JPS62156543A - Method and device for measuring density and partial pressure of gas - Google Patents

Abstract

PURPOSE:To derive exactly density and partial pressure of gas to be measured, by setting a part of a measuring light as a reference light and measuring its intensity, making the remaining measuring light pass through the gas to be measured, and thereafter, dividing it into a light beam which is absorbed by the gas to be measured, and a light beam which is not absorbed, and measuring the intensity of the light beam. CONSTITUTION:A light beam which is radiated from a light source 1 is partially brought to a spectral processing as a reference light, becomes a monochromatic light and made incident on a photodetector 8, by a filter 7 for making only a light beam of wavelength lambda1 transmit through, and a start intensity I1 of the reference light lambda1 is obtained. On the other hand, a parallel luminous flux which has transmitted through a beam splitter 5 transmits through gas to be measured 11 and made incident on the inside of a housing 13. A part of a light beam which is made incident on a beam splitter 14 goes to a monochromatic light as a reference light by a filter 16 for making only a light beam of wavelength lambda1 transmit through, made incident on a photodetector 17, and a final intensity I2 of the reference light lambda1 can be derived. Also, said light beam transmits through a filter 19 for making only a light beam of wavelength lambda2 transmit through and made incident on a photodetector 20, and a final intensity I3 is obtained. In such a way, density and partial pressure of gas to be measured are derived.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to the measurement of concentration and partial pressure of gases, and in particular to the measurement of gas concentrations and partial pressures.
For example, various heat treatment furnaces used in the steel industry, etc.
The present invention relates to a measuring method and apparatus for controlling the concentration and partial pressure of atmospheric gases used 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 control the concentration and partial pressure of gases. It is. 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. A method and apparatus for achieving this accuracy were invented and disclosed in Japanese Patent Application Nos. 59-169994, 59-169995 and 59-269996.

This method and device can accurately measure the concentration and partial pressure of gas components and are very effective, but since the measuring device has a mechanically driven part, depending on the usage environment There is a possibility that the driving part may be damaged.

[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. , the purpose is to correct these influences and accurately measure the concentration and partial pressure of the gas to be measured.

[Means for solving problems]

The present invention chops the measurement light emitted from the light source toward the gas to be measured, then splits a part of it and measures its intensity as a reference light, and uses the remaining measurement light to (containing multiple different gases), the light is divided into wavelengths of light that are absorbed by the gas being measured and light of wavelengths that are not absorbed, the intensity of each light is measured, and the intensity of each light is measured. A gas concentration and partial pressure measuring device characterized by determining the concentration and partial pressure of a gas to be measured;
In addition, a light source, a chopper that chops the measurement light emitted from the light source, and a beam splitter that splits a part of the measurement light and uses it as a reference light are arranged on the optical axis, and further opposite the beam splitter. A light emitting unit is equipped with a filter and a photodetector that transmit only the light of wavelength I, and a beam splitter is arranged on the optical axis of the measurement light.The measurement light split by the beam splitter is absorbed by the gas to be measured. At least one set of a filter and a photodetector is provided that transmits only the light of wavelength λ2 (including cases in which multiple components of the gas to be measured have absorption wavelengths of A3, A4, etc.), and A light-receiving section comprising a filter and a photodetector that transmits only light having a wavelength λ1 that is not absorbed by the gas to be measured is provided facing the beam splitter and facing the light-emitting section through the gas to be measured, The present invention relates to a gas concentration and partial pressure measuring device that includes a signal processing system that receives signals from a photodetector provided in the light projecting section and the light receiving section 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, a method for measuring the absorption intensity of a gas using light having a specific absorption wavelength and then measuring the concentration of the gas to be measured is disclosed, for example, in Japanese Patent Publication No. 5]-2090/1. 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 of this method is to measure the light intensity (hereinafter referred to as linear intensity) of the light intensity, and to measure the average value of the gas concentration along the optical path from these values.

In general, light absorption follows the Lambert-Beer law: I (L) = rOeXp (-a 0n 0
L). Here, I (o) 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 linear intensity. Note that the absorption coefficient α is a physical constant uniquely determined by the gas to be measured and the wavelength used.

The light intensities 11 to 3 obtained by the present invention are expressed as follows. Here, I is the signal output detected by the detector of the light projecting section, and I2 and ■ are the signal outputs detected by the two detectors of the light receiving section, respectively.

