JP2846869B2 - Pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of various chemical fluids and highly corrosive acid / alkali fluids used in the production of semiconductors and liquid crystals, or to detect the pressure of fluids in the field of handling them. Pressure sensor.

[0002]

2. Description of the Related Art For example, chemicals used for semiconductor production and liquid crystals are used in various processes necessary for the production process. Particularly in etching and cleaning processes, highly corrosive strong acid or strongly alkaline chemicals or gases are used. Is used. on the other hand,
These fluids require high-purity fluids in order to improve the degree of integration of semiconductors, and their piping systems and equipment must be made of materials that are not affected or eluted by the fluids. Optimum ones are PTFE and PFA, but plastic has a problem of gas permeation.

[0003] As a pressure sensor for detecting a pressure in supplying or reacting a chemical used in semiconductor production or liquid crystal, there is a pressure sensor having a structure as shown in Figs. Hereinafter, these structures and problems will be described. FIG. 5 is an example of a structure in which the element for detecting pressure uses a semiconductor sensor. The body 51 that is in contact with the chemical is made of PTFE or PFA. It is covered with a film 53 of PTFE or PFA. A gasket 54 is provided for airtightness between the body 51 and the contact surface between the semiconductor sensor 52 and the sensor is made of high-level fluorine rubber.

FIG. 6 shows an example of a structure in which an element for detecting pressure uses a strain gauge 60. Similarly to the above-described example, a body 61 to be contacted with a chemical is made of PTFE or PFA. Is covered with a film 63 made of PTFE or PFA so that the chemical solution does not come into contact with the thin plate portion 62 on which the gasket 64 is attached. This is an example of a sensor.

The sensors used in FIGS. 5 and 6 differ in the method of switching the pressure to an electric signal, but can detect the pressure of the fluid as it is, so that it is very often used for a non-corrosive fluid. However, for use in corrosive fluids, it is necessary to protect the fluid with a corrosion-resistant soft material so that the fluid does not come into direct contact with the sensor unit. in use. In this case, in order to accurately transmit the pressure of the fluid to the sensor, the thickness is appropriately about 0.2 mm.

However, since PTFE and PFA have a property that gas permeates between molecules like other plastics, corrosive fluid penetrates through the film due to gas permeation, and the above-mentioned PTFE and PFA are used. 0.2m
In a sensor using a film having a thickness of m, when used as a corrosive fluid, there is a problem that the permeated fluid corrodes the sensor main body, lowering its function or damaging it.
The gas permeability of not only fluororesin but also plastic is greatly related to its thickness. For example, in the case of PTFE, as shown in FIG. 7, the gas permeability becomes lower as the thickness becomes larger. In order to suppress gas permeation, the thicker the film, the better. Therefore, in the conventional sensor, a method of increasing the thickness of the film is conceivable. However, if the thickness is increased to 0.5 mm, at which the transmittance is negligible, the sensitivity of the sensor is reduced and the practicality is lost. .2 mm was optimal.

[0007] Incidentally, the addition of reference to Figure 7, which was measured by water vapor moisture permeability as a measure of the gas permeability, moisture permeability ^g / m 2 / 24hrs on the vertical axis, as a film thickness of mm in the horizontal axis, PTFE The molding pressure is a parameter, and the moisture permeability decreases as the film thickness increases. Also, the molding pressure is 100 kgf / cm
^In the case of No. ² , the moisture permeability is considerably high, but this is because voids are formed due to insufficient molding pressure. Therefore, a normal molding pressure of 200 kgf / cm ² or more is adopted. Films and molded bodies are made under these conditions.

As described above, since PTFE and PFA have gas permeation, gas permeation occurs in the method of protecting the sensor with a film as shown in FIG. 4 and FIG. There is a problem that the sensor is accumulated in the minute gaps, which promotes the clearance corrosion of the sensor body and shortens the life of the sensor.

