JP2014016313A - Laser type gas analyzer - Google Patents

Abstract

Even a gas whose absorption changes greatly according to the gas temperature by switching between gas concentration detection using a frequency modulation method and gas concentration detection using a differential absorption method according to a change in gas temperature. The present invention provides a laser gas analyzer that accurately measures gas concentration over a wide gas temperature range.
Based on a temperature signal from a temperature sensor for measurement gas, a switching control unit selects a frequency modulation type gas concentration measurement unit when the temperature exceeds a predetermined temperature, and the temperature is predetermined. When the temperature falls below, control is performed such that the differential absorption method gas concentration measurement unit 34 is selected. Thus, the laser gas analyzer 1 that accurately measures the gas concentration in a wide gas temperature range was obtained.
[Selection] Figure 1

Description

  The present invention relates to a laser gas analyzer that analyzes the presence and concentration of a measurement gas in a space.

It is known that each gaseous gas molecule has its own light absorption spectrum. For example, it has characteristics such as the absorption spectrum of NH ₃ gas in FIG. The gas analyzer using laser light measures the gas concentration based on the principle that the absorption amount at a specific wavelength is proportional to the gas concentration. Here, the attenuation at the frequency fc at the center of the absorption line is proportional to the gas concentration. Therefore, the gas concentration can be estimated by irradiating a semiconductor laser beam having an oscillation frequency of fc to the gas, measuring the attenuation, and multiplying the gas by an appropriate coefficient.

  As described above, the concentration measurement method based on the gas analysis using the laser beam includes a differential absorption method and a frequency modulation method. Usually, in the differential absorption method, the gas concentration can be measured with a relatively simple configuration. On the other hand, with the frequency modulation method, signal processing is complicated, but highly sensitive gas concentration measurement is possible.

  An apparatus for measuring a gas concentration by a differential absorption method is described in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 7-151681, “Gas Concentration Measuring Device”). As shown in FIG. 8 of Patent Document 1, this gas concentration measuring device is a device including a two-wavelength semiconductor laser, a gas cell, a light receiving lens, a light receiving unit, and a gas concentration measuring device.

Then, as shown in concentration measurement principle of the differential absorption method of FIG. 14, a laser beam for the laser beam to the center frequency f _c of the absorption line and the oscillation frequency, without center frequency f _r of the absorption line and the oscillation frequency, The gas is irradiated with the two types of laser light, and the signal intensity difference obtained by subtracting the intensity of the signal output from each light receiving unit is multiplied by an appropriate proportionality constant to be converted into a concentration.

  An apparatus for measuring a gas concentration by a frequency modulation method is also described in, for example, Patent Document 1 described above. As shown in FIG. 7 of Patent Document 1, this gas concentration measuring device is a device including a frequency modulation type semiconductor laser, a gas cell, a light receiving lens, a light receiving unit, and a gas concentration measuring device.

Then, as shown in concentrations measuring principle according to the frequency modulation scheme of Figure 15, the center frequency f _c, the output of the semiconductor laser is frequency-modulated at a modulation frequency f _m, is irradiated to the measurement gas of interest. Since the absorption line of the gas is almost quadratic function with respect to the frequency twice the frequency of the signal (second harmonic) is obtained in the modulation frequency f _m in the role played light receiving portion of the absorption lines discriminator It is done. The fundamental wave by amplitude modulation can be estimated by performing envelope detection at the light receiving unit, and the ratio of the amplitude of the fundamental wave to the amplitude of the second harmonic wave is phase-synchronized to be proportional to the gas concentration regardless of the distance. To get a value.

Japanese Patent Laid-Open No. 7-151681 (Title of Invention “Gas Concentration Measuring Device”)

  Such gas analyzers are installed, for example, in a flue of a garbage incinerator. The gas analyzer is calibrated at the gas temperature normally used at the installation site, but the gas temperature in the flue varies depending on the operating condition of the furnace, and a gas temperature change of the order of 100 ° C. occurs during the gas concentration measurement. In some cases. In general, when the gas temperature is low, the gas absorption is large (depending on the measurement gas and the measurement wavelength, the reverse may occur).

  For example, as shown in FIG. 16, when comparing HCl gas at 1000 ° C. and 25 ° C., the absorption is large at 25 ° C. Since the amount of absorption changes according to the gas temperature in this way, a gas temperature correction process such as the following equation is performed.

