JP3453932B2 - Pressure transducer - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure transducer, and more particularly to an improvement in a pressure transducer mounting structure which does not cause a measurement error due to stress at the time of screw-in mounting. FIG. 5 shows an example of a screw type pressure transducer. In the figure, a pressure introducing pipe 1 of a pressure transducer is fixed to a chamber wall 3 of a pressure chamber P in which a fluid to be measured is sealed. The pressure introducing pipe 1 is made of metal,
The parallel male screw portion 12 formed on the outer periphery is screwed and screwed into a parallel female screw portion 32 formed in the mounting hole 31 of the pressure chamber wall 3. The base end peripheral wall of the pressure introducing pipe 1 bulges inward and outward to form a thick portion 13, and at this portion, the outer peripheral surface rises with a right-angled step. The stepped surface 15 is in contact with the outer surface of the chamber wall 3. [0003] The base end of the pressure introducing pipe 1 is closed by a thin wall 11, which is a diaphragm which is deformed according to the applied pressure. A plurality of well-known strain gauges 2 constituting a bridge circuit are provided on the diaphragm 11, and the resistance of each strain gauge 2 changes according to the strain deformation (ie, stress) of the diaphragm 11. The output of the bridge circuit is sent to the electric circuit board 4 including the amplifier circuit. The amplified output signal is taken out of the housing 5 by a lead wire 6 extending from the inside of the housing 5. A ventilation pipe 52 is penetrated and buried in the substrate support 53, and the space above the diaphragm 11 communicates with the atmosphere from the ventilation pipe 52 through the ventilation groove 51 of the housing 5. In the above-mentioned mounting structure, a reaction force having the same magnitude as the axial force of the pressure introducing pipe 1 acts on the outer stepped surface 15 of the pipe 1 at the time of screwing connection (in FIG. Arrow), the reaction force generates a moment force as shown by the turning arrow in FIG. This moment force causes an initial distortion in the diaphragm 11 located close to the thick portion 13 and causes a measurement error as described below. FIG. 6 omits the structure of the electric circuit section. FIGS. 7 and 8 show output characteristics of the above-described conventional pressure transducer, in which loosening and tightening (screw-in) are repeated by tightening with a torque method. Since the tightening force usually has a variation of about ± 50%, this influences the diaphragm, and the offset particularly fluctuates by about ± 2% each time the tightening is repeated. In order to solve the above problem, various proposals have been made. For example, in the configuration shown in FIG. 9, a stress relief groove 16 having a predetermined depth is formed on the outer periphery of a pipe base thick portion 13. This prevents a moment force generated at a contact portion with the chamber wall from being transmitted to the diaphragm 11 (first conventional example). As another means for preventing the transmission of the moment force, as shown in FIG.
The mounting portion 7A also serving as the pressure introducing pipe 1 and the pressure converting portion 7B are separated (second conventional example), or, as shown in FIG. 17 is screwed and brought into contact with the surface of the chamber wall 3 (third conventional example). Further, Japanese Utility Model Laid-Open No. Hei 2-131639 discloses a configuration in which an attachment portion and a pressure conversion portion are separated via a cylindrical pedestal portion (fourth conventional example). There is also a type in which the moment force acts only locally. For example, as shown in FIG. 12, the mounting hole 31 of the pressure chamber wall 3 is stepped to have a small diameter, and the screwed pressure introducing pipe 1 is used as a tip. The moment force acts only at the insertion end of the pipe 1 by using a stop (fifth conventional example), or the pressure introduction pipe 1 is fixed to a tapered male thread as shown in FIG. 18, etc., so that the moment force acts only in the middle part of the pipe 1 (sixth conventional example). However, in the first and second prior arts, it is necessary to secure a space such as a groove for transmitting a moment force.