I,=I enter! (0) I2 = Kr input t (0) exp (-a input +
+n 1L) I3=KI enter 2 (0) exp (
a input y ・n-L) However, λl is the wavelength of the reference light, A2
is the wavelength of the measurement light.

αA1 is the absorption coefficient of the gas to be measured with respect to the wavelength λl.

αA2 is the absorption coefficient of the gas to be measured for wavelength λ2, ■A
1 (0) is the initial intensity of the reference light, 2 (o) 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, and K is a coefficient representing optical loss other than light absorption by the gas to be measured, representing loss due to dirt on window glass existing on the optical path, loss due to optical axis deviation, etc.

Light intensity ■1 represents the light source intensity, and the life of the light source can be estimated by monitoring the decrease in brightness due to deterioration of the light source.

Determine when it is time to replace it. The transmittance of the reference light is 1, which is t+=I2/11=Kexp (ct included t・n-L)
becomes. Since αA1 is not absorbed by the deposited constant gas.

The reference light may be set to 1 with α, and τ becomes =. Since τ1 represents unnecessary optical loss on the optical path,
Monitoring of dirt on window glass by monitoring τ1,
Determines when it is time to replace it and determines whether there is optical axis misalignment. Also, the transmittance of the measurement light is 2, r2=13/11==K[I*
z (0)/IAI (of) exp(-a A2 ・
n-L). Furthermore, the ratio τ of transmittance τl and τ2 is r
=τ2 /l l =(IA2 (0)/I input 1 (0
)) exp(−aA2·n), 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 are 1 in 1 (0) and IA2 (
0), and the value of ■A2(0) can be estimated from the value of IA1(O). Therefore, by simply measuring the light source intensity 1 (input 1 (0)), the ratio of the light intensities of the reference light and the measurement light (1 in 2 (0)/I in 1 (O)) can be determined. Now let this ratio be C, then t=c1exp(-aA2 +n 0L) °= (
1). If we take the logarithm of both sides of equation (1) and rearrange it for the volume molar concentration n of the body of electricity to be measured.

n = - (Q n t / c) / (a input 2 ・L
)-(2). Therefore, by combining equation (2) and the gas state equation p = n RT (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), p = CRTlCa
Input 2 ・L))Qn r/c-(3), and formula (3)
Therefore, 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. FIG. 1 shows an example of a device implementing the present invention, in which light emitted from a light source 1 housed in a light projector housing 9 is focused by an elliptical surface @2, and is further emitted off-axis. The object mirror 3 converts the light into a parallel light beam. This parallel light beam is further interrupted by a light chopper provided on the optical path that chops at a frequency f, and then reaches the beam splitter 5, where a part of it is separated and condensed by a condensing lens 6 as a reference light, and the wavelength The filter 7 allows only the incident light to pass through, so that it becomes monochromatic light and enters the photodetector 8. Therefore, the detection signal L of the photodetector 8
1 can be processed by a signal processing system 21, which will be described later, to obtain the initial intensity ■1 of the reference light λ1. On the other hand, the parallel light beam that has passed through the beam splitter 5 is radiated out of the housing through a window 10 provided in the emitter housing 9, passes through the gas to be measured 11, and passes through the window 12 provided in the light receiver housing 13 to the housing. 13. A beam splitter 14' is provided inside the light receiving unit housing 13 facing the window 12, and a part of the incident light is separated as a reference light and focused by a condensing lens 15.
Furthermore, the filter 16 transmits only the light of wavelength λ1, which converts the light into monochromatic light, which enters the photodetector 17. As a result, by processing the detection signal L2 of the photodetector 17 in the signal processing system 21, the line intensity I2 of the reference light λl can be determined. Further, the parallel light beam transmitted through the beam splitter 14 is condensed by a condensing lens 18, and is further condensed with a wavelength λ
The measured light beam passes through a filter 19 that transmits only the second light beam and enters the photodetector 20, and the detection signal LJ is processed by the signal processing system 21 to obtain the linear intensity I3 of the measuring light beam.

In this way, the light intensities (1) to (3) can be measured, so
From this, the transmittances τl and τ2 of the reference light and measurement light can be determined. Furthermore, the above formulas (1) and (2)
The volume molar concentration n of the gas to be measured is determined by equation (3)
The partial pressure P of the gas to be measured can be determined from . In this case, the temperature T of the gas to be measured is measured by, for example, a thermal lightning pair 37, and this is substituted into equation (3).

