JPH0515218B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for instantaneously measuring the gas concentration of ammonia gas mixed with sulfur dioxide gas in the exhaust gas, for example in a flue exhaust gas denitrification plant. ,
The present invention also relates to an ultraviolet absorption type ammonia gas analyzer that can perform continuous automatic measurements.

[Conventional technology]

Currently, in large denitrification equipment, ammonia (NH ₃ ) is injected into the exhaust gas and a catalyst is used to reduce nitrogen oxides (NO _x ) to harmless nitrogen (N ₂ ) and water (H ₂ O). do. In this case, when the concentration of unreacted ammonia gas reaches approximately 5 ppm or more, the sulfuric anhydride (SO ₃ ) in the exhaust gas reacts with the unreacted ammonia in the air heater located after the denitrification equipment, producing acidic ammonium sulfate or ammonium sulfate. Crystals will precipitate and the air heater will become clogged. This clogging phenomenon progresses rapidly when the ammonia gas concentration exceeds 5 ppm. Therefore, it is very important to accurately control this ammonia gas concentration.

On the other hand, petroleum is the main fuel used in boilers in thermal power plants and various factories, but in recent years some plants have begun to use coal instead of petroleum, which has limited reserves. When coal is used as fuel, the coal contains a large amount of sulfur (S), so the concentration of sulfuric anhydride (SO ₃ ) in the exhaust gas also increases. Therefore, in order to prevent the air heater from clogging, it is necessary to control the concentration of unreacted ammonia within a range of 1 to 2 ppm. This unreacted ammonia gas concentration is the amount of NO _x in the exhaust gas,
It varies greatly depending on the amount (volume) of exhaust gas, the activity of the reduction catalyst, the amount of ammonia injected, etc. Therefore, it is necessary to constantly and accurately measure the concentration of this unreacted ammonia gas.

In this way, an ammonia gas analyzer that utilizes the ultraviolet absorption effect of ammonia gas at a specific wavelength has been proposed as a device for directly and accurately measuring the ammonia gas concentration in exhaust gas. Publication No. 17462).

In other words, when ammonia gas is irradiated with ultraviolet rays, there are 207 nm to 207 nm in the ultraviolet spectrum.
A significant absorption spectrum occurs at the 211 nm wavelength. Therefore, by measuring the intensity of this absorption spectrum, the ammonia gas concentration can be measured. However, the above wavelengths of 207 to 211 nm are included in the absorption spectrum of sulfur dioxide gas. Therefore, we simultaneously measure the intensity of the absorption spectrum near 300 nm of this sulfur dioxide gas alone. 207 with sulfur dioxide gas alone
Since the relative relationship between the absorption spectrum intensity of 211nm to 211nm and the absorption spectrum intensity near 300nm is known, from the absorption spectrum intensity near 300nm,
Interference values for ammonia gas concentration at 207 to 211 nm can be calculated. Therefore, by subtracting the simultaneously measured absorption spectrum intensity near 300 nm and the interference value from the measured absorption spectrum intensity from 207 to 211 nm, the accurate gas of ammonia gas alone can be obtained by removing the interference of sulfur dioxide gas. It is possible to measure the concentration.

For reference, absorption spectra of ammonia gas and sulfur dioxide gas are shown in FIG. In the measurement of sulfur dioxide gas, the meaning of around 300 nm is the first
As can be understood from Figure 1, this means that the center wavelength of wavelength modulation should be matched to the absorption value or absorption minimum value in the range of 280 nm to 320 nm.

FIG. 8 is a block diagram showing the ammonia gas analyzer mentioned above. That is, the ultraviolet light beam irradiated from the light source 1 is irradiated with exhaust gas introduced from the outside in the light absorption cell 2, and then reflected by the collector 5 in the spectrometer 4 via the entrance slit 3.
The light is irradiated onto the diffraction grating 6. The light beam is diffracted into a dispersed spectrum by the diffraction grating 6 and is incident on the collector 7 . 207 to 207 reflected at collector 7
The dispersion spectrum of 211nm wavelength is the exit slit 8a.
The signal is converted into an electrical signal by the photoelectric converter 9a. The dispersion spectrum of the wavelength near 300 nm reflected by the collector 7 is reflected by the plane mirror 9 and the exit slit 8.
b, and is converted into an electrical signal by a photoelectric converter 9b. Then, in the arithmetic circuit 10, each photoelectric converter 9
The ammonia gas concentration is calculated from the electrical signals corresponding to the respective spectral intensities obtained in a and 9b.

