JPS62201334A - Method and device for measuring concentration and partial pressure of gas - Google Patents

Abstract

PURPOSE:To take a measurement securely by passing measurement light and reference light through gas to be measured without reference to conditions of the temperature, pressure, etc., of the gas to be measured. CONSTITUTION:Light beams from a light source 2 are made parallel and become pulse light beams by passing through a light chopper 5 and the pulse light beams reach a beam splitter 6; and part of it are reflected by the surface of the splitter 6 and enter a photodetector 9. The light beams are converted into an electric signal L1, which is the start intensity signal of the reference light. Light beams transmitted through the splitter 6, on the other hand, are emitted out of a window 17 and absorbed when passing through the gas 18 to be measured, and the light beams are reflected by a retroreflector 19 to reach the reverse surface of the splitter 6 and then reach a beam splitter 10. Part of it are incident on a photodetector 13 and converted into an electric signal L2 which is the end intensity signal of the reference light. Further, light beams passed through the splitter 10 are incident on a photodetector 16 and converted into an electric signal L3 and a lock-in amplifier extracts only a component corresponding to a synchronizing signal of frequency from the chopper 5 to become the end intensity signal of the measurement light. Thus, secure measuring operation is performed.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is for determining all the concentrations and partial pressures of gases, and particularly for determining the concentrations and partial pressures of gases in various heat treatment furnaces used in the steel industry. It is widely applied to measurements and management of atmospheric gas concentrations and partial pressures in various processes used in various industries.

[Conventional technology]

There are many processes, such as heating furnaces and annealing furnaces used in the steel industry, that are carried out in an atmosphere where the concentration and partial pressure of gases are controlled, and it is essential to measure the concentration and partial pressure of gases. It is. Therefore, currently,
Insert the measurement probe directly into the atmosphere to be measured.B111
There are methods in which the gas to be measured (hereinafter referred to as gas) is sucked in using an appropriate device and measured outside the process.

However, these methods cannot be used under harsh conditions, such as when the process atmosphere is at high temperatures and pressures, or when it consists of highly corrosive gas components. There are various problems such as limited corrosion performance and gas components being lost due to the gas being taken out, and it may not be possible to make accurate 41 measurements. there were.

The inventor of the present invention solved the above-mentioned problems and determined the concentration and partial pressure of gas components by using the absorption intensity of light and passing the measuring light directly through the controlled atmosphere during the process. Invented a method and device for accuracy, and filed Japanese Patent Application No. 59-169994, No. 5! J-L6!11995
No. 59-169996.

This method and device tX can accurately determine the concentration and partial pressure of gas components by 81g, and are very effective. There is a possibility that the middle drive part may be affected.

[Problem that the invention seeks to solve]

The present invention eliminates the mechanical drive part in the prior invention, further improves the durability and reliability of the device, and monitors the life of the light source, dirt on the optical system, misalignment of the optical axis, etc. , correct their shadow fJ.

The purpose is to accurately measure the concentration and partial pressure of all constant gases.

[Means for solving problems]

The present invention splits a part of the light emitted from the light source toward the gas to be measured, measures its initial intensity as a reference beam, and passes the remaining light through the gas to be measured, reflects it, and then measures it. Split the light, measure the final intensity of the reference beam from one side, and determine the intensity of the measurement beam from the other, and determine the concentration of the gas to be measured from the initial and final intensities of these reference beams and the intensity of the measurement beam. and partial pressure allll method: A chopper and a beam splitter are provided on the optical axis of the measurement light emitted from the light source, and a beam splitter that splits a part of the measurement light is placed opposite the surface of the beam splitter to absorb absorption into the gas to be measured. A beam splitter is arranged on the optical axis to serve as a filter that transmits only the light of wavelength input 1 that is not received, and a photodetector and a filter that transmits only the light of wavelength input 1 are arranged opposite to the beam splitter. A filter and a photodetector are provided opposite to the back surface of the beam splitter to transmit only the light of the wavelength A1, and a filter and a photodetector are provided on the back surface of the beam splitter to absorb the wavelength A1, which is absorbed by the gas to be measured. Equipped with a filter and photodetector that only transmits light.

