JP2008232920A - Gas detection device, and calibration method and wavelength confirmation method using device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform self-calibration of wavelength deviation in a device based on a detection signal corresponding to reference light of an LD module. <P>SOLUTION: Laser light emitted from the LD module 11 is branched into measuring light and the reference light by a half mirror. The measuring light is used for ordinary gas detection, and the reference light is received by a photodetector 12c for wavelength processing after passing a gas cell. While sweeping a driving temperature value of the LD module 11 with a prescribed swing width, the maximum 2f value taking the maximum value is calculated from among 2f values based on an intensity change of a 2f signal detected from a detection signal received by the photodetector 12c for wavelength processing, and the calculated maximum 2f value is compared with a reference 2f value stored in a storage part 31. When the maximum 2f value is higher than a prescribed reference of the reference 2f value, a set temperature value of the LD module 11 is calculated from the maximum 2f value, and a set temperature value stored in the storage part 31 is changed, to thereby perform wavelength calibration of the LD module 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gas detection device that uses a semiconductor laser as a light source and optically detects gas using the infrared absorption characteristics of gas, and has a simple configuration and is optimal in the device before starting gas detection or during gas detection. The present invention relates to a gas detection device capable of self-calibrating to a suitable wavelength, a calibration method using the device, and a wavelength confirmation method.

  For example, it is already known that gases such as methane, carbon dioxide, acetylene, and ammonia have an absorption band that absorbs light of a specific wavelength in accordance with molecular rotation, vibration between constituent atoms, and the like. In a gas detection device using this absorption band, a light source part and a light receiving part are arranged at a predetermined distance (the measurement optical path length is determined by this distance), and laser light frequency-modulated by a semiconductor laser of the light source part is used. It passes through the atmosphere containing the measurement target gas, and the transmitted light is received by the photodetector of the light receiving unit to detect the gas, and the gas concentration of the measurement target gas is measured from the output signal at this time. Further, as disclosed in Patent Document 1 below, there is also known a gas detection device configured such that the light source unit and the light receiving unit described above are accommodated in a common casing and can be carried. Even if the light source unit and the light receiving unit are arranged at the same position, the measurement optical path length is secured if the measurement light can be received as reflected light.

  Here, a large offset due to intensity modulation occurs in a fundamental phase sensitive detection signal (hereinafter referred to as “1f signal”) having a modulation frequency detected from the output signal of the light receiving unit. For this reason, in order to measure a particularly minute gas concentration with high sensitivity, a second harmonic phase sensitive detection signal (hereinafter abbreviated as 2f signal) having a considerably smaller offset than the 1f signal is used.

  When actually measuring the gas concentration, when the measurement light with the wavelength matched to the measurement gas absorption line passes through the measurement gas atmosphere, the measurement light is absorbed by the gas to be measured, and the intensity according to the gas concentration optical path length product. A 2f signal is generated by a change in intensity at a frequency twice the modulation frequency (2f signal component: 2f value). The ratio 2f / 1f between the intensity change of the 2f signal and the intensity change of the 1f signal (1f signal component: 1f value), which is the original modulation frequency, is proportional to the gas concentration optical path length product. Multiply the coefficient to get the gas concentration. As this type of conventional gas detection device, a gas concentration measurement device disclosed in Patent Document 1 below is disclosed.

As shown in FIG. 11, the gas concentration measuring device 51 of Patent Document 1 has a bottomed cylindrical casing 53 having a gun shape as a whole and having an opening hole 52 on one surface, and a rear end of the casing 53. And a grip portion 54 that grips the housing 53. A semiconductor laser unit 55 is incorporated in the housing 53, and a light receiver 56 is disposed at the back of the housing 53 on the central axis. The semiconductor laser unit 55 includes a semiconductor laser module 57 including a semiconductor laser that emits measurement light for detecting a gas in a measurement atmosphere, a laser pointer 58, and a multiplexing means 59. A condensing lens 60 for condensing the reflected measurement light from the measurement atmosphere accompanying the emission of the measurement light onto the light receiver 56 is fixed in the opening hole 52 of the housing 53. The laser pointer 58 is fixed to the rear of the condenser lens 60 of the housing 53 by an inverted V-shaped support member 61, and emits visible light as guide light for confirming the emission position of the measurement light. The multiplexing means 59 is disposed on the optical axis LL of the light receiver 56 behind the condenser lens 60 of the housing 53, and combines the measurement light and the guide light on the optical axis LL of the light receiver 56. Then, the light is emitted from the central glass window 62 of the condenser lens 60.
JP-A-2005-106521

  By the way, the detection accuracy of the measurement target gas leakage inspection (hereinafter also referred to as a leakage test) in this type of gas detection device including the gas concentration detection device of Patent Document 1 described above is a semiconductor laser that is a light source unit mounted on the device. Since it depends on whether or not the wavelength of the measurement light emitted from the module is stable, the gas detection device is required to accurately stabilize the wavelength.

  Therefore, in the current gas detection device, the wavelength stabilization is performed by using the wavelength stabilization method by phase detection as a confirmation method of the wavelength stabilization. There has been a problem that the cost of components constituting a wavelength stabilization circuit or the like for realizing the method increases.

  In addition, there is a request from a user who performs gas detection to confirm gas detection measurement after confirming that the gas to be actually measured can be reliably measured at the time of inspection before starting gas detection measurement. .

  Accordingly, the present invention has been made in view of the above problems, and is inexpensive and has a simple configuration, confirming wavelength stabilization before starting gas detection or during gas detection, and self-calibrating to an optimum wavelength. It is an object of the present invention to provide a gas detection device capable of performing highly accurate gas detection, a calibration method using the device, and a wavelength confirmation method.

