JPH05296893A - Switching equipment of dilution ratio of dilution sampling apparatus - Google Patents

Abstract

PURPOSE:To obtain switching equipment of a dilution ratio of a dilution sampling apparatus which can switch the dilution ratio easily without necessitating replacement of a capillary. CONSTITUTION:Branch open lines 5 connected to an air open line 4 and branch supply lines 6 connected to a mixed gas line 7 for supplying a mixed gas of a sample gas and a dilution gas are connected alternately in branch to a pressure regulating line 3 connected to a sample gas line 1 and a dilution gas line 2. The air open line 4 is provided with a pressure regulating means 8 for maintaining the pressure of the pressure regulating line 3 to be prescribed, while an on-off valve 9 is provided for each branch open line 5. Each branch supply line 6 is provided with a constant pressure reducing means 10 for making a gas flow rate prescribed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dilution ratio switching device of a dilution sampling device for analyzing exhaust gas emitted from an engine of an automobile.

[0002]

2. Description of the Related Art Generally, when analyzing a component contained in an exhaust gas discharged from an automobile engine, the exhaust gas is diluted with air or the like and collected, for example, FTIR.
(Fourier transform infrared spectrometer).

To dilute the exhaust gas, a diluter incorporating a capillary is often used. In this method, a sample gas and a diluent gas are passed through capillaries each having a predetermined resistance value and mixed to obtain a dilution ratio according to the resistance ratio.

[0004]

By the way, since the concentration of exhaust gas differs depending on the capacity of the engine and greatly changes depending on the operating condition, it may be better to change the above-mentioned dilution ratio for proper analysis. .. In such a case, it was necessary to change the resistance ratio of the capillaries, and the capillaries themselves had to be replaced each time, but the replacement required considerable time and effort.

The present invention has been made in view of such circumstances.
It is an object of the present invention to provide a dilution ratio switching device of a dilution sampling device that can easily switch the dilution ratio without requiring the replacement of capillaries.

[0006]

The present invention has means for solving the above-mentioned problems as follows. That is, for example, as shown in FIG.
To the pressure regulating line 3 connected to the dilution gas line 2 and
A plurality of branch open lines 5 connected to the atmosphere open line 4
(5a-5c) and a plurality of branch supply lines 6 (6a-6d) connected to a mixed gas line 7 for feeding a mixed gas of a sample gas and a diluent gas are alternately branched and connected, and The atmosphere opening line 4 is provided with pressure adjusting means 8 for keeping the pressure of the pressure adjusting line 3 constant, and each branch opening line 5 is provided with an on-off valve 9 (9a to 9c).
Each branch supply line 6 is characterized by being provided with constant decompression means 10 (10a to 10d) for keeping the gas flow rate constant.

[0007]

First, when only the on-off valve 9a is opened and the other on-off valves 9b and 9c are closed, the pressure in the pressure adjusting line 3 is kept constant by the pressure adjusting means 8 and the branch open line 6a is connected to the atmosphere open line 4. Communicate. Therefore, the sample gas is introduced into the branch supply line 6a and the diluent gas is introduced into the branch supply lines 6b, 6c, 6d, and the resistance of the constant pressure reducing means 10a to 10d provided in the branch supply lines 6a to 6d is changed. R ₁ and R respectively
₂ , R ₃ , R ₄ , the dilution ratio of the mixed gas supplied to the mixed gas line 7 is R ₂ R ₃ R ₄ / (R ₂ R ₃ R ₄ +
R ₁ R ₃ R ₄ + R ₁ R ₂ R ₄ + R ₁ R ₂ R ₃ ).
For example, if R ₁ = R ₂ = R ₃ = R _{4 then} the above-mentioned dilution ratio is 1/4. That is, the concentration of the sample gas is diluted to 1/4. The excessively supplied sample gas or dilution gas is released to the atmosphere through the atmosphere opening line 4.

Next, only the on-off valve 9b is opened and the other on-off valves 9
When a and 9c are closed, the pressure in the pressure adjusting line 3 is kept constant by the pressure adjusting means 8 and the branch open line 6b communicates with the atmosphere open line 4. Therefore, branch supply line 6
Sample gas is introduced into a and 6b, and diluent gas is introduced into the branch supply lines 6c and 6d, respectively, and the dilution ratio of the mixed gas is (R
₁ R ₃ R ₄ + R ₂ R ₃ R ₄ ) / (R ₂ R ₃ R ₄ + R ₁ R
₃ R ₄ + R ₁ R ₂ R ₄ + R ₁ R ₂ R ₃ ) and R ₁ =
If R ₂ = R ₃ = R ₄ , the dilution ratio will be 1/2.
That is, the sample gas is diluted to a concentration of 1/2.

