JP6985662B2 - Liquid level distance measuring device and multi-point liquid level distance collective measurement system - Google Patents

Description

The present invention relates to a liquid level distance measuring device and a multipoint liquid level distance collective measuring system.

As a liquid level distance measuring device that measures the water level of rivers and reservoirs, one that measures the water depth by detecting the water pressure at the bottom of the water, or a float that floats on the liquid surface and measures the distance with a laser rangefinder. A device that measures the distance to the liquid level as the water level is known.

As a float-type water level gauge, a guide was provided to prevent the float from moving up and down and floating, and the float was covered with a pipe to prevent the float from moving up and down violently due to the rippling of the liquid level due to wind and rain. A water level gauge has been proposed (Japanese Patent Laid-Open No. 10-281854). According to this water level gauge, it is said that it is possible to measure the water level with high accuracy by removing the influence of waves on the liquid level, but the water level gauge becomes a large-scale device, the production cost increases, and the installation location is limited. There is a risk of being damaged. In addition, since the water level gauge is covered with a pipe, it may not be possible to respond to changes such as a sudden increase in water.

Japanese Unexamined Patent Publication No. 10-281854

In view of the above inconvenience, the present invention has a liquid level distance measuring device capable of measuring the liquid level distance stably and with high accuracy with a simple configuration, and a liquid at multiple points collectively with a simple configuration. It is an object of the present invention to provide a multipoint liquid level distance measuring system capable of measuring a surface distance.

One aspect of the present invention made to solve the above problems is to measure the distance between the reference surface and the liquid surface based on the light receiving time difference between the reflected light reflected by the reference reflecting surface and the return light reflected by the liquid surface. A light source that emits pulsed light, a light transmitting / receiving unit that sends the pulsed light to the liquid surface and receives the return light, a light receiving unit that receives the reflected light and the return light, and the above. It is equipped with a signal processing unit that calculates the liquid level distance from the light receiving time difference between the reflected light and the return light, and the light transmission / reception unit makes the reference reflection surface and the pulsed light into a parallel light bundle and collects the return light. It is a liquid level distance measuring device characterized by having an optical system to be used and the optical system is a Schwarzschild optical system.

In the liquid level distance measuring device, the Schwarzschild optical system included in the light transmission / reception unit can irradiate the liquid surface with the emitted light irradiating the liquid surface as a bundle of parallel light rays, and the liquid in a predetermined range with a predetermined amount of light. The surface can be illuminated. Further, since the return light reflected on the liquid surface is collected by the optical system, the return light reflected on the liquid surface can be efficiently collected. Therefore, even if waves or bubbles are present on the liquid surface and a part of the irradiation light is diffusely reflected, the return light reflected by the other part of the liquid surface can be condensed, so that the water surface is stable. The liquid level distance can be measured even in the case of a non-swaying liquid level. Therefore, a light reflecting member such as a float is not required, a simple configuration can be obtained, and the liquid level distance can be measured stably. In addition, since the distance between the reference surface and the liquid surface is calculated from the time difference between the reflected light reflected by the reflection reference surface of the light transmission / reception unit and the return light reflected by the liquid surface, the water depth changes due to the change in water pressure. Compared to a water level gauge or the like that measures the liquid level, it has excellent followability to changes such as a sudden increase in water, and can measure the liquid level distance with high accuracy without being affected by the specific gravity value of the liquid.

The liquid level distance measuring device according to another aspect of the present invention, which has been made to solve the above-mentioned problems, has the above-mentioned liquid from the time difference between the emission of the pulsed light to the liquid surface and the reception of the return light reflected by the above-mentioned liquid surface. A device for measuring the distance between surfaces, including a semiconductor light source that emits pulsed light and a reflecting portion that combines the pulsed light into a bundle of parallel rays and condenses the return light. The semiconductor light source is the liquid. It is characterized in that it also serves as a light receiving unit that receives the return light from the surface.

Since the semiconductor light source also serves as a light receiving unit, the liquid level distance measuring device can be a liquid level distance measuring device having a simpler configuration.

The multipoint liquid level distance batch measurement system according to still another aspect of the present invention, which has been made to solve the above problems, is based on the light receiving time difference between the reflected light reflected by the reference reflecting surface and the return light reflected by the liquid surface. A system that collectively measures the distance between the reference surface and the liquid surface at multiple points, a light source that emits pulsed light containing multiple wavelengths, and a specific wavelength that demultiplexes light of a specific wavelength from the pulsed light. Demultiplexing unit, light transmission / reception unit that sends light of the specific wavelength to the liquid surface and receives the return light, optical fiber that propagates the pulsed light, reflected light, and return light, and the optical fiber. The liquid level distance is calculated from the light distribution unit that distributes the pulsed light propagating and the reflected light and the return light, the light receiving unit that receives the reflected light and the return light, and the light receiving time difference between the reflected light and the return light. A signal processing unit is provided, and the specific wavelength demultiplexing unit and the light transmission / reception unit are arranged at a plurality of points. It is characterized by having an optical system that collects light.

For example, when observing changes in water level at multiple points in a river, a water level distance measuring device including a light source and a signal processing unit that calculates the liquid level distance, and a transmitter that transmits the measurement results to the observation station are installed at each point. It will be a large-scale and complicated system. According to the multipoint liquid level distance batch measurement system, one light source and a signal processing unit for calculating the liquid level distance are arranged at an observation station or the like, and a plurality of light transmission / reception units for transmitting / receiving light of a specific wavelength to the liquid surface are provided. By arranging the light source and signal processing unit at the measurement points and connecting each light transmission / reception unit with an optical fiber, it is possible to collectively measure the liquid level distances at multiple points with high accuracy with a simple configuration.

The specific wavelength demultiplexer may include a three-terminal optical circulator and an optical device that reflects light of the specific wavelength. By including a 3-terminal optical circulator and an optical device that reflects light of a specific wavelength, the specific wavelength demultiplexer can reduce the amount of light loss and can perform more stable and highly accurate measurement.