[Equation 1]
Corrected gas concentration = α x measured gas concentration

Where α is a gas temperature correction coefficient.
By performing such processing, it is possible to accurately measure the gas concentration even when the gas temperature changes.

When the frequency modulation method is adopted, the circuit gain for outputting a synchronous detection signal or the like is adjusted according to the gas temperature normally used. When the gas temperature decreases and the absorption increases, the amplitude of the synchronous detection signal increases and the measurement gas concentration increases. When the gas temperature further decreases, saturation (saturation) occurs. Further, as shown in FIG. 17, in the case of SO ₂ gas having a broad absorption characteristic, if the absorption is further increased due to further gas temperature decrease, the amount of received light is also increased, so that the signal of the synchronous detection signal is reduced and the measurement is performed. The gas concentration starts to decrease. FIG. 18 shows the gas temperature-gas concentration characteristics in such a case.

  If it is the gas temperature range of the section A of FIG. 18, the gas temperature correction method shown in Formula 1 can be applied. However, when the gas concentration is measured in the gas temperature range of section B, the gas temperature correction method shown in Equation 1 cannot be applied.

On the other hand, in the case of the differential absorption method, since the sensitivity is lower than that of the frequency modulation method, the gas temperature correction of Formula 1 can be applied in a wider gas temperature range. However, as already described, since the sensitivity is lower than that of the frequency modulation method, the gas concentration measurement with the accuracy required in the flue may not be possible when the gas has low absorption (the gas temperature is high).
Both the frequency modulation method and the differential absorption method have both advantages and disadvantages.

  Therefore, the present invention has been made in view of the above problems, and its purpose is to detect a gas concentration using a frequency modulation method and a gas concentration detection using a differential absorption method according to a change in gas temperature. Thus, it is an object of the present invention to provide a laser gas analyzer that accurately measures the gas concentration in a wide gas temperature range even for a gas whose absorption varies greatly according to the gas temperature.

A laser type gas analyzer according to claim 1 of the present invention comprises:
A light emitting unit for emitting detection light by laser light;
A light receiving unit that receives the detection light propagated through the space where the measurement gas exists and outputs a detection signal;
A frequency modulation type gas concentration measurement unit that measures the gas concentration by the frequency modulation method based on the detection signal output from the light receiving unit, and a difference that measures the gas concentration by the differential absorption method based on the detection signal output from the light receiving unit An absorption method gas concentration measurement unit, a signal processing unit comprising:
A temperature sensor for measuring gas that measures the temperature in the space where the measuring gas exists and outputs a temperature signal;
A switching control unit for controlling the signal processing unit so as to select the gas concentration measurement method, the frequency modulation method or the differential absorption method based on the temperature signal from the temperature sensor for the measurement gas;
It was set as the laser type gas analyzer characterized by providing.

A laser gas analyzer according to claim 2 of the present invention is
The laser gas analyzer according to claim 1, wherein
The light emitting unit
A laser element;
A temperature detector of the laser element;
A temperature control unit of the laser element;
A temperature control unit that controls the temperature adjustment unit according to the temperature detected by the temperature detection unit so that the emission wavelength from the laser element becomes a predetermined value;
A wavelength scanning drive signal generator for generating a wavelength scanning drive signal for scanning the absorption characteristics of the measurement gas by changing a supply current to the laser element;
A high-frequency modulation signal generator for generating a high-frequency modulation signal;
A laser drive signal generator that modulates the wavelength scanning drive signal with a high frequency modulation signal to generate a drive signal for the laser element, converts the drive signal into a current signal, and outputs the current signal to the laser element;
With
The frequency modulation type gas concentration measurement unit of the signal processing unit,
A reference signal generator for generating a reference signal having a double frequency component of the high frequency modulation signal in the light receiving element, a synchronous detector for detecting the double frequency component from the output signal of the light receiving element, and an output signal of the synchronous detector A calculation unit for calculating the concentration of the measurement gas based on the value of
With
The differential absorption method gas concentration measurement unit of the signal processing unit is:
Filter unit that extracts the basic signal from the output signal of the light receiving element, signal storage unit that outputs the reference signal when there is no measurement gas, and calculates the concentration of the measurement gas based on the difference value obtained by subtracting the basic signal from the reference signal A laser type gas analyzer.

