JPH1038890A - Continuous analysis device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly obtain concentration of a specified component without lengthening a changeover cycle between a by-pass passage and a passage passing a converter. SOLUTION: A gas change-over valve 3 is switched onto a by-pass passage side so as to lead sample gas to a detector 5 without passing a converter 4, and detection signals are repeatedly sampled in a constant cycle. A signal change (a) rid of noise by a method of least square is obtained from a plurality of sampled data and made the final value of the NO detection value so as to estimate the detection value at time (te) immediately before following changeover timing. The gas changeover valve 3 is then switched onto the converter 4 side to lead the sample gas through the converter 4, and the final value SNOX of NOx is obtained in the same way. Concentration of NO2 is then obtained from SNOX-SNO.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various analyzers such as a continuous gas analyzer and a continuous water analyzer for measuring predetermined components continuously in time.

[0002]

2. Description of the Related Art In a continuous analyzer, when a component to be measured is a component that cannot be detected by a detector, a flow path through which a sample is continuously supplied is branched into two and then guided to a common detector. The branch point is provided with switching means which is alternately and periodically switched, and one of the branched flow paths is provided with a conversion means for converting a sample component which cannot be detected by the detector into a component which can be detected, and the other of the branched flow paths The channel is a bypass channel that directly leads the sample to the detector, and the concentration of a predetermined component is determined based on the difference between the detection values in the two branch channels.

For a more specific description, a chemiluminescent nitrogen oxide measuring apparatus will be described as an example. The chemiluminescence detector detects only nitrogen monoxide (NO) is nitrogen dioxide NO ₂ will not be detected. When trying to detect nitrogen dioxide, use a converter that converts NO ₂ to NO,
The value NOx (= NO + N) detected through the converter
And O _2), the relation of NOx-NO = NO ₂ from the difference between the value NO detected through the bypass flow path for guiding the direct detector without passing through the converter, calculates the NO _2.

The switching between the two branch channels is performed after the indication from the detector is stabilized, so that the switching is generally performed at a period of 5 seconds to 1 minute. FIG. 1 shows the relationship between sample switching in such a continuous analyzer and signals from a detector. Since it takes time to replace the gas in the piping, etc., the required signal data cannot be obtained immediately even if the gas is switched.Therefore, the signal should be taken only from the signal in the last part of the switching time (shaded area). It is sampled and used for calculation.

[0005]

Even if the signal of the last part in each cycle switched by the switching means is sampled, noise is increased with respect to the signal when a low-concentration sample is measured. Variations will increase with only one detection signal in the last period. Therefore, if an attempt is made to take an average value in the last period of sampling, the period during which the instruction is stable must be long, and the switching cycle will be long. However, for example, in the measurement of nitrogen oxides, since the concentrations of NO and NO ₂ change in a short time, there is a problem that if the switching cycle is lengthened, the change in the sample in a short time cannot be captured. . SUMMARY OF THE INVENTION It is an object of the present invention to accurately determine the concentration of a predetermined component without lengthening the switching cycle between a flow path passing through a converter and a bypass flow path.

[0006]

According to the present invention, after the branch flow path is switched, detection value data within a period in which the instruction is not stable is sampled at a constant period, and an arithmetic processing such as a least square method is performed from the data. To estimate the time change of the signal from which noise has been removed, and obtain the density of the predetermined component using the final value.

Therefore, in the present invention, as shown in FIG. 2, the data processing unit 20 includes a sampling control unit 24 for sampling the detection value of the detector 5 at a fixed time interval in each of the switched measurement periods. A calculation unit 26 for estimating a temporal change from a plurality of detection value data sampled in the measurement period to obtain a final detection value, and calculating a concentration of a predetermined component from a difference between the final detection values in both branch flow paths. ing. The switching control unit 28 includes a flow path passing through the conversion unit 4 that converts a sample component into a component that can be detected by the detector using the analyzer.
It controls the switching of the switching means 3 for switching between the bypass flow path that does not pass through the conversion means 4. The sampling control unit 24 converts the detected value signal from the amplifier 6 to a digital signal through the A / D converter 7 at a fixed cycle based on the timing at which the switching control unit 28 switches the flow path, and takes it into the arithmetic unit 26. Let

One example of a continuous analyzer to which the present invention is directed is the above-described nitrogen oxide measuring device, in which a NO ₂ -NO converter is used as a converting means and NO is detected as a detector. A chemiluminescent detector is used. Another example is an ammonia measuring device. In this case, a chemiluminescent detector for detecting NO is used as the detector, and a converter for converting ammonia to NO is used as the converting means. In the detection of ammonia, the ammonia concentration is determined from the difference between the NH ₃ + NO detection value when the gas passes through the converter and the NO detection value when the gas does not pass through the converter.

