JPH0463407B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a gas flow rate measurement and control device that measures and controls the flow rate of gas supplied into a vacuum container. The present invention relates to a gas flow rate measurement and control device in which the gas flow rate is controlled by a flow rate regulating valve.

[Technical background of the invention and its problems]

Fig. 1 shows a conventional gas flow rate measurement and control device of this type, and Fig. 2 shows a conventional device that automatically measures and controls gas flow rate. In both figures, reference numeral 1 indicates a gas supply (not shown). This is a pipe for supplying gas from a source to the vacuum container 2. Between the downstream end of this piping 1 and the vacuum vessel 2, there is provided a mass flowmeter measuring head 3 for measuring the flow rate of gas, a flow rate control valve 4 for controlling the gas flow rate, and a flow rate control valve 4 between the measuring head 3 and the flow rate. A pipe 5 connecting the control valve 4 and a pipe 6 connecting the flow control valve 4 and the vacuum vessel 2 are arranged in series. Also, inside the probe 3, there is a sensor tube 7 for measuring the mass flow rate of the internal fluid, as shown in FIG.
and a branch pipe 8 for adjusting the flow rate measurement range by the sensor tube 7 are connected to each other in parallel.

In addition to the above configuration, the automatic device shown in FIG. It is designed to be controlled by a control device 11. The vacuum vessel 2 also includes a turbo molecular pump 12, an oil rotary pump 13, and a vacuum gauge 1, as shown in FIG.
4 are provided respectively.

Thus, the mass flow rate of the gas flowing through the pipe 1 from a gas supply source (not shown) is measured as it flows through the sensor tube 7 in the probe 3. The gas flowing through the sensor tube 7 and the branch pipe 8 flows into the vacuum container 2 with its flow rate adjusted by the flow rate control valve 4.

Here, in the case of the manual device shown in FIG. 1, the opening degree of the flow rate control valve 4 is adjusted by the sensor tube 7.
carried out manually based on measurements taken at
In addition, in the case of the automatic device shown in Fig. 2, the indicator 1
This is automatically performed by the flow rate control device 11 based on the instruction value of 0.

That is, the measurement value measured by the sensor tube 7 of the probe 3 is converted into a flow rate value by the indicator 10, and is sent to the flow rate control device 11.
Here, a comparison calculation is made with a preset flow rate value.

As a result, if it is determined that the measured flow rate value indicated by the probe 3 is smaller than the set flow rate value of the flow rate control device 11, the flow rate of the flow rate control valve 4 is increased so that the measured flow rate value and the set flow rate value are equal. The drive device 9 is operated so that the Conversely, if it is determined that the measured flow rate value is larger than the set flow rate value, the flow rate control valve 4
The drive device 9 is operated to reduce the flow rate.

By the way, in the manual and automatic conventional devices having the above configuration, when attempting to control the flow rate value of the gas introduced into the vacuum container 2 to a constant value, serious problems as described below arise.

In other words, it is practically impossible to reduce the volume between the probe 3 and the flow control valve 4 to zero because the pipe 5 exists between them, and therefore gas remains inside the pipe 5. It is thought that this is the case.

For convenience of explanation, if it is assumed that the flow rate value measured by the probe 3 is smaller than the set flow rate value of the flow rate control device 11, the flow rate control valve 4 will be manually or automatically controlled to increase the flow rate. Become.

However, since there is residual gas in the pipe 5 as described above, there is a time delay in detecting an increase in the flow rate with the probe 3, and when the set flow rate value and the measured flow rate value become equal, , the flow rate control valve 4 adjusts the flow rate to a state slightly increased from the set value. Therefore, in the next stage, the measured flow rate value becomes larger than the set flow rate value, and the flow rate control valve 4 is manually or automatically controlled to decrease the flow rate.

However, as mentioned above, gas always remains in the pipe 5, so when the measured flow rate value and the set flow rate value become equal due to this adjustment control,
This means that the flow rate has already been reduced a little too much.
The flow rate control valve 4 is again controlled to increase the flow rate.

