JPH0565023B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is for measuring the concentration and partial pressure of gas, and is particularly suitable for measuring and managing the concentration and partial pressure of gas in various heat treatment furnaces used in the steel industry, and for use in various industries. It is applied to the measurement and management of the concentration and partial pressure of atmospheric gases in various processes. [Prior Art] There are many processes, including heating furnaces and annealing furnaces used in the steel industry, that are carried out in atmospheres where the concentration and partial pressure of gases are controlled. It is essential to measure. Therefore, currently there are methods in which measurements are taken by directly inserting a measurement probe into the atmosphere to be measured, and 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. ing. However, these methods cannot be used under harsh conditions, such as when the process atmosphere is at high temperature and pressure, or when it is composed of highly corrosive gas components. There are various problems such as there being a limit to the amount of gas, and gas components sometimes being lost due to the gas being taken out to the outside, and it has sometimes been impossible to perform accurate measurements. 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. 169994/1983.
It was disclosed in No. 59-169995 and No. 59-169996.
This method and device can accurately measure the concentration and partial pressure of gas components, and are very effective. There is a possibility that the middle drive part may be affected. [Problems to be Solved by the Invention] The present invention eliminates the mechanically driven part in the prior invention, further improving the durability and reliability of the device, and reducing the lifespan of the light source and the contamination of the optical system. ,
Monitors optical axis misalignment, etc. and corrects their effects,
The purpose is to accurately measure the concentration and partial pressure of a gas to be measured. [Means for Solving the Problems] The present invention splits a part of the light emitted from the light source toward the gas to be measured, uses it as a reference beam to measure the initial intensity, and uses the remaining light to direct the gas to the gas to be measured. After passing through and reflecting the measurement light, split the measurement light, measure the final intensity of the reference light from one of them, measure the intensity of the measurement light from the other, and calculate the initial and final intensities of these reference lights, and the measurement light. A method for measuring the concentration and partial pressure of a gas to be measured from the intensity of light; and a chopper and a beam splitter for splitting a part of the measurement light are provided on the optical axis of the measurement light emitted from the light source; A beam splitter is placed on the optical axis to act as a filter that faces the surface and transmits only light with a wavelength λ ₁ that is not absorbed by the gas to be measured, and further faces the beam splitter to serve as a filter that transmits only light with a wavelength λ ₁ that is not absorbed by the gas to be measured.
A filter and a photodetector that transmit only the light of the wavelength λ 1 are provided, and a filter and a photodetector that transmit only the light of the wavelength λ ₁ are provided opposite to the back surface of the beam splitter. A filter and a photodetector are provided on the back surface to transmit only the light of wavelength λ ₂ that is absorbed by the gas to be measured, and a retroreflector to reflect the measurement light is provided behind the gas to be measured onto which the measurement light is projected, and The present invention relates to a gas concentration and partial pressure measuring device characterized in that it is provided with a signal processing system that receives signals from each of the photodetectors and calculates the concentration and partial pressure of the gas to be measured. 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,
The 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 has already been carried out, for example, as disclosed in Japanese Patent Publication No. 51-20904. It is. In addition to the light having the above-mentioned specific absorption wavelength (hereinafter referred to as measurement light), the present invention uses light that is close to the absorption wavelength.
Light at a wavelength that does not undergo 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 final intensity) of the light intensity, and to measure the average value of the gas concentration along the optical path from these values. Generally, light absorption is expressed as I(L)=I ₀ exp (−α·n·L) according to Lambert-Beer's law. Here, I( ₀ ) is the initial intensity, n is the volume molar concentration of the gas to be measured, 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 uniquely determined by the gas to be measured and the wavelength used.

[Table] The light intensities I ₁ to _{I 3} obtained by the present invention are expressed as follows. Here, I ₁ is the signal output detected by the detector of the light emitter, I ₂ and I ₃ are the two of the light receiver, respectively.