Next, processing of the detection signal by the signal processing system 21 in the present invention will be explained. Figure 2 shows an example of this.
Detection signal L 1 measured by photodetector 8.17.20
+ t, 21 The case where L3 is smaller than LI+L2 among t, 3 is shown. In the case of the present invention, the photodetector of the light receiving section receives in addition to the signals that are originally required.

Stray light noise emitted from the measurement target is also detected.

However, in the case of the present invention, since the light from the light source is chopped by the chopper 4 at the frequency f as described above, among the detection signals detected by the photodetector, the frequency f changes in synchronization with the chopping of the light source. The component with is the desired signal. Therefore, stray light noise can be removed by inputting the signal detected by the photodetector to a lock-in amplifier or CR active filter and extracting the frequency f component. That is, for the detection signal LI+L2, the CR active filter 22.23 with the transmission frequency f
As for the light intensity L3, the lock amplifier 24 to which the synchronization signal from the light chopper 4 is applied extracts the light intensity signal TIyI2. Steps 11 to 3 thus obtained are guided to the calculation mechanism 26 via the A/D converter 25, and the equations (1), (2),
By performing arithmetic processing according to (3), the volume molar concentration n and gas partial pressure p of the gas to be measured can be determined.

FIG. 3 shows a case in which the present invention is applied to the measurement of the concentration and partial pressure of atmospheric gas near a steel plate housed in a heat treatment furnace. The housing 9 housing the light emitting unit is placed opposite to the window 27 via the flange joint 27, and the housing 13 of the light receiving unit is placed opposite to the window 30 via the flange joint 31, as shown in FIG. By performing the same operations as in the case above, it is possible to measure the concentration and partial pressure of the atmospheric gas 33 in the vicinity of the steel plate 29 in the furnace. In this case, if a chemical reaction is occurring between the steel plate and the surrounding atmosphere, it is possible to understand the progress of the chemical reaction by measuring the gas concentration 2 partial pressure near the interface, and it is possible to determine the progress of the chemical reaction. Obtain essential information for process control.

Further, the present invention can measure the concentration and partial pressure of each gas consisting of a plurality of components. FIG. 4 shows the case of measuring the concentration and partial pressure of two types of gases, in which a second beam splitter 34 is provided behind the condenser lens 18 on the light receiving section side of the measuring device shown in FIG. 1 minute of light is transmitted through a filter 35 that transmits only light of wavelength λ3, and is incident on a photodetector 36. The detected signal L4 is processed by a signal processing system 21. By this, the final intensity I4 of the measurement light can be obtained.

In this way, in the present invention, white light is transmitted through the gas to be measured, and a filter that transmits only light of a specific wavelength is used just before the photodetector to make it monochromatic, making it possible to simultaneously measure multiple components of the gas to be measured. This can be easily accomplished by simply adding a beam splitter, a filter, and a photodetector.

〔Example〕

Next, a case will be shown in which the concentrations of H2C and CO are simultaneously measured using the apparatus shown in FIG. λ1 = 1.6 as reference light
λ2=1.385 as measurement light corresponding to μm, H20
λ3 = 4.7 μm light is used as the measurement light corresponding to μm, Co, optical path length L = 3.4 m, gas temperature T = 80
The ratio τ of the transmittance of the reference light and the measurement light when the measurement was performed under the condition of 0° C. was plotted on a semilog plot. The results are shown in FIG. 5 for H2C and in FIG. 6 for CQ. Note that the horizontal axes are H2C and GO partial pressures, respectively.

As is clear from this, there is a proportional relationship between the logarithm of the ratio τ of partial pressure and transmittance, and from this, the volume molar concentration and partial pressure of the gas to be measured can be determined.

〔Effect 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 background noise is constantly eliminated.
While eliminating the effects of reduced light source brightness due to deterioration of the light source, effects of light loss due to dirt in the optical system such as transmission windows, and effects of light loss due to misalignment of the optical axis, it is possible to adjust the concentration and partial pressure of many types of gases. can be measured. Furthermore, since there is no mechanically driven part within the measuring device, the device has excellent durability and reliability, and reliable measurements can always be performed. Also,
Application of the present invention makes it possible to monitor chemical reactions online, so for example, control of stainless steel bright annealing furnaces in the steel industry, vacuum degassing equipment for molten steel, CVD processes in semiconductor manufacturing processes, control of diffusion furnaces 1 in food-related processes. Control of various drying lines including grains.