Further, only the on-off valve 9c is opened and the other on-off valves 9
When a and 9b are closed, the sample gas is diluted to a concentration of 3/4.

[0010]

The present invention will be described in detail below with reference to the drawings. FIG. 1 shows a basic dilution ratio switching device (DF). Reference numeral 1 is a sample gas line for introducing a sample gas from a sample gas introduction port A, and 2 is a dilution gas such as air introduced from a dilution gas introduction port B. Dilution gas line to do 3
Is a pressure regulating line connected between the two gas lines 1 and 2.

The pressure regulating line 3 is connected to the atmosphere release line 4
A plurality of branch open lines 5 (5a-5
c) and a plurality of branch supply lines 6 (6a to 6d) connected to the mixed gas line 7 are alternately branched and connected.

A pressure adjusting line 3 is provided in the above-mentioned atmosphere opening line 4.
A back pressure regulator (pressure adjusting means) 8 for maintaining a constant pressure is provided, and each branch opening line 5 is provided with an electromagnetic opening / closing valve 9 (9a-9c), while each branch supply line 6 is provided. Is provided with capillaries (constant decompression means) 10 (10a to 10d) for making the gas flow rate constant, and the downstream side of each capillary 10 is joined and connected to the mixed gas line 7.

A dilution ratio switching device DF having such a configuration
To explain the operation of, first open only the on-off valve 9a,
When the other on-off valves 9b, 9c are closed, the back pressure regulator 8 keeps the pressure of the pressure regulating line 3 constant and the branch open line 5a communicates with the atmosphere open line 4. Therefore, the sample gas is introduced into the branch supply line 6a, and the dilution gas is introduced into the branch supply lines 6b, 6c, and 6d, and the resistance of the capillaries (constant decompression means) 10 provided in each branch supply line 6 is changed. R ₁ , R ₂ , R
₃ and R ₄ , the dilution ratio of the mixed gas supplied to the mixed gas line 7 is R ₂ R ₃ R ₄ / (R ₂ R ₃ R ₄ + R ₁ R
₃ R ₄ + R ₁ R ₂ R ₄ + R ₁ R ₂ R ₃ ).

More specifically, since the pressure in the pressure adjusting line 3 is kept constant by the back pressure regulator 8, the gas flow rate Q flowing in each branch supply line 6 is Q ₁ R ₁ = Q ₂ R ₂ = Q ₃ R ₃ = Q
₄ The relational expression of R ₄ = K holds. Therefore, the concentration of the diluent gas flowing through the mixed gas line 7 is Q ₁ / (Q ₁ + Q ₂ + Q
₃ + Q ₄ ), which is the dilution ratio represented by the resistance value R described above. For example, if R ₁ = R ₂ = R ₃ = R _{4 then} the above-mentioned dilution ratio is 1/4. That is, the sample gas is diluted to a concentration of 1/4. The excessively supplied sample gas or dilution gas is released to the atmosphere through the atmosphere opening line 4.

Then, only the on-off valve 9b is opened and the other on-off valves 9
When a and 9c are closed, back pressure regulator 8
By this, the pressure of the pressure adjusting line 3 is kept constant and the branch open line 5b communicates with the atmosphere open line 4. Therefore, the sample gas is introduced into the branch supply lines 6a and 6b and the diluent gas is introduced into the branch supply lines 6c and 6d, respectively, and the dilution ratio of the mixed gas is (R ₁ R ₃ R ₄ + R ₂ R ₃ R ₄ ) /
(R ₂ R ₃ R ₄ + R ₁ R ₃ R ₄ + R ₁ R ₂ R ₄ + R ₁ R
₂ R ₃ ), and if R ₁ = R ₂ = R ₃ = R ₄ , the dilution ratio is 1/2. That is, the sample gas is diluted to a concentration of 1/2.

Further, only the on-off valve 9c is opened and the other on-off valves 9
When a and 9b are closed, the sample gas is diluted to a concentration of 3/4.