Furthermore, a retrolin reflector is provided behind the gas to be measured to which the measurement light is projected, and signals from each of the photodetectors are inputted, and signal processing is performed to calculate the concentration and partial pressure of the gas to be measured. The present invention relates to an apparatus for determining the concentration and partial pressure a1 of a gas, characterized in that the present invention is provided with a gas concentration and partial pressure a1 system.

First, the measurement principle of the present invention will be explained.

As shown in Table 1, gas molecules strongly absorb light of specific wavelengths in response to molecular vibrations. Therefore, a method of measuring the absorption intensity of a gas using light having a specific absorption wavelength and measuring the concentration of the gas to be measured is disclosed in, for example, Japanese Patent Publication No. 51-20' JO/I. This is already being done. In addition to the light having the above-mentioned specific absorption wavelength (hereinafter referred to as measurement light), the present invention also provides light with a wavelength close to the absorption wavelength but not subject to optical absorption (hereinafter referred to as reference light).
The measurement light and the reference light are used to pass through the light intensity of the light source (hereinafter referred to as the initial intensity) and the gas to be measured, and after receiving light absorption by the gas. The purpose is to measure the light intensity (hereinafter referred to as linear intensity) of the light intensity and to determine the average value of the gas concentration along the optical path from these values.

In general, light absorption follows the Lambert-neer law: I (L) = I oexp (-11・n
−L). However, ■ (.) is the initial intensity, the opening is the volume molar concentration of the a+15 constant gas, L is the optical path length, α is the absorption coefficient, and I (L) is the final intensity. Note that the absorption coefficient α is a physical constant that is determined entirely by the d1g constant gas and the wavelength used.

The force intensities 11 to I3 obtained by qB+ according to the present invention can be expressed as follows. Here, 11 is the in-bow output detected by the detector of the light projecting section, and I2 and I3 are the signal outputs detected by the two detectors 8 of the light receiving section, respectively.

11=[i1 (0) I2=KIAI (0) exp
(-(IAI・TI・L)I3
=K I A2 (0) ex
p (−α included 2 ・ n ・ L
) However, A1 is the wavelength of the reference light, and A2 is ill! l Constant wavelength of light.

αA1 is the absorption coefficient of the gas to be measured for wavelength λ1.

αA2 is the absorption coefficient of the constant gas at wavelength λ2.

IAI (0) is the initial intensity of the reference light, 1 in 2 (0) is the initial intensity of the measurement light, and n is the volume molar concentration of the gas to be measured.

L is the optical path length, which is a coefficient representing optical loss other than light absorption by the gas to be measured, such as loss due to dirt on window glass existing on the optical path, loss due to deviation of one optical axis, etc.

The light intensity I represents the light source intensity, and by monitoring the reduction in brightness due to deterioration of the light source, the life of the light source is estimated and the time for replacement is determined. Transmittance of reference light τ1τH=12/I
+ = K exp (-(EAI In-L). Since 6 people 1 are not absorbed by the gas to be measured.

The reference light may have α input of 1″-0, and τ1=l(. Since I1 represents unnecessary optical loss on the optical path,
Monitoring of dirt on window glass by monitoring I1,
Determines when it is time to replace it and determines whether there is optical axis misalignment. In addition, the transmittance of the measurement light is 2, which is τ2:I3/It =K(IA
2 (0) / I people + (0)) exp (a A2 ・n
・I-). Furthermore, the transmittance τ1. The ratio τ of τ2 is 2c
= I2 / T I = (IA2 (0) / Ixt
(0)) cxp((L A2 ・n・L), and the coefficient K that changes over time can be eliminated.