In this case, each exit slit 8a, 8b is used to accurately measure the desired absorption spectrum intensity by separating it from the surrounding background spectrum.
is vibrated at a constant frequency using the U-shaped tuning fork 11 shown in FIG. 9 to modulate the light input from each exit slit 8a, 8b to each photoelectric converter 9a, 9b.
Then, the electrical signals output from each photoelectric converter 9a, 9b are synchronously detected at a frequency twice the vibration frequency obtained from the tuning fork drive circuit 12.

The U-shaped tuning fork 11 is vibrated by an electromagnetic coil 13a, and its vibration amplitude is detected by another electromagnetic coil 13b, and is controlled by a tuning fork drive circuit 12 so that the vibration amplitude always remains at a constant value.

[Problem that the invention seeks to solve]

However, even in the ammonia gas analyzer configured as shown in FIGS. 8 and 9, the following problems still remain to be solved. That is,
The dispersion spectrum input to the photoelectric converter 9a via the exit slit 8a is 207 to 211 nm as described above.
In order to obtain light over a wavelength range, it is necessary to vibrate the exit slit 8a over a wavelength range from 207 nm to 211 nm in the imaging plane of the dispersion spectrum. This amplitude value changes depending on the distance between the diffraction grating 6 and the collector 7 and the distance from the collector 7 to the exit slit 8a, but it must be set to at least 1 mm to obtain a certain level of measurement accuracy. be. For example, U
One leg of the glyph tuning fork 11, length: 100mm,
If it is made up of square rods with a cross section of 4 x 5 mm, the vibration energy will be large in order to vibrate a metal with a weight equivalent to this volume with an amplitude of 1 mm.
There was a problem in that vibrations were propagated not only to the U-shaped tuning fork 11 but also to the entire spectrometer 4, resulting in a decrease in measurement accuracy.

In addition, as mentioned above, the ammonia gas concentration
Since the calculation is made from the absorption spectrum intensity in the wavelength range of 207 to 211 nm and the absorption spectrum intensity near the 300 nm wavelength, in order to obtain the measurement accuracy mentioned above, the setting accuracy of the measurement wavelength λ in each spectrum intensity measurement must be adjusted. It is necessary to keep the error within ±0.01 nm. That is, if the stability of this measurement wavelength is poor, the above-mentioned correction value due to sulfur dioxide gas will fluctuate. For example, if the measurement wavelength changes by 0.02 nm, the correction value changes by 1 to 2 ppm. As a result, there is a problem that the ammonia gas concentration calculated using this correction value also fluctuates greatly, making it impossible to obtain accurate measured values.

In addition, Figure 10 shows that the concentration of sulfur dioxide gas (SO ₂ ) in the exhaust gas detected near the 300 nm wavelength is 207 to 300 nm.
It is an interference correction curve diagram showing the ratio of ammonia gas concentration and sulfur dioxide gas concentration to the combined concentration value at a wavelength of 211 nm, that is, the degree of interference of sulfur dioxide gas concentration with ammonia gas concentration. As is clear from this figure, the degree of interference of the sulfur dioxide gas concentration varies greatly depending on the amplitude of the U-shaped tuning fork 11, that is, the size of the wavelength range included in this amplitude. Therefore, it is necessary to always control the amplitude of the U-shaped tuning fork 11 to a constant value during measurement.

However, the U-shaped tuning fork 11 shown in FIG.
The vibration amplitude is detected by the electromagnetic coil 13b.
When the vibration amplitude of the U-shaped tuning fork 11 is detected magnetically in this way, when the ambient temperature changes, not only the material properties of the U-shaped tuning fork 11 change, but also the vibration amplitude between the U-shaped tuning fork 11 and the electromagnetic coil 13b changes. The magnetic resistance of the air present in the magnetic gap changes. Therefore, it is difficult to accurately detect the amplitude of the U-shaped tuning fork 11 using this magnetic coil 13b. As a result, the amplitude of the U-shaped tuning fork 11 cannot always be accurately controlled to a constant value, resulting in a decrease in the measurement accuracy of the ammonia gas concentration.

In addition, two types are available: one for detecting a dispersive spectrum of 207 to 211 nm wavelength and one for detecting a dispersive spectrum of 300 nm wavelength.
U-shaped tuning forks 11 were required. Therefore, there is also the problem that the entire device becomes larger.

The present invention was developed based on the above circumstances, and its purpose is to modulate the light flux with a predetermined frequency and amplitude using a vibrator just before it passes through the light absorption cell and enters the diffraction grating. By optically detecting the amplitude of the transducer and controlling it to a constant value, high measurement accuracy can be maintained even if the ambient temperature changes significantly.The number of installed transducers can also be reduced, which reduces the overall cost of the device. The object of the present invention is to provide an ultraviolet absorption type ammonia gas analyzer that can be made smaller and lighter.