This is the signal output detected by two detectors. I ₁ = I〓 ₁ (0) I ₂ = KI〓 ₁ (0) exp (-α〓 ₁・n・L) I ₃ = KI〓 ₂ (0) exp (−α〓 ₂・n・L) However, , λ ₁ is the wavelength of the reference light, λ ₂ is the wavelength of the measurement light,
α〓 ₁ is the absorption coefficient of the gas to be measured for the wavelength〓 ₁ , α〓 ₂
is the absorption coefficient of the gas to be measured for the wavelength λ ₂ , I〓 ₁
(0) is the initial intensity of the reference light, I〓 ₂ (0) is the initial intensity of the measurement light, n is the volume molar concentration of the gas to be measured, L is the optical path length, and K is the optical loss other than light absorption by the gas to be measured. This is a coefficient representing loss due to dirt on window glass existing on the optical path, loss due to optical axis deviation, etc. The light intensity _I1 represents the light source intensity, and by monitoring the decrease in brightness due to light source deterioration, it is possible to estimate the light source life,
Determine when it is time to replace it. The transmittance τ ₁ of the reference light is τ ₁ = I ₂ /I ₁ = K exp(−α〓 ₁・
n・L). Since α〓 ₁ is not absorbed by the gas to be measured,
The reference light may be α〓 ₁ ≒0, and τ ₁ =K. Since τ ₁ represents unnecessary optical loss on the optical path, by monitoring τ ₁ , it is possible to monitor dirt on the window glass, determine when it is time to replace it, and determine the presence or absence of optical axis deviation. In addition, the transmittance τ ₂ of the measurement light is expressed as τ ₂ =I ₃ /I ₁ =K [I〓 ₂ (0) / I〓 ₁ (0)]
〓 ₂・
n・L). Furthermore, the ratio τ of transmittance τ ₁ and τ ₂ is τ=τ ₂ /τ ₁ = [I〓 ₂

[0]/I〓 ₁ (0)〕exp(−α
〓 ₂・
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 I〓 ₁ (0),
There is a certain relationship between I〓 ₂ (0), and I〓 ₁ (0)
The value of I〓 ₂ (0) can be estimated from the value of .
Therefore, simply by measuring the light source intensity I〓 ₁ (0), the ratio of the light intensities of the reference light and the measurement light I〓 ₂ (0)/I〓 ₁ (0) can be determined. Now let this ratio be C, then τ=C・exp(−α〓 ₂・n・L)…(1). Taking the logarithm of both sides of equation (1) and rearranging it for the volume molar concentration n of the gas to be measured, it becomes n=-(lnτ/c)/(α〓 ₂ ·L) (2). Therefore, by combining equation (2) and the gas state equation p=nRT (where p is the partial pressure of the gas to be measured, T is the temperature of the gas to be measured, and R is the gas constant), we get p=-[RT/ (α〓 ₂・L)] lnτ/c (3), and the partial pressure of the gas to be measured can be obtained from equation (3). The present invention is based on such a measurement principle,
The present invention 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. In the figure, 1 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 pulsed at a frequency f by a light chopper 5, reaching a beam splitter 6. The light is reflected by the surface of the beam splitter 6, passes through the condensing lens 7, and the filter 8, which transmits only light of wavelength ₁ that is not absorbed by the gas to be measured, and enters the photodetector 9, where its intensity is measured. is converted into an electrical signal L ₁ according to
Further, it passes through the CR active filter 20 and becomes the initial intensity signal _I1 of the reference light. On the other hand, beam splitter 6
The light that has passed through is emitted to the outside from the window 17 provided in the light emitting/receiving housing 1, is transmitted through the gas to be measured 18, is absorbed, is further reflected by the retroreflector 19, and is reflected again through the gas to be measured 18 and the window 17. It passes through the beam splitter 6, reaches the back surface of the beam splitter 6, is reflected, and reaches the second beam splitter 10. A part of it is reflected by the surface of the beam splitter 10, and is reflected by the condenser lens 1.
