JPS6070328A - Pressure measuring device - Google Patents

Abstract

PURPOSE:To improve accuracy, by bonding the sealed end of a diaphragm to the upper surface of a photoelastic element, and bonding the other open end of the diaphragm to a case, which is sealed in an airtight manner. CONSTITUTION:The bottom of a diaphragm is bonded to the pressure receiving surface of a photoelastic element 5. A case 11 of a pressure sensor part is strictly sealed in an airtight manner so the internal pressure always becomes one atm. In this case, the sealed end of the diaphragm 6 is bonded to the upper surface of the photoelastic element 5, and the other open end of the diaphragm is bonded to the case, which is sealed in the airtight manner. In this constitution, the pressure is efficiently applied to the photoelastic element and high accuracy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a pressure measuring device in a bad electromagnetic environment.

[Prior art]

A conventional device of this type is shown in FIG. In the figure, (1) is an optical transmitter, H (2b) is an optical fiber, (8a) and (8b) are gradient index lenses, (4) is a polarizer, (6) is a photoelastic element, (6) is the diaphragm, (
7) is a 7-wave plate, (8) is an analyzer, and (9) is an optical receiver.

Next, the operation will be explained. Light from an optical transmitter (1) is guided to a sensor section via an optical fiber (2a).

In the sensor section, this light is collimated by a gradient index lens (8a), then made into linearly polarized light by a polarizer (4), and passed through a photoelastic element (5), a 1-wavelength plate (7), and an analyzer (8). ,
Optical fiber (2b) again with gradient index lens (8b)
and guide it to the optical receiver (9). Polarizer (4)
The optical axis of the photoelastic element (5) and the stress application axis of the photoelastic element (5) form an angle of 45 degrees, and the optical axes of the polarizer (4) and the analyzer (8) are perpendicular to each other. The 7-wave plate (7) is for providing optical bias. The photoelastic element (5) is made of an amorphous material such as glass or epoxy resin. This photoelastic element is optically isotropic in the stress-free state, but when stress is applied, it exhibits so-called birefringence, in which the refractive index differs in the direction of stress application and in the direction perpendicular to it due to the photoelastic effect. present. Therefore, the linearly polarized light incident upon stress application becomes elliptical light on the exit side. This elliptically polarized light is transferred to a 7-wavelength plate (
7), convert it into a light intensity signal with an analyzer (8), and transmit it to an optical receiver (
9) to convert it into an electrical signal. Since the magnitude of this electrical signal and the applied stress are approximately proportional to each other, by monitoring the electrical signal, the stress, that is, the pressure, applied to the photoelastic element (5) can be determined. Stress on the photoelastic element (5) is applied through the diaphragm (6).

Conventional pressure measurement devices are configured as described above, but have the disadvantage that fluctuations in the optical power propagating through the optical fiber due to bending of the optical fiber or changes in the coupling efficiency between the light source and the optical fiber can lead to measurement errors. . Further, although pressure is applied as stress through the diaphragm, there is also a drawback that stress is not applied efficiently.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by using two light sources and a two-wavelength method, it improves measurement accuracy and improves the combination of a diaphragm and a photoelastic element. The aim is to provide a device that can apply stress efficiently by adding innovations.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. Second
In the figure, (2a) and (2b) are optical fibers (8a) (
8b) is a gradient index lens, (4) is a polarizer, (5)
is a photoelastic element, (6) is a diaphragm, and (7) is 1/4
A wavelength plate, (8) an analyzer, (10a) and (10b) dichroic mirrors, and αυ a sensor case.

The method of applying pressure to the photoelastic element (5) is as shown below. As shown in Figure 2, the bottom of the diaphragm (6) is adhered to the pressure receiving surface of the photoelastic element (5), and the case Oυ of the pressure sensor section is tightly sealed, so that the internal pressure is always maintained. This is done so that the atmospheric pressure becomes the same. When the external pressure is above 1 atmosphere, the diaphragm (6) expands and downward stress acts on the photoelastic element (5), and when the external pressure is below -atmosphere, the diaphragm contracts and the photoelastic element An upward stress will act on (5).