In order to achieve the above object, a gas detector according to claim 1 of the present invention includes an LD module 11 mounted with a semiconductor laser that emits laser light,
A half mirror 12a that branches the laser light emitted from the LD module into measurement light and reference light, a gas cell 12b in which the same kind of gas as the measurement target gas is sealed, and the reference light that has passed through the gas cell. A wavelength processing mechanism unit 12 including a wavelength processing light receiver 12c that receives and outputs a detection signal corresponding to the received reference light;
A storage unit 31 storing a set temperature value set in advance for driving the semiconductor laser at a predetermined oscillation frequency and a reference 2f value used as a reference value at the time of wavelength calibration;
A temperature stabilization control unit 32 for stabilizing the driving temperature value of the LD module to the set temperature value stored in the storage unit;
The fundamental frequency sensitive detection of the modulation frequency detected from the detection signal output from the wavelength processing mechanism unit while sweeping the driving temperature value of the LD module controlled by the temperature stabilization control unit with a predetermined amplitude. A wavelength for calculating a 2f value based on a change in intensity of a double phase sensitive detection signal that is a detection signal that is twice the signal, and calculating and outputting a maximum 2f value that is the maximum value from the calculated 2f values The calibration calculation unit 33Ba compares the maximum 2f value output from the wavelength calibration calculation unit with the reference 2f value stored in the storage unit, and the maximum 2f value is equal to or greater than a predetermined reference of the reference 2f value. If there is, the wavelength processing unit includes a wavelength calibration determination unit 33Bc that calculates a set temperature value of the LD module from the maximum 2f value, outputs the calculated set temperature value to the storage unit, and changes the value. A control unit 33,
It is provided with.

The gas detection device according to claim 2 is the gas detection device according to claim 1,
The wavelength processing mechanism unit 12 includes a temperature sensor 12d that outputs a temperature value detected in the vicinity of the gas cell 12b as a correction temperature value,
The wavelength processing control unit 33 corrects the 2f value calculated by the wavelength calibration calculation unit 33Ba based on the correction temperature value as necessary, and outputs the corrected 2f value to the wavelength calibration calculation unit. A wavelength calibration correction unit 33Bb is provided.

The gas detection device according to claim 3 is the gas detection device according to claim 1,
The storage unit 31 further stores a reference 2f / 1f value used as a reference value when checking the wavelength,
The wavelength processing control unit 33 includes a 1f value based on the intensity change of the fundamental frequency sensitive detection signal of the modulation frequency detected from the detection signal from the waveform processing light receiver 12c, and a detection signal twice the 1f value. A wavelength checking calculation unit 33Aa that calculates a 2f value based on an intensity change of a certain second harmonic phase sensitive detection signal, calculates a 2f / 1f value that is a ratio of the two values, and outputs the calculated value;
The calculated 2f / 1f value is compared with the reference 2f / 1f value stored in the storage unit. When the 2f / 1f value is within a predetermined range of the reference 2f / 1f value, A wavelength confirmation processing unit 33A having wavelength confirmation determination means 33Ac for determining that the wavelength of the LD module 11 is stabilized is provided.

The gas detection device according to claim 4 is the gas detection device according to claim 3,
The wavelength processing mechanism unit 12 includes a temperature sensor 12d that outputs a temperature value detected in the vicinity of the gas cell 12b as a correction temperature value,
The wavelength processing control unit 33 corrects the 2f / 1f value calculated by the wavelength check calculation unit based on the correction temperature value as necessary, and outputs the corrected 2f value to the wavelength check calculation unit. A wavelength confirmation correcting means 33Ab is provided.

A calibration method for a gas detection device according to claim 5 of the present invention is a calibration method using the gas detection device 1 according to claim 1,
Performing temperature stabilization processing of the LD module 11 in the temperature stabilization control unit 32;
It is a detection signal that is twice the fundamental sensitive detection signal of the modulation frequency detected from the detection signal output from the wavelength processing mechanism unit 12 while sweeping the drive temperature value of the LD module with a predetermined amplitude. Calculating a 2f value based on an intensity change of the second harmonic phase sensitive detection signal;
Calculating a maximum 2f value that is a maximum value from the calculated 2f values;
Comparing the calculated maximum 2f value with a reference 2f value stored in the storage unit 31;
A step of calculating a set temperature value of the LD module from the maximum 2f value and changing the set temperature value stored in the storage unit when the maximum 2f value is equal to or greater than a predetermined reference value of a reference 2f value; When,
It is characterized by including.

The wavelength confirmation method of the gas detection device according to claim 6 is a wavelength confirmation method using the gas detection device 1 according to claim 3,
Performing temperature stabilization processing of the LD module 11 in the temperature stabilization control unit 32;
The 1f value based on the intensity change of the fundamental sensitive detection signal of the modulation frequency detected from the detection signal output from the wavelength processing mechanism unit 12, and the second harmonic phase which is a detection signal twice the 1f value. Calculating a 2f value based on an intensity change of the sensitive detection signal, and calculating a 2f / 1f value that is a ratio of the two values;
Comparing the 2f / 1f value with a reference 2f / 1f value stored in the storage unit;
Determining that the wavelength of the LD module is stabilized when the 2f / 1f value is within a predetermined range of the reference 2f / 1f value;
It is characterized by including.

  According to the present invention, since the detection target gas sealed in the gas cell as in the prior art can be detected at all times, the target wavelength is shifted due to the deterioration of the semiconductor laser or the temperature change of the use environment. However, it can be confirmed that the wavelength has shifted due to a change in the detection signal of the reference light, and the wavelength shift can be self-calibrated in the apparatus.

