JPH03131724A - Level gauge - Google Patents

Abstract

PURPOSE:To measure the height of a liquid surface with high accuracy by projecting a modulated light wave from above the liquid surface, and receiving its reflected light and finding the liquid surface height from the phase difference of the modulated light wave. CONSTITUTION:Light from a light emitting element 3 is converged by a condenser lens 6, transmitted through a translucent mirror 4, and projected on the liquid surface 20 as parallel luminous flux (p) or divergent light p' through a large-diameter lens 2. The reflected light is reflected vertically upward and converged again by the large-diameter lens 2, reflected by the translucent mirror 4, and made incident on a light receiving element 5, which converts the light into an electric signal, thus constituting a liquid level measurement optical path. A plane reflecting mirror 9 is arranged on the straight prolongation of the optical axis of the light receiving element 5 and the light from the light emitting element 3 is reflected by the translucent mirror 4 and then the reflecting mirror 9, thus constituting an internal calibration optical path returning to the light receiving element 5 again. A solenoid 12 is turned on/off to measure the liquid level optical path and calibration optical path alternately and their difference is calculated to find the liquid surface height.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to water level meters used for various types of water level observation such as river, groundwater, and dam water levels, liquid level measurement used for various flow rate measurements, and storage of petroleum and chemical liquids. This invention relates to a liquid level gauge that measures the level of liquid in a tank.

[Conventional technology] Conventional liquid level gauges have a float suspended by a wire on the liquid level, and the amount of movement of the wire as it moves up and down in response to the rise and fall of the liquid level is recorded on a recorder via a pulley, or a pressure detector is used. It was common to submerge the liquid under the liquid level and extract the pressure changes caused by the rise and fall of the liquid level as an electrical signal, which was then displayed or recorded.

However, with the former, the float and recorder are mechanically connected by a wire, so the wire may come off the pulley, or
The drawback is that the mechanically movable parts often malfunction due to corrosion or other causes, resulting in missing measurements.

In addition, the latter has a number of drawbacks, such as the low accuracy of the pressure detector, making it impossible to accurately detect the liquid level, and the output cable of the detector below the liquid surface being cut by strong water currents or hot stones. Ta.

[Means for Solving the Problems] As mentioned above, conventional liquid level gauges have various drawbacks, so the liquid level gauge of the present invention uses a completely different measurement principle, and uses modulated light waves from above perpendicular to the liquid surface. The device projects the reflected light directly onto H1ait, receives the reflected light, and measures the phase difference of the modulated light wave to measure the surface height without contact.The measuring device has no moving parts and is airtight inside. In addition, the lens surface where light enters and exits is equipped with an air shower, etc. to constantly clean the lens surface, so there is almost no failure even at measurement sites in adverse environments, and it is possible to measure the phase of light waves. This problem was solved by making it possible to observe the liquid level with high accuracy.

[Function] The working principle of the liquid level gauge of the present invention is to project a light wave onto the liquid surface from vertically above, receive the reflected light from the liquid surface, and measure the time it takes for the light to travel back and forth on the liquid surface after being emitted. , which measures the liquid level. The speed at which light propagates through the air is 300,001LII/
Since it is seC, if the light is modulated at 15MH2, one wavelength is 20m, and if the round trip optical path length to the liquid surface is 20-, the height from the main body to the liquid surface is 10m, which is sufficient for measurement range as a liquid level meter. .

The amount of light reflected from the liquid surface, for example, the water surface, is said to be 4%, and 10%.
The amount of light reflected from the liquid surface at a height of m is (1000/10) 2 400 times the light receiving output can be obtained and measurement is easy.

The light wave is generated by modulating the light emitted from a light emitting diode or laser diode with 15MH2 excavated from a crystal oscillator, condensing the light onto the liquid surface with a large diameter lens, collecting the reflected light with the lens, and transmitting it to a light receiving element (PIN diode). By photoelectrically converting the light and measuring one wavelength of l/10.000 with a digital phase meter, it is possible to measure the liquid level with an accuracy of 1 meter.

