JPH03215731A - Gas analyzer - Google Patents

Abstract

PURPOSE:To accurately measure the concn. by separating an AC signal in which a first signal representing a differential gas concn. and a second signal representing a base gas concn. are superimposed into the first and second signals by a single detector and correcting the first signal with the second signal. CONSTITUTION:A sample gas G is passed through a sample gas passage 10, a first gas G1 is introduced into a cell 1 and a second gas G2 into a cell 2, a light chopper 8 is rotated at 5Hz (modulated output frequency), an IR is emitted from light sources 3 and 4, the light from the source 4 is turned on and off at 2Hz (light source modulated frequency), and a signal S, in which signals (y) and (x) corresponding to the base gas concn. Y and differential gas concn. are superimposed, is outputted from a detector 14. The signal S is amplified by a preamplifier 15, and then inputted to a signal processing part 16. The first signal (x) as the AC component is taken out in a processing series 21 and the second signal (y) as the AC component in a processing series 22 independently of each other. Since the signal (x) is affected by the signal (y), the signals are inputted to a correction circuit 23, the and signal (x) is corrected by the signal (y) by using the inverse function of a calibration curve K.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a gas analyzer, and particularly to an improvement of a differential measurement type gas analyzer.

[Prior Art] For example, the concentration of CO contained in a certain sample gas can be easily measured using an infrared gas analyzer as follows. That is, a sample gas is introduced into a reaction tank containing, for example, an oxidation catalyst to oxidize CO.
A sample gas containing CO produced by this conversion is supplied to an infrared gas analyzer. m degrees and obtain the CO concentration from this concentration.

However, CO. (This COt is referred to as haze gas), the sample gas that has passed through the reaction tank contains the haese gas and CO (this CO z) newly generated in the reaction tank. (referred to as differential gas) will coexist, so the above means cannot be adopted.

Therefore, conventionally, as shown in FIG. 5, two infrared gas analyzers 51. 52 is prepared, and a gas flow path 53 through which a sample gas containing C O z as a hese gas and CO as a measurement gas flows is divided into two branch gas flow paths 54 .
55, one branch gas flow path 54 is provided with a reaction tank 56 having the same configuration as described above, and the end of the branch gas flow path 54 on the downstream side of this reaction tank 56 is connected to the infrared gas analyzer 51. , the other branch gas flow path 55 is not provided with anything, and its downstream end is connected to an infrared gas analyzer 51 . 52, one infrared gas analyzer 51 measures the concentration of the differential gas, the other infrared gas analyzer 52 measures the base gas concentration, and the infrared gas analyzer 5
The output signal of 1 is divided by the output signal of the infrared gas analyzer 52 for correction.

In FIG. 5, in addition to an infrared gas analyzer 51 that measures the concentration of differential gas, an infrared gas analyzer 52 that measures the concentration of Haas gas is provided, and the output is corrected as described above. The reason for this is as follows.

In other words, as shown in Figure 6, the relationship between the concentration of heath gas and its output (the curve is called the calibration curve K) is that when the concentration of heath gas is relatively low (small), the two are in a proportional relationship; As the gas concentration increases, the proportional relationship breaks down and the output becomes saturated. Therefore, the width C of the output with respect to the width a in a region where the concentration of heath gas is relatively low and the width d of the output with respect to the width a in the region where the concentration of heath gas is high differ by cod. In other words, according to the configuration shown in FIG. 5 above, although the output signal from the infrared gas analyzer 51 indicates the concentration of the difference gas, it is greatly influenced by the Haas gas concentration. , it is necessary to correct it by dividing by the output signal of the infrared gas analyzer 52 that measures the base gas concentration.

In addition, in FIG. 5, 57. 58 is branch gas flow path 5
4. 55, respectively.

[Problem to be solved by the invention]

However, according to the prior art shown in FIG. 5 above,
In addition to the infrared gas analyzer 51 that measures the differential gas concentration,
Since an infrared gas analyzer 52 for measuring the base gas concentration is also required, the configuration becomes more complicated and costs increase. And two infrared gas analyzers 51. 5
2 has the following important problems. That is, two infrared gas analyzers 51. 52, there are some differences in measurement characteristics such as stability and responsiveness, but there is a great possibility that measurement errors may occur due to these differences.

The present invention has been made with the above-mentioned considerations in mind, and its purpose is to be able to measure the differential gas concentration with only one gas analyzer, and to perform predetermined concentration measurements at low cost and with high accuracy. The goal is to make it possible to do the following.