In the third conventional example as well, it is inevitable that the physical size of the pressure transducer becomes large, for example, it is necessary to secure a long male screw portion for screwing the lock nut. This is the same in the fourth conventional example, and in this case, there is a problem that the number of parts further increases. In the fifth conventional example, the size of the pressure transducer itself can be avoided, but there is a problem that the shape of the mounting hole in the chamber wall of the pressure chamber, which is usually the area on the user side, becomes complicated. Further, in the sixth conventional example, since the amount of screwing into the female screw is determined by the depth and ratio of the valleys and ridges of the screw, for which processing accuracy is difficult to obtain, the reproducibility of the screw tightening end position is a characteristic of the tapered screw. Worse, it is necessary to form an extra thread as a margin. Therefore, it takes time and effort for the manufacturing process, and the size of the pressure transducer also increases. Further, in each of the first to sixth conventional examples, the mounting structure is inevitably complicated. The present invention solves the problems in each of the above-mentioned prior art examples at a glance. The measurement error due to the stress at the time of screw-in installation is achieved by a simple and inexpensive structure without increasing the size and the number of parts. It is an object of the present invention to provide a pressure transducer in which generation of pressure is effectively prevented. According to a first aspect of the present invention, a thin diaphragm 11 is formed at a closed base end 13 of a pressure introducing pipe 1 so that the diaphragm 11 is subjected to deformation distortion. In the pressure transformer provided with the strain gage 2 for generating a corresponding output, a parallel female screw portion 32 of a mounting hole 31 provided in the chamber wall 3 of the pressure chamber P is provided on the outer periphery of the pressure introducing pipe 1.
And a taper surface 14 whose diameter gradually increases toward the base end 13 closer to the base end 13 of the pipe than the male screw part 12 is formed. While the pipe 1 is screwed into the mounting hole 31 by the male screw portion 12 and the female screw portion 32, the taper surface 14 is formed.
Are in pressure contact with the outdoor opening edge 311 of the mounting hole 31. In the first configuration, the pressure introducing pipe 1
The taper surface 14 on the outer periphery of the pipe 1 comes into pressure contact with the opening edge 311 of the mounting hole 31 at the time of screwing connection. Therefore, the reaction force against the axial force has an angle from the direction perpendicular to the taper surface 14 to the pressure introducing pipe 1. Act. Therefore, the moment force generated by the reaction force and the axial force is locally limited to the vicinity of the taper surface 14 forming portion of the pressure introducing pipe 1 and does not reach the diaphragm 11 at the base end 13. Thus, the pressure introduction pipe 1
No stress is generated in the diaphragm 11 due to the screwing of the diaphragm 11, and the occurrence of measurement error is prevented. In addition, the above table
Since the opening 14 penetrates into the mounting hole 31, the amount of projection of the pressure transducer from the pressure chamber wall 3 is suppressed, so that the installation space is reduced and the sealing performance of the pressure chamber P is also ensured. can do. Further, it is easily realized by a simple process of forming the taper surface 14 without increasing the number of parts. FIG. 1 shows an example of a screw type pressure transducer according to the present invention. The basic structure is the same as the already described conventional structure (see FIG. 5). That is, the pressure introducing pipe 1 of the pressure transducer is fixed to the chamber wall 3 of the pressure chamber P in which the fluid to be measured is sealed, and the parallel male screw portion 12 formed on the outer periphery of the pipe 1 is attached to the pressure chamber wall 3. It is formed in the hole 31, screwed into the parallel female screw part 32, and screwed and connected.
The base end peripheral wall of the pressure introducing pipe 1 bulges inward and outward and becomes thick, and the outer peripheral surface of the thick part 13 rises in two steps, one of which gradually extends toward the base end. The taper surface 14 has a large diameter. The tapered surface 14 is in contact with the outer opening edge 311 of the mounting hole 31. The opening edge 311 is chamfered in a shape along the taper surface 14. On the thin diaphragm 11 closing the base end of the pressure introducing pipe 1, a strain gauge constituting a bridge circuit is provided.