To solve the above problem, for example, FIG.
The bellows is used for the pressure transmitting part, and the liquid contact part including the bellows is made of a fluororesin (PTFE, PFA).
Etc.) and a pressure sensor that converts the propulsive force from the bellows into pressure by load conversion means.
Since there is a processing error in the resinous bellows, when a detection rod is provided to transmit the thrust of the bellows to the load converting means (load cell) by an external pressure type pressure sensor, the detection rod is integrated. In the conventional sensor having the configuration, there has been a problem that a gap is formed between the detection rod and the load cell, and a load is applied to the load cell from the time of assembly, so that the detection accuracy varies.

[0010]

According to the present invention, in order to solve the problem of the conventional pressure sensor shown in FIG. 4, the detection rod is divided into two parts in the axial direction. One part of the detection rod has the shape of a male screw and the other part has the shape of a female screw, and the screw part of the male screw and the female screw is screwed into each other, so that the distance between the load conversion means and the bellows in assembly is increased. It is an object of the present invention to provide a pressure sensor capable of adjusting the length of the detection rod according to the pressure.

[0011]

According to the present invention, there is provided a bellows for receiving a pressure of a fluid, and a load conversion means for transmitting a propulsive force of the bellows to convert a load into a pressure. Is a pressure sensor made of fluororesin, having a detection rod for transmitting the thrust of the bellows to the load converting means, wherein the detection rod is divided into two parts in the axial direction, and the divided detection part is One part of the rod is a male screw,
The other part has the shape of a female thread, and the detection rod has a configuration in which the male thread and the female thread are connected to each other by a thread part. A pressure sensor characterized in that the length of a rod can be adjusted.

In the pressure sensor of the present invention, it is preferable that a casing holding the bellows and the load converting means is provided in addition to the above configuration, and a ventilation hole is formed in the casing.

Further, in the pressure sensor of the present invention, the pressure scale is set with respect to the load scale so that the propulsive force of the bellows receiving the pressure of the fluid conforms to the scale of the output range of the load cell converted into the pressure. It is preferable that the effective diameter of the bellows, which is the working area of the propulsion force of the bellows, be adapted to the range of the load cell so that the values correspond to the integer values.

Furthermore, in the pressure sensor of the present invention, it is preferable that the thickness of the bellows is set to 0.4 mm or more.

[0015]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The drawings show a pressure sensor for detecting the fluid pressure of a high-purity chemical used in semiconductor manufacturing. FIG. 1 is a sectional view of a pressure sensor according to an embodiment of the present invention,
This pressure sensor 1 is made of PTFE (tetrafluoroethylene resin).
2 made of fluororesin such as PTFE or PFA (perfluoroalkoxy resin), bellows 3 made of PTFE, and inexpensive hard plastic such as polypropylene for fixing flange 3a of bellows 3 to body 2 side. A case 4 made of a material, a load cell 5 as a load converting means for converting the load into pressure by transmitting the propulsive force of the bellows 3, and a plastic material fixing the load cell 5 to the case 4. And a cap nut 6 provided.

The body 2 is integrally formed with a mounting boss 2b provided with a tapered screw portion 2a for screwing and fixing to a conduit for feeding a chemical solution, and a central portion in the axial direction of the body 2 is provided. An introduction port 7 for introducing the above-mentioned chemical solution to the outer peripheral side of the bellows 3 is formed.

The mounting flange 2 of the body 2 described above.
c, a screw portion 2d is formed on the upper outer periphery in the drawing, and the screw hole 2d is screwed into a screw hole 4a formed in a corresponding portion of the case 4, so that the body 2 and the case 4 The flange 3a of the bellows 3 described above is sandwiched and fixed between the opposed surfaces of the bellows 3.

Further, in this embodiment, in order to apply a fluid pressure to the outer peripheral portion of the bellows 3, a bellows-provided concave portion 2e communicating with the inlet 7 is formed in the upper portion of the body 2, and the bellows-provided concave portion 2e is formed in the bellows-provided concave portion 2e. The main part of the above-mentioned bellows 3 is arranged to be extendable and contractible. In addition, in order to ensure the positioning of the bellows 3, an annular positioning recess 2 f is formed at the upper end of the body 2 in the drawing (the end on the side opposite to the boss), while the lower surface of the flange 3 a of the bellows 3 is formed. The bellows 3 is positioned and held by integrally forming annular positioning projections 3b and fitting them in a concave and convex manner.