As described above, according to the present invention, the upstream ends of the respective branch supply lines 6 provided with the capillaries 10 are all connected to the pressure adjusting line 3, and the pressure adjusting line 3 is open to the atmosphere. Since the branch open line 5 connected to the line 4 is alternately branched and connected to each branch supply line 6,
Each branch supply line 6 is operated by selectively opening the branch opening line 5 by an opening / closing valve 9 and operating a back pressure regulator 8 provided in the atmosphere opening line 4.
The pressure at the upstream end of the can be adjusted to be equal. Therefore, even if the introduction amount of the sample gas or the dilution gas becomes excessive, the pressures of the gases introduced into the capillaries 10 are made equal by the pressure adjusting line 3, so that the dilution is always performed at an accurate ratio. You can do it. It should be noted that the branch opening line 5 and the branch supply line 6 that are branched and connected to the pressure adjusting line 3 may be provided in appropriate numbers.

A dilution sampling device incorporating such a dilution ratio switching device DF is suitable for use in, for example, an analyzer for exhaust gas from an automobile engine. That is, even if the amount of exhaust gas (sample gas) supplied varies, accurate dilution can always be performed at a constant ratio, so for example, the ratio that does not cause dew condensation can be maintained stable and reliable analysis values can be obtained. Can be obtained. An example thereof will be described below.

First, FIG. 2 is a block diagram schematically showing an example of an automobile exhaust gas analyzer according to the present invention. The analyzer comprises a first unit 37, a second unit 71 and a third unit 72. The first unit 37 is for setting / switching the dilution ratio, and is configured as shown in FIG. That is, in the first unit 37, a sample gas inlet A for introducing the exhaust gas 16,
A diluent gas inlet B for introducing air (described later) as a diluent gas, a gas outlet C for leading the diluted exhaust gas, a gas outlet D for discharging the overflowed gas, and a span gas. A gas inlet E for introducing the gas is provided.

The gas inlet port A is connected to the terminal a of the gas passage 29 shown in FIG. In the gas flow path 29, as already described, the exhaust gas 16 discharged from the engine 13 of the automobile 11 driven on the chassis dynamo 12 flows in an undiluted state, and thus, the undiluted exhaust gas is discharged. 16 (hereinafter simply referred to as exhaust gas 16) is the gas inlet A
Is introduced into the first unit 37 via.

A filter 39, a needle valve 38, a pump 40, and a flow rate adjusting capillary 41 are provided in the sample gas flow path (sample gas line) 1 (see FIG. 3) connected to the gas inlet A, respectively. A branch point F is provided on the downstream side of the capillary 41, while a solenoid valve 46 is provided in the dilution gas flow path (dilution gas line) 2 connected to the dilution gas introduction port B, and a regulator 47 for adjusting the dilution air 44 to a constant pressure. , Capillaries 48 are provided respectively, a branch point G is provided on the downstream side of the capillaries 48, and the pressure adjusting line 3 is provided between the branch point G and the branch point F. Then, the branch points H and I between the pump 40 and the capillary 41 in the sample gas flow channel 1 are respectively gas flow channels 14 and
Gas inlet E for introducing span gas through 15
And gas discharge port D to open the atmosphere to overflow gas
A needle valve 62 and a solenoid valve 63 are provided in the one gas flow path 14, and a back pressure regulator 59 is provided in the other gas flow path 15.

The above-mentioned pressure regulating line 3 is provided with three branch opening lines 5 (5a, 5b, 5c) arranged in parallel with each other and provided with cocks (open / close valves) 9 (9a, 9b, 9c). When,
A plurality of branch supply lines 6 (6a to 6j) arranged in parallel with each other and provided with capillaries 10 (10a to 10j) of the same resistance value are branched and connected so as to be surrounded by a chain line. The branch open lines 5a to 5c branch from the pressure adjusting line 3 alternately with the branch supply lines 6a to 6d, and the downstream sides of the branch open lines 5a to 5c join to form a gas flow path (atmosphere open line). 4, the gas flow path 4 is connected to a downstream side of the back pressure regulator 59 of the gas flow path 15 connected to the gas discharge port D, while the downstream side of each branch supply line 6 joins to form a gas outlet port. The gas outlet C is connected to the mixed gas line 7.