A plurality of ridges 2 are provided, and a bridge circuit output corresponding to the strain deformation (ie, stress) of the diaphragm 11 is obtained. This output is sent to an electric circuit board 4 including an amplifier circuit, and the amplified output signal is taken out by a lead wire 6 extending outside the housing 5. In the pressure transducer having the above structure, when the male thread portion 12 of the pressure introducing pipe 1 is screwed into the female thread portion 32 of the mounting hole 31, the pressure introducing pipe 1 is connected to the pressure introducing pipe 1 as shown by a thick arrow in FIG. Axial force and reaction force act. In this case, the reaction force is input from the direction perpendicular to the taper surface 14 as shown in the figure, and acts on the pressure introducing pipe 1 with an angle from the outside. Reference) It does not go to the base thick part 13 of the pipe 1. Therefore, the moment force generated by the axial force and the reaction force is locally limited to the vicinity of the taper surface 14 forming portion of the pressure introducing pipe 1 as shown by the turning arrow in the drawing. Thus, no stress is generated in the diaphragm 11 due to the screwing of the pressure introducing pipe 1, and the occurrence of measurement errors is prevented. FIGS. 3 and 4 show the effects of the present embodiment. Even when a repetitive tightening test similar to the conventional one is performed, both the change in the offset of the converter output and the change in sensitivity are small. In particular, the offset change is greatly improved to about ± 0.4% compared to the conventional about ± 2% (see FIG. 7). As described above, according to the pressure transducer of the present invention, the size of the pressure transducer can be increased by a simple and inexpensive structure in which a tapered surface is formed on the outer periphery of the pressure introducing pipe. It is possible to effectively prevent the occurrence of a pressure measurement error due to the screw connection without complicating the structure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall vertical sectional view of a pressure transducer mounted on a pressure chamber wall, showing one embodiment of the present invention. FIG. 2 is a schematic sectional view of a pressure transducer illustrating a force acting on the pressure transducer. FIG. 3 is a graph of an offset change amount showing an effect of the present invention. FIG. 4 is a graph of a sensitivity change amount showing an effect of the present invention. FIG. 5 is an overall vertical sectional view of a pressure transducer mounted on a pressure chamber wall, showing a conventional example. FIG. 6 is a schematic sectional view of a pressure transducer illustrating a force acting on the pressure transducer. FIG. 7 is a graph of an offset change amount in a conventional structure. FIG. 8 is a graph of a sensitivity change amount in a conventional structure. FIG. 9 is a schematic sectional view of a pressure transducer illustrating a conventional example and illustrating a force acting on the pressure transducer. FIG. 10 is a schematic cross-sectional view of a pressure transducer illustrating a conventional example and illustrating a force acting on the pressure transducer. FIG. 11 is a schematic sectional view of a pressure transducer illustrating a conventional example and illustrating a force acting on the pressure transducer. FIG. 12 is a schematic cross-sectional view of a pressure transducer illustrating a conventional example and illustrating a force acting on the pressure transducer. FIG. 13 is a schematic sectional view of a pressure transducer illustrating a conventional example and illustrating a force acting on the pressure transducer. [Description of Signs] 1 Pressure introduction pipe 11 Diaphragm 12 Parallel male screw portion 13 Pipe base end 14 Tapered surface 2 Strain gauge 3 Room wall 31 Mounting hole 311 Outdoor opening edge 32 Parallel female screw portion

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01L 19/00 101 G01L 9/04 101

Claims (1)

(57) [Claim 1] A pressure in which a thin diaphragm is formed at a closed base end of a pressure introducing pipe, and a strain gauge for generating an output corresponding to deformation strain is provided on the diaphragm. In the converter, a parallel male screw portion to be screwed into a parallel female screw portion of a mounting hole provided in a chamber wall of the pressure chamber is formed on an outer periphery of the pressure introducing pipe, and a pipe base end is larger than the male screw portion. A taper surface whose diameter gradually increases toward the proximal end is formed closer to the base end, and the pressure introducing pipe is screwed into the mounting hole by the male screw portion and the female screw portion, and the taper surface is formed on the outside of the mounting hole. A pressure transducer that comes into pressure contact with the opening edge.