JP2007271431A - Pressure measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure-measuring device that enables stable measurement of pressure over a long term, at low cost. <P>SOLUTION: The pressure-measuring device for measuring gas containing corrosive gas is provided with a dilution means, between a pressure gauge and a gas containing the corrosive gas for making the corrosive ingredient of corrosive gas reduced. The pressure loss in the dilution means is 10% or lower of the absolute value of pressure measured by the pressure-measuring device. The dilution means makes absorbent pass through, or to allow an inert gas to flow, immediately in front of the pressure-measuring device. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for measuring the pressure of a gas containing a corrosive gas, and enables measurement of a stable pressure at a low cost for a long period of time.

In the manufacturing process of various products, it is necessary to measure the pressure of gas containing corrosive gas. A typical example is a manufacturing process of an optical fiber preform.
Various methods for manufacturing an optical fiber preform have been proposed and developed. As an example, there are the following manufacturing methods.
First, a porous base material including a core is manufactured by a VAD (Vapor-phase axial deposition) method, and this is dehydrated and sintered using an electric furnace to prepare a core rod. A porous layer is further formed on the outer periphery of the obtained core rod by OVD (Outside Vapor Deposition), followed by further dehydration and sintering to produce an optical fiber preform.

The manufacturing process of the optical fiber preform by the VAD method and the OVD method includes, for example, depositing fine glass particles (SiO ₂ ) generated by the reaction of the following formula (1) on a starting material to form a porous preform or a porous layer. The reaction vessel is filled with corrosive chlorine-based gas.
SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl (1)
Further, in the above-described dehydration / sintering process, since dehydration is performed in a chlorine gas atmosphere, the reaction vessel is filled with a corrosive gas.

  On the other hand, in these production processes, pressure monitoring or control is indispensable in order to stably produce products. For example, Patent Document 1 discloses a VAD method for measuring the pressure in a reaction vessel, A pressure adjusting device is disclosed in which the pressure adjusting member is moved based on the measurement result so that the pressure in the reaction vessel is always constant. In Patent Document 2, the pressure in the reaction vessel is measured by the OVD method, and the porous base material is adjusted while changing the pressure in the reaction vessel by adjusting the exhaust amount from the exhaust duct based on the measurement result. A method of manufacturing an optical fiber preform to be manufactured is disclosed. Patent Document 3 discloses a dehydration and sintering apparatus that suppresses pressure fluctuation in the core tube by connecting a pressure fluctuation absorption container to the core tube.

Japanese Utility Model Publication No. 06-012441 JP 2003-073138 A Japanese Patent Laid-Open No. 06-127964

  Various types of corrosive gas pressure measuring devices have been developed and sold, but they are very expensive and it is difficult to measure accurately for a long time due to the influence of corrosive gases. There was a problem.

  An object of the present invention is to provide a pressure measurement device that enables low-cost and stable pressure measurement over a long period of time.

  In order to achieve the above object, a pressure measuring device according to claim 1 of the present invention is a device for measuring the pressure of a gas containing a corrosive gas, wherein the corrosive gas is interposed between a pressure gauge and the gas containing the corrosive gas. It has the dilution means which reduces the corrosive component of this.

  The pressure measuring device according to claim 2 of the present invention is the pressure measuring device according to claim 1, wherein the pressure loss in the diluting means is 10% or less of the pressure measured by the pressure measuring device. Features.

  The pressure measuring device according to claim 3 of the present invention is the pressure measuring device according to claim 1 or 2, characterized in that the diluting means allows an absorbent to pass through.

  The pressure measuring device according to claim 4 of the present invention is the pressure measuring device according to claim 1 or 2, characterized in that the diluting means flows an inert gas upstream of the pressure gauge. .

  As described above, according to the pressure measuring device of the present invention, it is possible to realize a pressure measuring device capable of measuring pressure stably for a long time at low cost.