[Means to solve the problem]

In order to achieve the above object, the gas analyzer according to the present invention uses light emitted from a light source to connect a first sample gas containing a heath gas, and a reaction section containing the heath gas in the same way as the first sample gas. With respect to the second sample gas whose concentration changes by
A detector is provided to correspond to the light that has passed through the first sample gas and the second sample gas, respectively, and the output signal of the detector is used to detect the first sample gas.
The configuration is configured to extract an AC component corresponding to the energy difference between the light energy that has passed through the sample gas and the light energy that has passed through the second sample gas, and further adjusts the intensity of the light emitted from the light source to the AC modulation frequency. is changed at a different frequency (light source modulation frequency), and the output signal of the detector is separated into a first signal of an alternating current component of the alternating current modulation frequency and a second signal of an alternating current component of the light source modulation frequency. , is characterized in that the first signal is corrected by the second signal.

[Effect]

In particular, in the gas analyzer of the present invention having the above characteristic configuration, the output signal of the detector is separated into a first signal of the AC component of the AC modulation frequency and a second signal of the AC component of the light source modulation frequency. Since the first signal is corrected by the second signal, it is possible to accurately measure the concentration.

C Example] Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 schematically shows the configuration of a gas analyzer according to a first embodiment of the present invention. In this example, 1 and 2 are cells of the same shape and size that are provided in parallel with each other. The section is provided with cell windows 1a and 2a that can sufficiently let in light from a light source 3.4, which will be described later.
Gas inlets 1b, 2b and gas outlets 1c, 2c are formed at appropriate positions.

A light source 3.4 is provided at one end of the cell 1.2 to illuminate each cell 1.2, and is designed to emit, for example, infrared light. 5.6 is the power source for each of the lights a3 and 4. A switching element 7 is interposed between the light source 4 and the voltage source a6, so that the light source 4 can be controlled at a predetermined frequency.
For example, 2} [O in Z? It is set to turn off. 8 is interposed between the cell 1.2 and the light s3.4, and the light source 3
．． An optical chopper is used to output an alternating current component from a detector 14, which will be described later, by intermittent infrared light from 4 at regular intervals, and 9 is a driving motor. The intermittent frequency of this optical chopper is, for example, 5 Hz.

1O is a sample gas flow path, which is branched into two branch gas flow paths 101 and 102 in the middle, and one of the branch gas flow paths (hereinafter referred to as the first sample gas supply path) 101 has a reaction tank 11. and a pump 12, the downstream side of which is connected to the gas inlet 1b of the cell 1.

Further, the other branch gas flow path (hereinafter referred to as the second sample gas supply path) 102 is provided with only a bomb 13, and its downstream side is connected to the gas inlet 2b of the cell 2.

In this embodiment, the sample gas G flowing through the sample gas flow path 10 is an exhaust gas containing CO as a haze gas and CO as a gas to be measured, and the inside of the reaction tank 11 is kept at an appropriate temperature. In addition to the heater for heating, C
It contains an oxidation catalyst that promotes the oxidation reaction of O.

Therefore, let the concentration of Haas gas be Y, and the difference gas concentration be X
Then, CO. in the first sample gas supply path 101.
The concentration becomes X+Y, and the second sample gas supply path 102
The CO2 concentration inside is Y.

A condenser microphone type detector 14 is provided at the other end of the cell 1.2, and its two light receiving chambers 141 and 142 are arranged to correspond to the cell 1.2, respectively. That is, the interior of this detector 14 is divided into two light receiving chambers 14L and 142 by a movable membrane 143, and each light receiving chamber 141, 142 contains C of a known concentration.
Filled with O2. Further, a fixed pole 144 is provided in the light receiving chamber 141 so as to face the movable film 143, and an output signal from the fixed pole 144 is supplied to a signal processing section 16, which will be described later, via a pre-amplifier 15. .

As is clear from the above description, this embodiment is configured as an infrared gas analyzer. And, in this infrared gas analyzer, test? CO in the gas flow path 10
When the sample gas G containing CO and CO is supplied, the first sample gas G containing CO and CO is passed through the first sample gas supply path 101. is introduced into the cell 1, and the second sample gas supply path 1
A second sample gas G2 having a CO₂ concentration of Y is introduced into the cell 2 through the second sample gas G2. In this state, the light from the light source 3.4 is intermittently changed by the optical chopper 8 at 5}{Z.
When the light source 4 corresponding to the cell 2 is turned on and off (light source change 1) with z, the detector 14 outputs an AC signal in the band around the AC output modulation frequency (5Hz) and the light source modulation. An output signal S on which an AC signal in a band around frequency (27) is superimposed is output.

