JPS63261140A - Gas concentration detector - Google Patents

Abstract

PURPOSE:To obviate generation of measurement errors with a change in the intensity of light radiation from a light source to the light projection window of a container by providing a long optical path photodetecting means and short optical path photodetecting means. CONSTITUTION:The light intensity (detected light intensity I1) of the optical path length L1 in a gas is detected by the 1st short optical path photodetector 19. The light intensity (detected light intensity I2) of the optical path length L2 in the gas is detected by the 2nd short optical path photodetector 22 and the (detected light intensity I3) is detected by the long optical path photodetector 25. n1=[1/alphaL2-alphaL1]ln(I1/I2) (where n: the volumetric molar concn. of the gas to be measured, alpha: the coefft. of absorption of the gas to be measured, L3: the optical path length in the gas) and n2=[1/alphaL3-alphaL2]ln(I3/I2) are respectively calculated by a CPU 29. The computed concn. value n2 is higher in reliability than n1 in the case of a low concn. gas and the opposite is true in the case of a high concn. gas. The computed concn. value of the higher reliability is, therefore, selected to meet the intended or estimated concn. region of the gas to be measured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas concentration detection device that uses light as a measuring medium, and is particularly applicable to various heat treatment furnaces used in the steel industry and other industries. The present invention relates to a device for detecting the concentration of atmospheric gas used in various processes.

[Conventional technology]

There are many processes, such as heating furnaces and annealing furnaces used in the steel industry, that are carried out in atmospheres where the concentration and partial pressure of gaseous components are controlled, and in which the concentration and/or partial pressure of gaseous components is measured. It is essential that

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 with a specific absorption wavelength and then measuring the concentration of the gas to be measured is, for example,
Tokuko Showa 51. This has already been done as disclosed in Japanese Patent No. 20904.

In general, light absorption is expressed as 11 = T Oexp (-α・n−L) according to Lamber's law, and from this, n = −CQ n(I+ /Io))/(α・L)
...(],). However, To is the initial intensity (intensity before transmission), n is the volume molar concentration of the gas to be measured, L is the optical path length passing through the gas to be measured, α is the absorption coefficient, and 11 is the final intensity (intensity after transmission). . Note that the absorption coefficient α is a physical constant uniquely determined by the gas to be measured, the wavelength used, and the like. Therefore, the initial intensity ■o and final intensity ■1 of the light having the absorption wavelength of the gas to be measured are detected, and these are introduced into equation (1) to obtain the volume molar concentration n.

In addition, from the gas equation of state (P is the partial pressure of the gas, T is the temperature of the gas, and R is the gas constant), p = -RT[:Qn(T+/In))/(α
・T−)=・(2), and the partial pressure P of the gas can be calculated.

[Problem that the invention seeks to solve]

Starting strength■. If the optical path characteristics between the detection position and the light projection window of the container containing the gas to be measured change due to, for example, dirt, the intensity of light incident on the container will change even if the characteristics of the light source are constant. , the measurement error becomes large or results in a measurement error. In addition, when the concentration of the gas to be measured is low, in order to increase the rate of change corresponding to the concentration in (1), it is sufficient to increase the light transmission distance in the gas, but if this distance is increased, the concentration will increase This causes the problem that the light detection intensity becomes too fine when measuring gases. In other words, it has been difficult to increase the measurement accuracy for both low and high concentrations.

The first object of the present invention is to provide a gas concentration detection device that is unlikely to cause measurement errors due to changes in light radiation intensity from a light source to a light projection window of a container. However, the second object is to provide a gas concentration detection device that can improve measurement accuracy.

[Means for solving problems]

In order to achieve the second object, the present invention includes a reflector that reflects the light projected onto the gas storage container to be measured multiple times within the container, and a long path light detector that detects the intensity of the light reflected multiple times. means, short path light detection means for detecting the intensity of light reaching the long path light detection means, and detecting the concentration of the gas to be measured based on the detected intensities of the long path light detection means and the short path light detection means. A computing means for computing is provided.