Hereinafter, the pressure measuring device of the present invention will be described in detail with reference to the drawings.
[Embodiment 1]
First, as Embodiment 1 of the present invention, an example in which the pressure measuring device of the present invention is applied to the pressure measurement in the reaction vessel of the VAD device 100 shown in FIG. 1 will be described.
The VAD device 100 includes a reaction vessel 12, an exhaust cylinder 17 that discharges used gas in the reaction vessel 12 to an exhaust gas treatment device (not shown), a pressure gauge 18 that measures the pressure in the reaction vessel 12, and an exhaust cylinder 17. It has the installed pressure control device 19, the core burner 4 that forms the porous base material 8, and the cladding burner 6.
Clean air is supplied from the upper part of the reaction vessel 12, and the pressure in the reaction vessel 12 is changed by changing the balance between the supply amount of clean air and the amount of used gas exhausted by the exhaust cylinder 17. Let In this embodiment, the pressure in the reaction vessel 12 is controlled by adjusting the amount of used gas exhausted from the exhaust cylinder 17 by the pressure controller 19 based on the pressure measured by the pressure gauge 18. To do.

The porous base material 8 is produced by spraying the glass fine particles formed by the flame hydrolysis reaction in the core burner 4 and the clad burner 6 toward the target rod. At this time, corrosive chlorine-based gas is generated in the reaction vessel 12 by the reaction of the above-described equation (1).
Between the reaction vessel 12 and the pressure gauge 18, a container containing an absorbent is installed as the diluting means 10 for reducing the corrosive components of the corrosive gas. The pressure gauge 18 is connected to the reaction vessel via the diluting means 10. The pressure in 12 is measured. In the present embodiment, activated carbon is used as the absorbent, but other materials may be used as long as they can absorb corrosive components.

  By installing the dilution means 10 for reducing the corrosive component of the corrosive gas between the reaction vessel 12 and the pressure gauge 18 as described above, the existing apparatus can be used as it is, and a stable pressure measurement can be easily performed for a long period of time. A possible pressure measuring device can be realized.

[Embodiment 2]
Next, as Embodiment 2 of the present invention, an example in which the pressure measuring device of the present invention is applied to the pressure measurement in the reaction vessel of the dehydrating and sintering apparatus 200 shown in FIG. 2 will be described.
The dehydration and sintering apparatus 200 includes a reaction vessel 22 made of quartz glass that contains a porous base material 8 to be dehydrated and sintered, a heater 23 that heats the porous base material 8 from the outside of the reaction vessel 22, and the reaction. A furnace body 25 that covers the outer periphery of the container 22 and accommodates the heater 23 via a heat insulating material 24 is provided.

The reaction vessel 22 is made of a quartz core tube, and an inert gas such as helium gas and halogen such as chlorine are required in the reaction vessel 22 from a gas supply port 26 provided in the lower portion thereof. The dehydrated gas contained is supplied. On the other hand, an exhaust port 27 for discharging used gas to an exhaust gas treatment device (not shown) is provided at the upper part of the reaction vessel 22.
On the other hand, a predetermined amount of inert gas such as nitrogen is supplied into the furnace body 25 from a gas supply port (not shown) so as to keep the pressure in the furnace body 25 higher than the external pressure. This is to prevent the heater 23 from being corroded or consumed due to moisture contained in the outside air.

Further, the dehydration sintering apparatus 200 is provided with a pressure gauge 28 for measuring the pressure difference in the reaction vessel (core tube) 22 and the pressure in the furnace body 25, and a pressure control device 29 installed at the rear stage of the exhaust port 27. It has been.
In general, the pressure in the reaction vessel 22 is kept slightly higher than the pressure in the furnace body 25 in order to prevent the outside air from being mixed into the reaction vessel 22 and to prevent the reaction vessel 22 from being deformed. Meanwhile, dehydration sintering is performed. That is, dehydration sintering is performed in the state of external pressure <pressure in the furnace body 25 <pressure in the reaction vessel 22.
In the present embodiment, the used gas exhausted from the exhaust port 27 by the pressure control device 29 based on the pressure difference between the pressure in the furnace body 25 measured by the pressure gauge 28 and the pressure in the reaction vessel 22. By adjusting the amount, the pressure in the reaction vessel 22 is controlled.

