JPH0215808B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a pressure measuring device using light.

Although pressure signal transmission devices using light beams have not been put to practical use so far, there are laboratory devices that convert pressure into displacement of a pressure-receiving element and measure the displacement using light beams.

FIG. 1 is a simple configuration diagram of a pressure measuring device using a Bourdon tube as a pressure receiving element. A pressure input section 2 of a Bourdon tube is connected to the pressure guiding hole 1 . One end of a C-shaped Bourdon tube 3 is connected to this pressure input section 2, and is configured to deform as shown by solid lines and dotted lines in response to the supplied pressure. A reflecting plate 4 is provided at the free end of the Bourdon tube 3 and is adapted to reflect light from a light source 5 onto a light receiving surface 6.

With this configuration, the Bourdon tube 3 deforms in response to changes in pressure, and the reflecting plate 4 at the tip of the Bourdon tube changes the direction of light reflection. As a result, the light on the light receiving surface 6 also changes positionally. Therefore, if the relationship between the position of the light on the light-receiving surface 6 and the magnitude of the pressure is determined in advance, the pressure can be measured from the position of the light.

Incidentally, in order to improve the linearity of the amount of movement of light on the light receiving surface 6 with respect to pressure, the amount of movement of the free end of the Bourdon tube 3 is generally made small. Therefore, it is necessary to increase the distance between the reflection plate 4 and the light-receiving surface 6, making it difficult to downsize the device.

Furthermore, when transmitting the amount of movement of the tip of the Bourdon tube 3 remotely, there is a drawback that it must be converted into a physical quantity suitable for remote transmission, such as an electric quantity.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and an object of the present invention is to provide a pressure measuring device that can be miniaturized, can accurately measure pressure, and can be transmitted remotely.

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

First, the basic principle of the present invention will be explained with reference to FIG. In the medium 7 with the delivered refractive index n, there is a refractive index n′,
A parallel plate 8 having a thickness h is provided. When monochromatic light L of wavelength λ ₀ is incident on this parallel plate 8 at an incident angle θ,
At surface a, the light is divided into reflected light with a reflection angle θ and transmitted light with a refraction angle θ'. The reflected light is converged by a condensing lens 9 and focused on a point P on the light receiving surface 10. On the other hand, the transmitted light is further divided into reflected light and transmitted light at surface b.
The transmitted light is refracted by the surface b, then converged by the condenser lens 11 and focused at a point Q on the light receiving surface 12. On the other hand, the reflected light is further divided into reflected light and transmitted light on the a-plane. The transmitted light is refracted by the surface a and then converged by the condenser lens 9 to a point P on the light receiving surface 10.
focus on. On the other hand, the reflected light is further divided into reflected light and transmitted light at the b-plane. Transmitted light is collected by condensing lens 1
1 and focuses on a point Q on the light receiving surface 12. The reflected light is further divided into reflected light and transmitted light on the a-plane. The following light processing process is similar to the process described above. As a result, as is clear from FIG. 2, since parallel light rays are incident on both the condenser lenses 9 and 11, interference fringes are generated at points P and Q. Due to the reflection at the surfaces a and b described above, a phase difference δ occurs in the reflected waves. The phase difference δ can be approximately expressed as δ=4π/λ ₀ n′hcosθ′.

Here, λ ₀ is the wavelength of the incident light beam, n' is the refractive index of the parallel plate 8, h is the thickness of the parallel plate 8, and θ' is the angle of the transmitted light with respect to the normal.

Therefore, when the phase difference δ is δ=2mπ, where m is an integer, the first transmitted light and the transmitted light due to reflection from the a-plane match in phase, so that the brightness at point Q becomes maximum. On the other hand, since the first reflected light and the transmitted light due to reflection from the b-plane differ in phase by π radians and have opposite phases, the brightness at point P becomes minimum. Also, when m is 1/2, 3/2, 5/2...
Since the phase relationship is exactly the opposite of the above, the brightness at point Q becomes minimum and the brightness at point P becomes maximum.