A pressure gauge 5 is provided in the gas passage 4 described above.
4, back pressure regulator 8 and flow meter for adjusting the pressure between the branch points FG, that is, the pressure adjusting line 3
56 is provided and is connected to the gas flow path 15 on the downstream side, and the dilution ratio is set by the regulator 8, the cock 9 provided in each branch opening line 5, the capillary 10 provided in each branch supply line 6, and the like. .Switching unit (dilution ratio switching device)
It composes the DF.

On the other hand, the dilution gas introducing port B has a second
This is for introducing the air 44 as the diluting gas, which has been subjected to the pressure adjustment processing in the unit 71, into the first unit 37, and the diluting gas passage 2 connected to this gas introducing port B has the same structure as described above. , A solenoid valve 46, a regulator 47 for adjusting the dilution air 44 to a constant pressure and a capillary 48 are provided, and a branch point G is provided on the downstream side of the regulator 47 and the capillary 47. An electromagnetic valve 66 is provided in a gas flow path 65 that connects the branch point 64 between the gas flow path 14 and the gas flow path 14. The temperature of the portion X surrounded by hatching is adjusted to a predetermined temperature.

In the first unit 37 thus constructed, the exhaust gas (sample gas) of a predetermined amount or more is used.
16 and the dilution air 44 are introduced from the sample gas introduction port A and the dilution gas introduction port B, and the cock 9 in the dilution ratio setting switching section DF is selectively opened to extremely set and switch the dilution ratio. It can be done easily. That is, as already explained in FIG. 1, when only the cock 9a is opened and the other cocks 9b and 9c are closed, the exhaust gas
16 flows only through the capillary 10a, while the diluent gas flows through all the other capillaries 10b to 10j, the dilution ratio becomes 1/10, and the mixed gas line 7 receives 1/10 of the exhaust gas.
The dilution gas having the concentration of will flow. The surplus exhaust gas 16 and the dilution air 44 are discharged through the gas discharge port D.

Then, only the cock 9b is opened and the cock 9a,
When 9c is closed, the exhaust gas 16 flows through the capillaries 10a and 10b, and the diluent gas flows through the other capillaries 10c to 10j, so that the dilution ratio becomes 1/5. When only the cock 9c is opened and the cocks 9a and 9b are closed, the dilution ratio is 3/10.
Becomes

As described above, according to this embodiment, it is possible to set and switch the dilution ratio very easily by selectively opening the cock 9. As described above, when the exhaust gas 16 is diluted with the dilution air 44, it is necessary to dilute the exhaust gas 16 at a ratio that does not cause dew condensation, but since the ratio is determined by the components contained in the exhaust gas 16, the ratio should be changed. In such a case, setting and switching can be performed without the need for replacing the capillary itself, which is required in the conventional case.

The resistance values of the capillaries 10 in the dilution ratio setting switching unit DF may not be the same, and a plurality of capillaries having different resistance values may be arranged in an appropriate combination.
It goes without saying that the branch open line 5 having the cock 9 may be provided in an appropriate number corresponding to the arrangement of the capillaries 10.

In particular, in this embodiment, the pressure of the exhaust gas 16 and the air 44 introduced into each capillary 10 is adjusted by the back pressure regulator 8 provided in the atmosphere opening line 4 to a predetermined equal pressure in the pressure adjusting line 3 in advance. Since the back pressure regulator 59 provided in the gas flow path 15 connected to the atmosphere opening line 4 can suppress the pulsation of the pump 40 that introduces the exhaust gas 16,
The above dilution ratio could be maintained stably and accurately, and the reliability of the analyzer could be improved dramatically. The dilution operation is smoothly performed by adjusting the dilution ratio setting / switching unit DF to a predetermined temperature.

Next, the second unit 71 is constructed as shown in FIG. In the second unit 71, a gas switching supply unit 74 for switching and supplying gas to the analysis unit 73 provided in the third unit 72 described later is provided. The gas switching supply unit 74 is configured as follows. That is, the gas passage 76 connected to the mixed gas line 7 and provided with the solenoid valve 75 is connected to the terminal g of the gas passage 27 (see FIG. 5), and the filter 77 and the solenoid valve 78 are connected in series. The gas flow path 79 and the terminal h of the gas flow path 30 (see FIG. 5) are connected, the gas flow path 82 in which the needle valve 80 and the solenoid valve 81 are interposed in series, and the gas flow path 33 ( (See FIG. 5) terminal i is connected, and a gas flow path 86 in which a filter 83, a needle valve 84, and a solenoid valve 85 are serially interposed is used as a pressure sensor.
The upstream side of a control valve 88 that controls the pressure in the analysis unit 73 to a constant pressure based on the detection result of 87 is connected in parallel with each other, and the downstream side of the control valve 88 is the gas inlet of the third unit 72. It is connected to J. In addition,
Reference numerals K, L and M shown in FIG.
The starting ends of the gas flow paths 79, 82, 86 to which h and i (see FIG. 5) are connected are shown.