[Effect]

Here, if the light intensity detected by the short-path light detection means is 11, and the light intensity detected by the long-path light detection means is 12, then
According to the Lambert-Beer law mentioned above, D1=Ioexp(-α・n-r-i)I2=
T Oexp (-α-n-T-2). Here, ■o is the intensity of the light projected onto the container containing the gas to be measured (initial intensity), ■1 is the intensity of the light that has traveled one step through the gas (final intensity), and ■2 is the intensity of the light projected onto the container containing the gas to be measured (final intensity). The intensity (final intensity) of the light that has traveled through the center (2), α is the absorption coefficient of the gas to be measured, and n is the volume molar concentration of the gas to be measured. From both formulas, ■ 1 / D2 ”0XIII l: α ・
n(r-2L, t)), and from this, n= (]/(αL2-αL+): 1Qn(T 1/
I2)...(3) Find n. The calculation corresponding to this equation (3) is performed by the calculation means. In this equation (3), the initial intensity ■o is not a calculation parameter, and both ■1 and ■2 are the final intensities that have passed through the measurement gas, so the characteristics from the light source to the short path light detection means ( Fluctuations in the light source, dirt on the light transmission window) do not affect the calculated density n.

When measuring low concentration gases, measurement accuracy can be improved by lengthening T-1 and L2 to increase light absorption by the gas, and when measuring high concentration gases, shortening Ll, ■, and 2 can improve measurement accuracy. Measurement accuracy is improved by reducing excessive light absorption by the gas.

Therefore, in the first embodiment of the present invention, the optical path length L in the gas
a first short optical path light detection means (detection light intensity I2) that detects a light intensity of L2 in the gas; It is equipped with a long optical path light detection means (detection light intensity I3), and the first calculation means calculates n1=[:1/(αT−7−αL+)]Qn(
11/T2')...(4), and the second calculation means calculates n2=[1'/(αL3-αL2')':1Qn(T
3/I2)...(5) is calculated. In the case of low-concentration gases, the force of the concentration calculation value n2 based on equation (5) (, is more reliable than the concentration calculation value nl based on equation (4), and in the case of high-concentration gases, Therefore, the concentration calculation value with higher reliability is selected corresponding to the planned or estimated concentration range of the gas to be measured.

By changing the incident angle of the light source light with respect to the reflector of the container, T, , 1 and 72 change. Accordingly, in one invention of the present application, the incident angle is changed by the switching means, that is, the number of apertures is changed, and the concentration rz (low/reflective (number of times of high reflection: for detecting a high concentration area) and density T12 (number of times of high reflection: for detecting a low concentration area).

Other objects and features of the invention will become apparent from the following description of an embodiment with reference to one drawing.

[Embodiment 1] - Fig. 1 shows the configuration of the first embodiment of the present invention. The light emitted from the light source 1 is focused by an ellipsoidal mirror 2, further converted into a parallel beam by an off-axis parabolic mirror 3, and pulsed into chopping light at a frequency f by a chopper 5 driven by a motor 4. is projected onto the window 11 of the container 6, is repeatedly reflected from the opposing reflecting surfaces 12 and 3 within the container 6, and is reflected at the beam splitter 14 by approximately 20
% of light exits the container 6, and a filter J7 and a condenser lens 1 selectively transmit only the light having the absorption wavelength of the gas to be measured.
8 to a first short-path photodetector 19, which generates an analog voltage proportional to its intensity. The light reflected by the beam splitter 14 is further repeatedly reflected by the reflectors 12 and 13, and at the beam splitter 15, approximately 137% of the light exits the container 6, and the absorption wavelength of the gas to be measured is reflected. It passes through a filter 20 that selectively transmits only light and a condensing lens 21 to reach a second optical path photodetector 22, which generates an analog voltage proportional to its intensity (2). .

The light reflected by the beam sub-litter 15 is further repeatedly reflected by the anti-encapsulants 12 and 13 and exits the container 6 at the light transmission window 16, selectively transmitting only the light having the absorption wavelength of the gas to be measured. Filter 23 and condensing lens 24
The light passes through the long optical path photodetector 25 (hereinafter referred to as the third detector), and the third detector 25 generates an analog voltage proportional to the intensity (3).

