JPH06103261B2 - Absorption spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention adopts a unique non-conventional method called a multi-fluid modulation method (this is the name named by the present inventors). The present invention relates to an absorption spectrometer capable of accurately measuring the concentration of a specific measurement target component in a sample gas from a low concentration to a high concentration while using only one detector.

The applicant of the present application has filed a patent application for the fluid analysis method using the multi-fluid modulation method on December 11, 1987.

[Conventional technology]

For example, an absorption spectrometer such as an infrared gas analyzer is one in which infrared rays are incident on a cell from a light source, the degree of absorption by the sample gas in the cell is measured, and the concentration of a specific measurement target component in the sample gas is measured. is there. This type of analyzer is based on Lambert-Beer's law as a basic principle. The incident light is I ₀ , the cell length is l, the absorption coefficient determined by the measurement wavelength and the measurement target component is k, and the measurement target component is k. ^Letting the density of C be C, the transmitted light I is expressed by the following formula: I = I ₀ e ^−kcl .

Therefore, as for the relationship between the concentration of the measurement target component and the output in the absorption spectrometer, as the concentration of the measurement target component increases, the curve of the curve representing the output increases. Therefore, in order to improve the measurement accuracy by using the portion close to the straight line in FIG. 3, conventionally, when the concentration of the measurement target component is high (large), the cell length is short, and When the concentration is low (small), a cell having a long cell length is used to selectively use the cell.

[Problems to be solved by the invention]

However, in order to properly use the cells as described above, it is necessary to prepare many kinds of cells having different cell lengths, and in the case of measuring a sample gas having a large concentration change of exhaust gas, etc. Has the drawback that it cannot be measured continuously.

The present invention has been made with the above matters in mind, and its object is to eliminate the need to prepare any number of cells having different cell lengths, and to measure sample gas with large concentration changes. It is another object of the present invention to provide an absorption spectrometer with a wide measurement concentration range capable of continuously measuring from low concentration to high concentration.

[Means for solving problems]

In order to achieve the above-mentioned object, the absorption spectrometer according to the present invention is provided with two cells having different cell lengths in series between a light source and a detector and comparing these two cells with a sample gas. One fluid modulation means is provided for each of the cells to switch the gas simultaneously and continuously in a constant cycle, and the modulation frequencies of the sample gas and the comparison gas by these two fluid modulation means are different from each other. The output signal from the detector is separated into signal components of each modulation frequency for each cell and rectified and smoothed respectively to measure the concentration of the component to be measured in the sample gas from low concentration to high concentration. I can do it.

[Action]

According to the above configuration, an output signal in a state in which two signal components corresponding to the respective cells are superposed is output from one detector provided in common to the two cells. Since both of these signal components are modulated at different frequencies, the output signal from the detector is separated into signal components of each modulation frequency for each cell and rectified and smoothed, respectively, in the sample gas. The concentration of the component to be measured can be measured from a low concentration to a high concentration, and the above object is completely achieved.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows an example of an infrared gas analyzer as an absorption spectrometer according to the present invention. In FIG. 1, 1 and 2 are cells that are arranged in series and have different cell lengths (hereinafter, long cells).
1, short cell 2), which is provided between the light source 3 for infrared radiation and the detector 4.

The detector 4 is, for example, a condenser microphone type detector, and the same gas as the component to be measured or a gas having an absorption band at a wavelength substantially the same as the characteristic absorption wavelength of the component to be measured is enclosed in the detector 4.

Reference numerals 5 and 6 denote fluid modulators for switching the sample gas S and the reference gas R to the long cell 1 and the short cell 2, respectively, simultaneously and continuously at a constant cycle, and are composed of, for example, rotary valves. The modulation frequencies of the sample gas S and the comparison gas R by the fluid modulation means 5 and 6 are different from each other. For example, the modulation frequency of the fluid modulation means 5 is 1 hertz and that of the fluid modulation means 6 is 2 Hz. Hertz.
Therefore, when the sample gas S and the comparison gas R are supplied to the long cell 1 and the short cell 2 by the fluid modulation means 5 and 6 having the above-mentioned modulation frequency, the detector 4 detects that the sample gas S and the comparison gas R are in the vicinity of the modulation frequency for the long cell 1. An output signal A in which the band signal and the band signal near the modulation frequency for the short cell 2 are superimposed is output.

Reference numeral 10 is a signal processing means connected to the output side of the detector 4 via the preamplifier 7, and its specific configuration is, as shown in FIG. 2, an output from the detector 4 input via the preamplifier 7. The signal A is divided into two signal processing sequences and processed.

