JP3918740B2 - Infrared gas analyzer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used for process monitors that measure gas concentrations in chemical factories and steelworks, combustion gas analysis of boilers and combustion furnaces, air pollution monitoring, automobile exhaust gas measurement, etc., and utilizes the infrared absorption effect inherent to gas molecules. The present invention relates to an infrared gas analyzer that continuously measures the concentration of a specific component in gas or vapor.
[0002]
[Prior art]
In a conventional infrared gas analyzer, infrared light from a light source is alternately irradiated onto a sample cell and a comparison cell by a sector, and infrared light transmitted through each cell is received by an infrared detector, and an AC signal measurement signal and a comparison signal, respectively. Detected as Both detected signals are integrated by a signal processing circuit, and the concentration of the measurement target component is measured based on the ratio of the respective integrated values (see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-8-327545 [0004]
[Problems to be solved by the invention]
Since the obtained comparison signal is used to correct the measurement signal, the magnitude of the comparison signal changes even if the magnitude of the measurement signal related to the measurement gas concentration of the sample gas (the amplitude of the AC signal) changes. Ideally not.
[0005]
However, in the process of moving from the measurement signal to the comparison signal, the comparison signal is dragged to the previous measurement signal, and the magnitude of the comparison signal varies depending on the difference in the magnitude of the measurement signal. If the comparison signal used for correcting the measurement signal is changed, the gas concentration measurement stability is impaired.
Accordingly, the object of the present invention is to improve the stability of gas concentration measurement by making the comparison signal less susceptible to the magnitude of the measurement signal.
[0006]
[Means for Solving the Problems]
The present invention includes a comparison cell in which a reference gas is sealed, a sample cell in which a sample gas is circulated, a measurement optical system that transmits infrared light to both of these cells, an infrared detector that detects infrared light transmitted through both the cells, and Infrared gas analysis provided with a data processing device for calculating a specific gas concentration in the sample gas based on both signals using the detection signal based on the transmitted infrared light of the comparison cell as a comparison signal and the detection signal based on the transmitted infrared light of the sample cell as a measurement signal The measurement optical system receives infrared rays from both cells to the infrared detector so that at least a comparison signal is obtained as a series of signals composed of a plurality of cycles of AC signals between the measurement signal and the next measurement signal. And the data processing device excludes at least the first one cycle signal of the series of comparison signals, and the remaining cycle signals. It is to use as a comparison signal for the gas concentration calculation.
[0007]
In the present invention, at least the comparison signal is obtained as a series of signals composed of AC signals of a plurality of periods, and the comparison signal of at least one period immediately after switching from the measurement signal to the comparison signal is not used. Make the signal less sensitive to the magnitude of the measurement signal. As a result, since the comparison signal can avoid interference due to the measurement signal, more stable measurement can be performed.
[0008]
In order to make the measurement signal less susceptible to interference from the comparison signal, the measurement optical system also has a plurality of cycles of AC between the comparison signal consisting of a series of signals and the comparison signal consisting of the next series of signals. Infrared rays are incident on the infrared detectors from both cells so that they can be obtained as a series of signals, and the data processing apparatus excludes at least the first cycle of the series of measurement signals. The signal of the remaining period is preferably used as a measurement signal for gas concentration calculation.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The measurement optical system that injects infrared light from both cells into the infrared detector so that both the comparison signal and measurement signal are obtained as a series of signals consisting of multiple periods of alternating current signals. It can be realized in various forms by including a light source having a luminous flux of a size that can be generated.
[0010]
The measurement optical system according to the first embodiment is arranged between the light source and the incident surfaces of both cells, and switches the incidence of infrared rays to both cells so that the infrared rays are continuously incident on each cell a plurality of times. It has a mechanism.
[0011]
The measurement optical system of the second embodiment is arranged between the emission surfaces of both cells and the infrared detector, and infrared rays are incident so that infrared rays are incident on the infrared detector a plurality of times continuously from each cell. It is provided with an intermittent mechanism for switching the incidence of infrared rays on the detector.