  According to the present invention, the absorption changes greatly according to the gas temperature by switching between the gas concentration detection using the frequency modulation method and the gas concentration detection using the differential absorption method according to the change of the gas temperature. It is possible to provide a laser type gas analyzer that accurately measures gas concentration over a wide gas temperature range.

1 is an overall configuration diagram of a laser type gas analyzer according to an embodiment of the present invention. It is a circuit block diagram of a light emission part. FIG. 3A is a characteristic diagram showing the relationship between the light emission wavelength of the laser element and the current, and FIG. 3B is a characteristic diagram showing the relationship between the light emission wavelength of the laser element and temperature. is there. It is a figure which shows a wavelength scanning drive signal. It is a figure which shows the drive signal with respect to a laser element. It is a block diagram of a frequency modulation type gas concentration measuring unit. It is a block diagram of a difference absorption system gas concentration measurement part. It is a figure which shows an example of a light reception signal. It is an example of the synchronous detection signal extracted by the synchronous detection part. It is an example of the received light intensity waveform extracted by the filter. Is an explanatory view of a comparison of the received light intensity waveform, FIG. 11 (a) illustrates the figure, FIG. 11 (b) receiving intensity waveform of the measurement gas flow showing the received light intensity waveform when N ₂ flow. It is an example of the difference signal of the light receiving intensity waveform of the measurement gas flow at the time of N ₂ flow. NH ₃ is a diagram showing the absorption spectrum of the gas. It is a figure which shows the density | concentration measurement principle by a differential absorption system. It is a figure which shows the density | concentration measurement principle by a frequency modulation system. It is a figure which shows the change by gas temperature of absorption of measurement gas. It shows the absorption spectrum of the SO ₂ gas. It is a gas temperature-measurement gas concentration characteristic figure which compared the measurement density | concentration by a measuring method.

Hereinafter, a laser gas analyzer according to an embodiment for carrying out the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of a laser type gas analyzer of this embodiment.
The laser gas analyzer 1 of this embodiment includes a light emitting unit 10, a light receiving unit 20, a signal processing unit 30, a measurement gas temperature sensor 40, a switching control unit 50, and an output unit 60.

As shown in FIG. 1, the light emitting unit 10 includes a laser drive control unit 11, a laser light emitting unit 12, a collimating lens 13, and a case 14.
As shown in FIG. 1, the light receiving unit 20 includes a condenser lens 21, a light receiving element 22, and a case 23.
As shown in FIG. 1, the signal processing unit 30 includes an I / V conversion unit 31, a switching unit 32, a frequency modulation type gas concentration measuring unit 33, a differential absorption type gas concentration measuring unit 34, and a switching unit 35.

And this form demonstrates as a laser type gas analyzer applied to various gas concentration measurement etc., such as a flue and exhaust gas.
As shown in FIG. 1, the light emitting unit 10 and the light receiving unit 20 are attached to walls 3a and 3b such as pipes, which are flues through which a measurement gas flows, via flanges 2a and 2b fixed by welding or the like. . The case 14 of the light emitting unit 10 is attached to the flange 2a, and the case 23 of the light receiving unit 20 is attached to the flange 2b.

  Next, the operation of each unit will be described. As shown in detail in FIG. 2, the light emitting unit 10 further includes a wavelength scanning drive signal generation unit 11a, a high frequency modulation signal generation unit 11b, a laser drive signal generation unit 11c, and a temperature control unit 11d as a laser drive control unit 11. . Further, the laser light emitting unit 12 further includes a laser element 12a, a temperature detecting unit (thermistor) 12b, and a temperature adjusting unit (Peltier element) 12c.

The laser element 12a can emit light at a frequency where the emission wavelength matches the light absorption characteristic of the gas and its peripheral region, and further, the emission wavelength can be made variable by the drive current as shown in FIG. Further, as shown in FIG. 3B, the emission wavelength can be made variable depending on the temperature. The laser element 12a is, for example, a laser diode called a DFB laser (Distributed Feedback Laser) or a VCSEL (Vertical Cavity Surface Emitting Laser). Other than the laser diode, other types of light emitting elements may be used as long as the above conditions are satisfied, that is, the wavelength can be swept in the absorption wavelength band of the measurement gas. In this embodiment, sulfur dioxide gas (SO ₂ gas) is measured as a specific example of the measurement gas, and a wavelength that absorbs sulfur dioxide gas (SO ₂ gas) is adopted as the wavelength.

