JPS6056223A - Light wave front level meter - Google Patents

Abstract

PURPOSE:To elevate the measuring accuracy of plane level by coaxially using an optical path in common for the entire effective diameter of an object lens both in the light transmitting optical system and the light receiving optical system. CONSTITUTION:According to a command from a measurement control circuit 35, first, the calibrated optical path length is measured when light emitted from a light emitting diode reciprocates in reflection on a eflection sheet 7 on the back of a shutter plate. Then, the shutter plate 6 is opened with a motor 10 to measure the external optical path length up to the water surface. By a final measuring command, the shutter plate is returned to the original closed position to complete a single measurement. Meanwhile, an arithmetic unit 34 in an electric circuit subtracts the internal optical path length from the external optical path length and the real measured value is shown on a display 36 or recorded with a recorder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical wavefront level meter, which measures the water level by projecting and reflecting light onto the water surface and measuring the time it takes for the light to travel back and forth on the water surface. The present invention provides an epoch-making light wave water level gauge that can perform contactless water level observation without requiring a float on the water surface or wires connected to the main body, unlike water level gauges.

Although the present invention is mainly used for water level measurement, it goes without saying that by using this principle, the heights of various liquid levels, snow levels, powder, etc. can be measured in exactly the same way.

To explain the principle of a light wave water level meter using the present invention with reference to FIGS. 1 and 2, the objective lens (2) shares the objective lens of the sending optical system and the objective lens of the receiving optical system, and The axes are coaxial, and a semi-transparent mirror (3) with an inclination of 45° to the optical axis is installed obliquely between the images, and a light emitting element (4) is placed at the focal point on the linear optical axis of the objective lens (2). Also, a semi-transparent mirror (3
), the light receiving elements (5) are arranged at the focal positions on the reflection optical axis of each of them.

The inventive element f41 generally uses an inventive diode or a laser diode, and as shown in the block diagram of FIG.
(z) is driven via the drive circuit (2(a)),
It is emitted as modulated light with brightness and darkness of 15M1 (z). If 15z7i- is used as the reference frequency, the interval at which one wavelength of the modulated B-C wave travels back and forth on the water surface corresponds to exactly 10 m.
The phase difference can be measured up to 1/1000 with a digital phase meter OQ with an accuracy of one scale.

The output of the power receiving element (5) is amplified by a preamplifier C26), and is added to the output of the crystal oscillator (25) obtained through the local oscillator GD in the mixer circuit (30) to perform heterodyne detection. The low frequency signal obtained from the mixer circuit c+ol is passed through a band pass filter (27) to remove noise and unnecessary bands, and the automatic gain adjustment circuit (2p ), the electrical output is fixed at a certain level.

The output of the automatic gain adjustment circuit (28) is the window comparator c! 9), and signals below and above a predetermined level width are cut. That is, when the output signal is at a high level, there is a lot of distortion, and when the output signal is at a low level, the S/N is poor, so the measurement is interrupted in either case. An output is generated from the window comparator ρω so that measurement is continued only when the output level reaches a proper value.

Wind comparator II! The output of q+ is given to a digital phase meter 03). This phase meter 03) detects a pulse signal within the pulse (measurement window) corresponding to the phase difference between the signal obtained by dividing the output of the crystal oscillator (24) by the frequency divider 07) and the output of the window comparator (291). It is configured to count the clock pulses from the clock oscillator 02 and output the 11 phase difference as a digital value. A calculation device that corrects for target variation (
As a result, 0 is sent to the display (3G) through 34J.
It is possible to measure and display the amount of change in water level from an arbitrary standard water level up to 1.0 m in units of 1 m. It is also possible to perform analog recording using a recorder.

In water level measuring instruments that use light waves, the time it takes for light to be emitted from the main body, reflected on the water surface, and received is extremely short < (1,5xl O-8 seconds 710m), making it difficult to measure one measurement value. Even if the measurement is repeated 100,000 times and the average value is calculated, the measurement will be completed within 10 seconds.

In this case, since the measurement accuracy is improved by the square root of the number of measurements, the accuracy of the average value of 100,000 times is improved by about 300 times compared to the single measurement 'IIIK.

A light wave water level meter directly measures the length to the water surface using the light transmitting and receiving device, but the phase of the transmitted light wave and the phase of the received signal within the receiving electric circuit fluctuate moment by moment due to external discharges such as power supply voltage and temperature changes. Therefore, a calibration optical path is always required in order to remove this 11.

The present invention forms this calibration optical path with an extremely simple structure, and also has the function of protecting the inside of the main body as an outdoor measuring instrument.