Reference numeral 16 denotes a signal processing section which processes the output signal S from the detector 14 which is manually input via the pre-amplifier 15 to obtain a signal representing the differential gas concentration. a processing sequence 21 for extracting a first signal as a difference density signal, which is formed by connecting a bandpass filter 17 and a smoothing circuit 19 in series to separate and extract (pass) only the signal of the light source modulation frequency; a processing system 22 for extracting a second signal as a base concentration signal, which is formed by connecting a bandpass filter 18 and a smoothing circuit 20 in series for separating and extracting (passing) only signals in the band; and a correction circuit 23 which inputs the second signal and corrects the I-th signal with the second signal.

In the infrared gas analyzer configured in this way, the sample gas G is caused to flow through the sample gas flow path 10, the first gas G1 is introduced into the cell 1, and the second gas G2 is introduced into the cell 2.
At the same time, the light source 3.4 emits infrared light, and the light from the light source 4 is rotated at a frequency of 2H different from the modulation output frequency.
When turned on and off with z (light source modulation frequency), the detector 14
A signal S in which signals y and x corresponding to the base gas concentration Y and the difference gas concentration X are superimposed is outputted from.

Then, this signal S is appropriately amplified in the pre-amplifier 15 and then input to the signal processing section 16. One processing line 2
1, the first signal of the alternating current component of the alternating current modulation frequency, that is, the signal X representing the differential gas concentration That is, the signals y representing the base gas concentration Y are extracted independently from each other. As already explained, since the signal X is influenced by the signal y, the correction circuit 2
and using the inverse function of the calibration curve K shown in Figure 6,
The signal X is corrected by the signal y.

Next, an example of this correction will be explained with reference to FIG.

Now, the spectrometer output y for a constant change in light amount is as shown by curve 1 (y = f (Y)) in Figure 4.
It changes only in response to the base gas concentration Y.

As already explained, the analyzer output X for the differential gas concentration X changes corresponding to X and Y, and the output X corresponding to the base gas concentration Y at a certain concentration X0 is as shown in FIG. curve II (x = g (Y)
), it changes. For example, when the differential gas concentration X is very small compared to the base gas concentration Y, it can be approximated as a/V e ''=b/X O in FIG.

In other words, (yo y)/ )'o = (xo x)/Xo
A relationship holds true. Therefore, X X0=-xy, ...
(1) y becomes.

Therefore, from the signals X and y, the output correction for the differential gas concentration X when the base gas concentration is 0 can be performed based on the above equation (1).

Note that y0 is determined in advance from the base gas concentration Y in the analyzer.

By performing the above-described correction, the signal processing section 16 outputs a signal S representing the correct difference density. In the first embodiment described above, the optical chopper 8 was used to output the alternating current component from the detector 14, but instead of using the optical chopper 8, the first sample gas Gl was used for the cell 1.2. and second sample gas G! It is also possible to perform so-called fluid modulation by alternately supplying these at a constant cycle. FIG. 2 schematically shows the configuration of a gas analyzer according to a second embodiment of the present invention that performs fluid modulation in this manner. In this figure, the same reference numerals as those shown in FIG. or its equivalent. In FIG. 2, 24 is a rotary pulp as a fluid modulating means provided between the sample gas flow path 10 and the cells 1 and 2, and a rotor 26 as a plate-shaped switching means is provided in the housing 25. ing.

Then, the housing 25 has four
The downstream end of the first sample gas supply path 101 is connected to the hole 27, and the hole 28 is connected to the downstream end of the first sample gas supply path 101.
is connected to the downstream end of the second sample gas supply path 102 , the hole 29 is connected to the gas inlet 1 b of the cell 1 via the connection path 31 , and the hole 30 is connected to the gas inlet 1 b of the cell 1 through the connection path 32 . It is connected to the gas inlet 2b of the cell 1.

Note that the gas outlet ports 1c and 2c of the cells I and 2 are connected to a discharge channel (not shown).

In the infrared gas analyzer configured as described above, the sample gas G is caused to flow through the sample gas flow path 10, and the rotor 26 of the rotary valve 24 is rotated in the direction of the arrow R.
First sample gas G1 and second sample gas G for cell 1.2
2 alternately, and the switching period is set to 1 cycle (modulated output frequency), the light source 3.4 emits infrared light, and the light from the light source 4 is set to the modulated output frequency. are turned on and off at different 27 (light source modulation frequencies). In this case as well, the detector 1
4, signals x.4 correspond to the differential gas concentration X and the base gas concentration Y, respectively. Since the signal S in which y is superimposed is output, this signal S may be similarly processed in the signal processing section 16.