The above-described case 4 has a cylindrical load cell mounting recess 4b having an open top, and a screw hole 6a of a cap nut 6.
And a screw portion 4c screwed into the load cell 5 between the mounting seat 4d of the case 4 and the inner bottom portion 6b of the cap nut 6.
The case 4 is formed with a plurality of, for example, two ventilation holes 9 communicating the internal space 8 of the bellows 3 and the outside of the case 4.

Further, the entire bellows 3 as a liquid contact part and the body 2 are made of fluororesin. In addition, 5b in FIG. 1 is a sensor code derivation part, 5c is a sensor code which outputs an electric signal corresponding to pressure. As described above, the pressure sensor 1 shown in FIG. 1 is configured to receive the fluid pressure at the outer peripheral portion of the bellows 3 and transmit the propulsive force of the bellows 3 to the load cell 5 to convert the load into the pressure.
In addition, the bellows 3 and the body 2 as liquid contact parts are made of a fluororesin.

The pressure sensor 1 has a detection rod 10 for transmitting the propulsive force of the main part of the bellows 3 to the load cell 5 between the bellows 3 and the load cell 5.
The detection rod 10 is composed of two vertically divided parts, a part 10a having a male screw shape and a part 10b having a female screw shape, and one detection rod 10a and 10b are connected to each other by a screw part. 10. By moving the screw portions to each other, the length of the detection rod 10 can be freely adjusted. A concave portion (not shown) for positioning the lower end of the detection rod 10 in a positioning manner is formed in the disk portion 3c of the bellows 3, and the detection rod 10 is held in the concave portion. Is also good. Further, in the pressure sensor of the present invention, a fastener such as a hexagon nut may be provided on the detection rod as a stopper.

In the pressure sensor 1, the length of the detection rod 10 is adjusted as follows. FIG. 3 is a schematic cross-sectional view showing the correlation between the case 4 and the bellows before fixing the load cell of the pressure sensor of the present invention. Upper portion on the drawing of the case 4 in FIG. 3 from to the upper surface of the circular plate portion 3c of the bellows 3 depth (anti boss portion end of) as the H _2, also an upper end in the drawing of the case 4 of FIG. 3 from parts, the depth of the bottom surface of the cylindrical load cell disposition concave portion 4b load cell 5 in the case 4 is held as H _1, distance H ₃ of the load cell and bellows, represented by H ₃ = H ₂ -H ₁ It is. By actually measuring the H _1, H _2, to detect the H _3, so that the length H ₄ of the detection rod becomes H ₃ = H _4, and the two parts 10a constituting the detection rod 10 10
It may be adjusted by moving the threaded portion b.

Further, the effective diameter D of the above-mentioned bellows 3 is set to a predetermined dimension as follows for the purpose of adapting to the rated load F (load cell detection scale) measurement range of the load cell 5. That is, the effective diameter D of the bellows is set so that the propulsion load when the fluid pressure P acts on the bellows 3 in the direction of the arrow in FIG. 1 can output a load corresponding to the output of the load cell 5. As an example, the rated load F of the load cell 5
Is 5 kgf, and the fluid pressure P for this rated value is 5 kf.
Assuming that gf / cm ² , the effective diameter D of the bellows 3 is obtained by the following [Equation 1].

[0024]

(Equation 1)

The pressure sensitivity of the bellows 3 will be described. If the thickness of the bellows 3 is 0.5 mm and the minimum pressure reading unit is 0.1 kgf / cm ² , the displacement of the bellows 3 per crest is as follows. It is obtained by [Equation 2].

[0026]

(Equation 2)

Therefore, if the number of peaks of the bellows 3 is set to 4,
(0.005cm = 0.05mm) × 4 × 2 = 0.4m
Thus, the load of the bellows 3 can be transmitted to the load cell 5. As described above, when the bellows 3 receives the fluid pressure of the high-purity chemical solution used for semiconductor manufacturing from the direction of the arrow in FIG. 1, the bellows 3 expands and contracts in accordance with the fluid pressure. The load is transmitted to the load cell 5 via the detection rod 10, and the load is converted into pressure by the load cell 5.