The optical path length from the window 11 to the beam splitter]2 is Ll, the optical path length from the window]1 to the beam splitter 15 is L2, and the optical path length from the window]1 to the window 16 is L3.

Since the incident light is a chopping light with a frequency f, the analog voltage (Iz~) also pulsates with a frequency f. The bandpass filters 261 to 263 extract only the pulsating portion of this frequency f. That is, only signals indicating the received light intensities 11 to 3 of wavelengths that are absorbed by the gas to be measured are extracted.

These signals are smoothed (converted to direct current) by integrators 271-273 and applied to hold circuits 281-283.

Hold circuit 28. ~283 has a microprocessor (
A CPU 29 (hereinafter referred to as CPU) provides a signal instructing hold. When the circuits 281 to 283 receive the signal, they hold the input voltage at that time until the signal is applied next time, and apply the held voltage to the A/C of the CPU 29.
It is applied to D conversion input terminals ADI to AD3.

The CPU 29 operates a switch 341 that specifies -times of measurement.
(Automatic return switch that closes only while it is pressed and returns to open when the pusher blade runs out); when it is pressed in the open state, it changes to the closed state and remains closed until it is pressed again; a predetermined time interval T
Switch 342 for specifying repeated measurements at 1. The detection signal (T1) of the detector 19 and the detection signal (T2) of the detector 22
), which specifies the concentration n1 calculation based on the high concentration range measurement instruction switch 351 and the detection signal of the detector 22 (Step 2)
In response to the low concentration range measurement instruction switch 352, which specifies concentration n2 calculation based on the detection signal (step 3) of the detector 25, lighting control of the lamp 1, rotational energization control of the motor 4,
Reads the detected value, calculates n, and outputs the calculated value.

-11= FIG. 2 shows the control operation of the CPU 29. When the device power is turned on and a predetermined voltage is applied to the CPU'29 (Step E: hereinafter, the word step is omitted in parentheses), the C'PU29 sets the output port to a standby signal and registers the internal register. , timer (program timer), counter, flag, etc. (2). Then, a high level H is given to the lamp driver 31 to instruct the lighting of the lamp 1 (3), a high level H is given to the motor driver 30 to instruct the rotation of the motor 4 (4), and the timer TO is started. , wait for the time To to elapse (5).This time To is the period after the lamp 1 is turned on, the lamp 1 reaches stable brightness, the motor 4 stabilizes at a constant speed, and then the integrator 271 This is a slightly longer time than the time it takes for the output of ~273 to stabilize at a voltage corresponding to the stable light intensity.

When the time To has elapsed, C'P U 29 switches switch 3.
Check the opening/closing of 41 and 342 (7°12).

If both switches are open, the timer flag is cleared (1 i), the lamp 1 is turned off (10), and the motor 4 is stopped (9).

When the switch 341 is closed (one measurement instruction), the "reading, calculation &output" subroutine (8) is executed.

That is, the lamp 1 is turned on (8" 1.), the motor 4 is driven (8.2), the timer To is started (,8,3), and the time To is waited for to elapse (84). Once it has elapsed, A hold instruction signal is given to the hold circuits 281 to 283 (85), and the A'/'D conversion input port AD
I+” AD2 and AD3 input voltage (-'I+~
Convert Ia) into digital data and read it (86-88
).

Then, the opening/closing of the switches 351 and 352 is checked (89.92). When the switch 351 is closed, a computation equivalent to the above formula (4) is executed (90), and data indicating the calculated nl and an indicator light 371 (indicating that the calculation was performed using the high concentration region computation formula (4)) are performed. )" lighting instruction data is output to the character display 33, and n
The latch 32 outputs data indicating l to the host computer.
(91).

Then, the process exits from subroutine (8) and returns to step 7.

When the switch 352 is closed, a calculation equivalent to the above formula (5) is executed (93), and data indicating the calculated n2 and an indicator light 372 (indicating that the calculation was performed using the low concentration region calculation formula (5)) It outputs the lighting instruction data to the character display 33, and latches the data indicating nl to the output latch 32 to the computer (91).
). Then, the process exits from subroutine (8) and returns to step 7.