  Furthermore, the gas leak test in the gas detector can be performed at low cost and can be easily adjusted in a short time. In addition, it can be confirmed that the detection of the gas to be measured can be reliably measured at the time of inspection before starting the gas detection.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. FIG. 1 is a schematic configuration diagram for explaining a configuration of a first embodiment of a gas detection device according to the present invention, and FIG. 2 is a diagram for explaining a configuration of an LD module mounted on the gas detection device according to the present invention. FIG. 3 is a schematic block diagram, FIG. 3 is a schematic block diagram for explaining the configuration of the wavelength processing control unit in the gas detection device according to the present invention, and FIG. 4 explains the wavelength confirmation processing of the gas detection device according to the present invention. FIG. 5 is a flowchart for explaining the wavelength calibration process of the gas detection device according to the present invention, and FIG. 6 is for explaining the second embodiment of the gas detection device according to the present invention. FIG. 7 is a schematic configuration diagram for explaining a third embodiment of the gas detection device according to the present invention, and FIG. 8 is a diagram for explaining a fourth embodiment of the gas detection device according to the present invention. 9 is a schematic configuration diagram of FIG. Is a schematic diagram for explaining the fifth embodiment of the gas detecting device according to the present invention, FIG 10 is a schematic diagram for explaining the sixth embodiment of the gas detecting device according to the present invention.

  As shown in FIG. 1, the gas detector 1 according to the first embodiment of the present example includes an emission unit 10 that emits measurement light in a measurement atmosphere, and a light receiving unit 20 that receives measurement light emitted from the emission unit 10. A controller 30 that performs various controls of the emitting unit 10 and the light receiving unit 20 is mounted on the apparatus main body.

  The emission unit 10 includes an LD module 11, a wavelength processing mechanism unit 12, and a laser pointer 13, and each component is provided on a heat sink 14 disposed at a predetermined location of the gas detection device 1.

  The LD module 11 is configured by a module including a semiconductor laser using semiconductor recombination light emission. The LD module 11 generates laser light having a wavelength that matches the absorption line unique to the measurement gas, and the laser light substantially coincides with the guide light (visible light laser) emitted from the laser pointer 13 at the measurement position. The light is emitted from a predetermined position toward the measurement atmosphere.

  Here, the configuration of the LD module 11 will be described with reference to FIG. As shown in FIG. 2, the LD module 11 includes a semiconductor laser 11a, a Peltier element 11b, a first temperature detection unit 11c, and a second temperature detection unit 11d that are hermetically housed in a sealed container 11e. Yes.

  The semiconductor laser 11a is a laser using semiconductor recombination emission, and is provided on the Peltier element 11b in this example. The semiconductor laser 11a is connected to a connection terminal portion 11f plated (for example, Au plating) in a sealed container 11e via a wire (for example, Au wire) 11g, and a predetermined energization current is transmitted via the wire 11g. The laser beam of a predetermined wavelength is emitted by being energized.

  The Peltier element 11b is a plate-like semiconductor element that utilizes the Peltier effect in which heat is transferred from one metal to the other when a current is passed through a junction of different kinds of metals. Has been implemented. The Peltier element 11b adjusts the temperature of the semiconductor laser 11a to a predetermined temperature by heat absorption / heat generation according to the energized current under the control of a temperature stabilization control unit 32 described later.

  The first temperature detecting means 11c is constituted by a temperature sensor using a change in resistance value due to a change in temperature, such as a thermistor or a platinum thin film temperature sensor, and the semiconductor laser 11a accommodated in the sealed container 11e. In order to measure the temperature of the Peltier element 11b synchronized with the temperature, it is mounted in the vicinity of the semiconductor laser 11a (mounted on the Peltier element 11b in this example) in the sealed container 11e. That is, measuring the temperature of the Peltier element 11b is equivalent to measuring the temperature of the semiconductor laser 11a. The first temperature detection means 11c detects the temperature of the Peltier element 11b, and outputs the detected temperature to the temperature stabilization control unit 32 as the first detection temperature.

  The second temperature detection means 11d is composed of a temperature sensor such as a thermistor similarly to the first temperature detection means 11c, and is a wire connected between the semiconductor laser 11a accommodated in the sealed container 11e and the connection terminal portion 11f. In order to measure the temperature of the connection terminal portion 11f including 11g, the temperature is provided on the connection terminal portion 11f connected to the semiconductor laser 11a and the wire 11g in the sealed container 11e. The second temperature detection unit 11d detects the temperature of the wire 11g connected between the connection terminal portion 11f and the semiconductor laser 11a, and outputs the detected temperature to the temperature stabilization control unit 32 as the second detection temperature. ing.

  The wavelength processing mechanism unit 12 includes a half mirror 12a, a gas cell 12b, a wavelength processing light receiver 12c, and a temperature sensor 12d. The wavelength processing mechanism unit 12 receives reference light for performing wavelength calibration of measurement light before and after the start of gas detection under the control of a wavelength processing control unit 33 described later, and wavelength-processes the received light reception signal. It is output to the control unit 33.

  The half mirror 12a is an optical mirror that divides a light beam into two (for example, 1: 1), and has an AR coating for preventing irregular reflection of external light on the surface in the transmission direction, and is emitted from the LD module 11. The laser light is incident and divided, one light is reflected to the gas cell 12b as reference light, and the other light is transmitted as measurement light into the measurement atmosphere.

  The gas cell 12b is composed of a container formed of glass or the like that does not attenuate the absorption wavelength of the sealed gas, and a gas to be measured such as methane, carbon dioxide, acetylene, and ammonia is sealed in the container. The reference light reflected by the half mirror 12a passes through the gas cell 12b and then enters the wavelength processing light receiver 12c.

