JPH0552456B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Purpose (Field of Industrial Application) The present invention is an analyzer used for monitoring and controlling gas concentrations in various industrial processes, measuring exhaust gas concentrations for pollution monitoring, etc. , relates to a non-dispersive infrared gas analyzer (NDIR) that uses the infrared absorption effect of gas molecules to measure the concentration of a specific component in a sample gas based on the strength of the infrared absorption of gas molecules.

(Prior art) In a conventional non-dispersive infrared gas analyzer,
There is no way to monitor dirt on the inside of the cell.
Efforts were made to make the light beam from the light source parallel so that it would be as unaffected by dirt on the inside as possible. In addition, in actual use, if the zero point and span point changes become large, one of the causes is dirt on the internal surface, so it is normal to disassemble the optical system and visually check the degree of dirt. It was hot.

(Problems to be Solved by the Invention) In conventional infrared gas analyzers, it is difficult to determine the degree of contamination on the inner surface of a cell unless the problem of changes in zero point and span sensitivity occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide an infrared gas analyzer that can automatically detect contamination during zero point calibration and can accurately and quantitatively determine the state of contamination before a problem occurs.

(B) Structure of the Invention (Means for Solving Problems) In the infrared gas analyzer of the present invention, the optical system is configured to independently detect the transmitted light of the comparison cell and the transmitted light of the measurement cell. In the detection signal processing system, there is a means for calculating the ratio between the comparison cell side measurement value and the measurement cell side measurement value at the time of zero point calibration, and a means for calculating the ratio value at the time of the first zero point calibration as a reference value. It is equipped with a means for storing, and a means for comparing the value of the ratio during the second and subsequent zero point calibration with a reference value, and calculating the ratio of both values as a value indicating the degree of contamination of the measurement cell.

(Function) When measurement is continued by flowing the measurement gas through the measurement cell, the inner surface of the measurement cell gradually becomes dirty and the amount of transmitted light decreases. Therefore, the ratio of the first measurements
Comparing the ratio Ri/Mi of the measured value after the inner surface of the measurement cell is dirty with respect to Ro/Mo, we find that (Ri/MI)/
By knowing the value of (Ro/Mo), it is possible to know how dirty the inner surface of the sample cell is.

(Example) FIG. 2 shows an optical system according to an embodiment of the present invention.

1 is a measurement cell, 2 is a comparison cell, and the measurement cell 1 has a gas inlet 3 at one end and a gas outlet 4 at the other end.

Reference numeral 5 denotes a light source, and infrared light from the light source 5 is alternately introduced into the measurement cell 1 and the comparison cell 2 by a sector 7 which is rotated at a constant speed by a motor 6. 8 is a detector for detecting the transmitted light of measurement cell 1 and comparison cell 2; 9;
is an amplifier that amplifies the output signal of the detector 8.

Measurement cell 1 is configured to alternately flow a measurement gas, a span gas containing a certain concentration of measurement components, and an inert zero gas that does not absorb infrared rays, such as _N2 , and comparison cell 2. is filled with an inert gas.

As shown in FIG.
A window 11 through which the amount of light is introduced is eccentrically opened at a separate position. Therefore, by rotating this sector 7, the amount of light from the light source 5 is alternately introduced into the measurement cell 1 and the comparison cell 2.

The detector 8 has a light receiving part common to the measurement cell 1 and the comparison cell 2, and is, for example, a one-way pressure detection system using a condenser microphone or a micro flow sensor, or a front-and-front chamber type detection system.
Or a semiconductor detector.

As shown in FIG. 4, the output waveform of the detector 8 alternates between a signal 20 based on the amount of light transmitted through the comparison cell and a signal 21 based on the amount of light transmitted through the measurement cell.

A signal processing system for detecting the degree of contamination of the measuring cell 1 during zero point calibration using the detection signal of the detector 8 is shown in FIG.

