JPH10274620A - Gas-analyzing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a time for calibration of a span. SOLUTION: Control pattern data are stored in a coefficient memory 22, which show a correspondence of a concentration coefficient and a time lapse so as to obtain a higher concentration than a predetermined concentration at a span gas introduction initial stage. After the introduction of a span gas is indicated to be started, a CPU 21 calculates flow rates of mass flow controllers 11, 12 in accordance with a control pattern read out from the coefficient memory 22. A component gas and a dilution gas are mixed in a mixing chamber 13 and supplied as the span gas to an analyzing part 14. Even if a component to be measured is adsorbed to an inner wall of a piping and the component is reduced at the initial stage, the span gas supplied to the analyzing part 14 is close to the predetermined concentration, and therefore a detection value of a concentration of the gas at the analyzing part 14 since promptly and becomes nearly constant in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas analyzer used for environmental air measurement such as monitoring and control of gas concentration in various industrial processes and measurement of exhaust gas concentration for monitoring pollution. The present invention relates to a gas preparation unit for preparing a standard gas for calibration in an apparatus.

[0002]

2. Description of the Related Art In the field of environmental air measurement such as monitoring and control of gas concentration in various industrial processes and measurement of exhaust gas concentration for pollution monitoring, non-dispersive infrared absorption method, ultraviolet fluorescence method, chemiluminescence method and the like are used. Gas analyzers are widely used. For example, in an infrared gas analyzer, by projecting infrared light onto a sample cell and a control cell, and comparing the absorption amount (or transmitted light amount) of infrared light of a specific wavelength by the gas in both cells,
The concentration of a specific component contained in the sample gas (hereinafter referred to as “sample gas concentration”) is measured. Specifically, first, a nitrogen gas or a standard atmosphere containing no measurement component is flown as a zero gas into the sample cell, and the detected value at this time is set as a zero point (zero calibration). Next, a gas containing a measurement component of a known concentration is flowed into the sample cell as a span gas, and the detected value at this time is set as a span point (span calibration). Thereafter, the sample gas is caused to flow into the sample cell, and the sample gas concentration is determined from the relative position between the zero point and the span point of the detected value at that time or on an extension thereof.

In order to accurately determine the sample gas concentration, it is preferable to perform span calibration using a span gas having a concentration as close as possible to the sample gas concentration. Generally, in a gas analyzer for measuring components in the ambient air, since the sample gas concentration is low, a span gas having a relatively low concentration is used. Since it is not preferable from the viewpoint of efficiency and the like to store and manage such a low-concentration gas in a cylinder or the like, the desired concentration is usually obtained by diluting a high-concentration component gas with a diluent gas at the measurement site. Is generally prepared for use in calibration.

[0004]

FIG. 5 shows a schematic configuration of a gas analyzer provided with the span gas preparation section. The component gas and the diluent gas are supplied to the mixing chamber 1 through first and second mass flow controllers (MFCs) 11 and 12, respectively.
3 where it is mixed well and the gas analyzer 14
Sent to The opening amounts of the first and second mass flow controllers 11 and 12 are adjusted so that a predetermined flow rate of the component gas and a predetermined flow rate of the diluent gas are supplied so that a predetermined concentration of the span gas is prepared. In the span calibration, if the calibration operation is completed before the span gas concentration is stabilized in the sample cell of the gas analyzer 14, accurate calibration cannot be performed. Therefore, after introducing the span gas into the sample cell, the stability of the detected value of the concentration is reduced. A method is adopted in which the calibration operation is terminated when the state is checked and settled substantially constant.