[0012]
The measuring optical system of the third form is arranged between the light source and the incident surfaces of both cells, and includes an intermittent mechanism that simultaneously interrupts both cells to make infrared rays incident, and an incident part or an emission part of one cell. Shielding plate that shields and releases the entrance and exit of the other cell and moves between the cells so that the detection signals of the infrared detectors by the transmitted infrared rays of each cell are in units of a plurality of periods of alternating current signals. It is equipped with.
[0013]
The measurement optical system according to the fourth aspect includes an intermittent mechanism that is disposed between the emission surfaces of both cells and the infrared detector and simultaneously interrupts transmitted infrared rays that enter the infrared detector from both cells, and one cell. Both cells so that the incident part or the emitting part of the other cell is shielded and the incident part and the emitting part of the other cell are released, and the detection signals of the infrared detectors by the transmitted infrared rays of each cell are in units of AC signals of multiple periods, respectively. And a shielding plate that can be moved between them.
[0014]
It is preferable that the intermittent mechanism in each form of the measurement optical system intermittently injects the infrared incident time so that the infrared incident time and the non-incident time from each cell to the infrared detector are substantially the same. In that case, since integral values can be obtained not only for signals that occur when infrared rays are incident but also for signals that occur when they are not incident, they can be used as detection data. This makes it possible to measure the concentration in half as much as before. Therefore, even when the concentration of the gas to be measured fluctuates relatively quickly, it is possible to measure the concentration with high accuracy. Since it is possible to acquire twice the data in the measurement time, there is an advantage that the S / N (signal to noise) ratio is improved and accurate density measurement with less noise is possible.
[0015]
Hereinafter, the present invention will be described in detail based on examples.
(First embodiment)
A first embodiment will be described with reference to FIGS.
[0016]
FIG. 1A is a schematic diagram of an infrared analyzer according to the present invention, and FIG. 1B is a plan view showing a sector as an intermittent mechanism used in the embodiment.
The sample cell 1a has a gas introduction port 1a ′ and a gas discharge port 1a ″, and a sample gas is supplied into the sample cell 1a from the gas introduction port 1a ′ and discharged from the gas discharge port 1a ″. The comparison cell 1b contains a so-called zero gas that is a reference gas.
[0017]
A measurement optical system for transmitting infrared light to the infrared detector 5 through both cells 1a and 1b so that both the comparison signal and the measurement signal are obtained as a series of signals composed of alternating signals of a plurality of periods, for example, two periods. , A light source 4 and a sector 2 as an intermittent mechanism.
[0018]
The light source 4 has a light beam having such a size that infrared rays can be simultaneously incident on the incident surfaces of both the cells 1a and 1b.
The sector 2 is disposed between the light source 4, the sample cell 1a, and the comparison cell 1b, and is rotationally driven by the motor 3 at a predetermined speed. The sector 2 is formed in a disk shape, and the sector 2 includes two adjacent transmission windows 2a-1 and 2a-2 that irradiate the sample cell 1a with infrared rays, and two adjacent transmission windows that irradiate the comparison cell 1b with infrared rays. The windows 2b-1 and 2b-2 are provided at an eccentric position so as to be evenly arranged over a 45 ° angle.
[0019]
The sector 2 is further provided with an identification hole 2c for recognizing that the sample cell 1a is irradiated with infrared rays at a position near the outer periphery close to the transmission window 2a-1. Thus, a photodetector 7 such as a photodiode is disposed at the end position of the sample cell 1a through which the identification hole 2c passes. The photodetector 7 detects that the identification hole 2c has passed the position of the sample cell 1a.
[0020]
The detector 5 has a gas to be measured enclosed therein, and a signal corresponding to the concentration of the gas to be measured in the sample cell 1a is generated by a pressure change that occurs when light having a specific wavelength is incident on the gas to be measured. appear.