Reference numeral 30 denotes an arithmetic means, which receives the signal 2 from the amplifier 9 during zero point calibration when zero gas is introduced into the measurement cell 1.
The amplified signals of 0 and 21 are input, their respective area values are calculated and used as a comparison signal R and a measurement signal M, and their ratio R/M is calculated. Reference numeral 31 is a memory for storing the values Ro/Mo at the time of initial zero point calibration. 32 is a comparison means, which compares the second and subsequent comparison signals Ri and measurement signals Mi.
(Ri/Mi)/(Ro/Mo) (1) is calculated by comparing the ratio Ri/Mi with the initial value Ro/Mo stored in the memory 31, and the value is displayed. Displayed by means 33.

Although not shown, this embodiment is equipped with a signal processing system for measuring the concentration of the measurement gas, which inputs the output signal from the amplifier 9 and outputs the comparison signal R and the measurement signal M. Difference Δ=(R-
The measurement gas concentration is measured by M). In other words, the value Δo when zero gas is introduced into measurement cell 1 is taken as the zero point, the value Δs when the span gas is introduced is taken as the span point, and the value Δ when the measurement gas is introduced is set between the zero point and the span point. By comparing and allocating, the measured gas concentration is determined.

Now, when zero point calibration is carried out at an appropriate frequency, if there is no dirt on the inside of the cell, then the above
The value of equation (1) is 1. However, normally, the inner surface of the sample cell becomes contaminated with the passage of time due to dust contained in the measurement gas, and the measurement signal M also decreases with each zero point calibration. Therefore,
According to this embodiment, the value of equation (1) displayed by the display means 33 increases with time.

Therefore, by looking at the displayed value, it is possible to quantitatively understand how contaminated the measurement cell 1 is.

Furthermore, in the infrared gas analyzer of the present invention,
For example, even if the light intensity fluctuates due to energy changes in the light source 5 or sensitivity decreases due to deterioration of the detector 8,
Since the comparison signal R and the measurement signal M are influenced at the same rate, these influences do not appear on the ratio R/M, and stable measurement results can be obtained.

The ratio of R and M may be R/M or M/R.

In addition to the above embodiments, the present invention can be modified in various ways. For example, by changing the shape of the sector and adding a set of measurement cells and comparison cells,
It can be used not only for measuring a single component as in the embodiment, but also for measuring multiple components.

Furthermore, in the above embodiment, the comparison signal R and the measurement signal M
Although the area value of the detector output waveform is used as the area value, similar arithmetic processing may be performed using the peak value at a specific position instead of the area value. However, in this case, the S/N is worse than the method using the area value of the embodiment.

(C) Effects of the Invention According to the present invention, the degree of contamination on the inner surface of the cell can be quantitatively grasped in advance, so that appropriate measures can be taken before problems such as complaints arise.

Furthermore, by managing the values of the first measured comparison signal and measurement signal, it is possible to improve the quality.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a signal processing system according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing an optical system according to an embodiment, and Fig. 3 is a plane diagram showing sectors used in the embodiment. 4 are waveform diagrams showing the detection output of the detector in the same embodiment. DESCRIPTION OF SYMBOLS 1...Measurement cell, 2...Comparison cell, 8...Detector, 30...Calculating means, 31...Memory, 32...
…A means of comparison.

Claims (1)

[Scope of Claims] 1. An infrared gas analyzer equipped with an optical system that alternately introduces transmitted light of a comparison cell and transmitted light of a measurement cell into a single detector and measures each independently, which has a zero point. means for calculating the ratio between the comparison cell-side measurement value and the measurement cell-side measurement value at the time of calibration; a means for storing the value of the ratio at the time of the first zero point calibration as a reference value; and a means for the second and subsequent zero point calibrations. The infrared gas is characterized in that its detection signal processing system is equipped with means for comparing the ratio value of the time with the reference value and calculating the ratio of both values as a value indicating the degree of contamination of the measurement cell. Analyzer. 2. The infrared gas analyzer according to claim 1, wherein the measured values R and M of each cell are values corresponding to the area of the detected waveform.