JPH05107185A - Gas analyzer - Google Patents

Abstract

PURPOSE:To obtain a gas analyzer capable of analyzing accurately and highly reliably. CONSTITUTION:A part of output signal VM1 in a measurement detector 3 side is compared in a comparator 15 with a standard voltage v1 corresponding to the full scale of the measuring range. If the output signal VM1 is over the standard voltage v1, a standard voltage v2 corresponding to the voltage over the full scale of the measuring range is output by, for example, sending a signal to an alarm generator 19 to generate alarm and also switching a switch 18 to (a) side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas analyzer mainly used for measuring the concentration or amount of a specific component to be measured in a sample gas.

[0002]

2. Description of the Related Art For example, when measuring NO concentration with an infrared gas analyzer, the main absorption band of NO in infrared rays is about 5.3 μm.
m, and its wavelength overlaps with the absorption band of H ₂ O, so
H ₂ O acts as an interference component.

Therefore, as an infrared gas analyzer in which the influence of the interference component gas is reduced, for example, the one shown in FIG. 2 is known.

In this infrared gas analyzer, a light source 32 is arranged on one side of a measuring cell 31 to which a measuring gas S is supplied, and
On the other side, a pneumatic detector for NO measurement (condenser microphone type detector, etc.) 33 and a pneumatic detector for compensating interference components in which a gas having substantially the same absorption band as H ₂ O is enclosed ( Similarly, a condenser microphone type detector and the like) 34 are arranged so that the measuring detector 33 is closer to the measuring cell 31. C ′ is a chopper for modulation which is provided between the measurement cell 31 and the light source 32 and is rotated by a drive mechanism (not shown), 36 is a comparison cell, and 37 is a light source on the comparison cell 36 side.

Thus, in the NO analyzer configured as described above, when the measuring cell 31 is irradiated with infrared light while the sample gas S is supplied to the measuring cell 31,
The infrared light passing through the measurement cell 31 receives a predetermined absorption in the measurement cell 31, then passes through the measurement detector 33, and is also incident on the interference component compensation detector 34. The output of 33 and the output of the compensating detector 34 are input to the subtractor 35, and the difference between the outputs is taken to remove the influence of the interference component and
I try to measure the concentration.

[0006]

However, in the infrared gas analyzer having the above structure, when a gas that greatly exceeds the full scale of the measurement range is incident on the measurement detector 33, the measurement detector 33 is used. The signal output from loses its linearity with respect to the concentration of the incident gas,
A saturation phenomenon occurs. That is, the concentration output value from the measurement detector 33 is lower than the actual output value, so the subtractor
When taking the output difference from the measurement detector 33 and the compensation detector 34 at 35, a very large error may occur.

Moreover, even if the upper limit value (full scale of the measurement range) is exceeded, some output is output from the subtractor 35, and therefore it is possible to judge what is the accurate analysis value from the output result alone. It was difficult and the reliability of the analysis results was low.

The present invention has been made in view of the above matters, and an object of the present invention is to provide a gas analyzer capable of performing accurate and highly reliable analysis. ..

[0009]

To achieve the above object, the present invention compares the output of a measuring detector with a reference voltage, and when the output of the measuring detector is greater than the reference voltage,
The feature is that a means for outputting a constant scale-over signal is provided.

[0010]

According to the above characteristic structure, when the concentration of the measuring gas is too high, that is, when the output of the measuring detector is larger than the reference voltage, a constant scale-over signal is output. It will be clear how accurately it can be measured. That is, a highly reliable analysis result can be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of an NO analyzer according to an embodiment of the present invention, which is a so-called double cell type. That is, in the figure, 1 is a measuring cell having a gas inlet 1a and a gas outlet 1b, and 20 is a comparison cell. Reference numerals 2a and 2b denote light sources provided to face one ends of the cells 1 and 20 and emit infrared light, for example.

Numerals 3 and 4 are measuring pneumatic detectors (hereinafter referred to as measuring detectors), which are arranged optically in series with each other on the other end side of the cells 1 and 20, and pneumatic components for interference component compensation. In the detector (hereinafter, referred to as compensation detector), the measurement detector 3 is arranged closer to the cells 1 and 20. C is the cell 1, 20 and the light source 2a, 2b
Is a chopper for modulation which is provided between and and is rotated by a drive mechanism (not shown).