Since the time for light to travel back and forth across the liquid surface is several microseconds, the above measurement is repeated to, ooo times for each measurement, and the average value is displayed. In addition, since the liquid surface does not necessarily maintain a horizontal surface and has ripples and fluctuations, the projected light is reflected by a large-diameter lens, either as a parallel beam or slightly divergent, so that the reflected light can be received even if the liquid surface is slightly tilted. If the reflected light deviates further outside the lens, the received light signal will become zero or will not reach the appropriate light receiving level, so the level comparator will exclude the measurement and the arithmetic circuit will detect the received light signal that is above the appropriate level. When the length measurement value of the number reaches 10,000 times, the average value will be displayed.

If the liquid surface is dirty or has little reflected light, a float equipped with a corner prism or cat's eye may be floated on the liquid surface.

Furthermore, in order to prevent water droplets from condensing and dust from adhering to the surface of a large-diameter lens exposed to the outside, the lens surface is always kept clean by wrapping a heat insulating heater around the lens frame or by providing an air shower.

[Example] The present invention will be explained with reference to the drawings as follows. 1st
In the figure, a large-diameter lens 2 is attached to the lower central surface of the main body 1 so that its optical axis is perpendicular to the main body 1, and a light-emitting element 3 is placed at its vertically upper focal point, and a semi-transparent mirror 4 is placed in the imaging space of the large-diameter lens 2. is arranged at an angle of 45° with respect to the optical axis, and the light-receiving element 5 is placed at a focal common range position on the reflection optical axis with the optical path bent by 90°. 6 is a light-transmitting condenser lens, and 7 is a light-receiving condenser lens. , 8 is an optical filter that transmits only the wavelength of light emitted from the light emitting element and cuts off natural light.

With the above optical structure, the light emitted from the light emitting element is focused by the condenser lens 6, transmitted through the semi-transparent mirror, and projected onto the liquid surface 20 as a parallel beam P or a diverging beam P' via a large aperture lens. Since the liquid surface is horizontal, the reflected light is reflected vertically upward, condensed again by a large-diameter lens, reflected by a semi-transparent mirror, and incident on the light receiving element 5, forming a liquid level measurement optical path where it is converted into an electrical signal.

- There is a flat reflecting mirror 9 on the optical axis straight extension line of the light receiving element, and the light emitted from the light emitting element is reflected by the semi-transparent mirror, reflected by the flat mirror, and returns to the light receiving element again to form an internal calibration optical path.

The liquid level measurement optical path and the internal calibration optical path are switched by a shutter mechanism 10. The shutter plate 10 has a rotating shaft 11, and when the solenoid 12 is ON, it is pulled to one side, opening the liquid level measurement optical path and closing the calibration optical path, and when it is OFF, it pulls it to one side. The shutter returns and conversely closes the liquid level measurement optical path and closes the calibration optical path, and by turning on and off the solenoid, the liquid level optical path and the calibration optical path are alternately measured, and the difference between them is calculated to determine the liquid level height.

This device is kept airtight inside with a cover 13, and the optical mechanism and electronic circuit 14 are integrally built into the main body, and the power source and output signals are connected to an external power source, recorder, etc. through a connector 19.

The main body 1 can be placed on a pedestal 16 with the optical axis perpendicular using three leveling screws 15 and a bubble tube 21.

In the liquid level gauge of the present invention, in order to prevent water vapor evaporating from boreholes, wave-dissipating tubes, etc. from condensing on the outer surface of the large-diameter lens, a heat-retaining heater 17 is wrapped around the outer circumference of the lens frame, or air is applied to the lens surface using a fan 18 using a small motor. This was done to keep the lens surface clean by spraying a shower to ensure stable measurements.