When both the switch 35] and the switch 352 are open, first, an operation corresponding to equation (4) is executed.95)
Next, the calculation equivalent to the above formula (5) is executed (96), and the data indicating the calculated nl is compared with the high/low concentration division value Ns (97). If nl is greater than or equal to Ns (high concentration region), the concentration data n1 calculated using the high concentration region calculation formula (4) and the indicator light 371 (indicating that it was calculated using the high concentration region calculation formula (4)). Lighting instruction data is output to the character display 33, and data indicating nl is latched to the output latch 32 to the host computer (91). Then, the process exits from subroutine (8) and returns to step 7.

When the switch 342 changes from open to closed, the CPU 29 proceeds to steps 7-1.2'-1, 3-1, and 5, and executes the subroutine 15 of "reading, calculation &output". The contents of this subroutine 15 are exactly the same as the contents of subroutine 8 described above. When this is executed, timer T1 is started (16a) and the timer flag is set (16
b). The process then returns to step 7 and then proceeds to step 12, where if the switch 342 is closed, there is a timer flag, so the process proceeds from step 13 to step 14 to check whether time T1 has elapsed. If not, step 14-7. -12-], 3-14, and waits for time T1 to elapse (timer T1 times out). When the time T1 has elapsed, the process proceeds to step 15, and a subroutine 15 of "reading, calculation &output" is executed. In this way, while the switch 342 is closed, "
Execute subroutine 15 of ``Read, Calculate &Output''. 11. When the switch 342 returns from closed to open, the timer flag is cleared. ), turn off lamp 110), motor 4
9) and proceed to step 7.

Note that even if there is no gas in the container 6, the first detector 1
9, the detection intensity ■1 is about 20% of the container incident light intensity lo, the detection intensity of the second detector 22 is about 30% of ■o, and the detection intensity of the third detector 25 is about 50%, Even in the absence of light absorption by the gas, the detector 19. , 22.2.
Since the light detection intensities of 5 are different, it is necessary to correct this. In this case, a standard gas that does not substantially absorb light at the absorption wavelength of the gas to be measured is stored in the container 6, and the first to third detectors 1
．． 9,,2j2. , 25 intensity detection values are read, and a correction coefficient is calculated to make the detection signal of each intensity detector positive and sharp (a coefficient that makes the detection values of all detectors the same value). , the detection value of the detector is multiplied by the coefficient, and then the concentration calculation 1 of the above equations (4) and (5) is performed.

CP and Uj9 calculate these correction coefficients and store them in the calculation parameter register. The setting of this correction coefficient is
This is done when the switch 4j is closed. Note that before closing the switch 41, the operator stores standard gas in the container 6.

When the switch 41 is closed, the CPU executes correction value setting control (not shown) to set the first to third detectors 25.
Read the detected value (1g1 to Is3) and set the correction coefficient Ka
1 = Isl, /Is3 and K 32 = ,
Calculate Is2/Is3 and write these to the calculation parameter register. - In the n1 calculation of step 290 and 'Cj95 described above, the CPU 29 multiplies X2 (measured value) by 32, sets the product to 12 for concentration calculation, and uses this for the calculation of ・nl. . In the n2 calculations in steps 93 and 96 described above, the CPU 29 calculates 32 to I3 (measured value).
Multiply by
Used for calculations. .

In the first embodiment described above, even if the characteristics of the optical path from the lamp 1 to the beam splitter 14 (emission intensity of the lamp and light transmittance of the optical path) change, this will not affect the detectors 1.9.
, '2 and 25 appear as changes in the same direction, and have no substantial effect on the density calculated by the above equation.

Therefore, measurement errors due to the light radiation intensity of the light source, dirt on the window 11, etc. are virtually eliminated. Furthermore, two sets of measurements with different optical path lengths (calculation according to the fourth equation and calculation according to the fifth equation) are possible, and highly accurate measurement corresponding to the gas concentration region is possible.

[Example 2] Figure 3 shows a second embodiment of another invention of the present application.
An example is shown.

In this second embodiment, lamp 1. An ellipsoidal mirror 2 and a parabolic mirror 3 are fixed to a base 38.