However, in the conventional device, the above operation is repeated, and the gas flow rate actually introduced into the vacuum container 2 oscillates around the set flow rate value as shown in Fig. 3, and this phenomenon causes the gas flow rate to change. The variation may be approximately 10% between the minimum and maximum flow rates.
There was also a large difference in the magnitude. Furthermore, since the flow rate cannot be controlled to be constant, there is a serious drawback that it is very difficult to control the pressure inside the vacuum container 2.

[Purpose of the invention]

The present invention was made in view of the current situation, and an object of the present invention is to provide a gas flow rate measurement and control device that can constantly control gas supplied into a vacuum container with high reliability and high precision.

[Summary of the invention]

The present invention is a gas flow rate measurement and control device in which a mass flow meter for measuring the gas flow rate and a flow rate adjustment valve for controlling the gas flow rate are respectively provided in piping for supplying gas to a vacuum container, and the device includes a flow rate adjustment valve for controlling the gas flow rate. The present invention is characterized in that the valve is disposed on the inlet side of a mass flowmeter that measures the gas flow rate, and a sensor tube having no branch pipe is provided at the measuring head of the mass flowmeter.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 shows an example of a gas flow rate measurement and control device according to the present invention. In the figure, 1 is a pipe for supplying gas from a gas supply source (not shown) to the vacuum container 2. As shown in FIG. 4, between the downstream end of the piping 1 and the vacuum vessel 2, there is a flow rate control valve 4 for controlling the gas flow rate, a mass flow meter probe 3 for measuring the gas flow rate, and the flow rate control valve 4 for controlling the gas flow rate. Valve 4 and probe 3
A piping 15 connecting the measuring element 3 and the vacuum vessel 2, and a piping 16 connecting the measuring element 3 and the vacuum vessel 2 are arranged in series. This device differs from the conventional manual device shown in FIG. (see Figure 1) is not provided at all, only the sensor tube 7 is provided, and furthermore, the piping 16 between the probe 3 and the vacuum vessel 2 is filled with gas that may cause a large fluctuation in the internal pressure. The configuration is such that there is no gas flow restriction device that restricts the flow of gas.

Next, the operation of this embodiment will be explained.

The gas flowing from a gas supply source (not shown) through the piping 1 first has its flow rate controlled by the upstream flow rate control valve 4, and then flows through the sensor tube 7 of the probe 3 and its mass flow rate is measured. be done. Thereafter, the opening degree of the flow rate regulating valve 4 supplied into the vacuum container 2 is manually adjusted based on the measured value from the sensor tube 7.

However, by configuring as above,
It is possible to reduce the accumulated gas in the piping 15 between the flow rate control valve 4 and the probe 3 to a point where it can be practically ignored, and the change in the pressure area of the probe 3 can reduce the amount of gas remaining in the branch pipe and sensor tube. It is no longer necessary to take into account the gas division of the sensor tube 7, and it has been found that the sensor tube 7 maintains sufficient accuracy even in low pressure areas, so it provides a device with excellent flow rate accuracy and good flow control characteristics. It becomes possible to do so.

These will be explained in detail below.

First, as shown in Figs. 5 and 6, the accumulated gas between the flow control valve 4 and the probe 3 is significantly reduced.
This will be explained with reference to the figures.

Figure 5 shows the pressure distribution in the piping when the length of the piping is taken in the direction of gas flow in the conventional device shown in Figure 1.The left side of point A on the horizontal axis is from the gas supply source. Piping 1, between A and B is the inside of the probe 3, between B and C is the piping 5 between the probe 3 and the flow rate control valve 4, and point C is the flow rate control part of the flow rate control valve 4, C and D The line between them indicates the piping 6 between the flow rate control valve 4 and the vacuum vessel 2, the area to the right of point D indicates the position inside the vacuum vessel 2, and the vertical axis indicates the pressure at each position on the horizontal axis.

The internal pressure of the pipe 1 from the gas supply source depends on the desired gas flow rate, but is generally 668 Pa, for example.
It is often selected to be around 1 MPa or 1 MPa, and for the sake of explanation here, 100 KPa will be used. On the other hand, inside the vacuum container 2
It is often at a low pressure of 10 ^-2 Pa or less, and for the sake of explanation here, it is assumed to be 10 ^-3 Pa.