By the way, when FTIR is used for the analysis unit 73, since infrared rays are radiated to the analysis unit cell to obtain an absorption spectrum, only nitrogen or dilution air which does not contain a sample gas in advance is supplied to the cell. The absorption spectrum C is obtained by dividing the signal (power spectrum B) obtained when the actual exhaust gas (diluted) is introduced into the cell by the signal obtained by the introduction (power spectrum A).
Therefore, if the pressure of the cell when the power spectrum A is obtained is different from the pressure when the power spectrum B is obtained, a large amount of water and carbon dioxide originally contained in the dilution air are contained in the exhaust gas. The effect of the components that are present appears in the actual analysis. Therefore, it is necessary to control the pressure inside the analysis unit 73 to be constant.

As already explained, the exhaust gas 16 discharged from the engine 13 of the automobile 11 is diluted with the dilution air 18 in the gas flow path 27 (see FIG. 5) to obtain a constant flow rate dilution. The exhaust gas 26 is made to flow, and also
The gas flow path 30 is provided with a bag 31 for collecting a part of the constant flow rate diluted exhaust gas 26 and storing it.
Since the bag 34 for collecting a part of the dilution air 18 flowing in the air introduction pipe 20 and storing the bag 34 is provided in the gas flow path 33, the solenoid valves 75, 78, 81, 85 and needles are provided. By appropriately opening and closing the valves 80 and 84, the constant ratio diluted exhaust gas 69 (see FIG. 2) diluted at a constant ratio in the dilution ratio setting switching unit DF, the constant flow diluted exhaust gas 26 which flows continuously.
(Refer to FIG. 5), either the constant flow rate diluted exhaust gas 26 in the bag 31 or the dilution air 18 in the bag 34 can be selectively supplied to the analysis unit 73 and used for a desired analysis. You can

P (see FIG. 4) is an inlet for the pressurized gas (pressurized air in this embodiment) provided in the second unit 71, and a filter is provided in the gas passage 89 connected to the inlet P. 9
0, a regulator 91, a pressure gauge 92, and a pressure sensor 93 are connected in series, and the downstream side thereof is connected to the dilution gas lead-out port Q and also to the control section of the control valve 88. The dilution gas outlet Q is connected to the dilution gas inlet B of the first unit 37 via the gas flow path 94. In addition, R is a drain discharge port.

S is a gas discharge port provided in the second unit 71. A gas tank 95 connected to the gas discharge port S is provided with a buffer tank 96 and a needle valve 97 in series. On the downstream side of 97, a solenoid valve 98, a suction pump 99, a buffer tank 100, and a flow meter whose temperature is adjusted appropriately.
101 is connected in series and is connected to the sample gas discharge port T, the gas discharge flow path 102, the solenoid valve 103, and the filter 10.
4 and the vacuum pump 105 are connected in series, and the gas discharge passage 106 connected to the discharge port U is connected in parallel with each other.

The gas discharge flow path 102 is for discharging the sample gas and the like used for the analysis when the analysis section 73 performs a predetermined analysis, and the gas discharge flow path 106 is for the analysis. Used when cleaning the inside of the portion 73. The buffer tanks 96 and 100 prevent the pulsation effect of the suction pump 99 from being transmitted to the analysis unit 73 and the flow meter 101, respectively. Also a buffer tank
96 and 100 are connected to the drain discharge port R through gas flow paths 109 and 110, respectively, which are provided with ball valves 107 and 108, respectively.

[0036] In V ₁ ~V _N calibration gas inlet port provided in the second unit 71, the gas passage 111 communicating with the respective calibration gas inlets V ₁ ~V _N, solenoid valve 112 is provided At the same time, their downstream sides are joined together, and a regulator 115 and a stop valve 116 are connected in series in a gas flow path 114 that continues to the joining point 113, and
The downstream side of the stop valve 116 is connected to the upstream side of the control valve 88.