In this device, the reference light and measurement light are obtained from the same light source, so the respective light source intensities T1(0) and IA2(
There is a certain relationship between 1iil of O), and Ii1(0)
Calculate from the value of . Can you estimate the value of (0)? Therefore, by simply determining the light source intensity I (0), the ratio of the light intensities of the reference light and measurement light is I2 (0)/IAI (0)
can be known. Letting this ratio be C, τ=C−exρ(−αA2 n−L) (1). Taking the logarithm of both sides of equation (1) and rearranging the volume molar concentration n of the gas to be measured, n = -(Q n c
/ c)/(αA2 ・L)”・(2). Therefore, equation (2) and the state equation of gas p == It RT (where p is the partial pressure of the gas to be measured and T is the gas to be measured temperature, R is a gas constant), then p = -(RT/(0
Person 2 ・L)) Qn becomes /c - (3) and 1 equation (
3), the partial pressure of the gas to be measured can be determined.

The present invention is based on such a measurement principle, and will be explained below with reference to the drawings. FIGS. 1 and 2 are explanatory diagrams of an example of an apparatus for implementing the present invention, with FIG. 1 showing an optical system of the present invention and FIG. 2 showing a signal processing system.

1 in the figure is the throw/receive case.

Reference numeral 2 denotes a light source, and the light passes through an ellipsoidal mirror 3 and an off-axis parabolic mirror 4 to become a parallel beam of light, and is then turned into a pulsed light beam intermittently at a frequency f by a light chopper 5, which reaches the beam 11 splitter 6. A part of the light is reflected by the surface of the beam splitter 6, passes through a condenser lens 7, and a filter 8 that transmits only the light of wavelength A1 that is not absorbed by the gas to be measured.
i: i 9k is enclosed, and an electrical signal according to its strength is ℃L.
It is converted into I, and further passes through the CR active filter 20 to become the starting intensity signal (1) of the reference light. On the other hand, the light transmitted through the beam splitter 6 is emitted to the outside through the window 17 provided in the light emitting/receiving housing 1, passes through the constant gas 18 of the object 41, is absorbed, is further reflected by the retroreflector 19, and is returned to the object to be measured. The gas 18 passes through the window 17, reaches the back surface of the beam splitter 6, is reflected, reaches the second beam splitter 10, a part of which is reflected by the surface of the beam splitter 10, and the condenser lens 11 Similar to the filter 8, the light at wavelength 1, which is not absorbed by the light to be measured, passes through the filter 12, and enters the photodetector 13, where it is converted into an electric signal L2 according to its intensity, and is then converted into an electrical signal L2 according to the intensity. After passing through the filter 20, the final intensity signal I2 of the reference light is generated. Further, the light transmitted through the beam splitter 10 is passed through the condensing lens 14,
1111 Wavelength input that is absorbed by a constant gas. It passes through a filter 15 that transmits only the light of Only the component corresponding to the synchronization signal is extracted and becomes the final intensity signal I3 of the measurement light. Since the light intensities 11 to 3 can be measured in this manner, the transmittances .tau.l and .tau.2 of the reference light and the measurement light can be determined from these as described above. Further, the volume molar concentration n of the gas to be measured can be determined from the above equations (1) and (2), and the partial pressure P of the gas to be measured can be determined from the equation (3). In this case, the temperature T of the gas to be measured is measured by, for example, a thermal lightning pair 22, and is expressed by the formula (3
). These calculations can be performed by leading the data through the A/D converter 23 to the calculation system 24 for processing.

(Example) Next, an example will be shown in which the present invention is applied to methane gas partial pressure measurement.

Input as reference light 1 = 1600μm, A2 as measurement light
= 3.31 μm light, light pressure fI&L = 3
The partial pressure of methane gas was measured under conditions of 4 cm and gas temperature rtT = 30°C. The results are shown in FIG. The vertical axis is a semilog plot of the transmittance ratio τ, and the horizontal axis is the partial pressure and molar concentration of methane gas. As is clear from this figure, the logarithm of the transmittance ratio τ, partial pressure, and concentration are expressed by the equation (
3) and equation (2), there is a proportional relationship, and therefore, the partial pressure or concentration of methane gas can be measured from the change in the transmittance ratio τ.