This base 38 has a long hole 42. '13 has been opened,
These long holes 42. Guide pins 44 and 45 fixed to a support (not shown) supporting the base are inserted at /13. A plunger arm 46 of a solenoid device 39 is connected to the base 38 .

When the solenoid device 39 is de-energized, the base 38 is in the solid line position as shown in FIG. 3, and the light emitted from the lamp 1 is emitted relatively few times as shown by the thin line (solid line). Reflected inside the container (with high concentration area measurement set). When the solenoid device 39 is energized, the plunger arm 46 of the solenoid device 39 pulls the base 38 to the lower left and the base 38 moves to the position shown by the dashed line in FIG. As shown by the dashed line,
It is reflected within the container relatively many times (when low concentration area measurement is set).

High concentration area measurement setting with the solenoid device 29 de-energized;
In any of the energized low concentration region measurement settings, container 1
A portion of the light reflected inside exits from the beam splitter 14 and the light transmission window 15 and is directed to the short path photodetector 19 and the long path photodetector 25.

In the high-concentration area measurement setting where solenoid device [29 is de-energized, the optical path length from window 1 of container 1 to beam splitter 14 is Ll, the optical path length from window] 1 to window 15 is r,2, and solenoid In the low concentration measurement setting where the device 29 is energized,
The optical path length from window 1] to beam splitter 14 is L3+
The optical path length from window 11 to window 15 is L4, and T-1
<I-3°T-, 2<Tla, and in this embodiment, the CPU 29 calculates n 1 = (1/(αL'2-'a T, 1))] Qn in the high concentration measurement setting.
(■1 /I3)...Calculate the concentration n1 using the formula corresponding to (6), and in the low concentration measurement setting, n2 == l:J, /(a T, 4-=L3')L
Qn(11'/'I3')...(7) 1131 degrees n2 is calculated using an arithmetic expression corresponding to the following.

FIG. 4 shows the control operation of Cp TJ '29 shown in FIG. 3. This control operation is roughly the same as the control operation shown in FIG. 2, but the content of the "reading, calculation &output" subroutine 8 is different. Explain the differences. In this embodiment, when the PU 29 proceeds to the subnode 8, it first checks the HJ closed state of the switches 341 and 342 (80a, 80b').

When the switch 351 is closed (high concentration region measurement setting), steps 81 to 87, 86, 87i 90+91 and 100 to 3, calculates n'+ using equation (6) in -1-, and outputs this.When the switch 342 is closed, steps 1.03 to 112 "
Execute the read &-n 2 operation, and use the formula (7) to calculate n2
Calculate and output this. Switches 351 and 35
When 2 is open, first, in subroutine I 1.3 of "read &n' 2 operation", steps 1, ' 03 to 11 are executed.
Calculate n2 in exactly the same manner as in 1. Next, de-energize the solenoid device 39 (1.14), wait for the time elapsed charge of To (115), and proceed to subroutine 11 of "read & n1 calculation".
6, calculate nl in exactly the same way as steps 8G, 87 and 90, and compare bl with Ns (117), n1≧
When Ns', output nl; otherwise, output nl.
Outputs 2.

This second embodiment also has the same effect as the first embodiment described above, and requires a mechanism for changing the incident angle of the light projected onto the window 11, but one set of detectors is required. This has the effect of being omitted.

Although two embodiments have been described above, the present invention can be implemented in other embodiments as well. For example, in the second embodiment, one of the detectors can be omitted, and one detector can serve both as a short optical path light intensity detector and a long optical path optical intensity detector. In this case, for example, as shown in FIG. The light is reflected by the reflecting mirror/I3 and projected onto the detector 19 through the beam splitter 42. Beam splitter 42 and reflector 4
A chopper (motor/14+rotary plate/I5) that chops at a frequency extremely lower than the chopping frequency f by the chopper (4, 5) is inserted between 3.
Rotating plate 45 blocks light from reflector 43 to beam 11 splitter 42 at certain times and allows it to pass at other times.

When the light transmitting aperture of the rotary plate 45 is located between the reflecting mirror 43 and the beam splitter 42, the first to sensor 46 generate a signal I].