In particular, when the reflectance at surfaces a and b is close to 1, the intensity of transmitted light becomes extremely small outside the narrow maximum range. Therefore, the interference fringes at the point Q become thin, shining interference fringes in an almost completely dark background. On the other hand, the interference fringes at the point P due to the reflected light are almost uniform and become thin, shining interference fringes in a bright background.

Therefore, when interference fringes are created using a white light beam instead of a monochromatic light beam, the relationship between the maximum or minimum wavelength and the thickness h of the parallel plate 8 becomes δ=2mπ=4π/λn′hcosθ′. However, λ is the wavelength of the interference fringe. Therefore, by knowing the wavelength of the interference fringes, the thickness h can be determined from the relational expression: h=mλ/2n'cosθ'.

FIG. 3 is a sectional view simply showing the structure of the first embodiment of the present invention. Differential pressure detection unit 13 of this embodiment
A white light source 14 is provided at a location away from the camera. The white light from this light source 14 is transmitted through an optical fiber 15 to a parallel beam optic 16 which obtains parallel beams. The parallel light beam from the parallel light optical device 16 is incident on the differential pressure detection section 13. The differential pressure detection unit 13 has a reflective surface 1 on a surface facing the light incident surface.
A differential pressure chamber 23 is partitioned into a high pressure part 21 and a low pressure part 22 by a measuring diaphragm 20 having a transparent plate 18 provided with a transparent plate 7 and a reflecting plate 19 provided in the center to reflect light from the transparent plate 18. A high pressure chamber 25 applies high pressure to the high pressure section 21 of the differential pressure chamber 23 through the pressure guiding hole 24, and a low pressure chamber 27 applies low pressure to the low pressure section 22 of the differential pressure chamber 23 through the pressure guiding hole 26. It is configured. The high pressure chamber 25 and the low pressure chamber 27 are both partitioned into pressure input parts 30, 31 and enclosure parts 32, 33 by seal diaphragms 28, 29, and the enclosure parts 32, 33 are incompressible. A liquid 34 is enclosed. This incompressible liquid 3
4 is also connected to the differential pressure chamber 23 via the pressure guiding holes 24 and 26.
is enclosed in a high pressure part 21 and a low pressure part 22,
Pressure input parts 30 and 31 of high pressure chamber 25 and low pressure chamber 27
The pressure applied to is transmitted to the differential pressure chamber 23 by the incompressible liquid 34. The reflected light from the differential pressure detection unit 13 is collected by a condenser lens 35 and transmitted to a light receiver 37 via an optical fiber 36 whose one end is installed at the focal point of the condenser lens 35 . As described in the explanation of the principle of the present invention, the light receiver 37 detects the light receiving surface 3 based on the light emitted from the optical fiber 36.
8 to form interference fringes corresponding to the interference wavelength.

In such a configuration, when white light is emitted from the light source 14, the white light guided to the parallel beam optical device 16 by the optical fiber 15 becomes a parallel beam and enters the transparent plate 17 of the differential pressure detection section 13. . This incident light is separated into reflected light and transmitted light by the reflective surface 17 of the transparent plate 18, and the reflected light is focused by the condensing lens 35. On the other hand, the transmitted light is reflected by the reflector 1
9 and reaches the reflective surface 17. Then, on this reflective surface 17, the light is further divided into transmitted light and reflected light, and the transmitted light is condensed by a condensing lens 35. On the other hand, the reflected light is reflected by the reflecting plate 19 and reaches the reflecting surface 17 again.

Thereafter, reflection is repeated in the same way, and the light beam condensed by the condensing lens 35 is transmitted to the light receiver 37 by the optical fiber 36. It forms interference fringes with wavelengths that correspond to the distance between the two.

