JP2001027601A - Infrared gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized infrared gas analyzer high in the stability of accuracy. SOLUTION: In an infrared gas analyzer, a multilayered membrane filter 16 is cylindrically changed in angles with respect to an optical axis by a moving mechanism 17 in such a state that infrared rays are allowed to be incident on a sample cell 5 from a light source to permit infrared rays absorbed by the gas to be measured in sample gas and infrared rays not absorbed by the sample gas to transmit and these infrared rays are detected by a detector 7. The detection value of infrared rays not absorbed by the gas to be measured is divided by the detection value of infrared rays not absorbed by the sample gas to be corrected to remove the error contained in measured concn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared gas analyzer used for measuring the concentration of a gas component, and more particularly to an infrared gas analyzer for continuously measuring the concentration of a specific component in a sample gas by utilizing the infrared absorption effect of gas molecules. For analyzers.

[0002]

2. Description of the Related Art FIG.₂Single light source for measuring gas concentration
1 shows a conventional infrared gas analyzer of the type. 1 is Nichrome wire
A light source heated by applying an electric current to any resistor.
The infrared light emitted from the
Intermittently and periodically optically modulated by the
You. 4.25 μm wavelength infrared light contained in this modulated light
The line indicates the CO in the sample cell 5. ₂Rambell in the process of transmitting
Some are absorbed according to Tovea's law,
A detector such as a semiconductor infrared sensor that passes through the membrane filter 6
7 and is converted into an electric signal. The electrical signal
Is converted into an instruction record input signal by the
Etc. at the receiver 9₂The gas concentration is indicated.

FIG. 6 shows a waveform of an electric signal obtained by converting a 4.25 μm infrared ray intermittently synchronized with the rotating sector 2 (FIG. 5) by the detector 7. A in FIG.
0, Ax, and A100 indicate that the CO ₂ gas concentration in the sample gas is 0.
%, X%, and the peak value at 100%, and the output signal at x% is calculated and output by the signal converter 8. Calibration of such an infrared gas analyzer is performed by alternately flowing the span adjustment gas and the zero adjustment gas through the sample cell 5 and adjusting the span and the zero adjuster provided in the signal converter 8.

[0004]

The conventional infrared gas analyzer is constructed as described above.
The output zero and span fluctuate due to changes in the light intensity of the light source and detector sensitivity, or contamination of the sample cell. In particular, in the conventional method, there is a problem in that a period during which light is blocked by the rotating sector occurs, so that the fluctuation of the zero point is large. In other words, there is no element for correcting errors in this method, and in order to maintain the accuracy of the infrared gas analyzer for a long time, the actual calibration using the zero adjustment gas and span adjustment gas before and during the measurement should be performed as much as possible. This has to be done, which has been a factor in delaying the measurement start time and reducing the effective measurement time.

Further, the chopper mechanism comprising the rotating sector 2 and the motor 3 is larger than other components, making it difficult to reduce the size of the infrared gas analyzer and causing inconvenience in portable movement to the measurement location. A double-flux infrared gas analyzer that uses a sample cell and a comparison cell to improve the stability of the zero point, etc., is also used. It is difficult. The present invention has been made in view of such circumstances, and it is possible to maintain a stable accuracy with respect to a change in the characteristics of a used component in environmental conditions and a long-time use, and to reduce the size of an infrared gas analyzer. The purpose is to provide a total.

[0006]

In order to achieve the above object, an infrared gas analyzer according to the present invention comprises a light source for emitting infrared light, a sample cell for circulating a sample gas and irradiating the infrared light, and selecting a wavelength. In the infrared gas analyzer provided with an infrared detector for detecting infrared light, a moving means for periodically moving the incident surface of the multilayer filter at a constant angle with respect to the optical axis, The method is characterized in that the sample gas component absorption light and the non-absorption light transmitted through the multilayer filter are detected, and the component concentration in the sample gas is measured.

The infrared gas analyzer of the present invention is constructed as described above. By moving the angle of the multilayer filter with respect to the optical axis, sample gas concentration detection light and sample gas concentration non-detection light are obtained, By performing signal processing utilizing the influence on both light beams, a small infrared gas analyzer with a stable zero point can be obtained.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the infrared gas analyzer of the present invention will be described below with reference to the drawings. FIG. 1 is a structural view of an embodiment of the infrared gas analyzer of the present invention. Note that FIG.
The same reference numerals are used for constituent elements having the same functions as in FIG. This infrared gas analyzer comprises a light source 1 in the infrared wavelength band, a sample cell 5 through which a sample gas flows, a multilayer filter 16 and a movable filter that fixes the multilayer filter 16 and periodically moves through a certain angle. A mechanism 17, a detector 7 for converting infrared light intensity into an electric signal such as a semiconductor infrared sensor, a signal converter 8 for converting the electric signal into a signal for a receiver, and reception of an indicator, a recorder, and the like. It comprises a vessel 9.