  The wavelength processing photoreceiver 12c is configured by a semiconductor element that uses the photovoltaic effect of an electrical phenomenon caused by light such as a photodiode, for example, and converts it into electrical energy proportional to light energy. The wavelength processing light receiver 12c receives the reference light that has passed through the gas cell 12b, and outputs an electrical signal corresponding to the received reference light to the wavelength processing control unit 33 as a detection signal.

  The temperature sensor 12d is a sensor that utilizes a change in resistance value due to a change in temperature, such as a thermistor or a platinum thin film temperature sensor. The temperature sensor 12d detects the temperature in the vicinity of the gas cell 12b in order to correct the oscillation wavelength due to the ambient temperature, and outputs the detected temperature to the wavelength processing control unit 33 as a corrected temperature value at the time of wavelength calibration.

  The laser pointer 13 emits position confirmation guide light (visible light) from which the measurement light emitted from the LD module 11 is emitted.

  The light receiving unit 20 includes a light receiving lens 21 and a detection light receiver 22, and collects and receives the measurement light reflected from the measurement atmosphere as the measurement light is emitted from the LD module 11.

  The light receiving lens 21 is composed of, for example, a fullnel lens, and is composed of a condensing lens that condenses the light that passes through the measurement atmosphere and is reflected by the reflecting object, and detects the measurement light reflected from the measurement object. 22 is condensed.

  The detection light receiver 22 is configured by a semiconductor element that uses the photovoltaic effect of an electrical phenomenon caused by light such as a photodiode, for example, and converts it into electrical energy proportional to light energy. The detection light receiver 22 receives the measurement light collected by the light receiving lens 21 and outputs an electrical signal corresponding to the received measurement light as a detection signal to the gas detection control unit.

  The controller 30 includes a storage unit 31, a temperature stabilization control unit 32, a wavelength processing control unit 33, and a gas detection control unit 34, and is output from each unit of the emitting unit 10 and the light receiving unit 20. Various processes are performed based on the signal.

  The storage unit 31 includes a storage medium such as a semiconductor memory such as a ROM or a RAM or an HDD. The storage unit 31 has a preset temperature value set in advance for driving the semiconductor laser 11a at a predetermined oscillation frequency, a reference 2f / 1f value used as a reference value at the time of wavelength confirmation by the wavelength confirmation determination means 33Ac, and wavelength calibration. In addition to storing a reference 2f value used as a reference value at the time of wavelength calibration by the discriminating means 33Bc, various processing control information relating to driving of each part of the gas detection device 1, various data relating to gas detection such as the gas concentration of the measurement gas, etc. Is remembered.

  The temperature stabilization control unit 32 corrects the temperature of the semiconductor laser 11a to the set temperature value stored in the storage unit 31 (that is, the drive temperature value of the semiconductor laser 11a necessary for emitting a desired oscillation wavelength). This is controlled to stabilize the temperature of the semiconductor laser 11a.

Here, the temperature stabilization process performed by the temperature stabilization control unit 32 will be described. As the temperature stabilization process, first, a second temperature detection value serving as a correction temperature value is acquired from the second temperature detection means 11d. And the set temperature value memorize | stored in the memory | storage part 31 is correct | amended using the 2nd temperature detection value acquired from the 2nd temperature detection means 11d, and LD target temperature value used as the target temperature of the semiconductor laser 11a is calculated. Next, an error value (temperature difference) between the current temperature of the semiconductor laser 11a and the calculated target temperature is obtained by subtracting the calculated LD target temperature value from the first temperature detection value input from the first temperature detecting means 11c. Is calculated. Then, a Peltier control set value for controlling the drive of the Peltier element 11b is calculated according to the calculated error value, and an energization current value supplied to the Peltier element 11b is controlled according to the Peltier element set value. The temperature of the semiconductor laser 11a, that is, the LD module 11, is stabilized so that the difference between the detected temperature value and the LD target temperature value becomes ± 0.
Further, the temperature stabilization control unit 32 corrects the set temperature value based on a temperature adjustment signal output from a wavelength confirmation determination unit described later.

  The wavelength processing control unit 33 includes a wavelength confirmation processing unit 33A and a wavelength calibration processing unit 33B, and performs various controls related to wavelength confirmation and wavelength calibration of the LD module 11 before and after the start of detection.

  The wavelength confirmation processing unit 33A includes a wavelength confirmation calculation unit 33Aa, a wavelength confirmation correction unit 33Ab, and a wavelength confirmation determination unit 33Ac.

  The wavelength confirmation calculating means 33Aa has a 1f value based on a change in intensity of a fundamental sensitive detection signal (hereinafter abbreviated as 1f signal) of a modulation frequency detected from the detection signal from the wavelength processing photodetector 12c, and the 1f value. A 2f value is calculated based on a change in intensity of a second harmonic phase sensitive detection signal (hereinafter abbreviated as a 2f signal), which is a detection signal of twice the value. Further, the wavelength confirmation calculating unit 33Aa calculates a 2f / 1f value that is a ratio of the calculated 1f value and 2f value, and outputs the 2f / 1f value to the wavelength confirmation correcting unit 33Ab.

  The wavelength checking correction unit 33Ab corrects the 2f / 1f value, which fluctuates depending on the ambient temperature, based on the corrected temperature value output from the temperature sensor 12d as necessary, and uses the corrected 2f / 1f value for wavelength checking. This is output to the discriminating means 33Ac.