That is, one signal processing sequence is provided with a bandpass filter 11 for separating and extracting (passing) only a signal (for example, a _L ) in a band near the modulation frequency (1 hertz) for the long cell 1, and In the subsequent stage, by the synchronization signal from the synchronization signal generator 5a attached to the fluid modulation means 5 for the long cell 1 (the actual fluid modulation operation by the fluid modulation means 5 is a signal: 1 hertz), only the hand-pass filter 11 is used. A hand-pass filter 11 is provided to supplement the separation action that may be insufficient to perform more accurate detection and at the same time to convert (rectify) the separated AC into DC.
The synchronous detection rectifier circuit 13 for synchronously rectifying the output signal a _L from the synchronous detection rectification circuit 13 is provided, and further, the synchronous detection rectification circuit 13 is provided in the subsequent stage.
A low-pass filter as an example of the smoothing circuit 15 is provided for smoothing the output signal a _L from the device and removing high frequency noise, and the other signal processing sequence includes the fluid modulator 6 for the short cell 2. Modulation frequency (2 hertz)
A hand-pass filter 12 for separating and extracting only a signal (for example, a _H ) in a nearby band is provided, and a sync signal from a sync signal device 6a attached to the fluid modulation means 6 for the short cell 2 is provided at the subsequent stage. By (actual fluid modulation operation by the fluid modulation means 6 is signal: 2 Hertz), the separation action which may be insufficient with the hand-pass filter 12 alone can be supplemented to perform more accurate separation and at the same time A synchronous detection rectifier circuit 14 for synchronously rectifying the output signal a _H from the hand-pass filter 12 so as to convert the generated alternating current into direct current is provided, and further, in the subsequent stage, the output signal from the synchronous detection rectification circuit 14 are those low-pass filter as an example of a smoothing circuit 15 for removing high-frequency noise is provided with smoothing an a _H, from the signal processing unit 10 has a length cell 1, the short cell 2 A _L and a _H is output at mutually independent state as the corresponding signal component Re respectively.

The signal processing means 10 is not limited to hardware means such as the above electric circuit, but Fourier analysis (corresponding to frequency separation processing) and absolute value averaging processing (corresponding to rectification / smoothing processing), etc. It is also possible to employ software-like means such as a computer system capable of performing the arithmetic processing of the numerical analysis.

Thus, in the absorption spectrometer having the above structure, the fluid modulation means
5, 6 and 6 sample gas S and comparative gas R
When 1 and 2 Hertz modulation frequencies of 1 and 2 Hertz are simultaneously and continuously supplied to the short cell 2 and the short cell 2, respectively, one detector 4 commonly provided for the long cell 1 and the short cell 2 is
Signal component (a signal component a _L corresponding to a low concentration region (for example, ppm to 1%)) and a signal component corresponding to the short cell 2 (a signal component corresponding to a high concentration region (for example, 1% or more))
a _H ) is output, and since both signal components a _L and a _H are modulated at different frequencies, the output signal A from the detector 4 is converted into a long cell 1 and a short cell To obtain the signals a _L and a _H respectively corresponding to the low concentration region and high concentration region of the measurement target component by separating the signal components a _L and a _H of each modulation frequency for 2 and rectifying and smoothing them respectively. Therefore, it is possible to obtain the concentrations of the measurement target component in the low concentration region and the high concentration region.

The present invention is not limited to the above embodiment, but can be applied to other absorption spectrometers such as an ultraviolet gas analyzer. The fluid modulation means 5 and 6 may be configured by a 4-way switching solenoid valve, a 3-way switching solenoid valve, or the like. Also, the detector 4
May be a solid-state detector. Furthermore, the absorption spectrometer according to the present invention may be combined with automatic range switching means.

〔The invention's effect〕

As described above, in the absorption spectrometer according to the present invention, two cells having different cell lengths are provided in series between the light source and the detector, and the sample gas and the reference gas are supplied to these two cells. , One fluid modulation means is provided for each of the cells to be switched simultaneously and continuously at a constant cycle, and the modulation frequencies of the sample gas and the comparison gas by these two fluid modulation means are different from each other, By separating the output signal from the detector into signal components of each modulation frequency for each cell and rectifying and smoothing them, the concentration of the measurement target component in the sample gas can be measured from low concentration to high concentration. Therefore, it is not necessary to prepare many kinds of cells having different cell lengths. Also, when measuring a sample gas with a large concentration change,
It has an excellent effect that it can continuously measure from low concentration to high concentration.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of an absorption spectrometer according to the present invention,
FIG. 2 is a block diagram showing an example of the signal processing means. FIG. 3 is a characteristic diagram showing the relationship between the concentration and the output in the absorption spectrometer. 1, 2 ... Cell, 3 ... Light source, 4 ... Detector, 5,6 ... Fluid modulation means, A ... Output signal, a _L , a _H ... Signal component, S ... Sample gas, R ... Comparison gas

Claims (1)

[Claims] 1. Two cells having different cell lengths are provided in series between a light source and a detector, and a sample gas and a reference gas are simultaneously and continuously supplied to these two cells at regular intervals. One fluid modulation means for switching and supplying is provided for each cell so that the modulation frequencies of the sample gas and the comparison gas by these two fluid modulation means are different from each other, and the output signal from the detector is An absorption spectrometer characterized in that it is possible to measure the concentration of the measurement target component in the sample gas from low concentration to high concentration by separating the signal components of each modulation frequency for each cell and rectifying and smoothing them respectively. .