JP2873591B2 - Liquid level indicator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a liquid level gauge used for industrial purposes, and more particularly to a liquid level gauge that continuously detects a change in liquid level without contact.

(Prior Art) Conventional liquid level gauges are roughly classified into a contact type and a non-contact type, and these are further referred to as a type called a point sensor for determining whether or not liquid exists at a certain point, and a liquid level. Are continuously classified. Among them, the liquid level gauges that continuously detect a change in the liquid level in a non-contact manner include (1) those that use the reflection of light on the liquid level, and (2) that use the reflection of ultrasonic waves on the liquid level. And (3) those that detect a change in pressure of a liquid have been put to practical use or developed.

(Problems to be Solved by the Invention) FIG. 4 is a schematic diagram showing the principle of a conventional liquid level meter utilizing reflection of light on a liquid surface. The light source 1 and the light receiver 2 are arranged above the liquid surface 3, and are adjusted so that the light receiver 1 receives the beam of the light source 1 reflected on the liquid surface 3. Liquid level 3
Changes to the position 3 ', the optical path from the light source 1 to the light receiver 2 changes, and the amount of light received by the light receiver 2 decreases. The change in the liquid level is detected from the decrease amount.

In this liquid level meter, a change in the amount of received light is detected in an analog manner, so that in order to detect a change in the liquid level with high accuracy, the light source 1 and the light receiver 2 need to be stabilized for a long time. However, there is a drawback such that an error occurs when the reflectance of the liquid surface changes.

FIG. 5 is a schematic view showing the principle of a conventional liquid level gauge utilizing the reflection of ultrasonic waves at the liquid level. The ultrasonic oscillator 4 and the receiver 5 are arranged in the liquid, and are adjusted so that the ultrasonic wave of the ultrasonic oscillator 4 reflected by the liquid surface 3 is received by the receiver 5. When the liquid level 3 changes to the position 3 ', the path from the ultrasonic oscillator 4 to the receiver 5 is shortened, and the propagation time of the ultrasonic wave is shortened. By detecting a change in the propagation time, a change in the liquid level can be detected.

This type of liquid level gauge has a drawback that the propagation speed of the ultrasonic wave varies depending on the density and temperature of the liquid, which causes an error.

FIG. 6 is a schematic view showing the principle of a conventional liquid level gauge utilizing the pressure of liquid. The pressure sensor 6 is arranged at a fixed position in the liquid, for example, at the bottom of the liquid container. And liquid level 3
When the pressure changes to the position 3 ', the pressure at the position of the sensor 6 decreases. Therefore, this pressure change is detected by the sensor 6, and the change in the liquid level is detected. The pressure sensor 7 is also arranged at a fixed position in the gas outside the liquid, and the pressure difference between the sensors 6 and 7 is detected.

This type of liquid level gauge has a disadvantage that it is affected by the density and specific gravity of the liquid.

An object of the present invention is to provide a liquid level gauge which eliminates the above-mentioned disadvantages.

(Means for Solving the Problems) According to the present invention, a light source for transmitting a parallel beam, and a photodetector for detecting a center position of a spot of the parallel beam transmitted from the light source and reflected on a liquid surface to be detected are provided. A data processor for calculating a change in the liquid level from a change in the center position of the spot of the parallel beam detected by the light receiver, wherein the light source is configured to transmit two parallel beams, The detector detects the center position of each spot of the two parallel beams reflected on the liquid surface to be detected, and the data processing device detects the intermediate position of the center position of each spot of the two parallel beams detected by the light receiver. , And a change in the liquid level is calculated from the change in the intermediate position, thereby obtaining a liquid level gauge.

(Embodiment) Hereinafter, an embodiment of the liquid level gauge of the present invention will be described in detail with reference to FIG. 1 to FIG.

FIG. 1 is a schematic configuration diagram of a liquid level gauge on which the present invention is based. As shown, a light source 8 and a light receiver 9 are arranged above the liquid level 3. The light source 8 emits a parallel beam 10 having a small spot diameter such as a laser beam. The light receiver 9 can detect the center position of a beam spot such as a one-dimensional optical sensor or a one-dimensional optical position sensor (PSD). When the liquid level is at position 3, the parallel beam 10 is reflected at point P on liquid level 3 and received at point R on the light receiving surface of light receiver 9. When the liquid level changes to the position 3 ', the parallel beam 10 is moved to the liquid level 3'.
The light is reflected at the upper T point and is received at the S point on the light receiving surface of the light receiver 9. The change in the liquid level is calculated by a data processing device 100 to which the output of the light receiver 9 is supplied by a calculation described later.

Next, the principle of calculating the change in the liquid level will be described. In FIG. 1, the amount of change when the liquid level drops from 3 to 3 'is defined as ΔL. The parallel beam 10 incident on the point P on the liquid surface 3 at the angle θ is incident on the point T on the liquid surface 3 'when the liquid surface drops to 3', which is equivalent to being reflected here. The distance between the point P and the point Q is ▼ = 2ΔLtanθ.