However, the pressure inside the pipe ranges from 100KPa to 10 ^-3 Pa.
However, it can be seen that most of this pressure change, ie, pressure loss, occurs in the flow rate adjustment section C of the flow rate adjustment valve 4, as shown in FIG. Therefore, the gas pressure inside the pipe 5 between the probe 3 and the flow control valve 4 is almost
It is safe to assume that it is 100KPa.

FIG. 6 shows the pressure distribution inside the pipe when the length of the pipe is taken in the direction of gas flow in the apparatus according to the present invention shown in FIG. Piping 1 from the supply source, point C is the flow control part of the flow control valve 4, between CA and A is the pipe 15 between the flow control valve 4 and the probe 3, and between B and D is the probe 3 and the vacuum vessel. 2, the right side of point D indicates the position inside the vacuum vessel 2, and the vertical axis indicates the pressure at each position on the horizontal axis. Moreover, the pressure inside the piping 1 and inside the vacuum container 2 is
This is the same as that explained in FIG. 5 above.

However, in the device according to the present invention, as shown in FIG. 6, almost all of the pressure loss from 100 KPa to 10 ^-3 Pa occurs in the flow rate regulating portion C of the flow rate regulating valve 4, as shown in the conventional device. I understand.
Therefore, it is safe to assume that the gas pressure inside the pipe 15 between the flow rate control valve 4 and the probe 3 is approximately 10 ^-3 Pa.

By the way, if the pressure of the gas is P, the volume is V, the number of moles is n, the gas constant is R, and the temperature is T, the following relationship holds between them: PV=nRT...(1), so n= (PV)/(RT) ...(2). That is, if the volume V and the temperature T are constant, the amount of gas is proportional to the pressure P.

Now, assuming that the internal volumes and temperatures of the pipes 1 and 15 are constant between the conventional device shown in FIG. 1 and the device according to the present invention shown in FIG.
The pressure ratio of 5 is (Pressure of the conventional device)/(Pressure of the device according to the present invention) = (1×10 ⁵ )/(10 ⁻³ )=10 ⁸ ...(3), and the pressure ratio of the device according to the present invention is It is confirmed that in this case, the amount of retained gas is reduced to 1/100 millionth, and the retained gas between the flow rate control valve 4 and the probe 3 can be significantly reduced.

Next, with reference to FIGS. 7 to 9, it will be explained how the accuracy of the gas mass flow rate measured using the sensor tube 7 of the probe 3 is maintained as in the prior art.

FIG. 7 schematically shows the sensor tube 7 of the mass flow meter. In the figure, 21 is a heat sink on the upstream side of the sensor tube 7, 22 is a heat sink on the downstream side, and 23 is a constant amount of heat applied to both the heat sinks 21 and 22. The power supply device to be supplied, F is the midpoint indicating the center position on the sensor tube 7, and 24 and 25 are the sensor tubes 7 provided symmetrically with respect to the midpoint F.
temperature detection element 26, both temperature detection elements 24, 2
5 is a measuring device for measuring the temperature difference of the sensor tube 7 detected by the sensor tube 7, and 27 indicates a gas inlet and 28 indicates a gas outlet of the sensor tube 7.

In the above configuration, a gas with a specific heat Cp flows at a mass flow rate M into the sensor tube 7 which is currently injected with a constant heat input H and maintained at a constant temperature distribution, and as a result, the sensor tube 7 has a temperature of ΔT. Suppose a temperature difference occurs. And the amount of heat carried away from the sensor tube 7 by the gas flowing through the sensor tube 7,
Assuming that the amount of heat supplied from the power supply device 23 to the sensor tube 7 is equal, the relationship Cp・M・ΔT=H (4) holds true. Therefore, the mass flow rate M is expressed as: M=H/(Cp·ΔT) (5).

For example, a gas with specific heat Cp = 0.17 cal/g°C flows through the sensor tube 7, resulting in a temperature difference △T = 10°C, and at this time, the external heat input H to the sensor tube 7 is H = 17 cal/min. Assuming that,
The mass flow rate M at this time is M = 17 [cal/min]/(0.17 [cal/g°C] × 10 [°C]) = 10 [g/min] (6).