Both detectors 3 and 4 are, for example, condenser microphone detectors. That is, NO (or a gas having an absorption band equivalent to NO), which is the component to be measured, is enclosed inside the measurement detector 3, and the interference component of NO is contained inside the interference component compensation detector 4. Is H ₂
A gas having substantially the same absorption band as O is enclosed.

Reference numerals 5 and 6 denote gain adjusters provided on the output side of both detectors 3 and 4, which amplify the outputs from both detectors 3 and 4 by a predetermined gain, and the output signals thereof are preamplifiers 7 and 8, respectively. After passing through the bandpass filters 9 and 10 and the rectifiers 11 and 12, they are input to the subtractor 13. Reference numeral 14 denotes an interference component correction volume for equalizing the sensitivity of the compensation detector 4 with respect to the interference component and the sensitivity of the measurement detector 3 with respect to the interference component.

A feature of the present invention is that a part of the output signal on the measuring detector 3 side is compared with a reference voltage in the comparator 15. That is, a part of the output signal rectified by the rectifier 11 is taken out and the comparator 15
In, the comparison is made with the reference voltage v ₁ corresponding to the full scale of the measurement range. In addition, 16 and 17 are smoothing devices such as low-pass filters, and 18 is a changeover switch for changing over the reference voltage v ₂ corresponding to the scale-over signal and the output signal from the subtractor 13.

When measuring gas in the NO analyzer constructed as described above, the sample gas S is introduced into the measuring cell 1, and infrared rays are emitted from the light source 2a,
When the modulation is performed by the chopper C, the infrared light passing through the measurement cell 1 receives a predetermined absorption in the measurement cell 1, then passes through the measurement detector 3, and is also transmitted to the interference component compensation detector 4. It is incident. The signals V _{M and} V _C output from these detectors 3 and 4 are gain adjusters 5 and 6, preamplifiers 7 and 8, bandpass filters 9 and 10, rectifiers 11 and 12, respectively.
After that, the output signals V _M1 and V _C1 are input to the subtractor 13.

On the other hand, a part of the signal V _M1 output from the rectifier 11 is compared with the reference voltage v ₁ in the comparator 15 via the smoother 16.

When the output signal V _M1 exceeds the reference voltage v ₁ , for example, a signal is sent to an alarm generator 19 which generates an alarm, and the changeover switch 18 is connected to the terminal a.
By switching to the side, the reference voltage v ₂ corresponding to the voltage above the full scale of the measurement range is output to a display device (not shown) or the like.

When the output signal V _M1 is equal to or lower than the reference voltage v ₁ , the changeover switch 18 is switched to the terminal b side so that the subtractor 13 outputs the output V _M1 from the measuring detector 3 and the compensating detector. The output signal obtained by subtracting the output V _C1 from 4 is output as a measured concentration signal V ₀ via a smoother 17 to a display (not shown) or the like, and the concentration or amount of the measurement target component is analyzed.

The present invention is not limited to the NO analyzer described above, but can be implemented in other gas analyzers (for example, CO analyzer). Also, the number of light sources, cells, detectors, etc. is not limited. Further, it can be widely applied to a gas analyzer having an interference correction mechanism.

[0022]

As described above, according to the present invention,
When the concentration of the measurement gas is too high, that is, when the output of the measurement detector is larger than the reference voltage, a constant scale-over signal is output, so it is clear how accurate the measurement is. Become. That is, a highly reliable analysis result can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a gas analyzer according to the present invention, showing a single-beam NO analyzer.

FIG. 2 is a diagram showing a gas analyzer having a conventional configuration.

[Explanation of symbols]

1 ... Measuring cell, 2a, 2b ... Light source, 3 ... Measuring detector,
4 ... Detector for interference component compensation, v ₁ ... Reference voltage, v ₂ ... Scale-over signal.

Claims (1)

[Claims] 1. A fluid introducing cell, a measuring detector, and an interference component compensating detector are arranged in this order and optically in series with respect to an irradiation light source, and the measuring detector and the interference component compensating device are arranged. In the gas analyzer, which is configured to extract the concentration signal by subtracting the output difference of the detector, the output of the measuring detector is compared with a reference voltage, and when the output of the measuring detector is larger than the reference voltage, A gas analyzer characterized by comprising means for outputting a constant scale-over signal.