In the second embodiment described above, the so-called fluid modulation was configured as a so-called 2-cell type using two cells 1.2, but only one cell was used and the first sample was placed in this cell. The gas G1 and the second sample gas G2 may be alternately switched at a constant cycle. Fig. 3 schematically shows the configuration of a fluid modulation type infrared gas analyzer using a single cell, and in this figure, the same symbols as those shown in Fig. 1 or 2 refer to the same or equivalent parts. shows.

In this FIG. 3, 33 is the first gas G and the second gas G.
t is supplied alternately at a constant period, and a cell window 33a is provided at both ends of the cell, and a gas inlet 33b and a gas outlet 33c are formed at appropriate positions. A light source 34 is provided facing one cell window 33a of the cell 33 to illuminate the cell 33, and a switching element 36 is interposed between the light source and the light source 35. For example, 2}{Z turns it on and off.

37 is a rotary valve as a fluid modulating means provided between the sample gas flow path 10 and the cell 33, and a rotor 39 as a plate-shaped switching means is provided in the housing 38 of the rotary valve. Then, the housing 38 has a circumference of 4
Four holes 40 to 43 are opened so as to divide it equally,
The hole 40 is connected to the downstream end of the first sample gas supply path 101 , the hole 41 is connected to the downstream end of the second gas supply path 102 , and the hole 42 is connected to the cell via the connection flow path 44 . 33, and the hole 43 is connected to a discharge channel (not shown). In addition. The gas outlet 33c of the cell 33 is connected to a discharge flow path (not shown).

44 is a detector provided opposite to the other cell window 33a of the cell 33, and is, for example, a pyro sensor. The operation of the infrared gas analyzer constructed in this manner is the same as that shown in Figure 2, so a description thereof will be omitted. The present invention is not limited to the above-described embodiments, but can be applied to other gas analyzers such as an ultraviolet gas analyzer. The rotary valve 24 shown in FIGS. 2 and 3. 37, a four-way switching valve, a three-way switching valve, or the like may be used. Furthermore, in the embodiment shown in FIG. 3, a condenser microphone detector may be used instead of the pyro sensor.

[Effects of the Invention] As explained above, in the present invention, an AC signal in which a first signal representing the differential gas concentration and a second signal representing the Haas gas concentration are superimposed is obtained using a single detector. Since the output from this detector is separated into a first signal and a second signal, and the first signal is corrected with the second signal, concentration can be measured accurately. Unlike the conventional method, there is no need to use two detectors, so the configuration is extremely simple and a gas analyzer with high measurement accuracy can be obtained at low cost.

[Brief explanation of drawings]

1 to 3 show embodiments of the present invention, and FIG. 1 is a first embodiment of the present invention.
A diagram showing the configuration of a gas analyzer according to an embodiment, FIG.
A diagram showing the configuration of a gas analyzer according to an embodiment, FIG.
FIG. 1 is a diagram showing the configuration of a gas analyzer according to an example. FIG. 4 is a graph for explaining an example of signal correction performed by the correction circuit. FIG. 5 is a diagram showing a conventional example. FIG. 6 is a diagram showing the relationship between haze gas concentration and output. 3.4.34...Light source, l1...Reaction part, 14.
44...Detector, G1...First sample gas, G2...
・Second sample gas, S...detector output signal, X...
1st signal, y... 2nd signal.

Claims (1)

[Claims] A first sample gas containing a base gas is irradiated with light emitted from a light source, and a second sample gas containing the base gas similarly to the first sample gas has a base gas concentration that changes by passing through a reaction section.
The sample gas is configured to pass through the sample gas at a constant period (AC modulation frequency), and a detector is provided to correspond to the light that has passed through the first sample gas and the second sample gas, respectively. is configured to extract an alternating current component corresponding to the energy difference between the light energy that has passed through the first sample gas and the light energy that has passed through the second sample gas from the output signal of the light source; is changed at a frequency different from the AC modulation frequency (light source modulation frequency), and the output signal of the detector is divided into a first signal of the AC component of the AC modulation frequency and a first signal of the AC component of the light source modulation frequency. Separate into 2 signals,
A gas analyzer characterized in that the first signal is corrected by the second signal.