In the illustrated example, in the gas flow passage 111, which is connected to the calibration gas introduction port V ₁ , the gas flow passage 11 extends from the upstream side of the solenoid valve 112.
7 is branched, and a needle valve 118 and a flow meter 119 are installed in series in this gas flow path 117, and the downstream side of the flow meter 119 is connected to the gas inlet W of the third unit 72 and purged. Is configured to introduce nitrogen gas for. The temperature in the shaded area Y is adjusted to a predetermined temperature (for example, 113 ° C.). Also, reference numeral 12
Reference numeral 0 is a thermometer that measures the temperature of the analysis unit 73.

Thus, in the self-exhausting analyzer having the above structure, the gas switching supply unit 74 for switching and supplying gas is provided upstream of the third unit 72 provided with the analysis unit 73. Therefore, by appropriately opening or closing the solenoid valves 75, 78, 81, 85 and the needle valves 80, 84 in the gas switching supply unit 74, it is possible to perform the same analysis as the conventional device of this type. Of course, by opening only the solenoid valve 75 and closing other solenoid valves, etc.
Since the constant ratio diluted exhaust gas 69 can be continuously supplied to the 73, the component concentration in the constant ratio diluted exhaust gas 69 can be sequentially obtained. In this case, since the dilution ratio is constant, the exhaust gas 16 emitted from the engine 13 of the automobile 11 can be converted by taking this into consideration.
The instantaneous component and its concentration in can be measured sequentially and accurately. Also, the total amount can be obtained if necessary.

In the above-described embodiment, the control valve 88 is arranged on the upstream side of the analysis section 73, but instead of this, the downstream side of the analysis section 72, for example, the upstream side of the buffer tank 76 of the gas flow path 95. A vacuum regulator may be provided on the side. Further, the solenoid valve and the needle valve used in the above embodiments may be replaced with other valves having the same functions. Further, in the above-described embodiment, the dilution ratio setting / switching unit DF, the gas switching supply unit 74, and the analyzing unit 73 are provided in the separate units 37, 71, 72, but this is not the only configuration. Instead of this, for example, the dilution ratio setting / switching unit DF and the gas switching supply unit 74 may be provided in the same unit.
Further, the analysis unit 73 may be composed of an analyzer other than FTIR. Also, instead of the pressurized air introduced from the inlet P, pressurized nitrogen gas may be used.

[0040]

As described above, according to the present invention, the pressure of the pressure regulating line can be kept constant by the pressure regulating means provided in the atmosphere releasing line, and the pressure can be provided in the branch opening line branched from the pressure regulating line. By selectively opening the open / close valve, the sample gas or the dilution gas can be distributed and supplied at a desired ratio to the branch supply line branched from the pressure regulating line alternately with the branch open line. As a result, the sample gas can be always diluted to a stable dilution ratio by the action of the constant pressure reducing means provided in each branch supply line.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic concept of a dilution ratio switching device of a dilution sampling device according to the present invention.

FIG. 2 is a configuration diagram showing the overall configuration of an automobile exhaust gas analyzer using the dilution sampling device of the present invention.

FIG. 3 is a system diagram of a first unit including the same dilution ratio switching device.

FIG. 4 is a system diagram showing a configuration of the second unit and the third unit.

FIG. 5 is an overall configuration diagram of an apparatus for collecting exhaust gas of the vehicle.

[Explanation of symbols]

1 ... Sample gas line, 2 ... diluting gas line, 3 ... pressure adjusting line, 4 ... atmosphere opening line, 5 ... branch opening line,
6 ... Branch supply line, 7 ... Mixed gas line, 8 ... Pressure adjusting means, 9 ... Open / close valve, 10 ... Constant depressurizing means.

Claims (1)

[Claims] 1. A pressure control line connected to a sample gas line and a dilution gas line, a branch opening line connected to an atmosphere opening line, and a mixed gas of a sample gas and a dilution gas for feeding. Branch supply lines connected to the mixed gas line are alternately branched and connected, and the atmosphere opening line is provided with pressure adjusting means for keeping the pressure of the pressure adjusting line constant, and each branch opening line is opened and closed. A dilution ratio switching device of a dilution sampling device, wherein a valve is provided, and each branch supply line is provided with a constant pressure reducing means for keeping a gas flow rate constant.