JP4319471B2 - Sample gas concentration meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sample gas concentration meter for measuring the concentration of a plurality of components in various gases or a component having a large concentration change, and in particular, a specified substance (component) measuring device in the atmosphere or measuring a specified substance in an automobile exhaust gas. It is useful to apply to a sample gas concentration meter used in the apparatus.
[0002]
[Prior art]
In recent years, the concentration of carbon monoxide (CO), sulfur oxides (SOx), nitrogen oxides (NOx), hydrocarbons (HC), oxidants (Ox) and dust in the atmosphere has been monitored to monitor air pollution. Many measuring devices are in operation, such as a specific substance measuring device in the atmosphere and a specific substance measuring device in automobile exhaust gas, which are continuously measured as management targets. Of these substances to be measured, NOx generally refers to a mixture of nitric oxide (NO) and nitrogen dioxide (NO ₂ ). Usually, as shown in FIG. While introducing into the detector 3 via the electromagnetic valve 2 (fluid A), the other is introduced into the detector 3 via the NO ₂ -NO converter 10 and the electromagnetic valve 2 (fluid B). The operation of the solenoid valves 2 and 2 is switched, and the fluids A and B are alternately introduced into the detector 3 to detect NOx, NO and NO2 calculated from the difference between the _two . At this time, a chemiluminescence method (CLD) is often used as a detector in addition to the non-dispersion infrared absorption method (NDIR) and the non-dispersion ultraviolet absorption method (NDUV).
[0003]
When the air D purified by the purifier 11 is introduced into the ozone generator 12 (ozone fluid), the CLD undergoes the following reaction with NO in the sample in the reaction tank in the detector, and the light generated at this time ( By measuring hν), the NO component in the sample can be detected.
NO + O ₃ → NO ₂ ^* + O ₂
NO ₂ ^* → NO ₂ + hν
The sample fluid or the ozone fluid is introduced into the detector by a method of providing a pump for pumping in each flow path, or by a suction method using a suction pump 6 provided at the subsequent stage of the detector 3 as shown in FIG. It is also possible to. In the case of the suction method, the pressure regulator 5 adjusts the internal pressure of the detector 3 to be constant while sucking air from the filter 4 to ensure a stable instruction.
[0004]
Here, in general, in order to ensure linearity or prevent the influence of coexisting components, particularly carbon dioxide (CO ₂ ), moisture (H ₂ O), etc., as shown in FIG. The structure which introduce | transduces into the detector 3 the sample diluted with the air D refine | purified by is taken (for example, refer patent document 1 or 2). That is, for the former, when a high-concentration sample is directly introduced into the in-detector reaction tank, the reaction is not completed in the layer, and linearity is deteriorated due to out-of-system light emission. The latter is in an excited state NO ₂ ^* is deprived of energy by collisions with molecules such as CO _2, it is affected by so-called quenching phenomenon. For this reason, the sample, that is, NO, CO ₂ or the like can be introduced into the reaction vessel under appropriate conditions without diminishing the responsiveness by diluting the sample.
[0005]
Further, in order to improve the stability of the CLD, the fluid switching means 13 as shown in FIG. 5 is used to modulate the sample fluid G and the reference (comparison) fluid R by switching them at a constant period, and thereby in the detector. There is known a fluid modulation type in which only a change in light emission amount is taken out as an AC signal. The reference fluid R can form a stable reference by introducing a part of the purified air through the throttle 14.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 7-301603 [Patent Document 2]
Japanese Patent Laid-Open No. 10-142120
[Problems to be solved by the invention]
However, the following problems may occur in the measuring apparatus described in the related art.
In other words, for example, when the NOx concentration in the sample fluid changes significantly, such as automobile exhaust gas, particularly when high concentration NOx is generated, the diluted sample may be as described above. It may exceed the optimum range of the detection part of CLD, and it may be necessary to increase the dilution rate.