The specific wavelength demultiplexer may further include a 4-terminal optical circulator. By further including the 4-terminal optical circulator in the specific wavelength demultiplexer, the specific wavelength demultiplexer can be configured more simply, the light amount loss can be further reduced, and more stable and highly accurate measurement can be performed. Can be done.

At least the optical fiber included in the optical transmission / reception unit may be a dual mode fiber. By using at least the optical fiber of the optical transmission / reception unit as a dual mode fiber, the core portion of the multimode fiber can be used as the core portion that receives the return light, and the optical pulse that does not return to the core portion of the single mode fiber. Can also be accepted. Therefore, the capture rate of the return light can be increased, and stable and highly accurate measurement can be performed.

As described above, according to the liquid level distance measuring device, it is possible to measure the liquid level distance stably and with high accuracy with a simple configuration. Further, according to the multipoint liquid level distance batch measurement system, it is possible to collectively measure the liquid level distance at multiple points with high accuracy with a simple configuration.

It is a schematic diagram which shows the structure of the liquid level distance measuring apparatus which is one Embodiment of this invention. It is a schematic cross-sectional view which shows the structure of the light transmission / reception part provided in the liquid level distance measuring apparatus of FIG. It is a schematic cross-sectional view which shows the structure of the light transmission / reception part different from FIG. It is a schematic sectional drawing which shows the structure of the liquid level distance measuring apparatus which concerns on other embodiment of this invention. It is a schematic diagram which shows the structure of the multipoint liquid level distance batch measurement system which concerns on another Embodiment of this invention. It is a schematic diagram which shows the structure of the specific wavelength demultiplexing part provided in the multipoint liquid level distance batch measurement system of FIG. It is a schematic diagram which shows the structure of the specific wavelength demultiplexing part different from FIG. It is a schematic diagram which shows the mode that the specific wavelength demultiplexing part of FIG. 7 transmits light of a wavelength other than the specific wavelength. It is a schematic diagram which shows the structure of the specific wavelength demultiplexing part different from FIG. 6 and FIG. It is a schematic diagram which shows the mode that the specific wavelength demultiplexing part of FIG. 9 transmits the light of the wavelength other than the specific wavelength. FIG. 5 is a schematic cross-sectional view showing a configuration of an optical transmission / reception unit included in the multipoint liquid level distance batch measurement system of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Liquid level distance measuring device]
[First Embodiment]
As shown in FIG. 1, the liquid level distance measuring device 1 according to the embodiment of the present invention mainly includes a light source 2, an optical coupler 3, a light transmitting / receiving unit 4, a light receiving unit 5, and a signal processing unit 6 and is electrically operated. It also has a harness 7. The liquid level distance measuring device 1 can measure the distance of the liquid level W by irradiating the liquid surface W of the container A with pulsed light and receiving the reflected light.

<Light source>
The light source 2 emits pulsed light and sends it to the optical coupler 3. The light source 2 is not particularly limited as long as it can emit pulsed light, and for example, a known light source such as a laser diode (LD) using a pulse generator and an LED (Light Emitting Diode) can be used. .. The pulsed light refers to light that repeatedly blinks at narrow (short) time intervals.

The lower limit of the pulse width of the light emitted by the light source 2, that is, the lower limit of the length of time that the light source 2 emits is not particularly limited, but it is preferable to set the emission time as narrow as possible. High resolution performance can be realized by narrowing the pulse width. However, a pulse width that is too narrow compared to the band of the receiver may be wasted from the viewpoint of increasing the measured pulse amplitude (pulse height, that is, signal component). Specifically, for example, when a Gaussian pulse waveform is obtained by using a light receiving circuit in a 10 GHz band, the lower limit of the pulse width can be 44 ps. On the other hand, the upper limit of the pulse width is not particularly limited, but can be determined from the shortest distance of the liquid level to be measured. That is, it can be obtained by the distance at which the distance from the reference reflection surface to the liquid surface to be measured is the shortest. Specifically, for example, when the shortest distance from the reference reflection surface to the liquid surface to be measured is 15 cm, the upper limit of the pulse width for measuring the liquid level distance is 1 ns, and the shortest distance is 150 cm. In this case, the upper limit of the pulse width can be 10 ns.

The pulse interval, that is, the time interval during which the light source 2 stops emitting light from the emission of one pulse light to the emission of the next pulse light is not particularly limited, but the pulse interval should be as narrow as possible. Is preferable. By narrowing the pulse interval, the pulsed light can be transmitted more frequently, so that when the liquid level is shaking, the probability that the pulse can be irradiated at the moment when the liquid level becomes flat can be improved. However, the lower limit of the pulse interval is limited by the maximum distance from the reference reflection surface to the liquid surface to be measured. Specifically, for example, in the liquid level distance measurement at only one point, the light source 2 to the optical transmission / reception unit 4 (measurement point) are connected by an optical fiber for wiring, and the length of this optical fiber is 10 m, and the reference reflection is performed. When the maximum distance from the surface to the liquid surface is 30 m, the lower limit of the pulse interval can be set to 300 ns. Similarly, in the case of multipoint liquid level distance batch measurement, the farthest measurement point is 10 km, that is, the length of the optical fiber connecting the light source and the measurement point is 10 km, and the propagation delay of this optical fiber is 5 μs / km. When the maximum distance from the reference reflection surface to the liquid surface is 30 m, the lower limit of the pulse interval can be 100 μs.

<Optical coupler>
The optical coupler 3 branches the pulsed light emitted by the light source 2, the reflected light reflected by the reference reflecting surface of the light transmission / reception unit 4, and the return light reflected by the liquid surface W. Specifically, the optical coupler 3 reflects the pulsed light emitted by the light source 2 toward the light transmission / reception unit 4, and transmits the reflected light reflected by the reference reflecting surface and the return light reflected by the liquid surface W. The light is received by the light receiving unit 5. The optical coupler 3 is not particularly limited as long as it can branch the pulsed light, the reflected light and the return light, and for example, a known one such as a beam splitter (BS) or an optical circulator can be used. ..