[Means for solving problems]

The ultraviolet absorption type ammonia gas analyzer of the present invention allows the ultraviolet light beam output from the light source to pass through a light absorption cell into which a medium to be measured containing ammonia gas and sulfur dioxide gas is introduced, and the passed light beam is By optically detecting the amplitude using the vibrator drive control device, the vibrator is vibrated at a constant amplitude and frequency, and by reflecting it on a plane mirror, the vibrator is vibrated at a constant amplitude and frequency. The reflected light beam is diffracted and dispersed by a diffraction grating to output a dispersed spectrum. Then, the first exit slit is placed at a position where it receives the oscillating dispersion spectrum of wavelengths from 207 nm to 211 nm, which corresponds to the absorption spectra of ammonia gas and sulfur dioxide gas, among the oscillating dispersion spectra output from the diffraction grating. A first photoelectric converter is provided that wavelength modulates the dispersion spectrum and converts the light emitted from the first exit slit, which is converted into a light intensity modulated signal by the wavelength modulation, into an electrical signal, and output from the diffraction grating. Among the oscillating dispersion spectra that correspond to the absorption spectrum of sulfur dioxide gas
A second exit slit is provided at a position to receive the oscillating dispersion spectrum of a wavelength of 300 nm and its vicinity, and the light emitted from the second exit slit, which is converted into a light intensity modulated signal by wavelength modulation, is converted into an electrical signal. A second photoelectric converter is arranged to convert the first photoelectric converter.
In this signal processing circuit, the electrical signal output from the first photoelectric converter is synchronously detected at a frequency twice the vibration frequency of the oscillator, and the first signal corresponding to the magnitude of the absorption spectrum in the wavelength range of 207 nm to 211 nm is detected. The magnitude of the amplitude of the optical intensity modulation signal is calculated, and the second signal processing circuit synchronously detects the electric signal output from the second photoelectric converter at a frequency twice the vibration frequency of the vibrator. The magnitude of the light intensity modulation signal corresponding to the magnitude of the absorption spectrum of the 300 nm wavelength and its neighboring wavelengths is calculated. Then, the correct ammonia gas concentration in the medium to be measured is calculated by subtracting the second amplitude from the first amplitude and the interference value found from the interference correction curve using a subtraction circuit. .

[Effect]

In the ultraviolet absorption type ammonia gas analyzer configured in this way, the ultraviolet light beam output from the light source forms an absorption spectrum in the light absorption cell at wavelengths of 207 nm to 211 nm and around a wavelength of 300 nm. The light beam with absorption spectra formed at two locations is modulated by a vibrator with a constant amplitude and frequency. Then, the modulated light beam is directly separated by a diffraction grating into an oscillating dispersion spectrum having each wavelength. Then, a first beam is placed at a position where the center wavelength of the oscillating dispersion spectrum is 207 to 211 nm.
An exit slit and a first photoelectric converter that receives the light intensity-modulated light emitted from the exit slit are provided, and a second exit slit and a first photoelectric converter that receives the light intensity-modulated light emitted from the exit slit are provided, and a second exit slit and a first photoelectric converter that receives the light intensity-modulated light emitted from the exit slit are arranged. A second photoelectric converter is disposed to receive the intensity-modulated light. As a result, the first and second signal processing circuits can
the amplitude of the first optical intensity modulation signal at and
The amplitude of the second light intensity modulation signal near 300 nm is calculated, and a subtraction circuit subtracts the second amplitude from the first amplitude and the interference value obtained from the interference correction curve, thereby eliminating the interference of sulfur dioxide gas. The concentration of ammonia gas alone is detected.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is an external view showing an ultraviolet absorption type ammonia gas analyzer according to an embodiment. In the figure, reference numeral 21 denotes an optical base on which each optical member is arranged and fixed, a light source 22 that emits ultraviolet rays is placed on this optical base 21, and a light beam 23 emitted from this light source 22 is transferred to a light absorption cell 2.
Collimator lens 25 that leads to light absorption cell 2
4, and the light flux 2 passing through this light absorption cell 24
A plane mirror 26 that refracts the optical axis of 3 at a right angle refracts the light beam 2.
3 along the optical axis. The light beam 23 refracted by the plane mirror 26 is condensed by a condensing lens 27 and introduced into the spectrometer case 29 through the spectrometer entrance slit 28.

The light source 22 is formed of a plasma emission type deuterium discharge tube, and its light emitting spot has a diameter of about 2 mm. Ideally, the spectrum of the ultraviolet light output from this light source 22 is flat within the measurement range from 200 nm to 300 nm.
Draw a gentle curve that is almost flat. Therefore,
Before starting actual ammonia gas concentration measurement, the measured values at each wavelength are calibrated using a gas that does not contain impurity gases.