On the other hand, the center of the beam spot on the incident surface of the light receiver 9 is set from the point R due to the drop of the liquid surface from 3 to 3 'because the incident surface of the light receiver 9 is installed substantially perpendicular to the reflected beam. Move to point S. At this time, the distance from the R point to the S point is ▲ ▼ = ▲ ▼ cosθ, and ▲ ▼ = 2ΔLsinθ from the equation, and the change amount of the liquid level Δ is given by the distance from the R point to the S point.
L can be obtained.

In actual measurement of the liquid level, the liquid level may vibrate, and the liquid level does not always become horizontal. Therefore, by surrounding a part of the liquid surface with the cylindrical body 11 as shown in FIG. 1, vibration of the liquid surface can be reduced.

FIG. 2 is a schematic view showing an embodiment of a liquid level meter according to the present invention suitable for detecting a change in the liquid level having a characteristic of forming a curved surface instead of a horizontal liquid level.

In this embodiment, the liquid level is measured using two parallel beams A and B according to the same principle as the apparatus shown in FIG. Assuming that the liquid surface 3 is horizontal, the reflected beams on this surface are A 'and B', but the reflected beams on the curved surface 31 are A 'and B'. From these relationships, the midpoint between the incident points of the reflected beams A 'and B' on the light receiving surface (not shown) is the same as the midpoint of the incident points of the reflected beams A 'and B' on the light receiving surface (not shown). Almost match. Therefore, when measuring the amount of change in the liquid level, the change in the position of the midpoint between the two reflected beams on the light receiving surface is detected and measured in the same manner as in the example of FIG.

FIG. 3 is a schematic diagram showing a reference example of a liquid level gauge having a curved surface as in the case of FIG. In the figure, a light source 8 and a light receiver 9 are arranged at positions symmetrical with respect to a virtual vertical axis 41 set on the liquid surface 3, and their optical axes are substantially equal to the virtual vertical axis 41 on the liquid surface 3. Each inclination is adjusted so as to intersect at the angle θ. When the liquid level changes from 3 to 3 ', the light source 8 and the light receiver 9 have their respective optical axes set to the vertical axis.
The inclination is adjusted as shown by 8 'and 9' so as to intersect with the liquid surface 3 'at substantially the same angle θ'. These inclination adjustments are performed under the control of a processing device (not shown).
This is performed by the inclination adjusting means of the light receiver 9. The tilt adjusting means has a drive unit for the light source 8 and the light receiver 9 and a tilt angle detection unit, and the processing device controls the drive unit based on an output of the tilt angle detection unit.

An example of this tilt adjustment will be described. First, assuming that the liquid level changes from 3 to 3 ', the light receiver 9 adjusts the tilt angle so that the incident point from the liquid level 3' coincides with the incident point at the liquid level 3. Is adjusted. Based on this adjustment tilt angle, the tilt angle of the light source 8 is adjusted this time. As a result, the tilt angle of the light receiver 9 is adjusted so that the shifted incident point on the light receiver 9 is returned to the original position. Hereinafter, this control operation is repeated so that the incident point from the liquid surface 3 'coincides with the incident point when the liquid surface 3 is at the same time, and the optical axes of the light source 8 and the light receiver 9 intersect with the virtual vertical axis 41 at an angle θ'. Is controlled as follows. In this embodiment, the change amount of the liquid level can be obtained from the change amount of the angle θ.

(Effect of the Invention) According to the liquid level meter of the present invention described above, a change in the liquid level can be detected with high accuracy without being affected by the reflectance of the liquid surface, the type of liquid, the ambient temperature, and the like. .

In addition, it is possible to measure the vibration of the liquid surface or the change even when the liquid surface is not horizontal.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a liquid level gauge on which the present invention is based, and FIG.
FIG. 3 is a schematic view of a liquid level gauge for detecting a change in a liquid level forming a curved surface, showing an embodiment of the present invention. FIG. 3 is a schematic view of a liquid level form showing a reference example of the present invention. The figure is a schematic diagram showing the principle of a conventional liquid level gauge. 3, 3 '... liquid level, 8 ... light source, 9 ... light receiver, 10 ...
Parallel beam, 100 ... Data processing device.

Claims (1)

(57) [Claims] 1. A light source for transmitting a parallel beam, a photodetector for detecting the center position of the spot of the parallel beam transmitted from the light source and reflected on a liquid surface to be detected, and a light beam of the parallel beam detected by the photodetector. A data processing device for calculating a change in the liquid level from a change in the center position of the spot, wherein the light source is configured to emit two parallel beams, and the light receiver is reflected by the liquid level to be detected. The center position of each spot of the two parallel beams is detected, and the data processing device calculates an intermediate position between the center positions of the spots of the two parallel beams detected by the light receiver, and calculates the intermediate position from the change in the intermediate position. A liquid level gauge, which calculates a change in liquid level.