<Light receiving part>
The light receiving unit 5 receives the reflected light and the return light, and converts this optical signal into an electric signal. The converted electric signal is transmitted to the signal processing unit 6 by the electric harness 7. The light receiving unit 5 is not particularly limited as long as it can convert the received optical signal into an electric signal, and a known one such as a photodiode (Photo Diode: PD) can be used.

<Electric harness>
The electric harness 7 connects the light receiving unit 5 and the signal processing unit 6. The electric signal converted from the optical signal by the light receiving unit 5 is transmitted to the signal processing unit 6 by the electric harness 7.

<Signal processing unit>
The signal processing unit 6 measures the time difference between the light receiving timing of the reflected light received by the light receiving unit 5 and the light receiving timing of the return light, and calculates the distance between the reference reflecting surface and the liquid surface W. This measurement result is displayed on a display (not shown) such as a liquid crystal display. The signal processing unit 6 is not particularly limited, and for example, a known one such as a pulse analyzer or an oscilloscope can be used.

<Optical transmission / reception unit>
The light transmission / reception unit 4 irradiates the pulsed light reflected by the optical coupler 3 and spreading radially as a parallel light bundle as substantially perpendicular to the liquid surface W. Further, the return light reflected by the liquid surface W of this pulsed light is focused on the light receiving unit 5. The light transmission / reception unit 4 has an optical system for condensing the return light from the liquid surface W on the light receiving unit 5 while forming a parallel light bundle of pulsed light reflected by the optical coupler 3 and spreading radially. The light transmission / reception unit 4 includes a reference reflection surface for reflecting a part of the pulsed light without irradiating the liquid surface W with the liquid surface W and causing the light receiving unit 5 to receive the reflected light. The distance to the liquid surface W is measured by the signal processing unit 6 by measuring the timing at which the light receiving unit 5 receives the reflected light reflected by the reference reflecting surface and the timing at which the return light reflected by the liquid surface W is received. Is calculated.

〔Optical system〕
In the optical system, the radial light reflected by the optical coupler 3 is made into a parallel light bundle, and the return light reflected by the liquid surface W is focused on the end portion. The optical system is a Schwarzschild optical system. As shown in FIG. 2, the Schwarzschild optical system includes a convex mirror 8 and a concave mirror 9. The convex mirror 8 reflects the radial light reflected by the optical coupler 3, and the concave mirror 9 further reflects the reflected light of the convex mirror 8. Therefore, a parallel light bundle can be easily formed. Further, by forming a part of the zenith portion of the convex mirror 8 on a plane perpendicular to the center of the radial ray axis reflected by the optical coupler 3, this plane can be used as the reference reflection surface 10. The plane positively reflects a part of the radial light reflected by the optical coupler 3, and is received by the light receiving unit 5 as the reflected light of the reference reflecting surface 10. The light reflected by the convex mirror 8 other than the plane is further reflected by the concave mirror 9, irradiates the liquid surface W, and a part of the light reflected by the liquid surface W is used as the return light of the liquid surface W to use the concave mirror 9 and the convex mirror 8. It is reflected and focused on the light receiving unit 5.

Further, it is preferable that the central portion of the convex mirror 8 has an opening 11 and the central axis of the opening 11 is on the center of the radial ray axis reflected by the optical coupler 3. By having the opening 11, a part of the radial light rays reflected by the optical coupler 3 can pass through the opening 11 and directly irradiate the liquid surface W. Further, a part of the return light reflected by the liquid surface W can be introduced into the opening 11 and incident on the light receiving portion 5. Therefore, it is possible to suppress the light loss of the pulsed light of the light source 2 and the return light of the liquid surface W.

The optical system can also be composed of a lens. For example, as shown in FIG. 3, it may have a lens 12, a lens holder 13, a lens protective glass 14, a cover 15 for fixing the lens holder 13, and a cover glass 16.

(lens)
The lens 12 uses the radial light reflected by the optical coupler 3 as a bundle of parallel light rays, and collects the return light reflected by the liquid surface W on the light receiving unit 5. The lens 12 is not particularly limited as long as it can form a radial light bundle into a parallel light bundle and can collect the parallel light bundle, and for example, a known lens such as a collimator lens can be used. ..

(Lens holder, lens protection glass)
The lens holder 13 holds the lens 12 and has a lens protective glass 14. The lens holder 13 is formed in a cylindrical shape such as a cylindrical shape or a square tubular shape, and has an open bottom. A lens protective glass 14 is provided on one bottom to protect the lens 12, and at the same time, one surface of the lens protective glass 14 is used as a reflection reference surface. A part of the radial light reflected by the optical coupler 3 is reflected by one surface of the lens protection glass 14 and is incident on the light receiving unit 5 as reflected light. The other part of the radial light reflected by the optical coupler 3 passes through the lens protection glass 14, is formed into a bundle of parallel light rays by the lens 12, and irradiates the liquid surface W. The lens 12 is arranged in the lens holder 13 so that the central axis of the lens surface of the lens 12 overlaps the central axis of the radial light bundle reflected by the optical coupler 3.

(cover)
The lens holder 13 is preferably housed in the cover 15. By housing the lens holder 13 in the cover 15 and the cover glass 16, the influence of disturbance can be suppressed, and particularly when the liquid level distance measuring device 1 is used outdoors, the influence of wind and rain and the like can be suppressed. It can be suppressed.