[0008]
Usually, as a method of increasing the dilution rate, a method of increasing the flow rate of the diluted fluid is conceivable. However, there is a possibility that the out-of-system light emission may occur with the increase of the flow rate to the detector. At this time, there is a method of discharging a part of the sample fluid after mixing with the dilution fluid to the bypass, but there is a possibility that the flow path becomes complicated. Also, an increase in the flow rate of the dilution fluid may increase the load on the purifier used to make the diluted fluid, and it may involve specialized work in equipment maintenance, such as checking and replacing the efficiency of the purifier. There is a need for maintenance of the purifier itself, and the work load is increased.
[0009]
In addition, when a method of reducing the sample flow rate to be introduced is adopted, a transient phenomenon at the time of switching occurs, which may adversely affect the measured value.
Specifically, in the line switching by the switching valves 2 and 2 as shown in FIG. 4, overshoot due to mixing with residues due to stagnation or adsorption in the piping between the valve 2 immediately after switching and the line coupling part a or b. Or undershoot may not be negligible. This corresponds to the hunting portion shown in FIG. 6 (A) or (B). Even in the case of the fluid modulation type as shown in FIG. 5, the same phenomenon may occur in the piping between the valve 13 and the line coupling part b. This corresponds to the hunting portion shown in FIG. 6 (C) or (D). Such a waveform disturbance may cause a ripple phenomenon as a final instruction of the densitometer.
[0010]
Accordingly, an object of the present invention is to solve the above-mentioned problems and to use a concentration meter having high stability and reliability of measurement values and high measurement accuracy in measurement of a sample gas in which the concentration change of the measurement component is large. It is to provide a measuring device. Further, in the case of the fluid modulation type, it is to prevent a transient phenomenon at the time of switching that may adversely affect the measured value.
[0011]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by the following densitometer and a measuring apparatus using the same, and have completed the present invention. It was.
[0012]
This is a fluid modulation type sample gas concentration meter that switches the sample gas and the reference (comparison) gas at a fixed period and introduces them into the detector for modulation, and extracts the change as an AC signal. diluted with a dilution means for injecting both before and after said changeover switching means switching means and the dilution gas is controlled, during the introduction of the sample gas, Ru is injected at the preceding stage of said switching means in accordance with the flow rate of introducing the sample gas The flow rate of the sample gas diluted in the first stage with the gas is increased, and further diluted in the second stage with the diluent gas injected in the subsequent stage and introduced into the detector, and when the sample gas is stopped, The dilution gas injected from the subsequent stage of the switching means is introduced into the detector as the reference gas, and the sum of the flow rates introduced into the detector is made substantially constant . With such a configuration, it is possible to provide a densitometer having high stability and reliability of measurement values and high measurement accuracy without causing a transient phenomenon at the time of switching, and a measurement apparatus using the same.
[0013]
In the case of the above-mentioned concentration meter, which is a sample gas whose component concentration varies greatly, a plurality of flow paths are provided in front of the switching means, and the concentration range is divided into several, and a sample gas flow rate suitable for each detector is set. The flow path can be switched according to the component concentration, and after the switching, the flow rate of the sample gas diluted in the first stage can be increased by the dilution gas injected in the previous stage of the switching means. Is preferred. With such a configuration, even if the sample concentration varies greatly, the sample flow rate is switched to a suitable one for the detector, and the measured values are stable and reliable without the occurrence of transients during switching. A highly accurate densitometer and a measurement apparatus using the same can be provided. Further, it is preferable that the sum of the set sample gas flow rate, the first-stage dilution gas flow rate, and the second-stage dilution gas flow rate is substantially constant. With such a configuration, there is no occurrence of a transient phenomenon due to switching, and there is no fluctuation factor due to a change in the concentration of the measurement component, so that the sample flow rate suitable for the detector is switched, and stability, reliability, and measurement accuracy are high. Measurements can be obtained.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The present invention is a sample gas concentration meter having a plurality of flow paths through which a sample gas or a reference gas flows, a switching means for the flow paths, and a dilution means for the measurement sample, and the dilution gas can be injected both before and after the switching means. It is characterized by. That is, the present inventor has found that a transient phenomenon at the time of switching of the flow path switching means can be prevented by preventing the flow rate of the gas passing through the flow path switching means from changing greatly. Thus, it is very effective when measurement is performed by a single detector after switching samples from a plurality of sampling points or switching samples subjected to different processing by dividing the same sample. With such a configuration, it is possible to provide a sample gas concentration meter that does not cause a transient phenomenon at the time of switching and has high stability and reliability of measurement values and high measurement accuracy, and a measurement apparatus using the sample gas concentration meter.