FIG. 8 shows the temperature distribution in the length direction of the sensor tube 7 when gas flows through the sensor tube 7, corresponding to FIG. 7. On the horizontal axis, the left side is the gas inflow side and the right side is the gas inflow side On the outflow side, F indicates the midpoint of the sensor tube 7, and the vertical axis indicates the temperature of the sensor tube 7 corresponding to each position on the horizontal axis. Further, a curve A in the figure represents the temperature distribution of the sensor tube 7 when there is no gas flow, and the shape is symmetrical to the left and right with respect to the midpoint F. Curve B is a temperature distribution when gas flows into the sensor tube 7 from the inlet 27 and flows out from the outlet 28, and has a shape that is biased toward the gas outflow side with respect to the midpoint F.

By the way, the change in the specific heat Cp of a gas gradually increases as the pressure rises from around 1 atm.
Conversely, when the pressure decreases from around 1 atm, the specific heat
Applicant's experiments have ensured that Cp is kept constant.

Figure 9 shows this. Hydrogen gas H, air
For each gas, AIR and argon gas Ar, the horizontal axis shows the gas pressure [atmospheric pressure], and the vertical axis shows the change in specific heat Cp [%]
It is expressed as . As is clear from Figure 9, the specific heat Cp of each gas H, AIR, and Ar gradually increases as the pressure increases from around 1 atm, but as the pressure decreases from around 1 atm, the specific heat Cp of each gas H, AIR, and Ar increases gradually.
It can be seen that Cp is kept constant. This is thought to be because when the pressure of a gas decreases, its properties approach those of an ideal gas, and therefore the specific heat Cp approaches that of an ideal gas.

Therefore, the sensor tube of a mass flow meter conventionally used in a high pressure region can maintain the same accuracy even in a low pressure region. Therefore, the present invention can be used in a low pressure region. It is confirmed that the accuracy of the mass flow rate of the gas to be measured is maintained in the same way as in the conventional case in the sensor tube 7 of the measuring head 3 according to the present invention.

Next, it will be explained that by providing the sensor tube 7 having no branch pipe inside the measuring element 3, there is no fluctuation in accuracy even if the pressure inside the measuring element 3 changes.

In the conventional device shown in FIG. 1, a branch pipe 8 is arranged in parallel with the sensor tube 7 inside the probe 3. Therefore, to maintain constant measurement accuracy,
It is necessary to always keep the division ratio of the gas flow between the sensor tube 7 and the branch pipe 8 constant. However, this flow division ratio generally differs depending on the pressure region inside the probe 3, and it is difficult to maintain measurement accuracy constant.

That is, taking air at 20°C as an example, in general, the ratio of the conductance of a circular conduit in an intermediate pressure region is C ₁ between the conductance and diameter [cm] of the first conduit and the second conduit. , D ₁ and C ₂ , D ₂ , C ₁ /C ₂ = (D ₁ /D ₂ ) ³・{1+271(D ₁ ) +4790(D ₁ ) ² }・ {1+316(D ₂ )}/ {1+271( _D2 )+4790( _D2 ) ² }・{1+316( _D1 )}...(7) However: It can be expressed as the average pressure in the conduit [Torr].

Now, the conductance of sensor tube 7 is
C ₁ , its diameter D ₁ is 3 mm, the conductance of the branch pipe 8 is C ₂ , its diameter D ₂ is 6 mm, and the average pressure of each conduit is 1 Torr, (C ₁ /C ₂ ) _P=1Tprr =0.541 ...(8) becomes. Similarly, if only the average pressure is changed to 0.5Torr, (C ₁ /C ₂ ) _P=0.5Tprr =0.576...(9). Therefore, (C ₁ /C ₂ ) _{P=1Tprr/C(C1/C2)} =0.5Torr=0.94
...(10) Therefore, the split flow ratio between the sensor tube 7 and the branch pipe 8 when =1 Torr is different from the split flow ratio when =0.5 Torr.