(Effects of the Invention) As explained below, according to the present invention, the measurement light and the reference light can be transmitted through the constant gas to be subjected to i1+1 regardless of the conditions such as the convexity and pressure of the constant gas to be treated. By simply letting it pass through, there are always problems such as noise, reduction in light source brightness due to deterioration of the light source, light loss due to dirt in the optical system such as the transmission window, light loss due to misalignment of the optical axis, etc. It is possible to control the concentrations and partial pressures of various gases while removing reliable dIg
can be determined. Furthermore, by applying the present invention,
Since it is possible to monitor chemical reactions online, it can be used, for example, to control stainless steel bright annealing furnaces in the steel industry, vacuum degassing equipment for molten steel, CVD processes in semiconductor AI manufacturing processes, control of diffusion furnaces 1, etc. in food-related processes. It has remarkable effects when applied to industrial processes that involve the production of various gases accompanied by chemical reactions and gaseous components, such as the ability to control various types of drying lines and the active control of surveying processes in various other industries. .

[Brief explanation of drawings]

1 and 2 are block diagrams showing the configuration of an embodiment of the present invention, with FIG. 1 showing an optical system and FIG. 2 showing a signal processing system. FIG. 3 is a graph showing the results of measuring the partial pressure of methane gas according to the present invention. 1: Light transmitting/receiving housing 2: Light source 3: Elliptical mirror 4: Off-axis parabolic mirror 5: Lie 1-Chopper 6: Bee 11 splitter 7: Condensing lens 8; Filter 9: Photodetector 10:
Beam splitter 11: Condensing lens 12: Filter I3: Photodetector body 14: Condensing lens 15: Filter 16: Photodetector 17: Window 1
8: Gas to be measured 19: Low reflector 20: CR active filter 21: Ronoquin amplifier 22: Thermocouple 23: A/D converter 24:
Calculation mechanism 1-1 + t, 21 L3: Electrical signal ll = Initial intensity signal of reference light ■2; Final intensity signal of reference light IJ: ifl'l Linear intensity signal of constant light ¥1 Figure 3rd eye CH4 minute L ( Torr)

Claims (3)

[Claims] (1) Divide a part of the light emitted from the light source toward the gas to be measured and measure its intensity as reference light,
After the remaining measurement light passes through the gas to be measured and is reflected, the measurement light is split, the final intensity of the reference light is measured from one part, the intensity of the measurement light is measured from the other part, and the initial intensity of these reference lights is measured. A method for measuring the concentration and partial pressure of a gas, characterized in that the concentration and partial pressure of a gas to be measured are determined from the intensity, final intensity, and intensity of measurement light. (2) A chopper and a beam splitter that splits a part of the measurement light are provided on the optical axis of the measurement light emitted from the light source toward the gas to be measured, and a beam splitter that splits a part of the measurement light is provided on the optical axis of the measurement light emitted from the light source toward the gas to be measured. A filter and a photodetector are provided that transmit only the light of the wavelength λ_1 that is not absorbed, and a filter and a photodetector are provided that transmit only the light of the wavelength λ_1 that is not absorbed.
A filter and a photodetector are provided on the surface of the beam splitter that transmit only the light of wavelength λ_2 that is absorbed by the gas to be measured, and a photodetector is provided on the surface of the beam splitter that transmits only the light of wavelength λ_2, and the measurement light is projected. A retroreflector for reflecting measurement light is provided behind the gas to be measured, and a signal processing system is provided for inputting signals from each of the photodetectors and calculating the concentration and partial pressure of the gas to be measured. Gas concentration and partial pressure measuring device. (3) Concentration of the gas according to claim 2, in which a light source, a chopper, first and second beam splitters, a transmission filter, a photodetector, etc. are housed in a housing, and the housing is further provided with a window. and partial pressure measuring device.