Therefore, when the input pressure of the high pressure chamber 25 and the low pressure chamber 27 changes, and the pressure of the pressure input parts 30 and 31 changes, this pressure change causes the seal diaphragm 2 to
8,29 fluctuate. This seal diaphragm 2
8 and 29 are caused by the high pressure part 21 of the differential pressure chamber 23 due to the incompressible liquid 34 filled in the sealed parts 31 and 32.
and is transmitted to the low pressure section. Depending on the resulting pressure difference between the high-pressure part 21 and the low-pressure part 22, the measuring diaphragm 20 moves upwards or downwards. In this measurement, since the diaphragm 20 is provided with a reflection plate 19, the reflection surface 19 is
The distance between the reflective surface 17 of the transparent plate 18 and the reflective surface 17 of the transparent plate 18 changes depending on the differential pressure. As a result, the light receiving surface 38
The wavelength that creates interference fringes changes. The wavelengths forming the interference fringes can be obtained in advance by analyzing the interference fringes. Therefore, if the relationship between the wavelength of the interference fringes obtained in this way and the differential pressure is obtained in advance, the differential pressure can be uniquely determined from the pattern of the interference fringes obtained on the light receiving surface 38. Can be done.

As explained above, in this embodiment, the optical interference phenomenon is used to convert the differential pressure into an optical signal, transmit it to a remote location via an optical fiber, and optically convert it back into pressure information at the remote location. This makes it possible to reduce the size of the device compared to conventional devices and to transmit pressure information remotely.

FIG. 4 is a sectional view simply showing the configuration of a second embodiment of the present invention. In the first embodiment, interference fringes based on reflected light were used, but in this embodiment, interference fringes based on transmitted light are used. Note that the same parts as in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

The differential pressure chamber 39 of the second embodiment has a lower surface with a reflecting surface 40.
The high pressure section 21 and the low pressure section 22 are separated by a measuring diaphragm 42 having a transparent plate 41 provided in the center. The center part of the top surface of the differential pressure chamber 39 is formed by a transparent plate 18 to allow light to enter, and the center part of the bottom surface is formed by a transparent plate 44 whose top surface is a reflective surface 43, which reflects and allows light to enter. It has become transparent. The light transmitted through the transparent plate 44 forming the lower surface of the differential pressure chamber 39 is collected by the condenser lens 35 and transmitted to the light receiver 37 by the optical fiber 36 .

With this configuration, the difference is that the reflected light of the first embodiment is replaced with transmitted light, and the other operations are the same. Therefore, the same effects as the first embodiment can be achieved.

FIG. 5 is a sectional view simply showing the configuration of a third embodiment of the present invention.

In differential pressure transmitters for high static pressure, the transparent plate is thick, so in order to obtain sharp interference fringes, extremely strict conditions are required for the parallelism of the light rays, that is, the absence of scattered light, and the parallelism between the transparent plate and the reflecting plate. required.
The third embodiment is suitable for such a case, in which an optical fiber, an optical device, etc. are placed in the sealed liquid. The same parts as in FIG. 1 are given the same reference numerals, and the explanation will be omitted. The differential pressure detection section 13 of this embodiment is partitioned into a high pressure section 48 and a low pressure section 49 by a measurement diaphragm 47 having a transparent plate 46 in the center with a surface 45 opposite to the light incident surface. The high pressure section 48 is further connected to a pressure input section 54 and an enclosure section 5 by a seal diaphragm 50.
It is divided into 2. The incompressible liquid 34 is sealed in the sealed portion 52 . Further, the enclosing part 52 includes a part of the optical fiber 15 that transmits the white light emitted from the light source 14, and a part of the optical fiber 15 that converts the light from the fiber 15 into parallel light beams and projects them onto the projection plate 46 of the measurement diaphragm 47. Lighting parallel ray optical device 1
6 is installed. On the other hand, the low pressure section 49 is further connected to the pressure input section 5 by a seal diaphragm 53.
4 and an enclosure section 55. Enclosure section 55
A transparent plate 56 is provided parallel to the transparent plate 46 of the measuring diaphragm 47 at a predetermined distance. Measuring diaphragm 47 of this transparent plate 56
The side surface forms a reflective surface 57. Furthermore, communication holes 58 are provided at both ends of the transparent plate 56, so that the incompressible liquid 34 filled in the enclosure 55 also fills the parallel gap between the measurement diaphragm 47 and the transparent plate 56. ing. Also, the enclosure part 5
The transparent plate 5 is placed on the side of the seal diaphragm 53 of 5.
A condensing lens 35 that condenses the transmitted light from 6 and a part of an optical fiber 36 that transmits the light from this lens 35 to a light receiver 37 at a remote location are installed.