An introduction pipe 31 for introducing high temperature exhaust gas from a flue (not shown) and an exhaust pipe 32 for discharging the introduced exhaust gas are attached to the light absorption cell 24. Note that the introduction pipe 31 is maintained at a high temperature of about 300° C. by a heater and a heat insulating material 33 (not shown). Further, this light absorption cell 24 is maintained at a high temperature of about 300° C. by a heater (not shown).

FIG. 1 is a schematic diagram showing the general structure of this ultraviolet absorption type ammonia gas analyzer. The ultraviolet rays output from the light source 22 are collimated by a collimator lens 25, pass through a light absorption cell 24, and then converged by a condenser lens 27 onto an entrance slit 28 of a case 29 of the spectrometer. The light beam 23 entering the case 29 is incident on a first plane mirror 36 attached to one free end of a U-shaped tuning fork 35 as a vibrator whose drive is controlled by a vibrator drive control device 34 .
Then, the light is reflected by the first plane mirror 36 and enters the collimator 37 . In addition, U-shaped tuning fork 3
5 is vibrated by an electromagnetic coil 38 disposed inside the tuning fork at a constant frequency F and constant amplitude W determined by the shape, weight, etc. of the tuning fork. Therefore, the light beam 23 reflected by the first plane mirror 36 becomes an oscillating light having a constant frequency F and a constant amplitude W.

The oscillating light reflected by the collimator 37 is incident on a blazed diffraction grating 39. The dispersion spectrum diffracted by this diffraction grating 39 is transmitted to the collector 4.
0. First and second exit slits 41a, 41b are arranged at positions where the oscillating dispersion spectrum reflected by the collector 40 forms an image, and the back surfaces of the first and second exit slits 41a, 41b are arranged. First and second photoelectric converters 42a and 42b are disposed adjacent to. The first exit slit 41a is arranged at a position where light having a wavelength of 209 nm, which is the center wavelength of the oscillating dispersion spectrum of 207 to 211 nm, is irradiated. That is, due to the vibration of the first plane mirror 36, the light flux on the imaging plane (that is, the dispersion spectrum) oscillates, and the light flux emitted from the exit slit 41a is wavelength-modulated in a range of approximately ±1.5 nm centered on 209 nm. It becomes light.

On the other hand, the second exit slit 41b is arranged at a position where light having a central wavelength of 300 nm in the oscillating dispersion spectrum is irradiated;
Light whose wavelength is modulated in a range of about ±1.2 nm centered around 300 nm from b is output. The first photoelectric converter 42a converts the light intensity modulation signal generated by the absorption characteristics of the ammonia gas and sulfur dioxide gas imaged onto the first exit slit 41a into a first electrical signal.
f ₁ , and the second photoelectric converter 42
b converts a light intensity modulation signal generated by the absorption characteristics of the sulfur dioxide gas imaged onto the second exit slit 41b into a second electrical signal _f2 .

The first and second electrical signals f ₁ and f ₂ containing DC and AC components output from the first and second photoelectric converters 42a and 42b are transmitted to the first and second signal processing circuits 43a and 43a, respectively. 43b. First and second signal processing circuits 43a, 4
3b is constructed as shown in FIG. That is, the input electric signals f ₁ and f ₂ are input to the DC amplifier 45.
The output corresponding to the DC component c in FIG. 6a is input to the next stage divider 46. Further, the electrical signals f ₁ and f ₂ are passed through a high-pass filter consisting of a capacitor 47 to remove the DC component c, and then sent out from the tuning fork drive circuit 49 of the vibrator drive control device 34 through a synchronous detection circuit 48. Synchronous detection is performed at a frequency 2F, which is twice the vibration frequency F of the shaped tuning fork 35, and an output corresponding to the depth a of the depression caused by absorption of the measured spectrum in FIG. 6a is input to the divider 46. . In the divider 46, division (a/c) is performed, and the result is output as a DC voltage g corresponding to the absorption spectrum value.

Note that the output stage of the synchronous detection circuit 48 has a built-in low-pass filter (not shown), and the value of the time constant τ of this low-pass filter has a relationship of at least τ>200/2F with respect to the synchronous detection frequency 2F. It is set to be. This is based on the results of experiments conducted by the inventors in order to maintain the S/N ratio of the intensity a of the measured absorption spectrum above a certain level. Therefore, in order to increase the S/N ratio without reducing the measurement response speed, it is necessary to make the above-mentioned time constant τ as small as possible, so the vibration frequency F of the U-shaped tuning fork 35 should be set high. Bye. In the embodiment, this vibration frequency F is set to a high value of about 2 kHz, as will be described later.