  In FIG. 2, the temperature of the laser element 12a is detected using a temperature detector 12b such as a thermistor. The temperature detection unit 12 b is connected to the temperature control unit 11 d of the laser drive control unit 11. The temperature control unit 11d performs PID control or the like so that the resistance value obtained from the temperature detection unit 12b such as a thermistor becomes constant in order to stabilize the emission wavelength of the laser element 12a and adjust the wavelength, and so on. The temperature control unit 12c is controlled to adjust the temperature of the laser element 12a.

  The output wavelength of the wavelength scanning drive signal generator 11a that changes the emission wavelength of the laser so as to scan the absorption wavelength of the measurement gas, and the emission wavelength by a sine wave of, for example, about 10 kHz for detecting the absorption waveform of the measurement gas When the output signal of the high frequency modulation signal generation unit 11b for frequency-modulating the signal is input to the drive signal generation unit 11c, the drive signal generation unit 11c combines the output signals to generate a drive signal. V-I conversion is applied to the laser element 12a.

Here, the modulation of the laser light will be described. FIG. 4 shows an output signal of the wavelength scanning drive signal generator 11a. The wavelength scanning drive signal S ₁ for scanning the absorption characteristic of the measurement gas linearly changes the drive current value of the laser element 12a to gradually change the emission wavelength of the laser element 12a. Scan characteristics. On the other hand, the signal S ₂ is not shifted wavelength laser device 12a the driving current value is maintained above the threshold current to stabilize, is intended for illuminating at a certain wavelength. Furthermore, keep the signal _{S 3,} the drive current value to 0 mA.

A waveform diagram of a modulation signal output from the high-frequency modulation signal generation unit 11b is illustrated below the high-frequency modulation signal generation unit 11b in FIG. 2. This modulation signal is, for example, a sine wave having a frequency of 10 kHz. The wavelength width is about 0.02 nm.
FIG. 5 is a waveform diagram of the drive signal (the combined signal of the output signal of the wavelength scanning drive signal generator 11a and the output signal of the high frequency modulation signal generator 11b) output from the laser drive signal generator 11c of FIG. . This drive signal has a trapezoidal shape that is repeated at a constant period. When the laser drive signal generator 11c changes the current to drive the laser and supplies this drive signal to the laser element 12a, the laser element 12a produces a light absorption characteristic of the measurement gas of about 0.2 nm and a wavelength width of about 0.02 nm. The modulated light that can be detected at is output.

  As a result, a laser beam having a predetermined wavelength that is frequency-modulated to scan the light absorption characteristics of the measurement gas is emitted from the laser element 12a. As shown in FIG. 1, the laser light emitted from the laser element 12 a is collimated by the collimating lens 13 to the parallel detection light 70 and then emitted. The temperature of the laser element 12a is adjusted in advance so that gas is measured at the central portion of the wavelength scanning drive signal.

  The detection light 70 is emitted through the light emitting unit 10. As shown in FIG. 1, the detection light 70, which is parallel light output from the light emitting unit 10, propagates through the interior of the flue, which is an internal section of the walls 3 a and 3 b (a space in which the measurement gas flows), and is transmitted between these Gas absorption when doing. The detection light that has received the gas absorption is received by the light receiving unit 20.

  Next, the light receiving unit 20 will be described. In the light receiving unit 20, the detection light 70 that is parallel light is collected by the condenser lens 21 and incident on the light receiving element 22, and the light receiving element 22 receives the detection light propagated through the space in which the measurement gas exists. A detection signal based on an electrical signal is output according to the amount of received light. The light receiving element 22 is, for example, a photodiode, and an element having sensitivity to the emission wavelength of the laser is applied.

  Next, the signal processing unit 30, the measurement gas temperature sensor 40, and the switching control unit 50 will be described. The signal processing unit 30 includes both the frequency modulation type gas concentration measuring unit 33 and the differential absorption type gas concentration measuring unit 34, and can measure the gas concentration by both methods. And the temperature sensor 40 for measurement gas, such as a thermocouple, measures the temperature in the space where measurement gas exists, outputs a temperature signal to the switching control part 50, and when temperature exceeds predetermined temperature based on this temperature signal The frequency modulation type gas concentration measuring unit 33 is selected (when it is in the gas temperature zone A in FIG. 18), and if the temperature is lower than the predetermined temperature (when it is in the gas temperature zone B in FIG. 18), the difference is selected. The switching control unit 50 controls the switching units 32 and 35 of the signal processing unit 30 so as to select the absorption method gas concentration measuring unit 34.