In addition, it is possible to actively control lateral processes in various industries, and has a remarkable effect when applied to various gas production accompanied by chemical reactions and industrial processes involving various gas components.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an apparatus for carrying out one aspect of the present invention, FIG. 2 is a block diagram showing an example of the configuration of a signal processing system used in the present invention, and FIG. 3 is a block diagram showing an example of the configuration of a signal processing system used in the present invention. 4 is a block diagram showing an example of the device configuration when simultaneously measuring the concentration n and partial pressure P of two types of gases, and FIGS. 5 and 6 are 3 is a graph showing measurement results according to the present invention. 1: Light source 2: Ellipsoidal mirror 3: Off-axis parabolic mirror 4 Nilight chopper 5: Beam splitter 6: Condensing lens 7: Interference filter 8: Photodetector 9: Light emitter part 10:! ! ! . ll: Gas to be measured 12: Window 13: Light receiving unit housing 14: Beam splitter 15:
Condensing lens 16: Filter 17: Photodetector
18: Condenser lens 19: Filter 20 Photodetector 21: Signal processing system 22. 23: CR active filter 24: Lock-in amplifier 25: A/D converter 26: Microcomputer 27: Transmission window 28: Flange joint 29: Steel plate 30: Transparent window
31: Flange joint 32: Furnace
33: Furnace atmosphere 34: Beam splitter 35:
Filter 36 - Photodetector 37: Thermocouple transparent permittivity

Claims (4)

[Claims] (1) After chopping the measurement light emitted from the light source toward the gas to be measured, part of it is divided and its intensity is measured as a reference beam, and the remaining measurement light is passed through the gas to be measured. After that, the light is divided into light with a wavelength that is absorbed by the gas to be measured and light with a wavelength that is not absorbed, the intensity of each light is measured, and the concentration and partial pressure of the gas to be measured are determined from the measured values. A method for measuring gas concentration and partial pressure, characterized by: (2) After chopping the measurement light emitted from the light source toward the gas to be measured, part of it is divided and its intensity is measured as a reference beam, and the remaining measurement light is passed through the gas to be measured. Then, the light is divided into light of each wavelength that is absorbed by each of the gases with different components that make up the gas to be measured, and light of a wavelength that is not absorbed by the gas to be measured, and the intensity of each light is measured. and the concentration and partial pressure of each component of the gas to be measured are determined from the measured values.
1) Method for measuring gas concentration and partial pressure as described in section 1). (3) A light source, a chopper that chops the measurement light emitted from the light source, and a beam splitter that splits a part of the measurement light and uses it as a reference light are placed on the optical axis, and the beam splitter is further opposed to the beam splitter. A beam splitter and a measurement beam split by the beam splitter are arranged on the optical axis of the measurement light. A filter and a photodetector are provided that transmit only the light of wavelength λ_2 that is absorbed by the gas to be measured, and furthermore, a filter and a photodetector are provided that transmit only the light of wavelength λ_1 that is not absorbed by the gas to be measured, facing the beam splitter. A light receiving section consisting of a filter and a photodetector is provided opposite the light emitting section via the gas to be measured, and signals from the photodetectors provided in the light emitting section and the light receiving section are inputted to detect the gas to be measured. A gas concentration and partial pressure measuring device comprising a signal processing system that calculates the concentration and partial pressure of gas. (4) A light source, a chopper that chops the measurement light emitted from the light source, and a beam splitter that splits a part of the measurement light and uses it as a reference light are arranged on the optical axis, and further facing the beam splitter. A beam splitter and a measurement beam split by the beam splitter are arranged on the optical axis of the measurement light. A filter and a photodetector are provided that transmit only light with a wavelength λ_1 that is not absorbed by the gas to be measured, and one or more beam splitters are provided on the optical axis behind the beam splitter, and each beam Wavelengths λ_3, λ_4, which are absorbed by each component constituting the gas to be measured on the optical path transmitted or reflected by the splitter, respectively.
A light receiving section equipped with a filter and a photodetector that transmits only the light of and a signal processing system for calculating the concentration and partial pressure of the gas to be measured.