JPH07151652A - High accuracy gas dilution system - Google Patents

Abstract

PURPOSE:To obtain a system for producing an uncontaminated sample gas diluted at high accuracy. CONSTITUTION:A main line 10 is provided with a flow rate sensor 16 and an exhaust gas flow rate control valve 15, fixed to an exhaust gas line 14, is controlled such that the flow rate sensor 16 will detect a preset flow rate of primary diluted gas. The primary diluted gas thus controlled is then admixed with a secondary diluted gas fed from a secondary diluted gas line 18 to produce a sample gas which is fed to the analyzer side through a sample gas supply line 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to an apparatus for producing a highly accurately diluted sample gas.

[0002]

2. Description of the Related Art Calibration of an analyzer is one of the most important factors when conducting trace gas analysis, and the standard gas currently available on the market is used for the determination of concentrations from ppb to sub ppb. Can't handle it. Therefore, it is necessary to further dilute this standard gas to create a calibration curve. However, dilution is susceptible to errors due to the large influence of the method and the performance of the equipment used. As a currently known general dilution method, as shown in FIG. 3, one standard gas line (main line) 1 is connected to a single-stage dilution gas line 3
Further, the two-stage dilution line 3a is connected, and a mass flow controller (MFC) 2 is attached to each of them to control the flow rates of the standard gas and the dilution gas. In the figure, 5 is a first-stage exhaust gas line, and 5a is a second-stage exhaust gas line. As described above, in order to further dilute the reference gas to obtain a high dilution rate gas, it is necessary to use a large number of MFC2. However, when a large number of MFC2 are used, the influence on the sample gas concentration is large due to the reliability of each device and the line purge property. In particular, in the case of the conventional example in which three MFCs 2 are used in the standard gas line 1, the flow rate through the MFC 2 is small, so the sample gas is It is easily polluted.

Therefore, a special dilution method shown in FIG. 4 has been proposed. This is a type that takes into account the pollution from MFC2. The feature of this flow is that the MFC2 attached to the standard gas line 1 has one on the supply side, and the MFC2 attached to the exhaust gas lines 5 and 5a respectively to control the flow rate of the standard gas line 1 while controlling the amount of exhaust gas. Then, a gas for dilution is mixed with this to dilute. According to this method, there is an advantage that the influence of water or the like, which causes the first pollution, is almost eliminated.

[0004]

However, the method of FIG. 4 has the following drawbacks.

A. The flow rate control error of each MFC 2 attached to the exhaust gas lines 5 and 5a is accumulated, resulting in poor accuracy.

B. After mixing the dilution gas and the standard gas,
Except for the required amount of gas, MFC in the exhaust gas lines 5 and 5a
Since this is a method of exhausting gas by means of 2, the accuracy of the MFC 2 that controls the exhaust flow rate is a major key in this method, and considering that the normal MFC accuracy is F / S ± 2%, the standard gas line 1 There is a problem that the flow rate cannot be accurately grasped.

The object of the present invention is to eliminate pollution as much as possible,
It is to propose a high-precision gas diluter that can accurately control the flow rate.

[0008]

The structure of the high precision gas diluting device proposed by the present invention is as follows. The main line to which the raw material gas is supplied, the MFC attached to the supply side of the main line, the one-stage dilution gas line with MFC connected to the downstream main line of the MFC, and the one-stage dilution gas line are connected. A single-stage exhaust gas line with an exhaust flow rate control valve provided by branching the downstream main line, a flow rate detection sensor attached to the downstream main line where the first-stage exhaust gas line is branched, and the flow rate detection Control the exhaust flow rate control valve so that the two-stage dilution gas line with MFC connected to the downstream main line where the sensor is attached and the flow rate detected by the flow rate detection sensor become a preset flow rate High-precision gas diluter consisting of a control circuit for

[0009]

The flow rate of the raw material gas (reference gas) supplied from the main line is controlled by the MFC, and the primary dilution gas supplied from the first-stage dilution gas line is also MF.
The flow rate is controlled by C to mix at a constant ratio.

The flow rate of the primary dilution gas diluted by this mixing is then detected by the flow rate detection sensor in the main gas line. The control circuit controls the exhaust flow rate control valve so that the primary dilution gas detected by the flow rate detection sensor has a preset flow rate, and controls the flow rate exhausted from the exhaust gas line. The primary dilution gas that exits the flow rate detection sensor is then mixed with the secondary dilution gas supplied from the two-stage dilution gas line to form the final dilution gas (sample gas), which is sent to the analyzer side. To be done.

[0011]

Embodiments of the present invention will be described in detail with reference to FIGS.