  Further, a container containing an absorbent is installed between the reaction vessel 22 and the pressure gauge 28 as the dilution means 20 for reducing the corrosive components of the corrosive gas. The pressure gauge 28 is connected via the dilution means 20. The pressure in the reaction vessel 22 is measured. In the present embodiment, activated carbon is used as the absorbent, but other materials may be used as long as they can absorb corrosive components.

  Thus, by installing the dilution means 20 for reducing the corrosive component of the corrosive gas between the reaction vessel 22 and the pressure gauge 28, the existing apparatus can be used as it is, and a stable pressure measurement can be easily performed for a long period of time. A possible pressure measuring device can be realized.

Hereinafter, the pressure measuring device of the present invention will be described in more detail using examples.
[Example 1]
In the VAD device 110 shown in FIG. 3, the pressure loss of the diluting means 10 was variously changed to manufacture a porous base material.
The VAD device shown in FIG. 3 is the same device as the VAD device 100 shown in FIG. 1, and as a pressure gauge, the pressure gauge 18 a that measures the pressure via the diluting means 10 and the pressure is measured without going through the diluting means 10. The difference is that a pressure gauge 18b is installed.
As pressure gauges 18a and 18b, EJ110 manufactured by Yokogawa Electric was used.

The pressure in the reaction vessel 12 was controlled based on the pressure measured by the pressure gauge 18a. The pressure gauge 18b is used to examine the difference in pressure measured by the pressure gauge 18a and the pressure gauge 18b at the start of manufacture of each condition, that is, the pressure loss of the diluting means 10, otherwise the pressure gauge 18b and the exhaust pipe 17 The valve 11 installed during the period was closed to leave it unused.
Under the conditions 1-1 to 6 in which the pressure in the reaction vessel 12 was set to −50 Pa with respect to atmospheric pressure and the pressure loss of the absorbent was varied between 0 to 20 Pa, the porous base material 8 was Manufactured. The pressure loss can be adjusted by changing the amount and particle size of the absorbent. The results are shown in Table 1.

In Table 1, the pressure loss is obtained from the difference in pressure measured by the pressure gauge 18a and the pressure gauge 18b at the start of production under each condition. The formation rate is the formation rate of the porous base material 8 and is a value calculated by the number of accepted products / number of products produced × 100. In addition, what was able to complete manufacture of the porous preform | base_material 8 normally was set as the pass. The pressure fluctuation σ indicates the standard deviation of numerical values obtained by collecting pressure data at intervals of 0.1 seconds during the production of one porous base material. Hereinafter, the pressure fluctuation σ in this specification will be used in this sense. The period until failure indicates the period from when the pressure gauge 18a is used until failure occurs.
Condition 1-1 is that the absorbent is not placed in the container of the diluting means 10, that is, the same state as when the diluting means 10 is not installed. Conditions 1-2 to 6 are absorptions of the diluting means 10 This is a case where the pressure loss of the agent is changed.
In addition, since the defect rate increased under conditions 1-5 and 1-6, the production was interrupted in one month, but if the production is continued, it is estimated that the period until failure will be six months or more.

As shown in Table 1, there is a large difference in the period until the pressure gauge 18a fails in the condition 1-1 and the condition 1-2 in which the dilution means 10 is not installed. The lifetime of 18a could be greatly extended. In addition, this result is a result at the time of not performing replacement | exchange of an absorbent, By exchanging an absorbent regularly (within conditions 1-2 within 2 months, within 1-3 months within 6 months), Furthermore, the lifetime of the pressure gauge 18a can be extended.
However, in the conditions 1-2 and 1-3, the pressure fluctuation σ was 2 Pa, which is the same as the condition 1-1 in which the diluting means 10 is not installed, whereas in the conditions 1-4 to 6, the pressure fluctuation σ There is an increase.
If the absolute value of the set pressure is 50 Pa and the pressure loss of the absorbent is 5 Pa or less, that is, 10% or less of the set pressure, the pressure fluctuation σ equivalent to the case where the diluting means 10 is not installed can be maintained. When it becomes larger, the pressure fluctuation σ tends to increase. Along with this, the defect rate has also increased.