[0015]
As an example of an embodiment of the present invention, a configuration example for measuring sample fluids from a plurality of sampling points is shown in FIG. Sample fluid G _1, G _2, the · · G _n, diaphragm _{1 (C 1, C 2,} ·· C n) and the channel switching means electromagnetic valve 2 is _{(V 1, V 2, ··} V n) It is introduced into the detector 1 through the diaphragm 1 and the purified fluid squeezed D 7 between the electromagnetic valve _{2 (D 1, D 2,} ·· D n) first by the addition and mixing via The second-stage dilution is performed by performing the second-stage dilution and adding and mixing the purified fluid D between the solenoid valve 2 and the detector 3 via the throttle 8. By turning ON the solenoid valve 2 in order, the sample fluids G ₁ , G ₂ ,... G _n are sequentially introduced into the detector.
[0016]
At this time, it is possible to adjust the sampling flow rate with the throttle 1 and the dilution rate with the throttle 7 according to the concentration of the sample. That is, if the concentration of the sample G ₁ was about 5 times the concentration of G _2, stop the flow in G ₁ to about 5 minutes about one of the flow rate of G ₂ by C _1, squeezing the reduced flow amount By increasing the flow rate of the diluted fluid by D ₁ , the flow rate that passes through the electromagnetic valve V ₁ can be made substantially the same as the flow rate that the sample G ₂ passes through the electromagnetic valve V ₂ . Therefore, there are no fluctuation factors associated with the switching of each line, the sample flow rate suitable for the detector, which is the object of the present invention, can be obtained, and a measurement value with high stability, reliability and measurement accuracy can be obtained. The above can be applied to a completely different sample, for example, when measuring a working atmosphere for measuring a working environment collected from a plurality of base points, or to multi-point measurement for monitoring product leakage in a factory.
[0017]
The present invention can also be applied to a case where two types of fluids obtained by different processing methods are measured by dividing one sample into two parts instead of samples from a plurality of sampling points. switched fluids a and B in the NOx measuring device mentioned can be obtained with high stability and reliability NOx, NO, the NO ₂ measurements. Or the same effect can be acquired also about the fluid modulation system which switches a sample fluid and a reference | standard fluid with a fixed period. The purified fluid D is preferably a fluid obtained by removing a measurement component (for example, NOx) in the air, moisture, or the like using a purification means (for example, activated carbon, a dehumidifier, or any other removal means).
[0018]
Further, the present invention is a concentration meter having switching means for controlling introduction and stop of the sample fluid and dilution means for the measurement sample, wherein the diluted fluid can be injected both before and after the switching means. . For example, in the fluid modulation type concentration meter as described above, not only the case where the reference fluid is detected but also the case where the sample introduction to the detector is stopped is included as the state of the concentration meter being zero. The present inventor has found that the present invention is effective even in a densitometer having this function. With such a configuration, it is possible to provide a densitometer having high reliability of measurement values and high measurement accuracy, and a measuring device using the same, in addition to the stability of the indication specific to the fluid modulation type, and without the occurrence of a transient phenomenon at the time of switching. it can.
[0019]
FIG. 2 shows an example of the configuration of the embodiment of the present invention.