In addition, the liquid contact part (see bellows 3 and body 2) including the above-mentioned bellows 3 is made of fluororesin and the thickness of the bellows 3 can be set sufficiently large. There is an effect that gas permeation can be prevented and corrosion of the load cell 5 can be reliably prevented. Further, there is an effect that a minute change in fluid pressure can be detected satisfactorily by the elasticity of the bellows 3 described above.

Further, since the ventilation holes 9, 9 are formed in the case 4 for holding the bellows 3 and the load cell 5, the pressure due to the volume change of the bellows 3 is balanced by the ventilation holes 9, 9. As a result, there is an effect that the pressure detection system can be improved. In addition, since the thickness of the bellows 3 is set to 0.5 mm or more, there is an effect that gas permeation of the chemical solution can be suppressed to a minimum.

Even if a very small amount of gas, which does not induce metal corrosion, permeates through the PTFE molecules constituting the bellows 3 due to the setting of the thickness of the bellows 3 and the formation of the ventilation holes 9, Since the minute leakage gas can be discharged from the vent hole 9 to the outside of the case 4, the gas does not fill the portion where the load cell 5 is disposed, and there is an effect that the service life can be further improved. .

Further, in the pressure sensor 1 shown in FIG.
Since the fluid pressure acts on the outer periphery of the bellows 3, the bellows diameter does not change due to this pressure.
Since there is no pressure fluctuation (pressure fluctuation due to a change in bellows diameter) that presses the load cell 5 via the detection rod 10, it is possible to satisfactorily cope with a subtle fluid change.

As a test example, the pressure sensor 1 of the embodiment was used to measure the display pressure with respect to the reference pressure based on the difference between the distance between the load cell and the bellows and the length of the detection rod. Table 1 shows the measurement results of the indicated pressure. Test Example 1: When there is a gap between the distance between the load cell and the bellows and the length of the detection rod (gap is a positive value) Test Example 2: When the distance between the load cell and the bellows is equal to the length of the detection rod (when the gap is Test Examples 3 and 4: When the detection rod is too long with respect to the distance between the load cell and the bellows, and there is an initial load from the beginning (gap is a negative value). Further, as a comparative example, the detection rod shown in FIG. Are measured with respect to a reference pressure by using a conventional sensor having an integrated configuration (Comparative Examples 1 and 2). Table 1 also shows the measurement results of the displayed pressure.

[0033]

[Table 1] Difference in displayed pressure with respect to reference pressure due to difference in distance between load cell and bellows and length of detection rod

As can be seen from the results of Test Examples 1 to 4, when there is a gap, the pressure is displayed low, and when the detection rod is too long, a high pressure is displayed even when the reference pressure is zero. Also, from the sum of the absolute values of [reference pressure−display pressure], the first embodiment
It can be seen that the error is smallest when the gap is adjusted to 0.0 mm. Further, in the case of a conventional sensor in which the detection rod is integrated, even if the gap is set to 0.0 mm, the display pressure is lower than the reference pressure, and the sum of the absolute value of [reference pressure-display pressure] is obtained. That is, the error is larger than that of the sensor of the first embodiment. Therefore, it can be seen that in order to increase the detection accuracy, it is necessary to adjust the length of the detection rod for each sensor to make the gap zero.

In correspondence between the configuration of the present invention and the above-described embodiment, the load converting means of the present invention corresponds to the load cell 5 of the embodiment, and similarly, the liquid contact portion is connected to the body 2 and the bellows 3. Correspondingly, the casing corresponds to the case 4, but the present invention is not limited to the configuration of the above-described embodiment.