1 enters the photodetector 13 through a filter 12 that transmits only light of wavelength ₁ which does not absorb the measured light, similar to the filter 8, and is converted into an electrical signal _L2 according to its intensity. , and further passes through the CR active filter 20 to become the final intensity signal _I2 of the reference light. In addition, the light transmitted through the beam splitter 10 is absorbed by the condensing lens 14 and the gas to be measured at a wavelength 〓 ₂
The light passes through a filter 15 that transmits only the light of
_Further , the lock-in amplifier 21 extracts only the component corresponding to the synchronization signal of the frequency f from the light chopper 5, resulting in the final intensity signal _I3 of the measurement light. In this way, the light intensity I ₁ ~ _{I 3}
can be measured, and from this, the transmittances τ ₁ and τ ₂ of the reference light and measurement light can be determined 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, the thermocouple 22, and substituted into equation (3). These calculations can be performed by leading the data to the calculation mechanism 24 via the A/D converter 23 for processing. (Example) Next, an example will be shown in which the present invention is applied to methane gas partial pressure measurement. As reference light = ₁ = 1600μm, as measurement light = ₂ =
The partial pressure of methane gas was measured using 3.31 μm light under conditions of optical distance L = 34 cm and gas temperature T = 30°C. The results are shown in FIG. The vertical axis is the transmittance ratio τ
is a semi-log plot, where 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, the partial pressure, and the concentration are in a proportional relationship as shown in equations (3) and (2), respectively, and therefore, from the change in the transmittance ratio τ, the Partial pressure measurements or concentration measurements can be made. (Effects of the Invention) As explained above, according to the present invention, the measurement light and the reference light are simply passed through the gas to be measured, regardless of the conditions such as the temperature and pressure of the gas to be measured, and the light is always in the background. While eliminating noise, the influence of light source brightness reduction due to light source deterioration, the influence of light loss due to dirt in the optical system such as the transmission window, the influence of light loss due to misalignment of the optical axis, etc., the concentration of various gases can be adjusted. and partial pressure.Furthermore, since there is no mechanically driven part within the measuring device, the device has excellent durability and reliability, and reliable measurements can be performed at all times.Furthermore, the present invention Application enables online monitoring of chemical reactions, so it can be used, for example, in the control of stainless steel bright annealing furnaces in the steel industry, vacuum degassing equipment for molten steel, and CVD in semiconductor manufacturing processes.
process, control of diffusion furnaces, control of various types of drying lines including grains in food-related processes,
In addition, it can actively control manufacturing processes in various industries, and has remarkable effects when applied to industrial processes involving the production of various gases accompanied by chemical reactions and various gaseous components.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing the configuration of an embodiment of the present invention.
The figure shows the 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 emitting and receiving housing, 2: light source, 3: ellipsoidal mirror,
4: Off-axis parabolic mirror, 5: Light chopper,
6: Beam splitter, 7: Condensing lens, 8: Filter, 9: Photodetector, 10: Beam splitter, 11: Condensing lens, 12: Filter, 13:
Photodetector body, 14: Condenser lens, 15: Filter, 16: Photodetector, 17: Window, 18: Gas to be measured, 19: Retroreflector, 20: CR active filter, 21: Lock-in amplifier, 22:
Thermocouple, 23: A/D converter, 24: Arithmetic mechanism,
L ₁ , L ₂ , L ₃ : Electrical signal, I ₁ : Reference light initial intensity signal, I ₂ : Reference light final intensity signal, I ₃ : Measurement light final intensity signal.

Claims (1)

[Claims] 1. Part of the light beam emitted from the light source toward the gas to be measured is divided, and its initial intensity is measured as a reference beam with a wavelength that is not absorbed by the gas to be measured, and the remaining beam is divided into two parts. After passing the measurement light beam through the gas to be measured and reflecting it, split the measurement light beam, measure the final intensity of the reference light having a wavelength that is not absorbed by the gas to be measured from one part, and measure the final intensity of the reference light having a wavelength that is not absorbed by the gas to be measured from the other part. The final intensity of the measurement light having a wavelength that is absorbed by the gas to be measured is measured, and the initial and final intensities of these reference lights,
and a method for measuring the concentration and partial pressure of a gas, characterized in that the concentration and partial pressure of the gas to be measured are determined from the final intensity of the 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 wavelength λ ₁ that is not absorbed, and a filter and a photodetector that transmit only the light of wavelength λ ₁ are provided opposite to the surface of the beam splitter. Furthermore, a filter and a photodetector are provided on the surface of the beam splitter to transmit only the light having a wavelength λ ₂ that is absorbed by the gas to be measured, and further the measurement light is reflected behind the gas to be measured onto which the measurement light is projected. 1. A gas concentration and partial pressure measuring device, comprising a retroreflector and a signal processing system that receives signals from each of the photodetectors and calculates the concentration and partial pressure of the gas to be measured. 3. The concentration and partial pressure of the gas according to claim 2, wherein the light source, chopper, first and second beam splitters, transmission filter, photodetector, etc. are housed in a housing, and the housing is further provided with a window. measuring device.