[0021]
As shown in FIG. 2, the signal processing circuit 6 as a data processing device includes a full-wave rectification circuit 6a, a comparison circuit 6b, and an arithmetic circuit 6c. Based on the detection signal of the photodetector 7, the signal processing circuit 6 identifies whether the detection signal from the detector 5 is a comparison signal based on the transmitted infrared rays of the comparison cell 1b or a measurement signal based on the transmitted infrared rays of the sample cell 1a. The specific gas concentration in the sample gas is calculated based on both signals using the detection signal based on the transmitted infrared rays from the comparison cell 1b as the comparison signal and the detection signal based on the transmitted infrared rays from the sample cell 1a as the measurement signal. Further, the signal processing circuit 6 performs an operation using the signals of the remaining periods except the first one of the comparison signal and the measurement signal as the comparison signal and the measurement signal for calculating the gas concentration. .
[0022]
Next, the operation of this embodiment will be described.
The sector 2 is rotationally driven by the motor 3 at a predetermined speed, so that the infrared rays from the light source 4 are transmitted through the transmission windows 2a-1, 2a-2 and 2b-1, 2b as shown in FIG. -2, the sample cell 1a is irradiated twice, then the comparison cell 1b is irradiated twice, and then the sample cell 1a is irradiated twice. Since these transmissive window windows 2a-1, 2a-2, 2b-1, 2b-2 are equally provided over an angle range of approximately 45 °, the time of infrared irradiation and non-irradiation is substantially the same. Become.
[0023]
A detection signal from the detector 5 is shown in FIG. The infrared light transmitted through the comparison cell 1b is detected as a large signal change as shown as a comparison signal because the wavelength unique to the measurement target gas is not absorbed in the comparison cell 1b, but transmitted through the sample cell 1a. Since the wavelength component specific to the measurement target gas is absorbed in the sample cell 1a according to the concentration of the measurement target gas contained in the sample gas, the infrared ray is absorbed as shown in the measurement signal. It is detected as a small signal change.
[0024]
The signal processing circuit 6 includes a full-wave rectification circuit 6a, a comparison circuit 6b, and an arithmetic circuit 6c. The full-wave rectification circuit 6a outputs an output signal from the detector 5 shown in FIG. The comparison circuit 6b compares the full-wave rectified signal with a predetermined reference voltage Vr to detect each rising edge of the comparison signal and the measurement signal, and outputs a pulse. Output as a signal. The arithmetic circuit 6c starts the integration of the detection signal by using the falling edge of the pulse signal as a trigger, stops the integration at the rising edge of the next pulse signal, and temporarily holds the value. At this time, the arithmetic circuit 6c is not affected by the comparison signals Rl and R2 because the comparison signals Rl and R2 immediately after switching from the measurement signal to the comparison signal are affected by the magnitude of the measurement signal. Similarly, since the measurement signals M1 and M2 immediately after switching from the comparison signal to the measurement signal are affected by the magnitude of the comparison signal, the measurement signals M1 and M2 are not used, and M3 and M4 are used as the measurement signals. , Integrating.
[0025]
Since the comparison signals R3 and R4 and the measurement signals M3 and M4 are obtained with the respective signals being hardly interfered with other signals, the measurement stability is improved by performing the gas concentration measurement using these signals.
[0026]
In this embodiment, the sector 2 is arranged between the cells 1a and 1b and the detector 5, and the infrared rays from the light source 4 are transmitted through both the cells 1a and 1b at the same time. May be intermittent. In that case, since it becomes difficult to use infrared rays from the light source 4 as a light source for detecting the identification hole 2c, a photo interrupter including a light source and a photodetector may be used.
[0027]
In this embodiment, the comparison signal and the measurement signal are each obtained continuously for two periods. However, by changing the sector structure, the comparison signal and the measurement signal can be obtained continuously for three periods or more. be able to. When the signal of the first period in which the signal interferes is discarded, if a multi-cycle signal is obtained in this way, the signal of the remaining two or more periods can be used for concentration measurement, which has the advantage of improving sensitivity. . When the comparison signal and the measurement signal are obtained for 3 cycles or more, it is possible to perform concentration measurement using the comparison signal and the measurement signal that are not subject to interference by setting the signal discarded because the signal interferes to 2 cycles or more. become.