According to the pressure sensor of the present invention, when the bellows receives the pressure of the fluid, the bellows expands and contracts in accordance with the fluid pressure, so that the thrust of the bellows is transmitted to the load converting means. The load is converted into pressure by the load conversion means. The pressure sensor of the present invention has a detection rod for transmitting the propulsive force of the main part of the bellows to the load conversion means (load cell). The detection rod is divided into two parts in the axial direction, and One part of the detected detection rod has the shape of a male screw and the other part has the shape of a female screw, and the male screw and the female screw are screwed to each other by a screw part and combined to form an assembly. In the above, the distance between the load conversion means and the bellows is measured, and the length of the detection rod can be adjusted according to the distance. That is, the depth of the detection rod mounting portion after the bellows is assembled to the body and the casing always varies, but the detection rod divided into two parts is screwed in so that the gap does not appear due to the variation. The load cell can be assembled by adjusting the detection rod to a length suitable for the length, and the detection accuracy can be increased.

Further, since the liquid contact part including the above-mentioned bellows is made of a fluororesin (PTFE, PFA, etc.) and the thickness of the bellows can be set sufficiently thick, the bellows prevents the permeation of the chemical gas. Thus, there is an effect that the corrosion of the load conversion means including the load cell and the like can be reliably prevented.

Further, there is an effect that a minute change in fluid pressure can be detected well due to the elasticity of the bellows.

According to the present invention, in addition, by forming a ventilation hole in the casing holding the bellows and the load converting means, even a small amount of permeated gas passing between the bellows thicknesses is collected at the sensor site. Since there is no sensor, there is no need to worry about corrosion of the sensor part, and the long life of the sensor can be achieved.

According to the present invention, the load is measured by changing the pressure of the fluid to the thrust of the bellows by adjusting the effective diameter of the bellows to the range of the load cell so as to conform to the detection scale of the load cell. Since the pressure is converted and read, the pressure conversion based on the measurement of the propulsive force from the fluid pressure becomes easy, and the detection scale of the load cell can be applied without any special calculation.

According to the present invention, the thickness of the above bellows is set at 0.4.
By setting it to be at least mm, there is an effect that gas permeation of the chemical solution can be suppressed to a minimum.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a pressure sensor of the present invention.

FIG. 2 is a sectional view showing another pressure sensor of the present invention.

3 is a schematic cross-sectional view showing a correlation between a case 4 and a bellows of the pressure sensor of FIG. 1 and a front view showing an example of a shape of a detection rod.

FIG. 4 is a sectional view showing an example of a conventional pressure sensor.

FIG. 5 is a cross-sectional view illustrating an example of a conventional pressure sensor.

FIG. 6 is a sectional view showing an example of a conventional pressure sensor.

FIG. 7 is an explanatory diagram showing moisture permeability data of PTFE.

[Description of Signs] 1 Pressure sensor 2 Body (Wetted part) 3 Bellows (Wetted part) 4 Case 5 Load cell (Load conversion means) 6 Bag nut 7 Inlet 8 Bellows internal space 9 Vent hole 10 Detection rod

Claims (4)

(57) [Claims] 1. A bellows receiving a pressure of a fluid, and a load converting means for transmitting a propulsive force of the bellows to convert a load into a pressure, wherein a liquid contact part including the bellows is made of a fluororesin. A sensor for transmitting the thrust of the bellows to the load converting means, wherein the detection rod is divided into two parts in the axial direction, and one part of the two divided detection rods is a male screw. And the other part has the shape of a female screw. The detection rod has a configuration in which the male screw and the female screw are connected to each other by a screw portion, and is adapted to the distance between the load conversion means and the bellows in assembly. Wherein the length of the detection rod can be adjusted. 2. The pressure sensor according to claim 1, wherein a casing is provided for holding said bellows and said load converting means, and a ventilation hole is formed in said casing. 3. The pressure scale of the bellows, which receives the pressure of the fluid, matches the scale of the load with an integer value so that the scale of the pressure matches the scale of the output range of the load cell converted into the pressure. 3. The pressure sensor according to claim 1, wherein the effective diameter of the bellows, which is the area of action of the thrust of the bellows, is adapted to the range of the load cell. 4. The pressure sensor according to claim 1, wherein the thickness of the bellows is set to 0.4 mm or more.