When the rotating plate '15 blocks light between the reflecting mirror 43 and the beam splitter 42, the photo I-sensor 46 generates an L signal. When the sensor 46 is generating H, the detector 19 is 1. ,=11 Detect earthwork 3, L
When this occurs, ■1 is detected. l3=I+3
■3 can be found using Is.

Similarly, in the first embodiment, a beam splitter and a low frequency chigopper are further provided, so that the detector can be integrated into one.
You can save on pieces.

〔Effect of the invention〕

As described in "2" below, according to the present invention, changes in emitted light intensity, transmittance, etc. from the lamp (1) to the light receiving window (11) of the container (6) affect the detected concentration value (n"rl+ + r12). It is stable without any problems.It provides highly reliable concentration detection.Also,
It is also possible to measure multiple sets with different optical path lengths, and it is also possible to measure with high accuracy corresponding to the gas concentration region.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. FIG. 2 is a flowchart 1- showing the control operation of the CPU 29 shown in FIG. FIG. 3 is a block diagram showing the configuration of another embodiment of the invention of the present application. Figure 4 shows the CPU 29 shown in Figure 3.
This is a flowchart 1 showing the control operation. FIG. 5 is a block diagram showing main parts of a modification of the embodiment shown in FIG. 3. ■ = Lamp (light source) 2: Elliptical mirror 3: Parabolic mirror 4: Motor 5: Rotating plate 6: Container (measured gas container) 7:
Pipe 8: Gas inlet 9: Pipe 1o: Gas outlet 11: Light transmission window 1.2.1-3: Reflector (reflector) 17I: Beam splitter J5: Beam splitter 16: Light transmission window 17, 20, 23: Filter 18.2], 24: Lens 1.9, 22: Photodetector (first and second short optical path light detection means) 25: Photodetector (long optical path light detection means) 261-163: Bandpass filters 271- 273: Integrators 281 to 283: Hall 1 to circuit 29: Microprocessor (calculating means, first calculating means, second calculating means) 30: Motor driver 3]: Lamp driver 32: Output latch 33: Character display 34, ．． 3
42,351.362,41. :Switch 361-3
63: Indicator light 38: Base 39: Solenoid device 40: Solenoid driver 42
．． 43: Long hole 44A5 Ni guide pin 46:
plunger arm

Claims (3)

[Claims] (1) A gas container to be measured, a light source that projects measurement light onto the container, a photodetector that detects the intensity of the light that has passed through the gas in the container, and a concentration of the gas to be measured based on the detected intensity. A gas concentration detection device comprising: a reflector that reflects the light projected onto the container multiple times within the container; a long path light detection device that detects the intensity of the light reflected multiple times; and a long path light detector that detects the intensity of the light reflected multiple times. short-path light detection means for detecting the intensity of light reaching the light-detection means; and calculation means for calculating the concentration of the gas to be measured based on the detected intensities of the long-path light detection means and the short-path light detection means; A gas concentration detection device comprising: (2) The short-path light detection means includes a first short-path light detection means that detects the intensity of light with a short optical path length, and a second short-path light detection means that detects the intensity of light with a long optical path length, The calculation means is a first calculation means for calculating the concentration of the gas to be measured based on the light intensity detected by the first and second short path light detection means;
and a second calculation means for calculating the concentration of the gas to be measured based on the light intensity detected by the second short-path light detection means and the light intensity detected by the long-path light detection means.
1) The gas concentration detection device described in section 1). (3) A gas container to be measured, a light source that projects measurement light onto the container, a photodetector that detects the intensity of the light that has passed through the gas in the container, and a concentration of the gas to be measured based on the detected intensity. A gas concentration detection device comprising: a reflector that reflects the light projected onto the container multiple times within the container; a long path light detection device that detects the intensity of the light reflected multiple times; and a long path light detector that detects the intensity of the light reflected multiple times. Short path light detection means for detecting the intensity of light reaching the light detection means; switching means for switching the number of reflections to the long path light detection means; and detection of the long path light detection means and the short path light detection means. A gas concentration detection device comprising a calculation means for calculating the concentration of a gas to be measured based on the intensity and the optical path length determined by switching by the switching means.