As shown in Figure 1, the main body (11) is always installed above the water surface of an observation well or river and is exposed to water vapor and dust from the outside world, so these may adhere to the surface of the objective lens (2). In order to prevent light waves from entering the main body, a shutter plate (6) is used to cover the entire surface of the objective lens (2), which is the entrance/exit opening for light waves.
I'm trying to close it with The above-mentioned calibration path is formed simply by bonding a reflective sheet (7) or a reflective prism to the back surface of this shutter plate (6).

The shutter plate (6) has a structure that it can be opened and closed by a motor 110) via its rotation shaft (8) and gear (9).

Based on the command from the measurement control circuit (3ω) shown in Figure 2, first the calibrated optical path length of the emitted light from the light emitting diode is reflected by the reflection sheet (7) on the back of the shutter plate, and then the shutter plate (6) The motor aO) causes the (
Open at the 6F position and measure the external optical path length to the water surface.
．． The last measurement command causes the shutter plate to return to its original closed position, completing one measurement.

During this time, the arithmetic unit C34+ in the electric circuit subtracts the internal optical path length from the external optical path length and displays the true measured value on the display (3).
6) Display or record on a recorder. Note that (111 is the outer cover of the main body, 17 is the electric circuit, and 17 is the connector for connecting the external garlic and output to a recorder, etc.).

Now, when actually performing water level observation using the device of the present invention, the main body is placed on the Cζ stable pedestal circle with three leveling screws 021 as shown in FIGS. Place the bubble in the center. At this time, the transmitted light wave passes through an objective lens and is projected perpendicularly onto the water surface as a parallel light beam. Approximately 4% of the light is reflected from the water surface, but if the water surface has no waves, the reflected light will be reflected in the vertical direction and will be incident on all effective apertures of the objective lens, where it will be photoelectrically measured.

However, in general, the water surface has waves and fluctuations, so a wave dissipating device (
Use the i mark to make a horizontal surface with no fluctuations on the water surface. The wave dissipating device consists of a cylindrical pipe a with glass beads (4) placed in the lower part and a large number of holes drilled on the side of the pipe.
When waves cannot be removed even with a wave absorber or when measuring a liquid surface with poor reflectivity, for example, as shown in Figure 4, a retroreflector plate (22) with many prismatic irregularities in the same circle as the borehole is used. All you have to do is attach it to the float □□□ and let it float on the liquid surface.

However, even if such a wave canceling device or a float with a reflector is used, the level of the received signal changes due to slight fluctuations in the liquid level, so as mentioned above, the optical water level meter of the present invention has an automatic gain adjustment circuit c! It has a function that allows accurate measurements for any water surface condition by using a wind comparator (2) that can stop measurement if the input signal level is low.

As explained above, the light wave water level meter of the present invention can observe the water level without any contact with the water surface, and since the lens surface and the inside of the main body are airtightly protected from water vapor and dust, it is possible to observe the water level without contacting the water surface. This allows for long-term stable observations. In addition, the calibration optical system using the reflective sheet 1171 on the back surface of the shutter plate (6) is suitable for downsizing and simplifying the device, and since the reflective sheet uses a retroreflector having many prismatic irregularities, the rotation mechanism is accurate. It has excellent features such as being able to significantly reduce manufacturing costs without requiring any additional equipment.

Furthermore, in the embodiment of the present invention, a semi-transparent mirror (3) is used to separate the light transmitting optical path and the light receiving optical path as described above. Semi-transparent mirrors have a large light transmission loss, which is disadvantageous for this type of measurement optical system.In general, optical systems that insert a reflecting prism or small-diameter mirror into the transmitting optical path to form the receiving optical path are used. It is used. In this case, an optical path is formed in which the effective diameter of the objective lens is divided into two by a light transmitting optical path portion and a light receiving optical path portion, and the field of view of the objective lens is limited. On the other hand, if a semi-transparent mirror is used as in this example,
Regarding the effective diameter of the objective lens, the transmitting optical path and the receiving optical path are common, and a sufficient viewing angle is ensured. When measuring based on reflected light from a surface whose condition fluctuates rapidly such as a water surface, or from a surface with many irregularities such as powder or snow, it is best to receive reflected light from as wide an area as possible to improve measurement accuracy due to the averaging effect. is enhanced. Therefore, by using a semi-transparent mirror to coaxially share the light transmitting optical path and the light receiving optical path, the effective field of view of the measuring optical path is expanded, and it is possible to obtain measurement values with higher precision.