The wavelength confirmation determination unit 33Ac compares and determines the 2f / 1f value output from the wavelength confirmation correction unit 33Ab and the reference 2f / 1f value serving as the reference stored in the storage unit 31. When the output 2f / 1f value is within a predetermined range of the reference 2f / 1f value (for example, within ± 10% of the reference 2f / 1f value), the wavelength of the LD module 11 is stabilized. Determine. If the output 2f / 1f value is outside the predetermined range of the reference 2f / 1f value, a temperature adjustment signal for correcting the current drive temperature value of the LD module 11 is provided to stabilize the wavelength. This is output to the temperature stabilization control unit 32.
If the 2f / 1f value is within the predetermined range of the reference 2f / 1f value, a wavelength confirmation processing completion notification or the like is output to a notification control unit (not shown), and the wavelength confirmation processing is performed for the operator. It is also possible to adopt a configuration for notifying the state.

  The wavelength calibration processing unit 33B includes a wavelength calibration calculating unit 33Ba, a wavelength calibration correcting unit 33Bb, and a wavelength calibration determining unit 33Bc.

  The wavelength calibration calculating unit 33Ba sweeps (changes) the temperature at which the LD module 11 is stabilized, that is, the current set temperature value of the semiconductor laser 11a controlled by the temperature stabilization control unit 32, with a predetermined amplitude. A 2f value based on the 2f signal of the modulation frequency detected from the detection signal from the wavelength processing photoreceiver 12c is calculated and output once to the wavelength calibration correcting means 33Bb. Then, the wavelength calibration calculating unit 33Ba calculates a maximum value from the 2f values output from the wavelength calibration correcting unit 33Bb (in this case, a plurality of 2f values are calculated because the temperature is swept with a predetermined amplitude). The maximum 2f value (which indicates the maximum value among the calculated 2f values) is calculated, and this maximum 2f value is output to the wavelength calibration discriminating means 33Bc.

  The wavelength calibration correcting unit 33Bb corrects the 2f value output from the wavelength calibration calculating unit 33Ba based on the corrected temperature value output from the temperature sensor 12d as necessary, and uses the corrected 2f value for wavelength calibration. This is output to the calculation means 33Ba.

The wavelength calibration discriminating means 33Bc compares and discriminates the maximum 2f value output from the wavelength calibration calculating means 33Ba and the reference 2f value serving as the reference stored in the storage unit 31. If the output maximum 2f value is not less than a predetermined reference value of the reference 2f value (for example, 70% or more of the reference 2f value), the set temperature value of the LD module 11 is calculated from the maximum 2f value, and the storage unit 31 to output the set temperature value. As a result, the oscillation wavelength of the LD module 11 is calibrated to a wavelength that matches the measurement gas absorption line.
In addition, when the output maximum 2f value is equal to or less than the predetermined reference value of the reference 2f value, the 2f value calculation signal for calculating the 2f value again is changed by changing the sweeping temperature range (increasing the swing range). This is output to the wavelength calibration calculation means 33Ba.

  The gas detection control unit 34 includes a measurement light amplification unit 34a, a light reception signal detection unit 34b, and a calculation unit 34c.

  The measurement light amplifying means 34a is composed of a preamplifier, and the 1f signal and 2f signal detected by the light reception signal detection means 34b for the detection signal corresponding to the measurement light input from the measurement light receiver 22 are equivalent in the measurement target gas concentration range. Thus, the amplification level is amplified to an optimum amplification level for each of the 1f signal and the 2f signal so as to be output to the received light signal detection means 34b.

  The received light signal detection unit 34b performs signal processing on the measurement light signal amplified by the measurement light amplification unit 34a, and phase-sensitively detects the 1f signal and the 2f signal.

  The calculating means 34c receives the 1f signal and 2f signal from the received light signal detecting means 34b, and the ratio 2f between the 2f value based on the intensity change of the 2f signal and the 1f value based on the intensity change of the 1f signal which is the original modulation frequency. The gas concentration of the measurement target gas is calculated based on / 1f.

  Next, the processing operation of the gas detection device 1 described above will be described with reference to FIGS. Here, the wavelength confirmation processing of the LD module 11 mainly performed at the time of inspection before the start of gas detection shown in FIG. 4 and the oscillation wavelength shift accompanying the drive temperature value of the LD module 11 shown in FIG. 5 are calibrated to correct absorption lines. A wavelength calibration process for this will be described.

  First, the wavelength confirmation process before starting the gas detection will be described with reference to FIG. As the gas detector 1 is driven, the temperature stabilization process described above is performed in order to drive the LD module 11 based on a predetermined set temperature value (ST1). Next, the laser light emitted from the LD module 11 is branched into measurement light and reference light by the half mirror 12a, and the branched reference light passes through the gas cell 12b and is received by the wavelength processing light receiver 12c. (ST2).

Then, a detection signal corresponding to the reference light received by the wavelength processing light receiver 12c in ST2 is output to the wavelength processing control unit 33, and the 1f value based on the 1f signal detected according to the detection signal, and the 1f value. The 2f value based on the 2f signal, which is a detection signal twice as large as (2), is calculated (ST3). Further, a 2f / 1f value that is a ratio of the calculated 1f value and 2f value is calculated (ST4).
In ST4, if the 2f / 1f value varies depending on the ambient temperature in the vicinity of the gas cell 12b, the 2f / 1f value is corrected based on the corrected temperature value output from the temperature sensor 12d as necessary.