With such a configuration, it is not necessary for the light beam to pass through a thick transparent plate unlike in the first and second embodiments, so that sharp interference fringes can be obtained. Other effects are similar to those of the first embodiment.

Note that the present invention is not limited to the first to third embodiments. For example, in the first to third embodiments, a white light source is used, but in this case, the number of interference fringes is extremely large, making it difficult to know the wavelength at which interference occurs. Therefore, if the wavelength range of the light source is limited as follows, it becomes easy to know the wavelength at which interference occurs. That is, when the distance h between the first to third reflecting surfaces changes from h ₀ to h ₀ +Δh, λmin and λmax are as follows: λmin=2π/2mπn′h ₀ cosθ′ λmax=2π/2mπn′(h ₀ +Δh )cosθ′, so the wavelength λ of the light source is λminλλmax
should be limited to. In addition, the ratio of λmin and λmax is calculated from the above two equations as follows: λmax/λmin=1+Δh/h ₀
It becomes a relationship.

It goes without saying that various other modifications can be made without departing from the gist of the present invention.

As explained above, the present invention obtains interference light by making parallel light rays incident on two reflective surfaces that are provided in parallel and facing each other with a predetermined distance apart, and whose facing distance changes according to the pressure difference. The interference light is focused by a condensing lens, then transmitted to a remote location via an optical fiber, and pressure is obtained based on the wavelength of the interference fringes formed on the receiving surface of this remote location, which was previously impossible to do. It is possible to provide a pressure measuring device that can accurately measure process pressure using a heated optical signal, can reliably measure pressure from a remote location, and can measure pressure without being influenced by various external factors.

[Brief explanation of drawings]

Fig. 1 is a simple configuration diagram of a conventional device, Fig. 2 is an explanatory diagram of the principle of the present invention, Fig. 3 is a simple sectional view showing the configuration of the first embodiment of the present invention, and Fig. 4 is a diagram of the present invention. FIG. 5 is a simple sectional view showing the structure of a second embodiment of the present invention, and FIG. 5 is a simple sectional view showing the structure of a third embodiment of the present invention. 14... Light source, 15... Optical fiber, 16... Parallel ray optic, 17... Reflective surface,
18... Transparent plate, 19... Reflection plate, 20... Measurement diaphragm, 23... Differential pressure chamber, 24... Pressure guiding hole, 25... High pressure chamber, 26... Pressure guiding hole, 27...
Low pressure hole, 28, 29...Seal diaphragm, 3
4... Incompressible sealed liquid, 35... Condensing lens,
36... Optical fiber, 37... Light receiver, 40... Reflective surface, 41... Transparent plate, 42...
Measuring diaphragm, 43...Reflecting surface, 44...Transparent plate, 45...Reflecting surface, 46...Transparent plate, 47...
...Measuring diaphragm, 56...Transparent plate, 57...
Reflective surface, 58...Communication hole.

Claims (1)

[Claims] 1. A parallel beam projector, a first reflecting plate fixedly disposed on the incident side of the parallel beams from the parallel beam projector, and facing parallel to the first reflecting plate at a predetermined distance. a second reflecting plate is attached to a member whose position changes according to a pressure difference, and the first and second reflecting plates change in accordance with a change in pressure upon receiving a parallel ray from the parallel ray projector; A pressure-to-light converter that obtains interference fringes with a wavelength that changes depending on the facing distance between the A pressure measuring device comprising pressure measuring means for receiving a signal through an optical fiber and measuring pressure based on the wavelength of interference fringes formed on the light receiving surface.