[0028]
(Second embodiment)
FIG. 4A is a schematic diagram of the infrared analyzer of the second embodiment, and FIG. 4B is a plan view showing a sector as an intermittent mechanism used in the embodiment.
[0029]
Compared to the embodiment shown in FIG. 1, the mechanism for intermittently making the infrared rays transmitted through the cells 1a and 1b incident on the detector 5 is different, and the other configurations are the same.
In FIG. 4, as shown in FIG. 3B, the sector shape is a sector shape over an angular range of approximately 90 ° so that the infrared rays from the light source 4 to the comparison cell 1b and the sample cell 1a can be interrupted at the same time. The two openings are arranged evenly. The sector 12 is disposed between the light source 4 and the cells 1a and 1b, and is rotated by the motor 3 at a constant rotational speed.
[0030]
A shielding plate 8 is arranged between the cells 1a, 1b and the detector 5 in order to select the infrared rays that are simultaneously interrupted by the sector 12 and transmitted through the cells 1a, 1b and enter the detector 5. The shielding plate 8 blocks the transmitted infrared light of the comparison cell 1b and makes only the transmitted infrared light of the sample cell 1a incident on the detector 5 (this is referred to as “first position”), and conversely the sample cell 1a. It is attached so that it can be moved by a solenoid or the like between a position where the transmitted infrared ray is blocked and only the transmitted infrared ray of the comparison cell 1b is incident on the detector 5 (this is referred to as a “second position”). Yes.
[0031]
When the shielding plate 8 is in the first position, the sector 12 rotates a plurality of times, and a measurement signal having a cycle twice the number of rotations of the sector 12 is obtained from the detector 5. Next, the shielding plate 8 is switched to the second position, and similarly, the sector 12 is rotated a plurality of times, and a comparison signal having a cycle twice the number of rotations of the sector 12 is obtained from the detector 5.
[0032]
As described above, the signal shown in FIG. 5A is obtained from the detector 5 by the switching of the shielding plate 8 and the rotation of the sector 12, and the signal is full-wave rectified by the signal processing circuit 6 and then shown in FIG. B). Similar to the first embodiment, the density calculation is performed from the multi-cycle comparison signal and the measurement signal so as not to employ the first to several cycles of signals.
[0033]
Further, in this embodiment, the sector 12 does not need the identification hole 2c provided in the sector 2 of the first embodiment and the photodetector for detecting the transmitted light, but is a signal for moving the shielding plate 8. It can be determined.
In the embodiment of FIG. 4, the positions of the sector 12 and the shielding plate 8 may be arranged between the light source 4 and the cells 1a and 1b and between the cells 1a and 1b and the detector 5.
[0034]
Also, the duty ratio for switching the position of the shielding plate 8 may not be 1: 1, and the time for obtaining the measurement signal by setting the time of the first position to be longer than the time of the second position. May be lengthened. In this case, since the time for obtaining the measurement signal is long, the measurement sensitivity is improved.
[0035]
The shape of the sector 12 is not limited to that shown in FIG. 4B, but may be any as long as it allows the infrared rays to enter both the cells 1a and 1b at the same time.
[0036]
【The invention's effect】
In the present invention, at least the comparison signal is obtained as a series of signals composed of AC signals of a plurality of periods, and the comparison signal of at least one period immediately after switching from the measurement signal to the comparison signal is not used. Since the signal can avoid interference due to the measurement signal, more stable measurement is possible.
[Brief description of the drawings]
FIG. 1A is a schematic configuration diagram showing an infrared analyzer of one embodiment, and FIG. 1B is a plan view showing a sector used in the embodiment.
FIG. 2 is a block diagram showing a signal processing circuit used in the embodiment.