  Next, the 2f / 1f value calculated in ST4 (if corrected, the corrected 2f / 1f value is used) and the reference 2f / 1f value serving as the reference stored in the storage unit 31 are compared ( ST5). When the output 2f / 1f value is within a predetermined range of the reference 2f / 1f value (for example, within ± 10% of the reference 2f / 1f value) (ST6-Yes), the wavelength of the LD module 11 is stable. It is confirmed that

  On the other hand, if the output 2f / 1f value is outside the predetermined range of the reference 2f / 1f value (ST6-No), the LD target temperature value is changed in ST7 in order to stabilize the wavelength of the LD module 11 again. After (for example, −0.1 ° C.), the process returns to ST1 to perform wavelength confirmation processing.

  In ST6-No, the process returns to ST1 in order to stabilize the wavelength of the LD module 11. However, if the wavelength of the LD module 11 cannot be stabilized even after repeating a predetermined number of times, an error is assumed as a failure of the apparatus itself. It is good also as a structure to output.

  Next, a wavelength calibration process for calibrating the oscillation wavelength shift accompanying the drive temperature value of the LD module 11 to a correct absorption line will be described with reference to FIG. First, in order to drive the LD module 11 based on a predetermined set temperature value, the above-described temperature stabilization process is performed (ST11). Next, the laser light emitted from the LD module 11 is branched into measurement light and reference light by the half mirror 12a, and the branched reference light passes through the gas cell 12b and is received by the wavelength processing light receiver 12c ( ST12).

In ST12, a detection signal corresponding to the reference light received by the wavelength processing light receiver 12c is output to the wavelength processing control unit 33, and the current drive temperature value of the LD module 11 is swept (changed) with a predetermined amplitude. However, the 2f value based on the 2f signal of the modulation frequency detected from the detection signal from the wavelength processing light receiver 12c is calculated (ST13). Next, a maximum 2f value is calculated from the calculated 2f values (ST14).
In ST13, if the 2f value varies depending on the ambient temperature in the vicinity of the gas cell 12b, the correction is made based on the corrected temperature value output from the temperature sensor 12d as necessary.

Next, the calculated maximum 2f value is compared with a reference 2f value serving as a reference stored in the storage unit 31 (ST15). When the output maximum 2f value is equal to or greater than a predetermined reference value of the reference 2f value (eg, 70% or more of the reference 2f value) (ST16-Yes), the set temperature value of the LD module 11 is calculated from the maximum 2f value. The calculated temperature is output to the storage unit 31 and the set temperature value is changed (ST17). As a result, the oscillation wavelength of the LD module 11 is calibrated to a wavelength that matches the measurement gas absorption line.
On the other hand, if the output maximum 2f value is less than or equal to the predetermined reference value of the reference 2f value (ST16-No), the temperature range to be swept is changed (enlarged swing width) (ST18), and the 2f value is calculated again. Return to ST13 for

As described above, in the gas detection device 1 described above, the laser light emitted from the LD module 11 is branched into measurement light and reference light by the half mirror. The measurement light is used for normal gas detection, and the reference light is passed through the gas cell and then received by the wavelength processing light receiver 12c. Based on the detection signal corresponding to the received reference light, the wavelength processing control unit 33 performs LD processing. Wavelength confirmation processing and wavelength calibration processing of the module 11 are performed.
As a result, the detection target gas sealed in the conventional gas cell can be detected at all times. Therefore, even when the wavelength of the semiconductor laser 11a is deviated due to deterioration of the semiconductor laser 11a or temperature change in the use environment. It is possible to confirm that the wavelength has shifted due to the change in the detection signal of the reference light, and to self-calibrate the wavelength shift in the apparatus. Further, it can be confirmed that the adjustment accompanying the wavelength confirmation can be easily performed in a short time at a low cost, and the detection of the gas to be measured can be reliably measured at the time of the inspection before the start of the gas detection measurement.

  By the way, in the above-described embodiment, a part of the laser light output from the LD module 11 is reflected by the half mirror 12a as reference light, and the reflected reference light is passed through the gas cell 12b, and then the wavelength processing photodetector 12c. The wavelength confirmation process and the wavelength calibration process of the LD module 11 are performed based on the detection signal corresponding to the received reference light. However, the present invention is not limited to this. Even if it is a form-a 6th form (FIGS. 6-10), there can exist an effect similar to the wavelength confirmation process and wavelength calibration process which were mentioned above.

As shown in FIG. 6, the gas detector 1 of the second embodiment has a structure in which a gas to be measured is filled in a sealed container of the LD module 11 and hermetically sealed. Further, in the gas detector 1 of the second form, the semiconductor laser 11a emits light from both the front and rear surfaces. Therefore, in the gas detector 1 of the second form, the laser light emitted from the front surface is used as measurement light, and the rear surface. The laser beam emitted from the laser beam is used as a reference beam for calibration, the reference beam is received by a wavelength processing light receiver 12c provided behind the semiconductor laser 11a, and the wavelength is determined based on a detection signal corresponding to the received reference beam. By performing confirmation processing and wavelength calibration processing, processing similar to the above-described best mode is possible.
In the second embodiment, since the measurement target gas is filled in the LD module 11, the measurement light emitted from the LD module 11 is absorbed by the measurement target gas filled in the LD module 11. It is emitted in the state. Therefore, when the measurement light reflected from the measurement atmosphere is collected by the light receiving lens 21 and received by the detection light receiver 22, the gas concentration of the measurement target gas filled in the LD module 11 is subtracted (offset). The gas concentration in the measurement atmosphere can be accurately detected.