This stress causes the photoelastic element (5) to exhibit birefringence, and by knowing the magnitude of this birefringence, the applied stress, ie, pressure, can be determined. The magnitude of birefringence can be measured as shown below. Light from two types of light sources, short wavelength λ1 and long wavelength λ2, is guided to the sensor section through one optical fiber (2a). In the sensor section, the dichroic mirror (10a) transmits the light of λ1 and reflects the light of λ2. The light passes through a polarizer (4) composed of a polarizing beam splitter, then passes through a photoelastic element (5) and a 7-wave plate (7).
The light passes through an analyzer (8) composed of a polarizing beam splitter, is recombined with the light of λ2 by a second dichroic mirror (10b), and enters an output optical fiber (2b). Now, if stress is applied to the photoelastic element (5) by the diaphragm (6), the light at λ1 undergoes intensity modulation proportional to the stress, but the light at λ2 passes through the sensor section without any modification. It will pass. Therefore, by separating the λ1 and ^2 lights using an optical receiver and taking the ratio of the signals of the λ1 and λ2 lights, even if the light intensity changes due to bending of the optical fiber or loss fluctuation of the optical connector, etc. A signal proportional only to pressure can be obtained without being influenced by these factors.

Separation of the λ1 and λ2 signals can be performed, for example, by alternately driving each light source with pulses, and sampling and holding the λ1 and λ2 signals in synchronization with the pulses in an optical receiver.

In addition, as the photoelastic element (5), polymer materials such as epoxy resin, various glass materials, LiNbO3,
Bi 12G'eO□. A single crystal material such as can be used.

In the above embodiment, the reference light λ2 is propagated as it is in the sensor, but as shown in FIG. 7a)
, an analyzer (8b). In this way, the temperature characteristics of the photoelastic element can be compensated for, so that even lζ
Measurement accuracy increases.

〔Effect of the invention〕

As described above, according to the present invention, the method of attaching the diaphragm is devised so that pressure can be efficiently applied to the photoelastic element, and a two-wavelength method is adopted. Therefore, there is an effect that a highly accurate product can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional pressure measuring device, FIG. 2 is a block diagram of a pressure measuring device according to Embodiment 1 of the present invention, and FIG. 8 is a block diagram of a device according to another embodiment of the present invention. be. (1)... Optical transmitter, (2a) (2b)... Optical fiber, (aa) (sb)... Gradient index lens, (
4) (4a)...Polarizer, (b) (5a)...Photoelastic element, (6)...Diaphragm, (7) (7a)
...-wave plate, (8) (8a) ... analyzer, (9)
...First receiver m machine, (10a) (10b)--Gicroic mirror, aυ...Sensor part case. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent: Masuo Oiwa, Figure 1, Figure 21', Proceedings Corrector, Commissioner of the Patent Office, 1. Indication of the case: 1.1 Application No. 181701/1982, 2.
Name of the invention Pressure measuring device 3, Person making the amendment Representative Hitoshi Katayama Department 4 Agent 5 Column for detailed description of the invention in the specification to be amended. 6. Contents of amendment (1) The description will be amended as follows.

Claims (4)

[Claims] (1) In devices that measure the pressure by utilizing the fact that the liquid rate of a photoelastic element changes depending on the pressure applied to it, one end of a diamura with one end sealed is glued to the top surface of the photoelastic element. and the other open end of the diaphragm is adhered to a hermetically sealed case, and a measuring device for the diaphragm. (2) Two wavelengths, a short wavelength and a long wavelength, are used as a light source, and the first dichroic mirror in the sensor section separates the short wavelength and long wavelength light, and the short wavelength light is the light that is glued to the polarizer and diamura. The measuring device passes through an elastic element, a single wavelength plate, an analyzer, and a second dichroic mirror. (3) The two light sources of short wavelength and long wavelength are pulse-driven alternately, sampled and held in synchronization with the light sources in the optical receiver, and then the ratio of the signals from the two lights is electrically calculated. A pressure measuring device according to claim 1. (4) The light source uses two wavelengths, a short wavelength and a long wavelength, and the first dichroic mirror installed in the sensor unit separates the short wavelength and long wavelength light, and the short wavelength light is glued to the polarizer and diaphragm. passed through a photoelastic element, a 7-wave plate, and an analyzer.
The long wavelength light passes through another polarizer, a photoelastic element in a free state, a 7-wave plate, and an analyzer, and then a second dichroic mirror combines the short wavelength light and long wavelength light. A pressure measuring device according to claim 1, characterized in that it leads to an optical receiver.