Specifically, the purified fluid D is introduced between the throttle 1 and the electromagnetic valve 2 through the throttle 7 in the configuration of FIG. According to the inventor's knowledge, for example, in a NOx meter using CLD, when measuring a low concentration (for example, 10 to 100 ppm), the sample flow rate is 20 to 30 ml / min, the dilution air flow rate is about 100 ml / min, and the ozone fluid flow rate is about. Assuming that 400 ml / min and a detector suction pressure of about (−) 10 kPa are suitable conditions, when measuring a high concentration (for example, 200 to 2000 ppm), the sample flow rate is 5 to 10 ml / min, It has been confirmed that the dilution air flow rate is about 20 ml / min, the second stage dilution air flow rate is about 80 ml / min, the ozone fluid and the suction pressure are the same as described above, so that there is no occurrence of a transient phenomenon due to switching.
[0020]
Moreover, although the case where CLD was used was described above, it can be applied to other measurement principles. For example, when applied to FID, a fuel gas (a gas containing hydrogen) and an auxiliary combustion gas (a gas containing oxygen) are introduced as an auxiliary fluid together with a sample gas, and C ⁺ ions generated by the following reaction are measured. Hydrocarbons in the sample can be detected, but when the introduction of the sample is stopped, a zero state can be created as in the case of introducing zero gas into the detector. Therefore, the conditions of the present invention can be satisfied and the application effect of the present invention can be obtained.
CmH ₂ n + n / ₂ O ₂ → mC ⁺ + nH ₂ O
In addition, it goes without saying that the present invention can be similarly applied to a densitometer that satisfies the above conditions.
[0021]
It is preferable that the densitometer has a sample flow rate switching function before the switching unit. For a sample whose component concentration varies greatly , divide the concentration range into several parts, set the sample flow rate suitable for each detector, and provide a restrictor and a switching valve in multiple channels of equal differential pressure. The flow path connected to the detector is switched in accordance with (flow rate switching valve). At this time, a purified fluid for dilution can be introduced between the flow rate switching valve and the flow path switching means, so that a concentration meter with high stability and reliability of measurement values and high measurement accuracy and a measuring apparatus using the same can be obtained. Can be provided.
[0022]
One configuration example of the embodiment of the present invention is shown in FIG. Diaphragm _{1 (C 1, C 2,} ·· C n) and a flow switching valve _{9 (V 1, V 2,} ·· V n) any one or more of the flow path of the plurality of channels having, then The sample fluid G is introduced into the detector 1 through the electromagnetic valve 2 which is a flow path switching means, and the purified fluid D is added and mixed between the throttle 1 and the electromagnetic valve 2 through the throttle 7 to thereby achieve the first. The first-stage dilution is performed, and the second-stage dilution is performed by adding and mixing the purified fluid D between the solenoid valve 2 and the detector 3 via the throttle 8. By turning the solenoid valve 2 on and off at a constant cycle, fluid modulation of the cycle can be performed, and transient effects associated with the operation of the solenoid valve 2 can be prevented.
[0023]
FIG. 3 further shows a configuration in which the presence or absence of the first stage dilution can be selected depending on the sample flow rate. For example, in a NOx meter using CLD, C _{1 is} for 5 ml / min, C _{2 is} for 10 ml / min, C _{3 is} for 20 ml / min, and C _n is for _N ml / min. When configured as a diaphragm, when measuring a high concentration (for example, 200 to 2000 ppm), V ₁ is turned on, the sample flow rate is about 5 ml / min via C ₁ , and the first stage dilution air flow rate is about 20 ml / min. Min, mix and dilute at the second stage dilution air flow rate of about 80 ml / min. On the other hand, when measuring a low concentration (for example, 10 to 100 ppm), V ₁ and V ₃ are turned on to set the sample flow rate to about 25 ml / min, and the first stage dilution is stopped to make the diluted air flow rate about 80 ml / min. Thus, there is no occurrence of a transient phenomenon due to switching. In this way, there are no fluctuation factors associated with changes in the concentration of the measurement component, and the sample flow rate suitable for the detector, which is the object of the present invention, is obtained, and measurement values with high stability, reliability, and measurement accuracy are obtained. Can do.