[Example 2]
The VAD device 120 shown in FIG. 4 is the same device as the VAD device 110 shown in FIG. 3, and instead of the container containing the absorbent as the diluting means 10b, nitrogen as an inert gas is added immediately before the pressure gauge 18a. The difference is that it flows through MFC (mass flow controller). The pipe diameter of the pipe 52 connecting the reaction vessel 12 and the pressure gauge 18a was 1/4 inch. In the VAD apparatus 120 shown in FIG. 4, the porous base material was manufactured by changing the flow rate of nitrogen flowing just before the pressure gauge 18a in various ways.

The pressure in the reaction vessel 12 was controlled based on the pressure measured by the pressure gauge 18a. The pressure gauge 18b is used for examining the difference in pressure measured by the pressure gauge 18a and the pressure gauge 18b at the start of manufacture of each condition, that is, the pressure loss of the diluting means 10b. In other cases, the pressure gauge 18b and the exhaust pipe 17 are used. The valve 11 installed during the period was closed to leave it unused.
The porous base material 8 was manufactured under conditions 2-1 to 6 in which the pressure in the reaction vessel 12 was set to −50 Pa with respect to atmospheric pressure and the flow rate of nitrogen was variously changed between 0 to 10 SLM. . The results are shown in Table 2.

The definition of each item in Table 2 is the same as that in Table 1. Further, the condition 2-1 is the same state as the case where nitrogen is not flowed from the MFC, that is, the diluting means 10b is not installed.
In addition, since the defect rate increased in Condition 2-5 and Condition 2-6, the production was interrupted in one month, but if the production is continued, it is estimated that the period until failure will be six months or more.
As shown in Table 2, there is a large difference in the period until the pressure gauge 18a breaks down between the condition 2-1 and the condition 2-2 in which the diluting means 10b is not installed, and the pressure gauge only by installing the diluting means 10b. The lifetime of 18a could be greatly extended.

However, in conditions 2-2 to 4, the pressure fluctuation σ was 2 Pa, which is the same as in condition 2-1 where the diluting means 10b is not installed, whereas in conditions 2-5 and 2-6, the pressure fluctuation σ There is an increase.
If the absolute value of the set pressure is 50 Pa or less and the pressure loss caused by flowing an inert gas is 5 Pa or less, that is, 10% or less of the set pressure, the pressure fluctuation σ can be maintained equivalent to the case where the diluting means 10b is not installed. When the pressure loss becomes larger than that, the pressure fluctuation σ tends to increase. Along with this, the defect rate has also increased.
In the present embodiment, the pipe diameter of the pipe 52 is set to 1/4 inch. However, when the pipe diameter is doubled, the flow rate of the inert gas is increased four times, which is the same as the present embodiment. An effect is obtained.

[Example 3]
In the dehydration and sintering apparatus 210 shown in FIG. 5, the pressure loss of the diluting means 20 was variously changed, and the porous base material was dehydrated and sintered to produce a glass rod.
The dehydration sintering apparatus shown in FIG. 5 is the same apparatus as the dehydration sintering apparatus 200 shown in FIG. 1, and does not go through the pressure gauge 28 a that measures the pressure via the dilution means 20 and the dilution means 20 as a pressure gauge. The difference is that a pressure gauge 28b for measuring pressure is installed.
As the pressure gauges 28a and 28b, EJ110 manufactured by Yokogawa Electric was used.

The pressure in the reaction vessel 22 was controlled based on the pressure measured by the pressure gauge 28a. The pressure gauge 28b is used to examine the difference in pressure measured by the pressure gauge 28a and the pressure gauge 28b at the start of manufacture of each condition, that is, the pressure loss of the diluting means 20, and otherwise, the pressure gauge 28b and the exhaust port 27 are used. The valve 21 installed during the period was closed to leave it unused.
Condition 3 in which the pressure difference between the furnace body 25 and the atmosphere is set to 50 Pa, the pressure difference between the reaction vessel 22 and the furnace body 25 is set to 300 Pa, and the pressure loss of the absorbent is variously changed between 0 to 100 Pa. In -1 to 7, the porous base material 8 was dehydrated and sintered to produce a glass rod. The pressure loss can be adjusted by changing the amount and particle size of the absorbent. The results are shown in Table 3.