(cover glass)
The cover 15 preferably has a cover glass 16. Further, it is preferable that the cover glass 16 is arranged so as to be inclined by 1 degree or more and 30 degrees or less from the state where the glass surface is perpendicular to the central axis of the radial light rays reflected by the optical coupler 3. When the glass surface is arranged perpendicular to the central axis of the radial light rays reflected by the optical coupler 3, a part of the light rays is specularly reflected by the cover glass 16, and a loss of the amount of light toward the liquid surface W occurs. In addition, the specularly reflected light may be incident on the light receiving unit 5 to cause measurement noise. If the inclination of the glass surface is less than 1 degree from the state where the glass surface is perpendicular to the central axis of the radial light rays reflected by the optical coupler 3, specular reflection may not be suppressed. On the other hand, when the inclination is 30 degrees or more, the cover glass 16 and the cover 15 may become unnecessarily large. The cover glass 16 is not particularly limited as long as it transmits light, but a filter that transmits only light having a wavelength required for measuring the liquid level W and does not transmit other wavelengths is preferable. By not transmitting light having a wavelength that is not used for measuring the liquid level W, the influence of disturbance is suppressed, measurement noise is reduced, and more accurate measurement can be performed.

<Advantage>
Since the liquid level distance measuring device 1 irradiates the liquid surface W with a parallel light beam bundle, at least a part of the parallel light beam bundle can be received as return light reflected by the liquid surface W. Therefore, even when the entire surface of the liquid surface is not flat, such as the presence of waves or bubbles in a part of the liquid surface W, the distance to the liquid surface W can be stably measured. If different measurements are obtained when performing multiple measurements in succession, it is judged that there are waves or bubbles on the liquid level W, and the average value of the different measurement results is calculated or extreme. It is possible to measure the distance to the liquid level W with high accuracy by excluding different measurement results. Further, since the liquid level distance measuring device 1 converts the propagation delay in the space of light into a distance by dividing it by the speed of light, there is almost no measurement error factor, and high-precision liquid level distance measurement can be performed. ..

[Second Embodiment]
The liquid level distance measuring apparatus 20 according to another embodiment of the present invention will be described with reference to FIG. The same configuration as the above-mentioned liquid level distance measuring device will be described by using the same reference numerals.

The liquid level distance measuring device 20 mainly includes a semiconductor light source 21 that emits pulsed light, a reflecting unit 22 that makes the emitted pulsed light into a bundle of parallel rays, a forward bias circuit unit 23 that emits the semiconductor light source 21, and a semiconductor light source. A reverse bias circuit unit 24 that applies a reverse bias to 21 to make the semiconductor light source 21 a light receiving element, a signal processing unit 6 that calculates the liquid level distance from the time difference between the timing when the semiconductor light source 21 emits light and the timing when the semiconductor light source 21 receives light, and a semiconductor light source. It has an electric harness 25 that connects 21, the forward bias circuit unit 23, the reverse bias circuit unit 24, and the signal processing unit 6.

<Semiconductor light source>
The semiconductor light source 21 emits pulsed light and reflects it by the reflecting unit 22, irradiates the liquid surface W with the pulsed light, and receives the return light reflected by the liquid surface W reflected by the reflecting unit 22. The received optical signal is converted into an electric signal and transmitted to the signal processing unit 6 by the electric harness 25. Since the semiconductor light source 21 irradiates the entire surface of the reflecting surface of the reflecting unit 22 with the pulsed light, it can include a lens or the like for diffusing the pulsed light. The semiconductor light source 21 is not particularly limited, and for example, known ones such as LD and LED can be used, but among them, light can be emitted at a wide angle and light is received by applying a reverse bias. It is preferable to use an LED that can be used.

<Reflective part>
The reflecting unit 22 reflects the pulsed light emitted by the semiconductor light source 21 on the liquid surface W as a bundle of parallel light rays. Further, the reflecting mirror 22 collects the return light that is irradiated and reflected by the liquid surface W on the semiconductor light source 21. The mirror surface processing of the reflecting surface is not particularly limited as long as it reflects light, but is coated with a coating that reflects only light having a wavelength required for measuring the liquid surface W and does not reflect other wavelengths. Is preferable. By not reflecting light of a wavelength that is not used for measuring the liquid level W, the influence of disturbance is suppressed, measurement noise is reduced, and more accurate measurement can be performed.

<Forward bias circuit section>
The forward bias circuit unit 23 includes a forward bias circuit and a pulse generator, and applies a forward bias to the semiconductor light source 21 to emit pulsed light.

<Reverse bias circuit section>
The reverse bias circuit unit 24 includes a reverse bias circuit, and is a light receiver that receives the return light reflected on the liquid surface by applying a reverse bias to the semiconductor light source 21 at the timing when the semiconductor light source 21 does not emit light. The forward bias circuit unit 23 and the reverse bias circuit unit 24 can be integrally configured.

<Signal processing unit>
In the signal processing unit 6 of the present embodiment, the timing at which the forward bias circuit unit 23 causes the semiconductor light source 21 to emit light and the reverse bias circuit 24 apply a reverse bias to the semiconductor light source 21 so that the semiconductor light source 21 reflects at the liquid surface W. The distance to the liquid level W is calculated from the time difference from the timing at which the return light is received. The distance of the liquid level W is the distance from the reference surface to the liquid level W, or the liquid level, with the height from the bottom of the measurement target to the liquid level W or the height of the semiconductor light source 21 as a virtual reference surface. It is possible to measure the amount of change of W per hour and the like.

<Electric harness>
The electric harness 25 connects the semiconductor light source 21, the forward bias circuit unit 23, and the reverse bias circuit unit 24. Specifically, the forward bias circuit unit 23 transmits a forward bias signal to the semiconductor light source 21, the reverse bias signal unit 24 transmits a reverse bias signal to the semiconductor light source 21, and the signal received by the semiconductor light source 21 is a signal processing unit 6. Send to.