However, the conventional measuring head 3, in which the branch pipe 8 is connected in parallel to the sensor tube 7, cannot maintain a constant measurement accuracy when the pressure region changes significantly, as explained in FIGS. 5 and 6. It is impossible to hold the

On the other hand, a sensor tube 7 that does not have a branch pipe like the measuring head 3 according to the present invention shown in FIG.
In the case of , the gas flow rate measurement accuracy does not change at all due to changes in the gas division ratio due to pressure changes.
Even if the pressure inside the probe 3 changes, the accuracy does not change at all.

Therefore, by adopting the device configuration as shown in FIG. 4, it is possible to significantly reduce the amount of accumulated gas between the flow control valve 4 and the probe 3 while maintaining the same gas flow rate measurement accuracy as before. Furthermore, even if the pressure region changes, the measurement accuracy can always be kept constant. As a result, the flow rate controlled by the flow rate control valve 4 can be measured accurately without any time delay, and the mass flow rate of the gas introduced into the vacuum container 2 can be
It becomes possible to perform stable and accurate measurement control.

FIG. 10 shows another embodiment of the present invention,
Unlike the previous embodiment, this embodiment automatically controls the measurement of the gas flow rate.

That is, between the downstream end of the pipe 1 through which gas flows from a gas supply source (not shown) and the vacuum container 2,
As shown in FIG. 10, a flow rate control valve 4 that controls the gas flow rate, a mass flow meter measuring head 3 that measures the gas flow rate, a pipe 15 that connects the flow rate control valve 4 and the gauge head 3, and the measuring head 3 and the vacuum vessel 2 are arranged in series.

Further, as shown in FIG. 10, a turbo molecular pump 12, an oil rotary pump 13, and a vacuum gauge 14 are connected to the vacuum container 2, respectively.

The flow rate control valve 4 is also provided with a drive device 9 as shown in FIG. It is designed to be driven and controlled via a flow rate control device 11. That is, it is controlled in the same way as the conventional automatic device shown in FIG.

However, even with this configuration, since the basic configuration is the same as that shown in FIG. 4, the same effects as in the previous embodiment can be expected.

〔Effect of the invention〕

As explained above, in the present invention, the flow rate control valve is disposed on the inlet side of the mass flowmeter, and the sensor tube without a branch pipe is provided in the measurement head of the mass flowmeter, so that the gas introduced into the vacuum container is Flow rate can be measured and controlled with high accuracy and stability.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional manual device, Fig. 2 is a block diagram showing a conventional automatic device, Fig. 3 is a graph showing that the gas flow rate oscillates around the set flow rate in the conventional device, and Fig. 4 is a configuration diagram showing an example of a manual gas flow rate measuring device according to the present invention, and FIG. 5 is a graph showing pressure distribution in piping in a conventional device.
Fig. 6 is a graph showing the pressure distribution inside the piping in the device shown in Fig. 4, Fig. 7 is a schematic diagram of the sensor tube of the mass flowmeter, and Fig. 8 shows the temperature distribution of the sensor tube corresponding to Fig. 7. Figure 9 is a graph showing the relationship between gas pressure and specific heat, Figure 10 is a graph showing the relationship between gas pressure and specific heat.
The figure is a configuration diagram showing an example of an automatically controllable gas flow rate measuring device according to the present invention. 1, 15, 16... Piping, 2... Vacuum container, 3
... Measuring head, 4 ... Flow control valve, 7 ... Sensor tube, 9 ... Drive device, 10 ... Indicator, 11
...Flow control device.

Claims (1)

[Claims] 1. In a gas flow rate measurement and control device in which a mass flow meter that measures the gas flow rate and a flow rate adjustment valve that controls the gas flow rate are installed in piping that supplies gas to a vacuum container, the flow rate adjustment valve is connected to the inlet side of the mass flow meter. and a sensor tube without a branch pipe is provided in the measuring head of the mass flow meter, and furthermore, an upstream heat sink that applies a certain amount of heat to the tube wall of the sensor tube on the upstream and downstream sides of the sensor tube, respectively. and a downstream heat sink, and a pair of temperature detection elements for detecting the temperature of the wall of the sensor tube at positions symmetrical with respect to the center position of the sensor tube.