However, after the supply of the span gas from the mixing chamber 13 to the gas analyzer 14 starts, some of the components in the span gas are adsorbed on the inner wall of the pipe leading to the gas analyzer 14. For this reason, as shown in FIG. 4A, the detected value of the gas analyzer 14 rises very slowly until reaching a substantially constant state, and a long time is required for the calibration operation. In particular, when the measurement target is a substance such as SO ₂ having a low concentration and a strong adsorption power to a pipe or the like, it may take several tens of minutes before the detection value reaches a substantially constant value. . If the calibration operation requires a long time as described above, the time during which measurement cannot be performed (missing time) increases, and this becomes a serious problem when it is desired to continuously monitor the ambient air.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to reduce the time required for the span gas concentration to stabilize, thereby reducing the time required for span calibration. An object of the present invention is to provide an analyzer.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of preparing a standard gas having a predetermined concentration by diluting a high-concentration component gas with a diluent gas and analyzing the standard gas. A) a gas analyzer that performs calibration by introducing it into the section, a) first flow rate adjusting means for adjusting the flow rate of the component gas, b) second flow rate adjusting means for adjusting the flow rate of the dilution gas, and c) the first flow rate adjusting means. Mixing means for mixing the component gas whose flow rate has been adjusted by the flow rate adjusting means and the diluent gas whose flow rate has been adjusted by the second flow rate adjusting means and sending the mixed gas to the analysis unit; d) a standard from the mixing means to the analysis unit; Control means for controlling the first and / or second flow rate adjusting means so that a standard gas having a concentration higher than the predetermined concentration is introduced during a predetermined period of the initial period of gas introduction. I have.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the gas analyzer according to the present invention, the control means includes, for example, the second flow rate adjusting means such that a certain amount of dilution gas flows to the mixing means from the start of introduction of the standard gas, that is, the span gas. On the other hand, the first flow rate adjusting means is controlled so that a larger amount of component gas flows by a predetermined amount than after the elapse of a predetermined time from the start of introduction of the span gas. In the initial stage of the introduction of the span gas, components in the span gas are adsorbed on the inner wall of the pipe to the analysis unit, etc., but since the span gas having a concentration higher than a predetermined concentration is sent out from the mixing means, a part of the components is absorbed by the adsorption. Even if the gas is captured on the way, the span gas having a concentration close to the predetermined concentration reaches the analysis unit. Also, before and after the point at which the adsorption is substantially saturated and its influence is eliminated, a span gas of a predetermined concentration is sent out from the mixing means. For this reason, the concentration of the span gas detected by the analyzer rises rapidly from the start of gas introduction and settles to a substantially constant state in a short time without being largely affected by the adsorption.

The control means includes, for example, storage means for storing the predetermined time and an increase coefficient of the concentration of the span gas during the predetermined time in association with each other, and first and second flow rates according to the storage contents of the storage means. Calculation means for calculating a control amount (for example, control voltage) for the adjustment means. Since the degree of the influence of the above adsorption differs depending on the concentration of the standard gas, the above-mentioned predetermined time and the increase coefficient are measured in advance for each gas concentration by experiments or the like, and the optimum values are obtained and stored, and the span calibration is performed. Sometimes, when a desired span gas concentration is set, an optimum value may be selected.

[0010]

According to the gas analyzer according to the present invention, the concentration of the span gas is temporarily increased from the set predetermined concentration at the initial stage of the introduction of the span gas into the analysis section.
The effect of a decrease in the amount of components in the span gas due to adsorption in a pipe or the like is reduced, and the gas concentration detected by the analyzer quickly settles to a constant state. Therefore, the time required for span calibration is short, and the missing time can be shortened.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the gas analyzer according to the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram of a main part of the gas analyzer of the present embodiment. The gas preparation unit includes a first mass flow controller 11, a second mass flow controller 12, a mixing chamber 13, a control unit 20, and an operation unit 25. The control unit 20 includes, for example, a microcomputer or the like, and includes a CPU 21 and a coefficient memory 2.
2. First D / A converter 23, Second D / A converter 24
Contains. The coefficient memory 22 stores data necessary for flow control as described later, and the CPU 21 reads out appropriate data from the coefficient memory 22 in accordance with an instruction given by the operation unit 25, and converts a control voltage into a digital signal according to the data. Output as a value. The control voltage is converted into an analog voltage by the first and second D / A converters 23 and 24, respectively, and is input to the first and second mass flow controllers 11 and 12.