  That is, when the temperature of the measurement gas exceeds the predetermined temperature (when it is in the gas temperature section A of FIG. 18), the switching units 32 and 35 are switched as shown in FIG. The path of the unit 32, the frequency modulation type gas concentration measuring unit 33, the switching unit 35, and the output unit 60 is selected. Further, when the temperature of the measurement gas is lower than the predetermined temperature (when it is in the gas temperature section B of FIG. 18), the switching units 32 and 35 are switched as shown in FIG. 7, and the I / V conversion unit 31, The path of the switching unit 32, the differential absorption method gas concentration measuring unit 34, the switching unit 35, and the output unit 60 is selected.

  Subsequently, when the temperature of the measurement gas exceeds the predetermined temperature (when it is in the gas temperature section A of FIG. 18), as shown in FIG. 6, the I / V conversion unit 31, the switching unit 32, the frequency modulation type gas concentration A case will be described in which the path of the measurement unit 33, the switching unit 35, and the output unit 60 is selected and gas concentration measurement is performed by a frequency modulation method.

  The detection signal input from the light receiving element 22 to the signal processing unit 30 is converted from a current signal to a voltage signal by the IV conversion circuit 31. This voltage signal has an output waveform as shown in FIG. This voltage signal is input to the synchronous detection unit 33a through the switching unit 32. Further, the reference signal generator (oscillator) 33b outputs a signal having a frequency twice the high frequency modulation signal by the high frequency modulation signal generator 11b of FIG. 2 to the synchronous detection unit 33a as a reference signal. The synchronous detection unit 33a extracts only the amplitude of the double frequency component of the modulation signal.

This is because the output of the laser element 12a is frequency-modulated at the center frequency f _c and the modulation frequency f _{m as} shown in the concentration measurement principle by the frequency modulation method of FIG. 15 described above, and the target measurement gas is irradiated. Then, since the absorption lines of the gas is almost quadratic function with respect to the frequency twice the frequency of the signal (second harmonic of the absorption lines discriminator role played light receiving unit 20 in the modulation frequency f _m ) Is obtained. Then, the fundamental wave by amplitude modulation can be estimated by performing envelope detection in the light receiving unit 20, and the ratio of the amplitude of the fundamental wave from the reference signal generator (oscillator) 33b and the amplitude of the second harmonic wave is phase-synchronized. A value proportional to the gas concentration is obtained regardless of the distance. This signal is input to the calculation unit 33c, and the concentration of the measurement gas is calculated in the calculation unit 33c.

Next, the principle of detecting the concentration of the measurement gas by the frequency modulation method will be described. Here, to detect the sulfur dioxide (SO ₂ gas). When the measurement gas, that is, sulfur dioxide (SO ₂ gas) has an absorption characteristic, a synchronous detection signal as shown in FIG. 9 is extracted from the synchronous detection unit 33a. The synchronous detection signal is output to the calculation unit 33c. Since the peak value of the gas concentration becomes the gas concentration, the calculation unit 33c may measure the peak amplitude or may integrate the signal change.

In one example, computing unit 33c can detect the gas concentration by multiplying the span calibration value G _A and gas temperature correction coefficient alpha _A such relative amplitude W _A of the synchronous detection signal as shown in FIG.

[Equation 2]
Measuring gas concentration _{= α A × G A × W} A

As long as the gas temperature correction coefficient α _A is a coefficient that is uniquely determined with respect to the gas temperature, the function format, the table format, and the like are not limited.

The computing unit 33 c sends this measured gas concentration to the output unit 60 via the switching unit 35. The output unit 60 is, for example, a display device or an alarm device, or a transmission device that transmits to another computer. Detection of the concentration of the measurement gas by the frequency modulation method is performed in this way.

  Subsequently, when the temperature of the measurement gas is lower than the predetermined temperature (when it is in the gas temperature section B in FIG. 18), as shown in FIG. 7, the I / V conversion unit 31, the switching unit 32, and the differential absorption method gas concentration. A case where the measurement unit 34, the switching unit 35, and the output unit 60 are selected to perform gas concentration measurement by the differential absorption method will be described.

  The detection signal input from the light receiving element 22 to the signal processing unit 30 is converted from a current signal to a voltage signal by the IV conversion circuit 31. This voltage signal is as shown in FIG. This voltage signal is input to the filter unit 34a through the switching unit 32. The filter unit 34a extracts a received light intensity signal as shown in FIG. 10 from the received light signal of FIG.