The DC voltages g 1 and _{g 2 corresponding} to the first and second absorption spectrum intensities output from the signal processing circuits 43 a and 43 b are input to the subtracter 50 . This subtracter 50 converts the DC voltage g ₁ corresponding to the absorption spectrum intensity indicated by the amplitude of the first light intensity modulation signal with a wavelength of 207 to 211 nm containing ammonia gas and sulfur dioxide gas into the vicinity of 300 nm of sulfur dioxide gas. DC voltage corresponding to the absorption spectrum intensity indicated by the amplitude of the second optical intensity modulation signal of the wavelength
By subtracting g ₂ and the interference value corresponding to this DC value, a signal corresponding to the absorption spectrum intensity of ammonia gas alone, that is, the ammonia gas concentration is displayed on the display unit 5.
Send to 1. The display unit 51 displays the input ammonia gas concentration as a measurement result.

In the vibrator drive control device 34, a second free end of the U-shaped tuning fork 35 is provided as shown in the figure.
A second plane mirror 52 is attached, and an LED is connected to this second plane mirror 52 through a condenser lens 53.
Detection light 55 output from a light emitting device 54 made up of light emitting elements such as the above is incident. The detection light 55 reflected by the second plane mirror 52 becomes vibration light of a constant frequency F, and is input to an amplitude measuring device 56 composed of a position sensor or the like that measures the vibration amplitude of the detection light 55. . This amplitude measuring device 56
The vibration amplitude signal of the detection light 55 measured at U
Electromagnetic coil 38 incorporated inside the glyph tuning fork 35
The signal is input to a tuning fork drive circuit 49 that drives the tuning fork. This tuning fork drive circuit 49 sends out a synchronizing signal with a frequency of 2F to each of the synchronous detection circuits 48 and controls the lighting of the light emitting device 54 .

FIG. 4 is a perspective view showing a schematic configuration of the U-shaped tuning fork 35. The U-shaped portion 57 is, for example, piano wire with an outer diameter of approximately 2 mm, and the leg portion 58 of the U-shaped tuning fork 35 is
also uses the same piano wire. The length of the U-shaped portion 57 is approximately 30 mm, and the width is approximately 10 mm. First and second plane mirrors 36 and 52 each having a shape of 7×5 mm are attached to each free end of this U-shaped portion 57. An electromagnetic coil 38 is wound around a core 59 disposed inside this U-shaped portion 57. This U
The vibration frequency F of the shaped tuning fork 35 is determined by the shape and material of the U-shaped portion 57, but by adopting the dimensions described above, the vibration frequency F can be set to approximately 2 kHz.

FIG. 5 is a block diagram showing a tuning fork driving circuit 49 for driving the U-shaped tuning fork 35 in vibration. 6 in the diagram
Reference numeral 1 denotes a light emitting element driving circuit that supplies a driving current to a light emitting element such as an LED of the light emitting device 54. 62 in the diagram
is a position sensor that constitutes the amplitude measuring device 56, and this position sensor 62 is a kind of photoelectric conversion element that outputs a signal proportional to the displacement of the irradiation spot on the element, and the amplitude of the detected light 55, that is, The amplitude of the second plane mirror 52 is detected by directly moving the irradiation spot. The output signal of the position sensor 62 is input to a change detection circuit 63 and converted into an AC signal e ₁ as a vibration amplitude signal that changes as the second plane mirror 52 vibrates. The AC signal e ₁ is converted into a DC output voltage E ₁ by the detection circuit 64 . The output voltage E ₁ output from the detection circuit 64 is input to the deviation detection circuit 66 together with the set voltage E ₂ output from the amplitude setter 65 .
The deviation detection circuit 66 outputs a deviation voltage _E3 between the DC signal _E1 and the set voltage _E2 . The deviation voltage E ₃ outputted from the deviation detection circuit 66 is integrated by the integrating circuit 67 and becomes the control signal voltage E ₄ of the gain control amplifier 68.
become.

On the other hand, the AC signal e ₁ output from the change detection circuit 63 is input to the phase shift circuit 69.
9, the vibration phase of the U-shaped tuning fork 35 is matched.
The matching signal e ₂ output from the phase shift circuit 69 is input to the gain control amplifier 68, and is also input to the waveform shaping circuit 70 where the waveform is shaped. The waveform shaping circuit 70 then sends the synchronizing signal _e3 to each synchronous detection circuit 48 of each of the signal processing circuits 43a and 43b. Further, the gain control amplifier 68 converts the input matching signal e ₂ into the control signal voltage E ₄
The U-shaped tuning fork 35 is amplified with an amplification factor determined by
is output as a drive current I of the electromagnetic coil 38.