Further, in the embodiment of the present invention, as described above, the calibration optical path is also used in common with the light transmission optical path and the light reception optical path. In this type of measurement optical system, the calibration optical path is generally provided independently in the vicinity of the measurement optical path using a prism or the like, which causes a narrowing of the constant field of view as described above. Therefore, in this embodiment, as shown in Fig. 1, a reflective sheet (7) or a prism is provided outside the objective lens (2) so that it can be inserted into and removed from the measurement optical path, and a calibration optical path is formed using the measurement optical path. I'm trying to make it happen. As a result, the field of view of the objective lens (2) is not obstructed except during calibration, and calibration data for the measurement optical path itself can be obtained, resulting in an excellent effect of reducing calibration errors.

In addition, as a secondary effect, the shutter plate (6) equipped with a reflector to form a calibration zero path covers the entire outer surface of the objective lens (2) except during measurement, allowing it to penetrate inside the lens surface and body. A desirable feature of protection against water vapor and dust is also obtained.

In the present invention, as described above, since the light transmitting optical system and the light receiving optical system coaxially share the optical path over the entire effective diameter of the objective lens, the field of view of the objective lens with a limited diameter can be made sufficiently large. Surface level measurement accuracy can be improved.

In addition, the calibration optical system is constructed by attaching a reflector to the shutter that covers the objective lens, which simplifies the optical system and allows for accurate calibration of the internal optical path itself, which is comprised of the transmitting optical system and the receiving optical system. In addition, by closing the shutter when not measuring, the objective lens surface and the inside of the main body can be protected from water vapor and dust.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing the optical structure of a light wave water level meter to which the present invention is applied, Fig. 2 is a block diagram showing an electric circuit, and Fig. 6 is an example of an example of water level observation using a wave dissipating device. A schematic sectional view showing an example. FIG. 4 is a schematic sectional view showing an embodiment in which water level observation is carried out by attaching a retroreflector to a float without using a wave dissipating device. In addition, in the symbols used in the drawings, (II...................................Body (2)...
・・・・・・・・・・・・Objective lens (3)・・・・
・・・・・・・・・・・・Semi-transparent mirror (4)・・・・・・
......Light emitting element (5)...
...... Light receiving element (6) ......
・Shutter board (7)・・・・・・・・・・・・・・・
・Reflective sheet or reflective prism (8)...
・・・・・・Rotation axis (9)・・・・・・・・・・・・
・・・Gear 00)・・・・・・・・・・・・Motor Uυ・・・・・・・・・・・・Outer cover of main body (12+・・・・・・・・・・・・・・・Leveling screw 0
3)・・・・・・・・・・・・・・・Circular bubble tube (+4
1・・・・・・・・・・・・・・・ Frame u51・・・・
・・・・・・・・・・・・Water surface (le・・・・・・・・・
・・・・・・Electrical circuit (17)・－・・・・・・・・・
...Connector (Country...)
・Wave-dissipating pipe (1, 1・・・・・・・・・・・・・・・
Wave-dissipating pipe small hole Cυ・・・・・・・・・・・・・Glass piece (2)・・・・・・・・・・・・・−・Borehole (2 thirst・・・−・・・・・・・・・・Retroreflector (c)・・・・・・・・・・・・Float (2
41・・・・・・・・・・・・Light emitting element drive circuit (251・・・・・・・・・・・・Crystal oscillator (
1)・・・・・・・・・・・・Preamplifier (5)
・・・・・・・・・・・・・・・Band pass filter (a)・・・・・・・・・・・・Automatic gain adjustment circuit e9)・・・・・・・・・・・・・・・・・・・・・ Wind comparator (to)・・・・・・・・・・・・Mixer Oυ・・・・・・・・・・・・Local oscillator 02・・・・・・・・・・・・・・・・・Clock oscillator■・・・・・・・・・・・・・・・Digital phase meter (
34)・・・・・・・・・・・・Arithmetic device cl!
51・・・・・・・・・・・・Measurement command circuit ■・
・・・・・・・・・・・・Display unit G7)・・・・・・
・・・・・・・・・It is a frequency divider. Agent Masaru Saturn I Yoshio Tsuneko I Shunji Sugiura Figure 1/n/no 0 1g/- Figure 3 Figure 4

Claims (1)

[Claims] A light transmitting optical system and a light receiving optical system are arranged substantially coaxially through a semi-transparent mirror placed on the optical axis of the objective lens facing the measurement surface, and a lid that can be opened and closed in front of the objective lens. a shutter, and a reflector that is not attached to the shutter and is used as a calibration optical system for part of the light transmitting optical system and the light receiving optical system; The internal optical path length is measured by the optical system and the light receiving optical system, and when measuring the surface level, the shutter is opened and the light transmitting optical system and the light receiving optical system share the optical path coaxially over the entire surface of the effective diameter of the objective lens. An optical wavefront level meter that measures the length of an external optical path with a measurement surface interposed therebetween, and measures the surface level based on the difference between the external optical path length to the measurement surface and the internal optical path length.