Reference numeral 10 is a main line, 11 is a mass flow controller (hereinafter referred to as "MFC") which is mounted on the supply side of the main line 10 and measures the flow rate, 12 is a one-stage dilution gas (nitrogen gas) line, and 13 is MFC, 14 is a one-stage exhaust gas line branched from the main line 10, and 15 is an exhaust flow control valve attached to the one-stage exhaust gas line 14.

Reference numeral 16 is a flow rate detection sensor attached to the main line 10. The exhaust flow rate control valve 15 is controlled by the control circuit 17 so that the flow rate detected by the flow rate detection sensor 16 becomes a preset flow rate. Controlled.

Reference numeral 18 denotes a main line 10 which is a two-stage dilution gas (nitrogen gas) line with an MFC 19 connected to the downstream side of the flow rate detection sensor 16, and 20 is a sample gas delivery line.

Next, the operation of the embodiment will be described. The raw material gas supplied from the main gas line 10 has its flow rate controlled by the MFC 11, and the primary dilution gas supplied from the first-stage dilution gas line 12 also has its flow rate controlled by the MFC 13 and is mixed at a constant ratio. It

The flow rate of the primary dilution gas diluted by this mixing is detected by the flow rate detecting sensor 16. The control circuit 17 controls the flow rate of the gas exhausted by the exhaust flow rate control valve 15 so that the flow rate detected by the flow rate detection sensor 16 becomes a preset flow rate. The primary dilution gas that has flowed out of the flow rate detection sensor 16 is then mixed with the secondary dilution gas whose flow rate is controlled by the MFC 19 via the second-stage dilution gas line 18, and the final dilution gas (sample gas) is obtained. Then, the gas is delivered from the sample gas delivery line 20 to the analyzer (not shown) side.

In the embodiment, the two-stage dilution gas line 18 is used.
Although the final dilution is performed by using the above, if further required, the two-stage exhaust gas line 21 is further branched from the main line 10 as shown by the alternate long and short dash line in FIG. 22 is attached, and the flow rate of the gas exhausted by the control circuit 24 is controlled by the control circuit 24 so that the flow rate (secondary dilution gas) of the main line 10 detected by the flow rate detection sensor 23 becomes a preset flow rate. The secondary dilution gas is supplied to the third dilution gas line 25 through M
It is also possible to mix the third dilution gas controlled by the FC26 to perform the third dilution, and send this as the sample gas.

[0018]

As described above, according to the present invention, only one MFC is attached to the supply side of the main line, and the exhaust gas is exhausted so that the flow rate detected by the flow rate detection sensor attached to the main line becomes constant. The sample flow rate was controlled by mixing the secondary flow rate with the secondary dilution gas. As a result, the following effects are achieved.

A. Only one MFC and flow rate sensor are attached to the main line. As a result,
In the process of manufacturing the sample gas by providing the dilution gas lines in multiple stages, unlike the conventional case, the control valve in the MFC is not used, so that the problem of contamination caused by the passage can be eliminated.

B. In the case of MFC that measures the gas flow rate by the flow dividing ratio of the amount of gas flowing through the main line to the bypass line by the orifice, there was an error in the flow rate of the pi-bus portion, but MFC was installed only on the supply side. All other flow rates flowing through the main line are accurately measured by a method that directly measures them with a flow rate detection sensor, and the flow rate of exhaust gas is controlled based on this value to control the flow rate of gas flowing through the main line. Therefore, the problem of error is completely eliminated, and high precision control (dilution) is possible.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the concept of a high precision gas diluting device according to the present invention.

FIG. 2 is a flow sheet showing details of the embodiment.

FIG. 3 is an explanatory view of a conventional general diluting device.

FIG. 4 is an explanatory diagram of a conventional diluter in which an MFC is attached to an exhaust gas line to control the flow rate of gas flowing through a main gas line.

[Explanation of symbols]

 10 Main line 11 MFC 12 First-stage dilution gas line 13 MFC 14 First-stage exhaust gas line 15 Exhaust flow control valve 16 Flow rate detection sensor 17 Control circuit 18 Second-stage dilution gas line 19 MFC 20 Sample gas delivery line

Claims (1)

[Claims] 1. A main line to which a raw material gas is supplied, an MFC attached to the supply side of the main line, a one-stage dilution gas line with MFC connected to a downstream main line of the MFC, and the one-stage A one-stage exhaust gas line with an exhaust flow control valve provided by branching a downstream main line to which a dilution gas line is connected, and a flow rate detection sensor attached to the downstream main line where the one-stage exhaust gas line is branched. And a two-stage dilution gas line with MFC connected to the downstream main line to which the flow rate detection sensor is attached, and the exhaust gas so that the flow rate detected by the flow rate detection sensor becomes a preset flow rate. A high-precision gas diluter consisting of a control circuit that controls the flow control valve.