JPH02310473A - Acceleration measuring instrument - Google Patents

Abstract

PURPOSE:To provide the measuring instrument which is light in weight and is hardly affected by electrical noises by allowing a movable metallic plate to execute translation motion according to an input acceleration, thereby changing the capacity of a capacitor. CONSTITUTION:The random polarized light emitted from a laser 4 is condensed by a lens 14a and is passed through a polarizer 7 by which the light is polarized to linearly polarized light. This light is further passed through a quarter wave plate 8 and is thereby polarized to circularly polarized light which is then put into an electrooptical crystal 2. The voltage to be impressed to the crystal 2 is determined by the change in the electrostatic capacity of the capacitor arising from the translation motion of the movable metallic plate 12 by the input acceleration. The impressed voltage V is expressed by equation when the displacement of the metallic plate 12 is designated as X and if this displacement is assumed to be very slight. Namely, the power level of the elliptically polarized light which is the signal light past the crystal 2 is proportional to the voltage V and, therefore, the acceleration signal is obtd. from the change rate thereof and the equation. The power level of the signal light is propagated in an optical fiber 6b and is measured by a photodetector 5 via a lens 14b after the elliptically polarized light is converted to linearly polarized light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an acceleration measuring device using an optical fiber.

[Prior art] This type of conventional acceleration measuring device detects changes in the capacitance pickoff as the pendulum rotates around its hinge due to input acceleration, and detects changes in the capacitance of the capacitance pickoff, and detects changes in the capacitance of the capacitance pickoff. The configuration was such that a rebalance current was supplied to the torquer coil so that it remained stationary near the null, and acceleration was measured based on the amount of supplied current.

[Problems to be Solved] The conventional acceleration measuring device described above has a mechanism that balances the rotational movement of the pendulum due to input acceleration using a torquer coil and a torquer magnet, so there is a problem in that the overall weight of the device increases. .

Furthermore, since the input acceleration is converted into an electrical signal, there is also the problem that it is easily affected by electrical noise during transmission.

The present invention has been made in view of the above-mentioned conventional problems, and it is an object of the present invention to provide an acceleration measuring device that is lightweight, uses light for signal propagation, and is not affected by electrical noise.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an acceleration measuring device including a capacitor whose capacitance is changed by causing a movable metal plate to perform a translational motion in response to an input acceleration, and a capacitance change of the capacitor. It consists of an electro-optic crystal that receives an applied voltage that changes in accordance with be.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention. In the figure, there is a cylinder 1, and a fixed metal plate 11 is fixed to one end of the cylinder 1, and a space between the cylinder 1 and the bottom surface of the cylinder 1 is fixed to the other end. A movable metal plate 12 whose position is variable by a spring 13 sandwiched therein is provided. These cylinder 1, fixed metal plate 11, and movable metal plate 12 constitute a variable capacitance capacitor.

Further, in the figure, reference numeral 2 denotes an electro-optic crystal, and this electro-optic crystal 2 is integrated with a fixed metal plate 11, with an electrically insulating plate lO interposed between the two. The capacitor configured as described above and the electro-optic crystal 2 are electrically connected in series, and a voltage is applied by a constant voltage source 3.

On the other hand, the output signal generation and transmission system includes a laser 4, lenses 14a and 14b, optical fibers 6a and 6b, and a polarizer 7.1.
It is composed of a /4 wavelength plate 8, an electro-optic crystal 2, an analyzer 9, and a photodetector 5.

Next, the operation of this embodiment will be explained.

The randomly polarized light emitted from the laser 4 is transmitted through the lens 14.
The light is focused at point a, propagates through the optical fiber 6a, passes through a polarizer 7 to become linearly polarized light, further passes through a quarter-wave plate 8 to become circularly polarized light, and then enters the electro-optic crystal 2. electro-optic crystal 2
The voltage applied to is.

It is determined by the capacitance change of the capacitor accompanying the translational movement of the movable metal plate 12 due to input acceleration. Assuming that the displacement X of the movable metal plate 12 is small, the applied voltage V is expressed by the following equation.

V=Vo(1-(1/2)・(x/ e ωRs)2)
However, vo2 constant voltage, ε: dielectric constant, R: electro-optic crystal 2
Electrical resistance, S diagonal resistance, ω; AC frequency of constant voltage source 3.

As can be seen from the above equation, the power level of the elliptically polarized light, which is the signal light that has passed through the electro-optic crystal 2, is proportional to the applied voltage V, so the acceleration signal can be obtained from the amount of change and the above equation. Here, the power level of the signal light is measured by converting elliptically polarized light into linearly polarized light by an analyzer 9, propagating it through an optical fiber 6b, passing through a lens 14b, and using a photodetector 5.

In addition, as electro-optic crystals that can be adopted in the present invention, LiTaO5, LiNb0z, B i I2s i
There are 0zo (BSO), etc.

[Effects of the Invention] As explained above, the present invention changes the capacitance of a capacitor by causing a movable metal plate to perform a translational motion in accordance with input acceleration, and converts the applied voltage that has changed in accordance with the change in capacitance of the capacitor into an electric current. By applying the light to the optical crystal and measuring the level of light propagating through the optical fiber as an acceleration output,
Since the input acceleration can be converted into a voltage signal applied to the electro-optic crystal, the weight of the device can be reduced, and since the final acceleration output is light, there is no need to use electricity during transmission. This has the effect of being able to avoid being affected by noise.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention. 1 Nijilinda 2: Electro-optic crystal 3: Constant voltage source 4: Laser 5: Photodetector 6a, 6b = Optical fiber 7: Polarizer 8: 1/4 wavelength plate 9: Analyzer 10: Electrical insulating plate 11: Fixed Metal plate 13: Spring 12: Movable metal plate 14a, 14b = Lens agent Patent attorney Kihei Watanabe Figure 1

Claims (1)

[Claims] An acceleration measuring device comprising: a capacitor whose capacitance changes by causing a movable metal plate to perform a translational motion in accordance with input acceleration; an electro-optic crystal which receives an applied voltage that changes in accordance with the change in capacitance of the capacitor; and an optical fiber. An acceleration measurement device comprising an output signal generation system and a signal transmission system, and measures the level of light propagated through the optical fiber as an acceleration output.