pressure change amount ΔP (t) As a configuration using another method, the fitting range is a long time interval in a time zone where the gas pressure is small, while the fitting range is a short time interval in a time zone where the gas pressure change ΔP (t) is large. Also good.

(3) In the gas analyzer 1 described above, the configuration in which the fitting process is performed using the quadratic function is shown, but the configuration in which the fitting process is performed using another method may be employed.

  The present invention can be used for a gas analyzer or the like that measures specific gas amount information in a gas.

DESCRIPTION OF SYMBOLS 1 Gas analyzer 10 Light source part 20 Light receiving part 32 Pressure sensor 41a Laser control part 41d Gas pressure change amount calculation part 41e Acquisition signal creation part 41f Correction signal creation part 41g Calculation part 50 Engine (measurement object)

Claims (3)

A light source unit that irradiates measurement light in a measurement object with measurement light in a predetermined wavelength range ν _{1 to} ν ₂ at predetermined time intervals;
A light receiving unit that receives the light intensity I of the measurement light that has passed through the measurement target gas;
A gas analyzer comprising: an arithmetic unit that calculates specific gas amount information in an n-th cycle by using a light intensity change I _n (ν) of measurement light in a predetermined wavelength range ν _{1 to} ν ₂ in an n-th cycle. ,
A pressure sensor for detecting a gas pressure P of the measurement target gas;
A gas pressure change amount calculation unit that creates a time change P (t) of the gas pressure P and calculates a gas pressure change amount ΔP (t) at each time t;
An acquisition signal generator for generating a temporal change I _ν (t) of light intensity at each wavelength ν;
In a time zone in which the gas pressure change amount ΔP (t) is small, the fitting process is performed using the time change I _v (t) in a long time section, while the gas pressure change amount ΔP (t) is large. In the band, a correction signal generating unit that generates the time change i _v (t) of the correction light intensity at each wavelength ν by performing the fitting process using the time change I _v (t) in a short time interval. And
The calculation unit calculates the light intensity change i _n (ν) of the measurement light in the predetermined wavelength range ν _{1 to} ν ₂ of the nth period using the time change i _ν (t) of the corrected light intensity at each wavelength ν. A gas analyzer characterized by creating and calculating specific gas amount information in the nth period. _2. The gas analysis according to claim 1, wherein the light source unit includes a laser element and a laser control unit that oscillates measurement light in a predetermined wavelength range ν _{1 to} ν ₂ from the laser element at a predetermined period n. apparatus. The gas analyzer according to claim 1 or 2, wherein the measurement object is an internal combustion engine that executes an intake process, a compression process, a combustion process, and an exhaust process in a predetermined cycle in this order.

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