In Table 3, the pressure loss is obtained from the difference in pressure measured by the pressure gauge 28a and the pressure gauge 28b at the start of production under each condition. Further, the pressure fluctuation σ indicates the standard deviation of the numerical value obtained by collecting pressure data at intervals of 0.1 seconds during the dehydration sintering of one porous base material. The period until failure indicates the period until the pressure gauge 28a breaks down from the start of use.
Condition 3-1 is the same as when no absorbent is placed in the container of the dilution means 20, that is, the dilution means 20 is not installed. Conditions 3-2 to 7 are absorptions of the dilution means 20. This is a case where the pressure loss of the agent is changed.
In addition, in conditions 3-6 and 3-7, since the pressure fluctuation σ increased, the production was suspended in one month. However, if the production is continued, it is estimated that the period until failure will be 6 months or more. .

As shown in Table 3, there is a large difference in the period until the pressure gauge 28a breaks down between the condition 3-1 and the condition 3-2 in which the dilution means 20 is not installed. The life of 28a could be greatly extended. In addition, this result is a result at the time of not performing replacement | exchange of an absorbent, By exchanging an absorbent regularly (within conditions 3-2 within two months, 3-3-7 within six months), Furthermore, the lifetime of the pressure gauge 28a can be extended.
However, the pressure fluctuation σ in the conditions 3-2 to 5 was 2 Pa, which is the same as the condition 1 in which the diluting means 20 is not installed. Be looked at.
If the absolute value of the set pressure is 300 Pa and the pressure loss of the absorbent is 30 Pa or less, that is, 10% or less of the set pressure, the pressure fluctuation σ equivalent to the case where the diluting means 10 is not installed can be maintained. When it becomes larger, the pressure fluctuation σ tends to increase.

  In order to investigate the relationship between pressure loss and pressure controllability in more detail, the pressure difference between the furnace body 25 and the atmosphere is fixed to 50 Pa, and the set pressure difference between the reaction vessel 22 and the furnace body 25 is set to 50 Pa to 50 Pa. The pressure fluctuation σ was examined by changing 500 Pa and the pressure loss between 2 and 100 Pa, respectively. The results are shown in Table 4.

In Table 4, “◯” indicates that the pressure fluctuation σ is 3 Pa or less, which is equivalent to that when the dilution means 20 is not installed, “Δ” is greater than 3 Pa and less than 5 Pa, “×” is greater than 5 Pa, and “−” is not measured. Means that.
As shown in Table 4, if the pressure loss is 10% or less of the absolute value of the pressure measured by the pressure gauge 28a, the pressure fluctuation σ will not be deteriorated even if the dilution means 20 is installed.

[Example 4]
A dehydration and sintering apparatus 220 shown in FIG. 6 is the same apparatus as the dehydration and sintering apparatus 210 shown in FIG. 5, and an inert gas is used immediately before the pressure gauge 28a instead of the container containing the absorbent as the diluting means 20b. The difference is that nitrogen, which flows through the MFC, is passed. The pipe diameter of the pipe 62 connecting the reaction vessel 22 and the pressure gauge 28a was ¼ inch. In the dehydration and sintering apparatus 220 shown in FIG. 6, the flow rate of nitrogen flowing immediately before the pressure gauge 28a was variously changed, and the porous base material was dehydrated and sintered to produce a glass rod.

The pressure in the reaction vessel 22 was controlled based on the pressure measured by the pressure gauge 28a. The pressure gauge 28b is used to examine the difference in pressure measured by the pressure gauge 28a and the pressure gauge 28b at the start of manufacture of each condition, that is, the pressure loss of the diluting means 20, and otherwise, the pressure gauge 28b and the exhaust port 27 are used. The valve 21 installed during the period was closed to leave it unused.
Conditions 4-1 in which the pressure difference between the furnace body 25 and the atmosphere is 50 Pa, the set pressure difference between the reaction vessel 22 and the furnace body 25 is 300 Pa, and the flow rate of nitrogen is variously changed between 0 and 10 SLM. 7, the porous base material 8 was dehydrated and sintered to produce a glass rod. The results are shown in Table 5.