In the tuning fork drive circuit 49 having a type of servo system configuration, the amplitude of the second plane mirror 52, that is, the output voltage _E1 of the detection circuit 64 is set by the amplitude setter 65.
When the set voltage E2 becomes equal to ₂ , the deviation detection circuit 6
The deviation voltage E ₃ output from 6 becomes 0. Therefore, the value of the control signal voltage E ₄ output from the integrating circuit 67 does not change. As a result, the vibration amplitude of the U-shaped tuning fork 35 does not change. Further, when the output voltage E ₁ of the detection circuit 64 is not equal to the set voltage E ₂ of the amplitude setter 65, a deviation voltage E ₃ corresponding to the difference is inputted to the integrating circuit 67. Then, the control signal voltage output from the integrating circuit 67
_E4 changes corresponding to the deviation voltage _E3 . the result,
The vibration amplitude of the U-shaped tuning fork 35 changes so that the output voltage E ₁ of the detection circuit 64 becomes equal to the set voltage E ₂ of the amplitude setter 65. Therefore, by changing the set voltage E ₂ of the amplitude setter 65, the amplitude of the U-shaped tuning fork 35 can be easily adjusted.

The operating principle of the ultraviolet absorption type ammonia gas analyzer constructed in this way will be explained using FIGS. 6a and 6b. The spectrum intensity is measured while modulating the wavelength λ around (λ ₀ ±Δλ) around the center wavelength of the depression in the absorption spectrum caused by the gas component to be measured, that is, the absorption peak wavelength λ ₀ of the absorption spectrum. . The spectral intensity waveform measured at this time has an average DC component e and an amplitude d as shown in the figure.
A waveform D is obtained by superimposing alternating current components (ripple components). The frequency of the AC component d of this waveform D is 2F, which is twice the wavelength modulation frequency F. Therefore, if this waveform D is detected at a frequency of 2F in synchronization with wavelength modulation, the original spectral intensity can be obtained. In reality, by removing the DC component e shown in Figure 6b with a high-pass filter and performing synchronous detection, a value d corresponding to the depth a of the depression shown in Figure 6a caused by absorption can be obtained. . The depth a of this depression is proportional to the gas concentration. Further, the depth a of this depression is approximately proportional to the light source intensity which can be approximately represented by the DC component c. Therefore, in order to remove the influence of the light source intensity and obtain an output proportional only to the gas concentration, the depth a of the depression must be adjusted to the ratio (a/
It can be expressed as c).

To explain this principle with reference to the embodiment shown in FIG. It is reflected by a first plane mirror 36 attached to the end, further reflected by a collimator 37, and input into a diffraction grating 39. Since the U-shaped tuning fork 35 vibrates with a constant amplitude W and a constant frequency F, this diffraction grating 39
The incident angle θ of the light beam 23 incident on the light beam 23 also oscillates within a certain angular range (θ±Δθ). As a result, the dispersed spectrum oscillates on the first exit slit 41a, and the wavelength of the light beam 23 emitted from the first exit slit 41a oscillates in the range of λ ₀ ±Δλ. That is, wavelength modulation is applied. Therefore, the intensity of the light leaking from the exit slit 41a has a waveform in which an alternating current component d is superimposed on a direct current component e, as shown in waveform D in FIG. 6b. This waveform D is converted into an electrical signal f ₁ by the first photoelectric converter 42a. Therefore, the DC component e is removed by the capacitor 47, and the signal synchronously detected by the synchronous detection circuit 48 using the synchronous signal _e3 from the tuning fork drive circuit 49 having a frequency of 2F is as shown in FIG. 6a. This corresponds to the depth a of the depression.

Therefore, from each signal processing circuit 43a, 43b, a signal g ₁ g ₂ corresponding to the depth a of each depression at each center wavelength of 209 nm and 300 nm, that is, each absorption spectrum intensity is obtained. Then, the subtracter 50 obtains the gas concentration of ammonia gas alone, with the interference of sulfur dioxide gas removed.

In such an ultraviolet absorption type ammonia gas analyzer, the U-shaped tuning fork 35 is used as a vibrator that modulates the wavelength of the dispersion spectrum on each exit slit 41a, 41b. Diffraction grating 3 that separates into spectra
9, the number of U-shaped tuning forks installed can be reduced to 2 compared to the conventional device shown in Figure 8.
It can be reduced from 1 to 1. Also, U-shaped tuning fork 35
For example, the size of the embodiment shown in FIG. 4 can be reduced to a fraction of that of the conventional example shown in FIG. 9, provided that almost the same level of measurement accuracy is obtained. Therefore, the output of the tuning fork driving circuit 49 for exciting the U-shaped tuning fork 35 may also be small. Also, the amplitude W
Since the value of the vibration energy is also much smaller than that of the conventional device, the value of the vibration energy is small, and the diffraction grating 39, collimator 37, collector 40, and each exit slit 41a, 4
Vibration does not have an adverse effect on optical members such as 1b. In particular, the wavelength λ measured by vibration
fluctuations can be suppressed as much as possible. Therefore,
Deterioration in measurement accuracy due to the non-flatness of the spectral intensity characteristics of the light source 22 described above can be prevented, and measurement accuracy can be significantly improved compared to the conventional devices shown in FIGS. 8 and 9.