FIG. 3 shows the coefficient memory 22 in the present embodiment.
FIG. 3 is a diagram showing an example of a control pattern of gas concentration stored in the storage device. This control pattern sets the predetermined concentration of the span gas to 1
The density ratio is expressed as a density coefficient as time elapses.

Hereinafter, the operation of the gas preparation unit when the flow rate control is performed according to the control pattern shown in FIG. 3A will be described. When the start of span calibration is instructed by an operation from the operation unit 25, the CPU 21 sequentially reads the density coefficient of the control pattern from the coefficient memory 22 according to the elapse of the internal timer, and reads the density coefficient read to the set target span gas concentration. To calculate the control target concentration. Further, the required flow rates of the component gas and the diluent gas are calculated in accordance with the control target concentrations, and control voltage values for obtaining the required flow rates are obtained. As a result, the first and second mass flow controllers 11 and 12 flow the component gas and the diluent gas at predetermined flow rates, respectively, and
The span gas prepared by mixing at the gas analyzer 1
4 is sent.

According to the control pattern shown in FIG. 3A, the density coefficient is 1 during the span calibration start time t0 to the time t1.
Is larger than C1. Therefore, the control target concentration in this period is higher than the target span gas concentration by (C1-1).
× 100 [%]. Next, during the period from time t1 to time t2, the density coefficient is C2 which is larger than 1 and smaller than C1. For this reason, the control target concentration during this period is (C2-1) × 1 higher than the target span gas concentration.
It increases by 00 [%]. Therefore, in the first and second mass flow controllers 11 and 12, each flow rate is controlled in accordance with the increase in the concentration.

When the supply of the span gas is started, a part of the components to be measured in the span gas is adsorbed on an inner wall or the like in a pipe extending to the gas analyzer 14, so that the components to be measured reaching the gas analyzer 14 decrease. . That is, the concentration of the span gas that has reached the gas analyzer 14 is lower than the concentration of the gas immediately after leaving the mixing chamber 13. Such adsorption to the inner wall of the pipe is large immediately after the start of the supply of the span gas, but gradually decreases with the passage of time, becomes saturated after a certain period of time, and is hardly adsorbed thereafter.

When the concentration of the span gas is controlled as described above, the concentration of the span gas sent from the mixing chamber 13 is increased during a period in which the amount of adsorption is large. The concentration of the span gas that has reached the gas analyzer 14 is close to the set target span gas concentration. Thus, the time change of the detected value of the gas concentration obtained by the gas analyzer 14 is as shown in FIG. That is, a predetermined time Δ from the span calibration start time t0
After the span gas arrives at the gas analyzer 14 with a delay of t, the detected value rises sharply, quickly approaches the target span gas concentration, and settles to a substantially constant value. Therefore, span calibration can be completed within a short time.

The component to be measured once adsorbed on the inner wall of the pipe or the like is mainly carried away by the zero gas flowing through the pipe when the next zero calibration is performed. For this reason,
Immediately after the initial stage of span calibration, adsorption of the measurement target component in the span gas occurs again. By repeating such a measurement operation, the amount of the component to be measured adsorbed becomes substantially constant every time the span calibration is performed. For this reason, if the target span gas concentration is high, the adsorption is saturated during a short period of time at the initial stage of the introduction of the span gas. In such a case, FIG.
When the flow rate is controlled in accordance with the control pattern shown in FIG. 1, there is a possibility that a span gas having a concentration greatly exceeding the target span gas concentration may flow into the gas analyzer 14. At this time,
The time change of the detection value in the gas analysis unit 14 is a large overshoot as shown in FIG. 4C, and it takes time to settle down to a substantially constant level.