The definition of each item in Table 5 is the same as that in Table 3. Condition 4-1 is the same as in the case where nitrogen is not flowed, that is, the dilution means 20b is not installed.
As shown in Table 5, nitrogen is not flowed immediately before the pressure gauge 28a, that is, the condition 4-1 and the condition 4-2 in which the diluting means 20 is not installed is large in the period until the pressure gauge 28a breaks down. There was a difference, and the life of the pressure gauge 28a could be greatly extended simply by installing the diluting means 20b.
However, in conditions 4-2 to 5, the pressure fluctuation σ was 2 to 3 Pa, which is about the same as in condition 1 in which the diluting means 20 is not installed, whereas in conditions 4-6 and 4-7, the pressure fluctuation There is an increase in σ.
If the absolute value of the set pressure is 300 Pa or less and the pressure loss caused by flowing an inert gas is 30 Pa or less, that is, 10% or less of the set pressure, the pressure fluctuation σ equivalent to the case where the diluting means 20b is not installed can be maintained. When the pressure loss becomes larger than that, the pressure fluctuation σ tends to increase.

  In order to investigate the relationship between the pressure loss and the controllability of the pressure in more detail, the set pressure difference between the reaction vessel 22 and the furnace body 25 is set to 50 Pa while the pressure difference between the furnace body 25 and the atmosphere is fixed at 50 Pa. The pressure fluctuation σ was examined by changing the pressure loss between ˜500 Pa and the pressure loss between 2 and 100 Pa (nitrogen flow rate 2 to 10 SLM). The results are shown in Table 6.

In Table 6, “◯” indicates a pressure fluctuation σ of 3 Pa or less equivalent to that when the diluting means 20b is not installed, “Δ” indicates a value greater than 3 Pa and less than 5 Pa, “x” indicates a value greater than 5 Pa, and “−” does not measure. Means that.
As shown in Table 6, if the pressure loss is 10% or less of the absolute value of the pressure measured by the pressure gauge 28a, the pressure fluctuation σ will not be deteriorated even if the dilution means 20b is installed.

As an embodiment of the present invention, an example in which the pressure measuring device of the present invention is applied to a VAD device and a dehydration sintering device has been shown. However, the pressure measuring device of the present invention is not an OVD device or an optical fiber manufacturing device. It can also be suitably used for pressure measurement of gas containing corrosive gas.
Moreover, the pressure measuring device of this invention is used especially suitably when the pressure to measure is -1 kPa or more and 1 kPa or less.

It is a schematic diagram which shows an example which applied the pressure measuring apparatus of this invention to the VAD apparatus. It is a schematic diagram which shows an example which applied the pressure measuring apparatus of this invention to the dehydration sintering apparatus. It is a schematic diagram which shows another example which applied the pressure measuring apparatus of this invention to the VAD apparatus. It is a schematic diagram which shows another example which applied the pressure measuring apparatus of this invention to the VAD apparatus. It is a schematic diagram which shows another example which applied the pressure measuring apparatus of this invention to the dehydration sintering apparatus. It is a schematic diagram which shows another example which applied the pressure measuring apparatus of this invention to the dehydration sintering apparatus.

Explanation of symbols

8 Porous base material 10, 10b Dilution means 11 Valve 12 Reaction vessel 17 Exhaust cylinder 18, 18a, 18b Pressure gauge 19 Pressure control device 20, 20b Dilution means 21 Valve 22 Reaction vessel 25 Furnace body 26 Gas supply port 27 Exhaust port 28 , 28a, 28b Pressure gauge 29 Pressure control device

Claims (4)

In an apparatus for measuring the pressure of gas containing corrosive gas,
A pressure measuring apparatus comprising a diluting means for reducing a corrosive component of the corrosive gas between the pressure gauge and the gas containing the corrosive gas.   The pressure measuring device according to claim 1, wherein the pressure loss in the diluting means is 10% or less of the absolute value of the pressure measured by the pressure measuring device.   The pressure measuring device according to claim 1, wherein the diluting unit is configured to pass an absorbent.   The pressure measuring apparatus according to claim 1 or 2, wherein the diluting means is a flow of an inert gas upstream of a pressure gauge.

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