Furthermore, the vibration amplitude W of the U-shaped tuning fork 35 is optically measured using the detection light 55 and the position sensor 62, and the amplitude W is controlled to a constant value based on the measurement results. Unlike other devices, it is not affected by changes in ambient temperature.
Therefore, the amplitude can always be constant,
Since the wavelength modulation width for measurement is always controlled to a constant value, the interference value due to sulfur dioxide gas can be accurately grasped, and the measurement accuracy of ammonia gas concentration can be improved.

Furthermore, as shown in FIG.
A case that is heat-shielded, is spaced apart from the optical base 21, and is maintained at approximately 42° C. by housing the U-shaped tuning fork 35, the diffraction grating 39, the collimator 37, the collector 40, and the exit slits 41a and 41b. By installing the light absorption cell 24 apart from the light absorption cell 24, it is possible to prevent each optical member from being adversely affected by the heat of the light absorption cell 24 as much as possible.

In this case, by fixing each optical member except the light absorption cell 24 to one optical base 21,
It is possible to suppress the zero point fluctuation caused by the movement of the entrance spot on the entrance slit 28 of the spectrometer due to the fluctuation in the irradiation direction of the light beam 23 from the light source 22 due to the movement of the light source 22, and further improve the measurement accuracy. .

FIG. 7 is an external view showing an ultraviolet absorption type ammonia gas analyzer according to another embodiment of the present invention.
In this embodiment, all optical members except the light absorption cell 24 are housed in a case 82 having a notch 81. The light absorption cell 24 is disposed within the notch 81. A light beam 23 outputted from a light source disposed on an optical base in the case 82 is guided into the light absorption cell 24 through a quartz 83a fitted in a window formed in one wall of the notch 81. The light beam 23 that has passed through the light absorption cell 24 is guided into the case 82 through a quartz 83b fitted in a window formed in the other wall of the notch 81.

In this way, the high temperature light absorption cell 24 is transferred to the light source 2.
By completely separating all the optical members including 2 and each lens from the case 82, it is possible to further reduce the adverse effects caused by temperature on each optical component. Moreover, the above-mentioned effect can be further improved by housing all the optical members including the light source 22 and each lens in the case 82 whose temperature is controlled to be constant at, for example, 42°C.

Note that the present invention is not limited to the embodiments described above. In the embodiment, a U-shaped tuning fork 35
The measurement light 55 for measuring the amplitude of the second plane mirror 52
was irradiated from the collimator 37 side, but the second
The reflective surface of the plane mirror 52 may be mounted upside down, and the detection light 55 may be irradiated from the electromagnetic coil 38 side. The details of the method of irradiating the detection light 55 to this U-shaped tuning fork 35 are given in Japanese Patent Application No. 60-62341.
has been reported.

〔Effect of the invention〕

As explained above, according to the present invention, the luminous flux just before passing through the light absorption cell and inputting to the diffraction grating is modulated with a predetermined frequency and amplitude by the oscillator, and the vibration of the oscillator is optically detected. is controlled to a constant value. Therefore, even if the ambient temperature changes significantly, high measurement accuracy can be maintained, and the number of vibrators installed can be reduced, making it possible to reduce the size and weight of the entire device.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the general configuration of an ultraviolet absorption type ammonia gas analyzer according to an embodiment of the present invention, Fig. 2 is an external view of the embodiment, and Fig. 3 is a signal processing circuit of the embodiment. 4 is a perspective view showing the U-shaped tuning fork of the same embodiment, FIG. 5 is a block diagram showing the tuning fork drive circuit of the same embodiment, FIG. 6 is a diagram showing the operating principle, and FIG. 7 is a diagram showing the tuning fork drive circuit of the same embodiment. FIG. 8 is a schematic diagram showing a conventional ammonia gas analyzer; FIG. 9 is a diagram showing a U-shaped tuning fork of the conventional device; Figure 10 is an interference correction characteristic diagram showing the degree of interference of sulfur dioxide gas concentration with ammonia gas concentration;
The figure is an absorption spectrum characteristic diagram of ammonia gas and sulfur dioxide gas. 21... Optical base, 22... Light source, 23... Luminous flux,
24...Light absorption cell, 25...Collimator lens, 2
7...Condensing lens, 28...Entrance slit, 29,8
2... Case, 33... Heat insulating material, 34... Vibrator drive control device, 35... U-shaped tuning fork, 36... First plane mirror, 37... Collimator, 38... Electromagnetic coil, 39
...Diffraction grating, 40...Collector, 41a...First exit slit, 41b...Second exit slit, 42
a...first photoelectric converter, 42b...second photoelectric converter, 43a...first signal processing circuit, 43b...second
signal processing circuit, 46... divider, 48... synchronous detection circuit, 49... tuning fork drive circuit, 50... subtracter, 51
...Display section, 52...Second plane mirror, 54...Light emitting device, 55...Detection light, 56...Amplitude measuring device, 62...Position sensor, 63...Change detection circuit, 81...Notch, 83a, 83b...Quartz .