Here, since the gas concentration changes due to absorption, for example, signal processing is performed in which the ratio of a signal of a gas that is not absorbed, such as nitrogen, and a signal that is absorbed by the measurement gas is regarded as a concentration. In the case of a gas that is not absorbed, such as N _2, the received light intensity waveform is as shown in FIG. On the other hand, when it is absorbed by the measurement gas, it changes as shown in FIG. Therefore, allowed to advance _{N 2} intensity signals stored in the signal storage unit 34b as the received-light-intensity-signal having a received light intensity waveform as shown in FIG. 11 (a), a subtractor 34c, _{N 2} intensity signal shown in FIG. 11 (a) Then, when a received light intensity signal having a received light intensity waveform as shown in FIG. 11B is subtracted to obtain a difference value, a differential signal having an output waveform as shown in FIG. 12 is obtained.

  Note that the differential absorption method of this embodiment does not use a two-wavelength laser, and one differs from the pure differential absorption method described as the prior art in that a registered value is used. However, the reference waveform has been found to function sufficiently as a differential absorption method even if a value registered in the signal storage unit 34b is adopted, and can be regarded as a differential absorption method. As described above, the differential absorption method according to the present invention does not require a laser element having a plurality of wavelengths, and thus the configuration can be simplified and is excellent.

Thus, by taking the difference between the signal intensity of the wavelength λ _a when the reference gas measured in advance and not the measurement gas flows, and the signal intensity of the wavelength λ _a when the measurement gas is present, The concentration can be measured. The input to the signal storage unit 34b is performed at the time of calibration or factory shipment. The difference signal is input to the calculation unit 34d, and the concentration of the measurement gas is calculated in the calculation unit 34d. By multiplying the span calibration value G _B and the gas temperature correction coefficient alpha _B relative amplitude W _B of the difference signal can be detected gas concentration.

[Equation 3]
Measuring gas concentration _{= α B × G B × W} B

As long as the gas temperature correction coefficient α _B is a coefficient uniquely determined with respect to the gas temperature, the format such as the function format and the table format is not limited.

The calculation unit 34d sends the measured gas concentration to the output unit 60 via the switching unit 35. The output unit 60 is, for example, a display device or an alarm device, or a transmission device that transmits to another computer. Detection of the concentration of the measurement gas by the differential absorption method is performed in this way.

Although the present invention has been described above, the present invention can be variously modified.
For example, in the embodiment described above, when the temperature exceeds a predetermined temperature based on the temperature signal from the measurement gas temperature sensor, the frequency modulation type gas concentration measurement unit is selected, and when the temperature falls below the predetermined temperature. Is described as being a switching control unit that controls the signal processing unit so as to select the differential absorption type gas concentration measurement unit.

  However, generally, when the gas temperature is low, the gas absorption is large, but depending on the measurement gas and the measurement wavelength, the opposite case may be described. In the opposite case, when the gas temperature is low and the absorption is small, a highly accurate gas concentration detection using a frequency modulation method is adopted, and when the gas temperature is high and the absorption is large, a differential absorption method is used. By adopting gas concentration detection, highly accurate detection is possible. In this case, the switching control unit selects the frequency modulation type gas concentration measurement unit when the temperature is lower than the predetermined temperature based on the temperature signal from the temperature sensor for the measurement gas, and when the temperature is higher than the predetermined temperature. Controls the signal processing unit to select the differential absorption type gas concentration measurement unit. Such a configuration may be adopted.

Further, according to the laser gas analyzer of the present invention, FIG. 4, paying attention to a point which is a signal S ₃ signal is output for each cycle as shown in Figure 5, a predetermined from the detection of the signal S3 Since the peak value of the output waveform of the synchronous detector appears when the time has elapsed, the concentration should be calculated at this timing.
Although the concentration is measured, the presence or absence of the measurement gas can be detected by determining that the measurement gas does not exist when the concentration is almost zero.

In the above-described embodiment, the oxygen sulfide gas (SO ₂ ) is described as an example. However, the present invention is not limited to this, and oxygen gas (O ₂ gas), chlorine gas (HCl gas) is not limited thereto. Other component gases such as carbon dioxide gas (CO ₂ gas), carbon monoxide gas (CO gas), and ammonia gas (NH ₃ ) may be used. In that case, a laser element having a wavelength capable of detecting a gas of another component is employed, and the calculation processing content of the calculation unit is changed and used so as to be detected at this wavelength.