Therefore, in the gas analyzer of the present embodiment, an experiment is performed in advance to check the target span gas concentration and the optimum control pattern corresponding to the target span gas concentration. Then, this control pattern is associated with the target span gas concentration and the coefficient memory 2
Store it in 2. When the measurer operates the operation unit 25 to set the target span gas concentration during span calibration, the CPU 21
Reads the optimal control pattern from the coefficient memory 22 in accordance with the set density and executes the flow rate control as described above.

FIG. 3B shows an example of a control pattern corresponding to a high-concentration span gas. In the period from time t0 to time t3, a concentration coefficient C3 slightly larger than 1 is set. Is set to 1. According to this control pattern, the mixing chamber 13 is initially set at the beginning of the span gas introduction.
Is only slightly higher than the target span gas concentration, the overshoot as shown in FIG. 4C can be prevented. For a higher-concentration span gas, a control pattern in which the concentration coefficient is maintained at 1 as shown in FIG.

Thus, in the preparation of span gas having a wide range of concentrations, the value detected by the gas analyzer 14 can be made substantially constant in a short time.

FIG. 2 is a block diagram showing another embodiment of the gas analyzer according to the present invention. In the present embodiment, the CPU 21
, The detected value of the gas concentration in the gas analyzer 14 is input. That is, the CPU 21 basically controls the flow rate based on the control pattern data read from the coefficient memory 22 as in the above embodiment, but corrects the control based on the actual gas concentration detection result.

For example, if the detected value exceeds a certain value at the time t1 after the control is started according to the control pattern shown in FIG. 3A (for example, when overshoot occurs). , The time t2 at which the coefficient is set to 1 is earlier than the prescribed control pattern. As a result, it is possible to suppress a prolonged time until the detected value largely overshoots and stabilizes. Conversely, after starting the control according to the control pattern shown in FIG.
If the detected value is lower than a certain value at 1, the time t2 is made later than the prescribed control pattern. As a result, it is possible to suppress a prolonged time from the time required for rising to the time required for stabilization. Further, the CPU 21 is provided with a learning function to store that the correction is necessary as described above, and when the same target span gas concentration is set next time, the data read from the coefficient memory 22 is automatically stored. The flow rate control may be performed by correcting the flow rate. Also,
The data content itself of the coefficient memory 22 can be rewritten.

The above embodiment is merely an example, and it is apparent that changes and modifications can be made within the spirit of the present invention.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of a gas analyzer according to the present invention.

FIG. 2 is a configuration diagram of another embodiment of the gas analyzer according to the present invention.

FIG. 3 is a view showing an example of a control pattern of a span gas concentration in the embodiment.

FIG. 4 is a diagram illustrating an example of a change in a detection value in a gas analyzer in the present embodiment.

FIG. 5 is a schematic configuration diagram of a conventional gas analyzer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... 1st mass flow controller 12 ... 2nd mass flow controller 13 ... Mixing chamber 14 ... Gas analysis part 20 ... Control part 21 ... CPU 22 ... Coefficient memory 23, 24 ... D
/ A converter 25: Operation unit

Claims (1)

[Claims] 1. A gas analyzer for preparing a standard gas having a predetermined concentration by diluting a high-concentration component gas with a diluent gas, introducing the standard gas into an analysis unit, and performing calibration. First flow rate adjusting means for adjusting the flow rate, b) second flow rate adjusting means for adjusting the flow rate of the dilution gas, c) component gas whose flow rate is adjusted by the first flow rate adjusting means, and the second flow rate adjusting means A mixing means for mixing the diluted gas whose flow rate has been adjusted with the mixture and sending the mixed gas to the analysis unit; d) a standard gas having a concentration higher than the predetermined concentration during a predetermined period at the initial stage of introduction of the standard gas from the mixing means to the analysis unit. And a control means for controlling the first and / or second flow rate adjusting means so as to be introduced.