Specifically, for example, when the semiconductor light source 21 is an LED, a forward bias pulse is applied to the LED from the forward bias circuit unit 23 to emit light, and the return light from the liquid surface is reverse biased from the reverse bias circuit unit 24. The LED receives light as a photodiode. Using the electric harness 25 as a coaxial cable, a terminating resistance value is selected so that the sum of the series resistance and the terminating resistance of the LED matches the characteristic impedance of the coaxial cable. The voltage drop across the terminating resistor due to the light current flowing in the opposite direction to the LED is received by the measurement pulse receiving circuit included in the signal processing unit 6, and the signal processing unit 6 measures the relative delay of the light emitting and receiving pulses. When the pulse time width of light emission and light reception is larger than the liquid level distance propagation time of the light emitted, the light reception pulse is differentiated and the delay of the light emission pulse corresponding to the rise of the original pulse waveform is measured to measure the liquid level. The distance propagation time can be measured.

<Advantage>
In the liquid level distance measuring device 20, since the semiconductor light source 21 has both light emission and light reception, the distance of the liquid level W can be measured with a simpler configuration. Further, by reducing the size of the reflecting portion 22, the liquid level distance measuring device 20 can be installed in a place where it is difficult to install a large liquid level distance measuring device. Further, by increasing the size of the reflecting portion 22, a large parallel light beam bundle can be easily obtained, so that the irradiation area to the liquid surface W can be increased, and the liquid surface W such as a turbid flow or a large wave becomes large. Even in the case of a rough and unstable swaying liquid surface, the distance of the liquid surface W can be measured stably and with high accuracy. Further, when the semiconductor light source 21 is used as an incoherent light source, the light irradiating the liquid surface W is not regarded as a vertical plane wave, so that the reception probability of the return light reflected by the liquid surface W can be improved, and the shaking liquid surface can be improved. Measurement can be performed easily, more stably, and with high accuracy.

[Multi-point liquid level distance batch measurement system]
[Third Embodiment]
The multipoint liquid level distance batch measurement system 30 according to another embodiment of the present invention will be described with reference to appropriate figures. The same configuration as the above-mentioned liquid level distance measuring device will be described by using the same reference numerals.

As shown in FIG. 5, the multipoint liquid level distance batch measurement system 30 has a light source 31 that emits pulsed light including a plurality of wavelengths, and a specific wavelength demultiplexing unit 32 that demultiplexes light of a specific wavelength from the pulsed light. The light transmission / reception unit 33 that irradiates the liquid surface W with light having the specific wavelength, and the optical fiber 34 that propagates the pulsed light, the reflected light reflected by the reference reflecting surface described later, and the return light reflected by the liquid surface W. The light distribution unit 35 that distributes the pulsed light, the reflected light, and the return light in the optical fiber 34, the light receiving unit 36 that receives the optical signals of the reflected light and the return light and converts them into an electric signal, and the signal processing unit 37. Mainly prepare.

The multipoint liquid level distance batch measurement system 30 includes a transmission side light amplification unit 38 for amplifying pulsed light propagated through an optical fiber 34, and a reception side light amplification unit 39 for amplifying reflected light and return light. Further, an electric harness 7 for transmitting an electric signal converted by the light receiving unit 36 to the signal processing unit 37, and an optical fiber terminator (not shown) arranged at the terminal portion of the optical fiber 34 can be further provided.

<Light source>
The light source 31 emits pulsed light including a plurality of wavelengths and sends it to the optical fiber 34. The light source 31 is not particularly limited as long as it can emit pulsed light including a plurality of wavelengths, and for example, a known light source such as a wavelength sweep type laser using a pulse generator or a supercontinuum light source can be used.

<Optical amplifier>
The transmitting side optical amplifier 38 amplifies the light emitted by the light source 31, and the receiving side optical amplifier 39 amplifies the reflected light reflected by the reference reflecting surface and the return light reflected by the liquid surface W to obtain pulsed light. The reflected light and the return light are regarded as stable optical signals. The same optical amplifier can be used for the transmitting side optical amplifier 38 and the receiving side optical amplifier 39. The optical amplifier is not particularly limited, and for example, a known one such as an erbium-dropped fiber amplifier (EDFA) can be used.

<Optical fiber>
The optical fiber 34 communicates with the light source 31, the specific wavelength demultiplexing unit 32, the light transmission / reception unit 33, the light distribution unit 35, and the light receiving unit 36, and propagates the pulsed light, the reflected light, and the return light. Further, the optical fiber 34 included in the optical transmission / reception unit 33 is fixed at its end substantially vertically toward the liquid surface W, and the end portion emits pulsed light toward the liquid surface W and is emitted from the liquid surface. Accepts the return light. The optical fiber 34 is not particularly limited as long as it can efficiently transmit light, and for example, a known one such as a single mode fiber (Single Mode Fiber: SMF) and a multimode fiber (Multi Mode Fiber: MMF) can be used. Can be used.

At least, the optical fiber 34 included in the optical transmission / reception unit 33 is preferably a dual mode fiber (DMF). Since the DMF has the characteristics of both SMF and MMF, for example, the pulsed light emitted by the light source 31 is transmitted by the SMF having less light dispersion, and is reflected by the liquid surface W by the MMF having a larger core diameter than the SMF. Can accept return light. Therefore, the pulsed light emitted by the light source can be efficiently applied to the liquid surface W, and the return light can be efficiently received, so that stable and highly accurate liquid level distance measurement can be performed. ..

The optical fiber 34 used elsewhere is preferably SMF. By using an optical fiber 34 used for other purposes as an SMF having a small dispersion of light, it is possible to measure a remote place, for example, several tens of kilometers away.

The core diameter of the MMF portion of the DMF used in the multipoint liquid level distance batch measurement system is not particularly limited, but can be a general 100 μm. The lower limit of the core diameter of the MMF portion is preferably 150 μm, more preferably 200 μm. By increasing the clad diameter of the MMF portion, the probability of receiving return light (capture rate) can be improved. The core diameter of the SMF portion of the DMF is not particularly limited, but can be a general 10 μm.