As shown in FIG. 7, the gas detector 1 of the third form has a structure in which a gas cell 12 b is provided in front of the LD module 11. And in the gas detector 1 of 3rd form, the laser beam which served as the measurement light and the reference light emitted from the LD module 11 is emitted into the measurement atmosphere after passing through the gas cell 12b, and the laser light reflected from the measurement atmosphere is reflected. The light is collected by the light receiving lens 21, received by the detection light receiver 22, and subjected to wavelength confirmation processing and wavelength calibration processing based on the detection signal corresponding to the received reference light. Processing is possible.
In the third embodiment, since the gas cell 12b filled with the measurement target gas is provided in front of the LD module 11, the laser light emitted as measurement light at the time of gas detection is filled in the gas cell 12b. The light is emitted while being absorbed by the measured gas. Therefore, at the time of gas detection, when the laser beam reflected from the measurement atmosphere is collected by the light receiving lens 21 and received by the detection light receiver 22, the gas concentration of the measurement target gas filled in the gas cell 12b is subtracted (offset). Thus, the gas concentration in the measurement atmosphere can be accurately detected.

As shown in FIG. 8, in the gas detector 1 of the fourth embodiment, a gas cell 12b is provided in front of the LD module 11, and one of the reflectors is pivotally supported in front of the gas cell 12b so as to be swingable at a predetermined angle. 23 is provided. And in the gas detector 1 of the 4th form, at the time of gas detection, the reflecting plate 23 exists in the position of the broken line in a figure, and the measurement light radiate | emitted from the LD module 11 is radiate | emitted in measurement atmosphere, and is reflected from measurement atmosphere The measured light is condensed by the light receiving lens 21 and received by the detection light receiver 22 to perform gas detection. Further, at the time of wavelength confirmation or wavelength calibration, the reflecting plate 23 is swung to the position of the solid line in the figure, and the reference light that has passed through the gas cell 12b from the LD module 11 is directed to the detection light receiver 22 by the reflecting plate 23. The reflected reference light is received by the detection light receiver 22, and the wavelength confirmation process and the wavelength calibration process are performed based on the detection signal corresponding to the received reference light. It is possible to perform the same processing as.
In the fourth embodiment, since the gas cell 12b filled with the measurement target gas is provided in front of the LD module 11, the laser light emitted as measurement light at the time of gas detection is filled in the gas cell 12b. The light is emitted while being absorbed by the measured gas. Therefore, at the time of gas detection, when the laser beam reflected from the measurement atmosphere is condensed by the light receiving lens 21 and received by the detection light receiver 22, the gas concentration of the measurement target gas filled in the gas cell 12b is subtracted (offset). Thus, the gas concentration in the measurement atmosphere can be accurately detected.

As shown in FIG. 9, the gas detector 1 of the fifth embodiment has a structure in which a gas cell 12 b is provided in front of the detection light receiver 22. And in the gas detector 1 of 5th form, the laser beam which served as the measurement light and the reference light emitted from the LD module 11 is emitted into the measurement atmosphere after passing through the gas cell 12b, and the laser light reflected from the measurement atmosphere is reflected. The light is collected by the light receiving lens 21, received by the detection light receiver 22, and subjected to wavelength confirmation processing and wavelength calibration processing based on the detection signal corresponding to the received reference light. Processing is possible.
In the fifth embodiment, since the gas cell 12b filled with the measurement target gas is provided in front of the LD module 11, the laser light emitted as the measurement light at the time of gas detection is filled in the gas cell 12b. The light is emitted while being absorbed by the measured gas. Therefore, at the time of gas detection, when the laser beam reflected from the measurement atmosphere is collected by the light receiving lens 21 and received by the detection light receiver 22, the gas concentration of the measurement target gas filled in the gas cell 12b is subtracted (offset). Thus, the gas concentration in the measurement atmosphere can be accurately detected.

As shown in FIG. 10, the gas detector 1 of the sixth embodiment has a structure in which a gas cell 12 b is provided in front of the light receiving lens 21. And in the gas detector 1 of 5th form, the laser beam which served as the measurement light and the reference light emitted from the LD module 11 is emitted into the measurement atmosphere after passing through the gas cell 12b, and the laser light reflected from the measurement atmosphere is reflected. The light is collected by the light receiving lens 21, received by the detection light receiver 22, and subjected to wavelength confirmation processing and wavelength calibration processing based on the detection signal corresponding to the received reference light. Processing is possible.
In the sixth embodiment, since the gas cell 12b filled with the measurement target gas is provided in front of the LD module 11, the laser light emitted as the measurement light at the time of gas detection is filled in the gas cell 12b. The light is emitted while being absorbed by the measured gas. Therefore, at the time of gas detection, when the laser beam reflected from the measurement atmosphere is collected by the light receiving lens 21 and received by the detection light receiver 22, the gas concentration of the measurement target gas filled in the gas cell 12b is subtracted (offset). Thus, the gas concentration in the measurement atmosphere can be accurately detected.

  As mentioned above, although the best form in this invention was demonstrated, this invention is not limited with the description and drawing by this form. That is, it is a matter of course that all other forms, examples, operation techniques, and the like made by those skilled in the art based on this form are included in the scope of the present invention.