[0009]

FIG. 3 shows a chemiluminescent nitrogen oxide measuring apparatus as an example of an analyzing apparatus to which the present invention is applied. In the flow path from the sample inlet to the sample outlet where the sample is continuously supplied, a filter 1 for removing solids in the sample gas, a pump 2 for sucking the sample gas, and a pump 2 are sucked in order from the upstream side. A gas switching valve 3 for switching the sample gas between a flow path through the NO ₂ -NO converter 4 and a bypass flow path that directly leads to the detector is provided. Both the flow path through the converter 4 and the bypass flow path are led to the chemiluminescent NO detector 5. After the sample gas is detected by the detector 5, it is discharged to the sample outlet.

The detection value of the detector 5 is amplified by an amplifier 6 and then converted into a digital signal by an A / D converter 7 to be used by a CPU.
Incorporated in 8. The CPU 8 realizes both the function of the data processing unit 20 shown in FIG. 2 and the function of the switching control unit 28 for controlling the switching operation of the gas switching valve 3. The RAM 9 temporarily stores the sampled data,
This is for use in the calculation by the CPU 8.

An example of the operation will be described with reference to FIGS.
In order to measure the NO value, the gas switching valve 3 is switched to the bypass channel side, the sample gas is led to the detector 5 without passing through the converter 4, and the detection signal is repeatedly sampled at a constant cycle. The sampled data is shown in FIG.
1, S2,. . . As a signal containing noise. A signal change a from which noise has been removed by the least squares method is obtained from the plurality of fetched data. The detection value at the time te immediately before the next switching timing is estimated as the final value S _NO of the NO detection value.

Next, in order to measure the NOx value, the gas switching valve 3 is switched to the converter 4 side, and the sample gas is led to the detector 5 through the converter 4. Then, repeatedly sampling at a constant period a detection signal in the same manner to obtain the signal change which eliminates noise by the least squares method, obtaining the final value S _NOX of NOx at the time te of immediately before the timing of the next switching. Then, a concentration of NO ₂ from S _NOX -S _NO. This operation is repeated, and NO ₂ is continuously measured. The operation is the same in other continuous analyzers.

[0013]

According to the present invention, the time change is estimated by increasing the number of data by using not only the final detected value data in the measurement cycle after switching the branch flow path but also the previous detected value data in the cycle. As a result, the final data is obtained, so that a stable measured value with a small variation can be obtained even in a low concentration measurement. It is not necessary to add a special function as an analyzer, and only the calculation in the data processing unit needs to be changed, so that the analyzer can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional sampling operation in a nitrogen oxide measuring device.

FIG. 2 is a block diagram illustrating the present invention.

FIG. 3 is a flow chart showing one embodiment.

FIG. 4 is a flowchart illustrating an example of an operation.

FIG. 5 is a diagram showing a sampling operation and an operation in the present invention.

[Explanation of symbols]

 Reference Signs List 3 switching valve 4 converter 5 chemiluminescent detector 7 A / D converter 8 CPU 20 data processing unit 24 sampling control unit 26 arithmetic unit 28 switching control unit

Claims (1)

[Claims] 1. A flow path to which a sample is continuously supplied is branched into two and guided to a common detector, and a switching means for switching periodically and alternately is provided at the branch point. In addition, one of the branched flow paths is provided with a conversion unit that converts a sample component that cannot be detected by the detector into a component that can be detected, and the other branched flow path is a bypass flow path that directly leads the sample to the detector. In a continuous analyzer in which a data processing unit obtains a concentration of a predetermined component based on a difference between detection values in both branch flow paths, the data processing unit may detect a detection value of a detector in each of the switched measurement periods. And a sampling control unit that samples at a fixed time interval, and obtains a final detection value by estimating a temporal change from a plurality of detection value data sampled in each measurement period, and obtains a final detection value in the two branch flow paths From the difference Continuous analysis apparatus is characterized in that and a calculation unit for determining the concentration of a constant component.