<Light distribution unit>
The light distribution unit 35 branches the pulsed light emitted by the light source 31, the reflected light reflected by the reference reflecting surface of the light transmitting / receiving unit 33, and the return light reflected by the liquid surface W. Specifically, the light distribution unit 35 sends out the pulsed light emitted by the light source 31 toward the specific wavelength demultiplexing unit 32, and the reflected light reflected by the reference reflecting surface and the return light reflected by the liquid surface W. Is branched and sent to the light receiving unit 5. The light distribution unit 35 is not particularly limited as long as it can branch the pulsed light, the reflected light, and the return light, and for example, a known light such as an optical circulator can be used.

<Specific wavelength demultiplexer>
The specific wavelength demultiplexing unit 32 extracts light having a specific wavelength from the pulsed light of the light source 31, and sends the specific wavelength light to the light transmission / reception unit 33. The extracted light having a wavelength other than the specific wavelength light passes through the specific wavelength demultiplexer 32 and is transmitted to the next specific wavelength demultiplexer. The specific wavelength demultiplexer 32 is not particularly limited as long as it can extract light having a specific wavelength from light containing a plurality of wavelengths. For example, as shown in FIG. 6, a pair of optical demultiplexers 40 Can be included. By including the pair of optical duplexers 40, only the light having a desired wavelength can be taken out by each specific wavelength demultiplexer 32.

(Optical demultiplexing element)
In order to extract the desired wavelength by the specific wavelength demultiplexing unit 32 including the pair of optical demultiplexers 40, the light including a plurality of wavelengths propagating through the optical fiber 34a is demultiplexed by the optical demultiplexing element 40a at predetermined wavelength intervals. Will be done. Light having a wavelength λ (1) is taken out from the demultiplexed light at a predetermined wavelength, branched into an optical fiber 34b, and transmitted to an optical transmission / reception unit 33 (not shown). Lights of other wavelengths are combined into one light by the photosynthetic element 40b and transmitted by the optical fiber 34c. Subsequently, in order to extract light having a wavelength of wavelength λ (2), light containing a plurality of wavelengths propagating through the optical fiber 34c is demultiplexed by an optical demultiplexing element 40c at a predetermined wavelength in the same manner as described above. Light of wavelength λ (2) is taken out from the demultiplexed light for each wavelength, branched into the optical fiber 34d, and transmitted to a light transmission / reception unit 33 different from the light transmission / reception unit 33. Light of other wavelengths is combined into one light by the photosynthetic element 40d and transmitted to the optical fiber 34e.

The reflected light and the return light of the wavelength λ (1) propagating from the light transmission / reception unit 33 to the optical fiber 34b are transmitted to the optical fiber 34a together with the light of other wavelengths and transmitted to the light receiving unit 36. The reflected light and the return light of the wavelength λ (2) propagating from the other light transmission / reception unit 33 through the optical fiber 34d are transmitted to the optical fiber 34c together with the light of the other wavelength and transmitted to the light receiving unit 36.

(Optical circulator)
The specific wavelength demultiplexing unit 32 may include a 3-terminal optical circulator 41 and a Bragg grating optical fiber (FBG) 42, which is an optical device that reflects the emitted light of the specific wavelength. By including the 3-terminal optical circulator 41 and the FBG 42, light having a specific wavelength can be extracted with a simple configuration, and light loss can be suppressed.

A case where the specific wavelength demultiplexing unit 32 includes the 3-terminal optical circulator 41 and the FBG 42 and extracts the light having the wavelength λ1 will be described with reference to FIG. 7. Light containing a plurality of wavelengths propagating through the optical fiber 34a is transmitted to the optical fiber 34f by the three-terminal optical circulator 41a. The light of wavelength λ (1) is reflected by the FBG 42a, which can reflect only the light of wavelength λ (1), and is transmitted to the optical fiber 34 g by the three-terminal optical circulator 41a. Further, the light having the wavelength λ (1) is transmitted to the optical fiber 34b by the three-terminal optical circulator 41b and directed to the light transmission / reception unit 33 (not shown). The reflected light and the return light of the wavelength λ (1) propagating from the optical transmission / reception unit 33 to the optical fiber 34b are transmitted to the optical fiber 34h by the three-terminal optical circulator 41b. The return light of the wavelength λ (1) is reflected by the FBG 42b that can reflect only the light of the wavelength λ (1) arranged at one end of the optical fiber 34h, and is transmitted to the optical fiber 34g by the three-terminal optical circulator 41b. Further, it is transmitted to the optical fiber 34a by the 3-terminal optical circulator 41a and transmitted to the light receiving unit 36.

Light having a wavelength λ (1 + n) other than the wavelength λ (1) propagating through the optical fiber 34a is transmitted to the optical fiber 34f by the three-terminal optical circulator 41a as shown in FIG. Light of wavelength λ (1 + n) passes through FBG42a, which can reflect only light of wavelength λ (1), propagates through the optical fiber 34i, and is transmitted to the optical fiber 34c by the three-terminal optical circulator 41c. The reflected light and return light of wavelength λ (1 + n) propagating through the optical fiber 34c are transmitted to the optical fiber 34j by the 3-terminal optical circulator 41c, pass through the FBG 42b, propagate through the optical fiber 34h, and propagate through the optical fiber 34h, and the 3-terminal optical circulator 41b. Is transmitted to the optical fiber 34g, further transmitted to the optical fiber 34a by the 3-terminal optical circulator 41a, and transmitted to the light receiving unit 36.

It is more preferable that the specific wavelength demultiplexing unit 32 further includes a 4-terminal optical circulator 43. By further including the 4-terminal optical circulator 43, the specific wavelength demultiplexing unit 32 can be made into a simpler configuration, and the optical loss can be further suppressed.