It is a schematic block diagram for demonstrating the structure of the 1st form of the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the structure of LD module mounted in the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the structure of the wavelength processing control part in the gas detection apparatus which concerns on this invention. It is a flowchart figure for demonstrating the wavelength confirmation process of the gas detection apparatus which concerns on this invention. It is a flowchart figure for demonstrating the wavelength calibration process of the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the 2nd form of the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the 3rd form of the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the 4th form of the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the 5th form of the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the 6th form of the gas detection apparatus which concerns on this invention. It is a schematic block diagram for demonstrating the structure of the conventional gas detection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas detection apparatus 10 Output part 11 LD module 12 Wavelength processing mechanism part 12a Half mirror 12b Gas cell 12c Wavelength processing light receiver 12d Temperature sensor 13 Laser pointer 20 Light receiving part 21 Light receiving lens 22 Measurement light receiver 30 Controller 31 Storage part 32 Temperature stabilization control unit 33 Wavelength processing control unit 33A Wavelength confirmation processing unit 33Aa Wavelength confirmation calculation means 33Ab Wavelength confirmation correction means 33Ac Wavelength confirmation determination means 33B Wavelength calibration processing section 33Ba Wavelength calibration calculation means 33Bb Wavelength calibration correction means 33Bc Wavelength calibration discriminating means 34 Gas detection control unit 34a Measurement light amplification means 34b Light reception signal detection means 34c Calculation means

Claims (6)

An LD module (11) mounted with a semiconductor laser for emitting laser light;
A half mirror (12a) that branches the laser light emitted from the LD module into measurement light and reference light, a gas cell (12b) in which the same kind of gas as the measurement target gas is sealed, and the gas cell passed A wavelength processing mechanism (12) including a wavelength processing light receiver (12c) that receives the reference light and outputs a detection signal corresponding to the received reference light;
A storage unit (31) for storing a preset temperature value set in advance for driving the semiconductor laser at a predetermined oscillation frequency and a reference 2f value used as a reference value during wavelength calibration;
A temperature stabilization controller (32) for stabilizing the driving temperature value of the LD module to the set temperature value stored in the storage unit;
The fundamental frequency sensitive detection of the modulation frequency detected from the detection signal output from the wavelength processing mechanism unit while sweeping the driving temperature value of the LD module controlled by the temperature stabilization control unit with a predetermined amplitude. A wavelength for calculating a 2f value based on a change in the intensity of a second harmonic phase sensitive detection signal that is a detection signal that is twice the signal, and calculating and outputting a maximum 2f value that is the maximum value from the calculated 2f values The calibration calculation means (33Ba) compares the maximum 2f value output from the wavelength calibration calculation means with the reference 2f value stored in the storage unit, and the maximum 2f value is a predetermined reference of the reference 2f value. If it is the above, wavelength calibration determination means (33Bc) that calculates the set temperature value of the LD module from the maximum 2f value, outputs the calculated set temperature value to the storage unit, and changes it. Have Wavelength processing control unit (33),
A gas detection device comprising: The wavelength processing mechanism (12) includes a temperature sensor (12d) that outputs a temperature value detected in the vicinity of the gas cell (12b) as a correction temperature value.
The wavelength processing control unit (33) corrects the 2f value calculated by the wavelength calibration calculation unit (33Ba) based on the correction temperature value as necessary, and calculates the corrected 2f value for the wavelength calibration calculation. The gas detection apparatus according to claim 1, further comprising a wavelength calibration correcting means (33Bb) for outputting to the means. The storage unit (31) further stores a reference 2f / 1f value used as a reference value when checking the wavelength,
The wavelength processing control unit (33) includes a 1f value based on a change in intensity of a fundamental sensitive detection signal having a modulation frequency detected from a detection signal from the waveform processing light receiver (12c), and twice the 1f value. A wavelength checking calculation means (33Aa) for calculating a 2f value based on a change in intensity of the second harmonic phase sensitive detection signal, which is a detection signal of, and calculating and outputting a 2f / 1f value which is a ratio of the two values; ,
The calculated 2f / 1f value is compared with the reference 2f / 1f value stored in the storage unit. When the 2f / 1f value is within a predetermined range of the reference 2f / 1f value, The gas detection apparatus according to claim 1, further comprising a wavelength confirmation processing unit (33A) having a wavelength confirmation determination unit (33Ac) for determining that the wavelength of the LD module 11 is stabilized. The wavelength processing mechanism (12) includes a temperature sensor (12d) that outputs a temperature value detected in the vicinity of the gas cell (12b) as a correction temperature value.
The wavelength processing control unit (33) corrects the 2f / 1f value calculated by the wavelength check calculation unit based on the correction temperature value as necessary, and uses the corrected 2f value as the wavelength check calculation unit. 4. The gas detection device according to claim 3, further comprising a wavelength checking correction means (33Ab) for outputting. A calibration method using the gas detection device (1) according to claim 1,
Performing temperature stabilization processing of the LD module (11) in the temperature stabilization control unit (32);
While detecting the drive temperature value of the LD module with a predetermined amplitude, the detection signal is twice the fundamental sensitive detection signal of the modulation frequency detected from the detection signal output from the wavelength processing mechanism (12). Calculating a 2f value based on an intensity change of the second harmonic phase sensitive detection signal,
Calculating a maximum 2f value that is a maximum value from the calculated 2f values;
Comparing the calculated maximum 2f value with a reference 2f value stored in the storage unit (31);
A step of calculating a set temperature value of the LD module from the maximum 2f value and changing the set temperature value stored in the storage unit when the maximum 2f value is equal to or greater than a predetermined reference value of a reference 2f value; When,
A gas detection device calibration method comprising: A wavelength confirmation method using the gas detector (1) according to claim 3,
Performing temperature stabilization processing of the LD module (11) in the temperature stabilization control unit (32);
The 1f value based on the intensity change of the fundamental frequency sensitive detection signal of the modulation frequency detected from the detection signal output from the wavelength processing mechanism section (12), and the 2 × detection signal that is twice the 1f value. Calculating a 2f value based on an intensity change of the wave phase sensitive detection signal, and calculating a 2f / 1f value that is a ratio of both values;
Comparing the 2f / 1f value with a reference 2f / 1f value stored in the storage unit;
Determining that the wavelength of the LD module is stabilized when the 2f / 1f value is within a predetermined range of the reference 2f / 1f value;
A method for confirming the wavelength of a gas detector, comprising:

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