Claims (1)

[Scope of Claims] 1. A light source that emits ultraviolet rays; A light absorption cell that allows the light beam from the light source to pass through a medium to be measured containing ammonia gas and sulfur dioxide gas; and a light absorption cell that reflects the light beam that has passed through the light absorption cell. a vibrator having a plane mirror to vibrate the vibrator; a vibrator drive control device that vibrates the vibrator at a constant amplitude and frequency by optically detecting the amplitude of the vibrator; a diffraction grating that diffracts the reflected light beam and outputs an oscillating dispersion spectrum; out of the oscillating dispersion spectrum output from the diffraction grating, a range from 207 nm to 207 nm corresponding to the absorption spectrum of the ammonia gas and sulfur dioxide gas;
a first exit slit disposed at a position to receive a dispersion spectrum with a wavelength of 211 nm, for emitting the oscillating dispersion spectrum and modulating the wavelength of the emitted light flux; the ammonia gas and the sulfur dioxide gas; a first photoelectric converter that converts the light emitted from the first exit slit into an electrical signal, which is converted into an optical intensity modulated signal by the presence of a light beam and wavelength modulation; It is arranged at a position to receive the dispersion spectrum of the 300 nm wavelength corresponding to the absorption spectrum of sulfur dioxide gas and its neighboring wavelengths out of the dispersion spectrum of the a second exit slit for wavelength modulation; converting the light emitted from the second exit slit, which is converted into a light intensity modulation signal by the presence of the sulfur dioxide gas and the wavelength modulation, into an electrical signal; a second photoelectric converter; synchronously detecting the electric signal output from the first photoelectric converter at a frequency twice the vibration frequency of the vibrator;
a first signal processing circuit that calculates the magnitude of the amplitude of a first optical intensity modulation signal corresponding to the magnitude of the absorption spectrum of the 211 nm wavelength; A second wave corresponding to the absorption spectrum of the 300 nm wavelength and wavelengths in its vicinity is detected by synchronous detection at a frequency twice the vibration frequency of the child.
A second step that calculates the amplitude of the optical intensity modulation signal of
a signal processing circuit; calculating the correct ammonia gas concentration in the medium to be measured by subtracting the magnitude of the second amplitude and the interference value found from the interference correction curve from the magnitude of the first amplitude; An ultraviolet absorption type ammonia gas analyzer characterized by comprising a subtraction circuit for calculation. 2. The ultraviolet absorption type ammonia gas analyzer according to claim 1, wherein the vibrator is constructed using a U-shaped tuning fork. 3. The vibrator drive control device includes: an electromagnetic coil for driving the U-shaped tuning fork; and a first coil for reflecting the light flux that has passed through the light absorption cell attached to one free end of the U-shaped tuning fork. a second plane mirror attached to the other free end of the U-shaped tuning fork for detecting the vibration amplitude of the reflected light beam;
a light emitting device that irradiates the second plane mirror with a detection light for detecting the vibration amplitude of the reflected light beam; a light emitting device that receives the detection light reflected by the second plane mirror, and detects the vibration amplitude of the reflected detection light; an amplitude measuring device for measuring;
The ultraviolet absorber according to claim 2, further comprising a drive circuit that controls the excitation of the electromagnetic coil so that the vibration amplitude value measured by the amplitude measuring device is always a constant value. Ammonia gas analyzer. 4. The amplitude measuring device includes a position sensor that outputs a signal according to the light receiving position of the detection light irradiated onto the light receiving surface; 4. The ultraviolet absorption type ammonia gas analyzer according to claim 3, further comprising a change detection circuit for converting into a changing AC vibration amplitude signal. 5. The light absorption cell is spaced apart from the optical base on which the light source, the vibrator, the diffraction grating, etc. are arranged,
The ultraviolet absorption type ammonia gas analyzer according to claim 1, wherein the ultraviolet absorption type ammonia gas analyzer is arranged in a heat shielded state.