FIG. 2 is a block diagram illustrating the electrical circuit of the liquid level gauge of the present invention. The light emitting element 3 is driven by the drive circuit 23 to emit a 15MH2 modulated light wave oscillated by the crystal oscillator 22.

The received signal received by the light receiving element 5 is amplified by a preamplifier 24, converted to a low frequency by a mixer circuit 25 using a signal from a local crystal oscillator 26, and noise is removed by a bandpass filter 27.

A phase difference corresponding to the optical path length is measured by a digital phase meter 29 including a clock oscillator 30 via a level comparator 28 which supplies only a signal of an appropriate light reception level to the next circuit.

Measurement commands are issued from the timer 33 at fixed time intervals, and the shutter lO is operated by the solenoid 12 to alternately measure the liquid surface optical path length and the calibration optical path length, and calculate the difference between them to the calculation circuit 31.
It is calculated and displayed on the recording device or display device 32. In addition to this, the arithmetic circuit receives only the appropriate level signal of the amount of light reflected from the liquid surface.
,000 measurements and calculate the average value to improve measurement accuracy.

[Effects of the Invention] As explained above, the liquid level meter of the present invention has a completely different measurement principle from the conventional float method or pressure detection method, has no mechanical moving parts, does not require a cable to the liquid surface, and is non-contact. It can measure the liquid level and is easy to install, with almost no failures during long-term observation even in adverse environments.

In addition, since it uses a high-speed modulated wave, the response speed is fast and the measurement accuracy is high.If sampling measurements are performed at intervals of several minutes, the power consumption is minimal, and even in remote areas without power sources, long-term measurements can be performed with a small battery.It has a waterproof structure. It has many features, such as being equipped with an insulating heater and an air shower, allowing stable liquid level observation even in harsh environments.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the optical structure of the liquid level gauge of the present invention;
The figure is a block diagram of an electrical circuit. Explanation of symbols 1...Main body, 2...Large diameter lens, 3...Light emitting element, 4...Semi-transparent mirror, 5...Light receiving element, 6...Light sending and condensing lens, 7 ... Light receiving condensing lens, 8 ... Optical filter 9 ... Plane reflecting mirror, lO ... Shutter 11 ... Shutter plate rotation axis, 12 ... Solenoid, 13 ... Cover 14 ...・Electronic circuit, 15...
・Leveling screw, 16... Frame, 17... Heat retention heater 18... Fan, I9... Connector 20...
・Liquid level, 21...Bubble tube, 22...Crystal oscillator, 2
3... Drive circuit, 24... Preamplifier, 25...
Mixer circuit, 26...Local crystal oscillator 1.27
... Band pass filter 28 ... Level comparator 29 ... Digital phase meter, 30 ... Clock oscillator, 3! ...Arithmetic circuit, 32...Display device, 33...Timer P...Projected parallel light flux, P'.
・Projected divergent light flux

Claims (1)

[Claims] A light-emitting element is placed at the upper focal point of a large-diameter lens with its optical axis vertical, and a semi-transparent mirror that bends the optical path by 90 degrees is arranged in the imaging space of the large-diameter lens, and the reflection optical axis of the semi-transparent mirror is A light receiving element is placed at the confocal focal position, and a modulated light wave is emitted from a light emitting element, which is parallel or slightly diverging from a large aperture lens and projected directly onto the liquid surface, or by a corner prism or cat's eye attached to a float floating on the liquid surface. At the same time, the reflected light is received to measure the optical path length to the liquid surface, and the light emitted from the light emitting element and reflected by the semi-transparent mirror is reflected in the same direction by a plane mirror and transmitted through the semi-transparent mirror. To prevent fogging of the lens by receiving light with the light receiving element and measuring the internal optical path length, and by alternately switching the optical path to the liquid surface and the internal optical path with a shutter to measure the liquid level height from the difference in the respective optical path lengths. A liquid level gauge that consists of a large-diameter lens with a heater wrapped around it, or a fan motor that sprays an air shower onto the lens surface.