A case where the specific wavelength demultiplexing unit 32 further includes the 4-terminal optical circulator 43 and extracts the light having the wavelength λ (1) will be described with reference to FIG. Light containing a plurality of wavelengths propagating through the optical fiber 34a is transmitted to the optical fiber 34k by the 4-terminal optical circulator 43. The light having the wavelength λ (1) is reflected by the FBG 42c capable of reflecting only the light having the wavelength λ (1), transmitted to the optical fiber 34b by the 4-terminal optical circulator 43, and directed to the light transmission / reception unit 33 (not shown). .. The reflected light and the return light of the wavelength λ (1) propagating from the optical transmission / reception unit 33 to the optical fiber 34b are transmitted to the optical fiber 34l by the 4-terminal optical circulator 43, and the wavelength λ (1) arranged at one end of the optical fiber 34l. ) Is reflected by the FBG 42d, which can reflect only the light. Further, it is transmitted to the optical fiber 34a by the 4-terminal optical circulator 43 and transmitted to the light receiving unit 36.

As shown in FIG. 10, the light having a wavelength λ (1 + n) other than the wavelength λ1 propagating through the optical fiber 34a is transmitted to the optical fiber 34k by the 4-terminal optical circulator 43 and reflects only the light having the wavelength λ (1). It passes through the capable FBG 42c, propagates through the optical fiber 34m, and is transmitted to the optical fiber 34c by the three-terminal optical circulator 41d. The reflected light and the return light having a wavelength λ (1 + n) propagating through the optical fiber 34c are transmitted to the optical fiber 34n by the 3-terminal optical circulator 41d, pass through the FBG 42d, pass through the optical fiber 34l, and are passed through the optical fiber 34l by the 4-terminal optical circulator 43. Is transmitted to the light receiving unit 36.

<Optical transmission / reception unit>
The light transmission / reception unit 33 directs the end portion of the optical fiber 34 toward the liquid surface W substantially vertically, and irradiates the liquid surface W with light having a specific wavelength. Further, the return light reflected by the liquid surface W of the specific wavelength light is collected at the end of the optical fiber 34 and transmitted to the light receiving unit 36. The light transmission / reception unit 33 is for forming parallel light bundles of specific wavelength light emitted from the end of the optical fiber 34 and spreading radially, and for concentrating the return light from the liquid surface W on the end of the optical fiber 34. It has an optical system. Further, it has a reference reflecting surface for reflecting a part of the specific wavelength light emitted from the end portion of the optical fiber 34 without irradiating the liquid surface W and transmitting the reflected light to the light receiving unit 36. The distance to the liquid surface W is calculated by measuring the timing at which the light receiving unit 36 receives the reflected light from the reference reflecting surface and the timing at which the return light from the liquid surface W is received by the signal processing unit 37. ..

〔Optical system〕
The optical system forms a radial specific wavelength light emitted from the end of the optical fiber 34 as a parallel light bundle, and collects the return light reflected by the liquid surface W on the end. The optical system is not particularly limited as long as it has a configuration in which the radial light emitted at the end thereof is a bundle of parallel light rays and the return light can be focused on the end portion, and is shown in FIG. 8, for example. As described above, it is possible to have a fiber connector 46, a cover 47, and a cover glass 16 for fixing the end portions of the lens 12, the lens holder 45, and the optical fiber 34 to the lens holder 45. Alternatively, the above-mentioned Schwarzschild optical system can be used.

(Lens holder)
The lens holder 45 holds the end of the optical fiber 34 and the lens 12. The lens holder 45 is formed in a cylindrical shape such as a cylinder or a square cylinder, one of which is bottomed and the other of which is open. The bottomed portion has a through hole, and the end portion of the optical fiber 34 is fitted into the through hole by the optical fiber connector 46. The end of the optical fiber 34 sends light of a specific wavelength into the lens holder 45. The lens 12 is arranged in the lens holder 45 so that the central axis of the lens surface of the lens 12 overlaps the central axis of the light beam emitted from the end portion of the optical fiber 34. The specific wavelength light emitted from the end of the optical fiber 34 is made into a bundle of parallel rays by the lens 12 and heads toward the liquid surface W. The return light reflected by the liquid surface W is collected by the lens 12 at the end of the optical fiber 34, propagates through the optical fiber 34, and is received by the light receiving unit 36.

(cover)
The lens holder 45 is preferably housed in the cover 47. By housing the lens holder 45 in the cover 47 and the cover glass 16, the influence of disturbance can be suppressed, and particularly when the liquid level distance measuring device 1 is used outdoors, the influence of wind and rain and the like can be suppressed. It can be suppressed.

[Reference reflection surface]
The reference reflecting surface reflects a part of the specific wavelength light emitted from the end of the optical fiber 34, and transmits the reflected light to the light receiving unit 36. The reference reflecting surface is not particularly limited, and for example, the end portion of the optical fiber 34 can be used as the reference reflecting surface. Alternatively, the cover glass 16 can be used as the reference reflecting surface.

<Light receiving part>
The light receiving unit 36 receives the reflected light reflected by the reference surface included in the light transmitting / receiving unit 33 and the reflected light reflected by the liquid surface W and converts them into an electric signal, and this electric signal is signal-processed through the electric harness 7. It is transmitted to the unit 37. The light receiving unit 36 is not particularly limited, and a known one such as a photodiode can be used.

<Signal processing unit>
The signal processing unit 37 receives the electric signal converted by the light receiving unit 36 and calculates the liquid level distance. Specifically, the light receiving unit 36 converts the reflected light of the reference reflecting surface having a specific wavelength and the return light of the liquid surface W transmitted from the light transmitting / receiving unit 33 into an electric signal, and transmits the light to the signal processing unit 37. The signal processing unit 37 calculates the distance from the reference reflecting surface to the liquid surface W from the difference between the timing at which the reflected light of the reference reflecting surface is received and the timing at which the return light of the liquid surface W is received, and is a display (not shown). For example, it is displayed on a liquid crystal display or the like.