[0024]
Here, it is preferable that the switching of the sample flow rate is arbitrarily operable based on an instruction from the outside of the apparatus or a measured value. In recent years, it has become common to perform remote operation or remote control for devices that perform automatic operation for a long period of time, such as observation devices or measurement devices, as described above, and further remote maintenance (remote maintenance). Requests are getting stronger. In addition, for example, the range of change in the component concentration tends to increase with the expansion of the range in which the measuring device is used, such as the presence or absence of a catalyst device in an automobile or the measurement of exhaust gas in a running test under severe conditions. The automatic flow path switching function in the present invention is very effective as a means for answering such a demand, and can be switched by a function inside the apparatus and can be arbitrarily switched from the user interface.
[0025]
The above has mainly described the measurement device for NOx or HC in the atmosphere or the measurement device for automobile exhaust gas, but the technology of the present invention is not limited to such an application range. It can be applied in a wide range including a concentration measuring device for a specific substance in various processes such as a material measuring device, and can be said to be a technology having wide versatility.
[0026]
【The invention's effect】
The present invention relates to a concentration meter having a plurality of flow paths through which a sample fluid or a reference fluid flows and a concentration meter having a switching means for controlling the introduction and stop of the sample fluid. It is possible to provide a densitometer having high stability / reliability and measurement accuracy, and a measuring apparatus using the same.
[0027]
Further, the concentration meter has a function of switching the sample flow rate in the previous stage of the switching means, so that even a sample whose component concentration greatly changes is switched to a sample flow rate suitable for the detector, and It is possible to provide a densitometer having high stability and reliability of the above-described switching measurement value and high measurement accuracy.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a first configuration example of a densitometer according to the present invention.
FIG. 2 is an explanatory diagram showing a second configuration example of the densitometer according to the present invention.
FIG. 3 is an explanatory diagram showing a third configuration example of the densitometer according to the present invention.
FIG. 4 is an explanatory diagram showing a configuration example of a conventional densitometer 1;
FIG. 5 is an explanatory diagram showing another configuration example of a conventional densitometer.
FIG. 6 is an explanatory diagram showing an example of the operation of a conventional densitometer.
[Explanation of symbols]
1, 7, 8, 14 Aperture 2 Solenoid valve 3 Detector 5 Pressure regulator 6 Suction pump

Claims (3)

A fluid modulation type sample gas concentration meter that switches between a sample gas and a reference (comparison) gas at a fixed period, introduces it into a detector, modulates it, and extracts the change as an AC signal,
A switching means for controlling the introduction and stop of the sample gas and a dilution means for injecting a dilution gas both before and after the switching means;
During the introduction of the sample gas, increasing the flow rate of the diluted sample gas to the first stage by the preceding stage in injected Ru diluent gas of said switching means in accordance with the flow rate of introducing the sample gas, further injected in a subsequent stage Diluted to the second stage with the diluted gas and introduced into the detector,
When the sample gas is stopped, the dilution gas injected from the subsequent stage of the switching means is introduced into the detector as the reference gas,
A sample gas concentration meter, characterized in that the sum of the flow rates introduced into the detector is substantially constant . In the case of a sample gas whose component concentration varies greatly, a plurality of flow paths are provided in front of the switching means, the concentration range is divided into several parts, and a sample gas flow rate suitable for each detector is set. 2. The flow path of the sample gas diluted in the first stage by the dilution gas injected in the previous stage of the switching means is further increased after the switching, and the flow rate of the sample gas diluted in the first stage is increased. Sample gas concentration meter. 3. The sample gas concentration meter according to claim 2, wherein the sum of the set sample gas flow rate, the first-stage dilution gas flow rate, and the second-stage dilution gas flow rate is substantially constant.

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