As shown in FIG. 2, the moving mechanism 17 includes a lever (A) 17b connected by a joint 17a.
Is connected to a solenoid 17d via a joint 17c, and the other end of the lever (B) 17e is connected to a fixture 17g via a fulcrum 17f. In addition, the fulcrum 17h, the solenoid 17d, and the fixture 17g are all appropriately fixed to necessary places.

When the excitation power supply of the solenoid 17d is turned on and off at a constant cycle by the control unit 18 (FIG. 1), the moving axis of the solenoid 17d reciprocates in the horizontal direction, and the multilayer film mounted and fixed to the lever (B) 17e. Filter 16
Reciprocates within the angle θ range. This angle θ is approximately 0
It is determined by light having a wavelength necessary for transmission within a range of ~ 45 °. FIG. 3 shows transmittance characteristics of the multilayer filter 16 at angles θ1 and θ2 with respect to the optical axis. For example, when analyzing the CO ₂ concentration, positioning is performed so that the peak transmittance at the angle θ1 is 4.25 μm and the angle θ2 is 3.7 μm.

In the above configuration, when infrared rays are incident on the sample cell from the light source 1 and irradiate the CO ₂ molecules in the flowing sample gas, the 4.25 μm wavelength light is absorbed in proportion to the CO ₂ concentration. 16 is incident. When the multilayer filter 16 is at the angle θ1, light having a wavelength of 4.25 μm passes through the multilayer filter 16, and the light intensity is converted by the detector 7 into an electric signal. When the multilayer filter 16 is at the angle θ2, only light having a wavelength of 3.7 μm passes through the multilayer filter 16.

FIG. 4 is a waveform diagram of the output signal of the detector 7 in this embodiment. In the figure, A0, Ax, A100
Means that the CO ₂ concentration of the 4.25 μm wavelength light is 0%, x%,
The peak output value of the detector 7 at 100%, B is 3.7
It is a peak output value of light having a wavelength of μm. If Ax changes to Ax + ax due to a change in the light intensity of the light source 1, B also changes to B + b. Since these errors occur in infrared rays from the same light source, both error rates (ax / Ax and b / B) are almost equal in magnitude, and the positive and negative signs match. The signal converter 8 divides the measured value of Ax (Ax + ax) by the measured value of B (B + b), using B as a value at the time of calibration as shown in the following equation. (Ax + ax) / (b + B) = Ax / B That is, for the fluctuation factor of ax / Ax = b / B, the left side of the above equation becomes equal to the right side, and the error ax is removed. Further, this Ax / B is converted into a signal for a receiver by the signal converter 8 and output.

The above-mentioned arithmetic processing method uses a digital signal. For example, synchronous rectification is performed for each cycle of the angles θ1 and θ2, and the analog signal is divided by an analog divider to convert the analog signal. Can also be used. The moving mechanism 17 includes a lever (A) 17b
May be directly connected to a small pulse motor, and the rotation direction may be changed for each fixed number of pulses to change the angle θ. Further, the wavelength may be selected by making the film thickness in the multilayer filter 16 into a wedge shape and moving linearly with respect to the optical axis.

[0014]

The infrared gas analyzer of the present invention is constructed as described above, and periodically detects infrared light absorbed by the measurement component gas and infrared light not absorbed by the sample gas in the sample gas. By correcting the detection value of the infrared ray absorbed by the infrared ray with the detection value of the infrared ray not absorbed, the measured density can be corrected and the error can be reduced. As a result, stable measurement can be performed for a long period of time, and the apparatus can be downsized by eliminating the rotating sector.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of an infrared gas analyzer of the present invention.

FIG. 2 is a side view of a moving mechanism of the multilayer filter in the embodiment of the present invention.

FIG. 3 is a transmittance characteristic diagram of the multilayer filter according to the embodiment of the present invention.

FIG. 4 is an output waveform diagram of a detector according to the embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional infrared gas analyzer.

FIG. 6 is an output waveform diagram of a detector in a conventional infrared gas analyzer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Rotating sector 3 ... Motor 5 ... Sample cell 6, 16 ... Multilayer film filter 7 ... Detector 8 ... Signal converter 9 ... Receiver 17 moving mechanism 17a, 17c joint 17b lever (A) 17d solenoid 17e lever (B) 17f, 17h fulcrum 17g fixture 18 ...・ Control unit

Claims (1)

[Claims] 1. An infrared gas analyzer comprising a light source for emitting infrared light, a sample cell for flowing a sample gas and irradiating the infrared light, a multilayer filter for selecting a wavelength, and an infrared detector for detecting infrared light. A moving means for periodically moving the incident surface of the multilayer filter at a fixed angle with respect to the optical axis, detecting sample gas component absorbed light and non-absorbed light transmitted through the multilayer filter, and An infrared gas analyzer characterized by measuring the concentration of a component.