<Advantage>
Since the multipoint liquid level distance batch measurement system 30 collectively measures a plurality of measurement points with a tree-type network by branching the pulsed light emitted by the light source 31, the light source 31 and the light receiving unit are at each measurement point. Since it is not necessary to deploy 36, a signal processing unit 37, etc., and it is not necessary to supply power to each measurement point, it is possible to collectively measure the liquid level distances at multiple points with a simple configuration. Further, since the light source 31 and the light receiving unit 36 are connected to the plurality of light transmitting / receiving units 33 by the optical fiber 34, the light source is less susceptible to lightning damage and the influence of the induced current is small. Therefore, the stability of signal transmission / reception is excellent, and the liquid level distance at a remote place can be measured with high accuracy. Furthermore, because it uses an optical pulse, it is possible to measure the liquid level without contact even in a narrow space such as a manhole or a cave, compared to a method that uses ultrasonic waves or radio waves, and the propagation delay in the space of light. Is converted to the distance by dividing by the speed of light, so that there is almost no measurement error factor and high-precision distance measurement can be performed. In addition, since no mechanical parts are used, there is almost no deterioration due to wear or rust, and the durability is excellent.

[Other embodiments]
The liquid level distance measuring device and the multipoint liquid level distance collective measuring system of the present invention are not limited to the above-described embodiment.

It is also possible to use an OTDR (Optical Time-Domain Reflectometer) in place of the light source, signal processing unit, optical coupler or reflected light distribution unit, and light receiving unit described above.

In the first embodiment, the light source 2, the optical coupler 3, and the light receiving unit 5 are integrally configured, but each of them is communicated with each other by an optical fiber, and one end of the optical fiber emits an optical pulse to the optical transmission / reception unit 4. It can also be configured to be.

In the second embodiment, the signal processing unit 6 causes the semiconductor light source 21 to emit light at the timing when the forward bias circuit unit 23 causes the semiconductor light source 21 to emit light, and the reverse bias circuit 24 applies a reverse bias to the semiconductor light source 21 so that the semiconductor light source 21 is at the liquid level W. The distance to the liquid level W was calculated from the time difference from the timing when the reflected return light was received. However, the reflection reference surface is arranged in the liquid level distance measuring device to measure the reflected light from the reflection reference surface. It is also possible to calculate the distance to the liquid surface W from the time difference between the timing at which the light is received and the timing at which the return light reflected by the liquid surface W is received. Alternatively, the apex of the reflecting unit 22 can be used as the reflection reference plane, and the light that is specularly reflected at the apex can be used as the reflected light.

Further, the liquid level distance measuring device described above is not limited to the liquid level distance measurement, and can be used as a distance measuring meter by directing a bundle of parallel light rays in a horizontal direction toward an object to be measured.

As described above, the liquid level distance measuring device and the multipoint liquid level distance collective measuring system of the present invention can perform stable and accurate measurement even when waves or bubbles are present on the liquid level, so that the liquid level in a small container can be measured. It is suitably used from distance measurement to water level observation of rivers, lakes and seas.

1,20 Liquid level distance measuring device 2,31 Light source 3 Optical coupler 4,33 Light transmission / reception part 5,36 Light receiving part 6,37 Signal processing part 7,25 Electric harness 8 Convex mirror 9 Concave mirror 10 Reference reflection surface 11 Opening 12 Lens 13, 45 Lens holder 14 Lens protection glass 15, 47 Cover 16 Cover glass 21 Semiconductor light source 22 Reflector 23 Forward bias circuit section 24 Reverse bias circuit section 30 Multipoint liquid level distance batch measurement system 32 Specific wavelength demultiplexer 34, 34a ~ 34n Optical Fiber 35 Optical Distributor 38 Transmitter Optical Amplifier 39 Receiver Optical Amplifier 40 Optical Demultiplexer 40a, 40c Optical Demultiplexer 40b, 40d Optical Combiner 41, 41a to 41d 3 Terminal Optical Circulator 42, 42a ~ 42d Bragg lattice optical fiber (FBG)
43 4 terminal optical circulator 46 optical fiber connector A container W return light

Claims (4)

A device that measures the distance between the reference surface and the liquid surface based on the light receiving time difference between the reflected light reflected by the reference reflecting surface and the return light reflected by the liquid surface.
A light source that emits pulsed light and
An optical transmission / reception unit that sends the pulsed light to the liquid surface and receives the return light.
A light receiving unit that receives the reflected light and the return light,
It is equipped with a signal processing unit that calculates the liquid level distance from the light receiving time difference between the reflected light and the return light.
The light transmitting / receiving unit has a reference reflecting surface and an optical system for condensing the return light while forming a parallel light bundle of the pulsed light.
The optical system, Ri Schwarzschild optical system der including convex mirror and concave mirror,
Liquid level distance measuring apparatus characterized that you have opening is formed in the center of the convex mirror. It is a system that collectively measures the distance between the reference surface and the liquid surface at multiple points based on the light receiving time difference between the reflected light reflected by the reference reflecting surface and the return light reflected by the liquid surface.
A light source that emits pulsed light containing multiple wavelengths,
A specific wavelength demultiplexer that demultiplexes light of a specific wavelength from the pulsed light,
An optical transmission / reception unit that sends light of the specific wavelength to the liquid surface and receives the return light.
An optical fiber that propagates the pulsed light and the reflected light and the return light.
An optical distribution unit that distributes the pulsed light propagating through the optical fiber and the reflected light and the return light.
It is equipped with a light receiving unit that receives the reflected light and the return light, and a signal processing unit that calculates the liquid level distance from the light receiving time difference between the reflected light and the return light.
The above-mentioned specific wavelength demultiplexing section and light transmission / reception section are arranged at multiple points.
The optical transceiver unit is the reference reflecting surface, and thereby into a parallel light beam of the pulse light, possess an optical system for condensing the return light,
A multipoint liquid level distance batch measurement system characterized in that the specific wavelength demultiplexing unit includes a 3-terminal optical circulator, a 4-terminal optical circulator, and an optical device that reflects light of the specific wavelength. The multipoint liquid level distance batch measurement system according to claim 2 , wherein at least the optical fiber included in the optical transmission / reception unit is a dual mode fiber. The multipoint liquid level distance batch measurement system according to claim 2 or 3 , wherein the optical system is a Schwarzschild optical system.

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