  The present invention has been described above. According to the laser type gas analyzer of the present invention, since the frequency modulation method and the differential absorption method are selectively used according to the temperature of the measurement gas, highly accurate measurement is possible regardless of the temperature of the measurement gas.

  The laser gas analyzer of the present invention is optimal for measuring combustion exhaust gas such as boilers and garbage incineration. In addition, gas analysis for steel [blast furnace, converter, heat treatment furnace, sintering (pellet equipment), coke oven], fruit and vegetable storage and ripening, biochemistry (microorganism) [fermentation], air pollution [incinerator, flue gas desulfurization / Denitration], automobile exhaust gas (remove tester), disaster prevention [explosive gas detection, toxic gas detection, new building material combustion gas analysis], plant growth, chemical analysis [oil refinery plant, petrochemical plant, gas generation plant], It is also useful as an analyzer for environmental [landing concentration, tunnel concentration, parking lot, building management], and various physics and chemistry experiments.

1: Laser gas analyzer 10: Light emission unit 11: Laser drive control unit 11a: Wavelength scanning drive signal generation unit 11b: High frequency modulation signal generation unit 11c: Laser drive signal generation unit 11d: Temperature control unit 12: Laser light emission unit 12a : Laser element 12b: Temperature detector (thermistor)
12c: Temperature control unit (Peltier element)
13: Collimating lens 14: Case 20: Light receiving unit 21: Condensing lens 22: Light receiving element 23: Case 30: Signal processing unit 31: I / V conversion unit 32: Switching unit 33: Frequency modulation type gas concentration measuring unit 33a: Synchronous detection unit 33b: reference signal generation unit 33c: calculation unit 34: differential absorption method gas concentration measurement unit 34a: filter unit 34b: signal storage unit 34c: difference unit 34d: calculation unit 35: switching unit 40: temperature sensor for measurement gas 50: Switching control unit 60: Output unit 70: Detection light

2a, 2b: Flange 3a, 3b: Wall

Claims (2)

A light emitting unit for emitting detection light by laser light;
A light receiving unit that receives the detection light propagated through the space where the measurement gas exists and outputs a detection signal;
A frequency modulation type gas concentration measurement unit that measures the gas concentration by the frequency modulation method based on the detection signal output from the light receiving unit, and a difference that measures the gas concentration by the differential absorption method based on the detection signal output from the light receiving unit An absorption method gas concentration measurement unit, a signal processing unit comprising:
A temperature sensor for measuring gas that measures the temperature in the space where the measuring gas exists and outputs a temperature signal;
A switching control unit for controlling the signal processing unit so as to select the gas concentration measurement method, the frequency modulation method or the differential absorption method based on the temperature signal from the temperature sensor for the measurement gas;
A laser gas analyzer comprising: The laser gas analyzer according to claim 1, wherein
The light emitting unit
A laser element;
A temperature detector of the laser element;
A temperature control unit of the laser element;
A temperature control unit that controls the temperature adjustment unit according to the temperature detected by the temperature detection unit so that the emission wavelength from the laser element becomes a predetermined value;
A wavelength scanning drive signal generator for generating a wavelength scanning drive signal for scanning the absorption characteristics of the measurement gas by changing a supply current to the laser element;
A high-frequency modulation signal generator for generating a high-frequency modulation signal;
A laser drive signal generator that modulates the wavelength scanning drive signal with a high frequency modulation signal to generate a drive signal for the laser element, converts the drive signal into a current signal, and outputs the current signal to the laser element;
With
The frequency modulation type gas concentration measurement unit of the signal processing unit,
A reference signal generator for generating a reference signal having a double frequency component of the high frequency modulation signal in the light receiving element, a synchronous detector for detecting the double frequency component from the output signal of the light receiving element, and an output signal of the synchronous detector A calculation unit for calculating the concentration of the measurement gas based on the value of
With
The differential absorption method gas concentration measurement unit of the signal processing unit is:
Filter unit that extracts the basic signal from the output signal of the light receiving element, signal storage unit that outputs the reference signal when there is no measurement gas, and calculates the concentration of the measurement gas based on the difference value obtained by subtracting the basic signal from the reference signal A laser type gas analyzer.

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