FIG. 3 is a waveform diagram showing the operation of the embodiment.
4A is a schematic configuration diagram showing an infrared analyzer according to another embodiment, and FIG. 4B is a plan view showing a sector used in the embodiment.
FIG. 5 is a waveform chart showing the operation of the same example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1a Sample cell 1b Comparison cell 2,12 Sector 4 as an intermittent mechanism Light source 5 Infrared detector 6 Signal processing circuit 8 as a data processor 8 Shielding plate

Claims (7)

A comparison cell in which a reference gas is sealed, a sample cell in which a sample gas flows, a measurement optical system that transmits infrared light to both of these cells, an infrared detector that detects infrared light transmitted through both of the cells, and the comparison cell In an infrared gas analyzer equipped with a data processing device for calculating a specific gas concentration in a sample gas based on both signals using a detection signal based on transmitted infrared rays as a comparison signal and a detection signal based on transmitted infrared rays of the sample cell as a measurement signal,
The measurement optical system causes infrared light to enter the infrared detector from both cells so that at least a comparison signal is obtained as a series of signals composed of a plurality of cycles of AC signals between the measurement signal and the next measurement signal. Is,
Infrared gas characterized in that the data processing device uses a signal of the remaining period except a signal of at least the first period among a series of signals of the comparison signal as a comparison signal for gas concentration calculation. Analyzer. The measurement optical system also obtains a measurement signal from both cells so that a measurement signal can be obtained as a series of signals consisting of alternating signals of a plurality of periods between a comparison signal consisting of a series of signals and a comparison signal consisting of the next series of signals. Infrared rays are incident on the infrared detector,
2. The data processing apparatus according to claim 1, wherein the data signal is also used as a measurement signal for calculating a gas concentration, except for at least the first one cycle signal of the series of measurement signals. Infrared gas analyzer. The measurement optical system is disposed between a light source having a luminous flux of a size that allows infrared rays to be incident on the incident surfaces of both cells at the same time, and between the light source and the incident surfaces of both cells, and is continuous with each cell. The infrared gas analyzer according to claim 2, further comprising an intermittent mechanism for switching the incidence of infrared rays to both cells so that the infrared rays are incident multiple times. The measurement optical system is disposed between a light source having a light beam having a size capable of allowing infrared rays to simultaneously enter the incident surfaces of the two cells, and between the emission surfaces of the two cells and the infrared detector. The infrared gas analyzer according to claim 2, further comprising an intermittent mechanism that switches infrared incidence to the infrared detector so that infrared rays are incident on the infrared detector a plurality of times successively. The measuring optical system is disposed between a light source having a light beam having a size capable of allowing infrared rays to be incident simultaneously on the incident surfaces of the two cells and the light source and the incident surfaces of the two cells, and is intermittently connected to both the cells simultaneously. And an intermittence mechanism for injecting infrared rays, and blocking the incident portion or the emitting portion of one cell and releasing the incident portion and the emitting portion of the other cell. The infrared gas analyzer according to claim 2, further comprising a shielding plate that is moved between the two cells so that a plurality of periods of AC signals are used as a unit. The measurement optical system is disposed between a light source having a light beam having a size capable of allowing infrared rays to be incident on the incident surfaces of the two cells at the same time, and between the emission surfaces of the two cells and the infrared detector. The intermittent mechanism that interrupts the transmitted infrared light incident on the infrared detector at the same time, the incident part or the outgoing part of one cell is shielded, the incident part and the outgoing part of the other cell are released, and the transmitted infrared of each cell The infrared gas analyzer according to claim 2, further comprising: a shielding plate that is moved between the cells so that each detection signal of the infrared detector is a unit of an AC signal having a plurality of periods. The said intermittent mechanism interrupts infrared incident time so that the infrared incident time and non-incident time from each said cell to the said infrared detector may become substantially the same, The any one of Claim 3 to 6 Infrared gas analyzer.

Images