JPS6044611B2 - liquid level detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous liquid level detector using optical means, particularly suitable for use in kerosene tanks of hot air heaters and the like.

Conventional continuous liquid level detectors use a float floating on the liquid surface to mechanically move an arm, convert this movement of the arm into a change in electrical resistance, and detect the liquid level based on the amount of change. There are known devices in which the reflection time of ultrasonic waves from the liquid surface is measured using an ultrasonic transmitter, and the liquid level is detected based on the measured value.

However, these detectors are difficult to miniaturize and may not be able to measure at close range, and they also have problems in terms of durability, making it difficult to measure the liquid level in kerosene tanks, etc. It was inappropriate to use it for detection.

The present invention has been made in view of the above points, and an object of the present invention is to provide a continuous liquid level detector that is small in size and has a long life.

To summarize the present invention, a light emitting element and a light receiving element are provided at the top of a long cylinder, a float is placed inside the long cylinder, and the position of the liquid surface to be detected is determined by detecting the amount of light reflected from the float by the light receiving element. It is characterized in that it is designed to detect continuously.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a structural diagram of a liquid level detector according to an embodiment of the present invention.

In the figure, a long cylinder 1 has a circular cross section, has liquid and air inlets and outlets 2a and 2b at the bottom and upper part, and has a uniform reflectance on its inner wall.

A hemispherical float 3 is placed in a free state inside the long tube 1, and moves up and down in the long tube 1 according to the displacement of the liquid level A to be detected.
It is made to move. At the upper end of the long tube 1, an infrared light emitting diode 4 and a phototransistor 5 are arranged in parallel facing the float 3.

This light emitting diode 4 is used as an element so as to radiate a luminous flux in a diffusing direction without using any particular lens or reflecting mirror.

Due to this configuration, a part of the light emitted from the light emitting diode 4 is reflected on the upper surface of the float 3 either directly or through reflection on the inner wall of the long cylinder 1, and travels in the opposite direction to reach the phototransistor 5. become.

In this case, the amount of light that reaches the phototransistor 5 changes depending on the position of the float 3 due to the spread of the light beam and attenuation due to reflection from the wall of the long tube 1.
As the value decreases, the amount of light also decreases. Therefore, from the output of the phototransistor 5, the float position, that is, the liquid level of the liquid to be measured can be detected.

Although not shown in FIG. 1, it goes without saying that an infrared light emitting diode drive circuit, a phototransistor output amplification circuit, a liquid level display circuit, etc. are separately provided.

As is clear from the above configuration, this liquid level detector can use the light emitting diode 4 that emits a normal luminous flux in a diffused direction without using a special lens or reflector as a light emitting element. It can be manufactured inexpensively and compactly.

Furthermore, since the upper surface of the float 3 does not necessarily have to be a mirror surface, the structure of the float 3 is simple and can be manufactured at low cost. Furthermore, with this liquid level detector,
Since the light from the light emitting diode 4 is diffused, in order to prevent this light from being diffused to the surroundings and the amount of received light decreasing rapidly, the light emitting diode, phototransistor 5 and float 3 are housed in the long tube 1. Since the light can be reflected on the inner wall of the long tube 1, the light from the light emitting diode 4 can be effectively utilized!
In addition, there is no need to converge the reflected light onto the phototransistor 5 by the slope, and the light intensity distribution in the cross-sectional direction within the long tube becomes uniform, making it easier to attach the light emitting diode 4 and the phototransistor 5. The requirements for accuracy regarding position and angle can be relaxed3, and as a result, variations in performance between individual detectors can be reduced. Furthermore, since the light is reflected by the float 3, it is possible to obtain a stronger reflected light than the direct reflected light from the liquid surface.
Further, there are advantages in that it is less susceptible to fluctuations in the liquid level and does not depend on whether the liquid is transparent or not.

In addition to the above-described advantages, the detector of this embodiment can easily realize preferred modifications as described below by partially changing or adding the structure.

First, since the optical system and the float are placed inside the long cylinder, simply installing a filter at the entrance and exit of the liquid can prevent the intrusion of dust and the like, making the interior less likely to get dirty.

Secondly, by making the liquid entrance and exit structure difficult for outside light to enter, it is possible to use the device not only in the tank but also in normal bright places.

This will lead to a wider range of uses for the detector. Thirdly, although the reflectance of the inner wall of the long cylinder was made uniform in the above example, by changing the reflectance of the inner wall in the vertical direction, that is, in the direction of change in the liquid level, it is possible to respond to changes in the liquid level. The rate of change of the phototransistor output can be changed.

For example, if you want to make the rate of change of the phototransistor output steeper with respect to changes in the liquid level, it would be better to make the reflectance of the inner wall decrease as you move away from the phototransistor.
stomach. Fourth, if you want to reliably determine that the liquid level is below a certain level, for example, when you want to know whether the liquid level is close to empty, you can move the long cylinder at a point corresponding to the certain level. This can be achieved by bending.

A concrete example of this is shown in FIG. As is clear from the figure, when the liquid level falls below the curved part, the reflected light from the float 6'' decreases rapidly, and the output of the phototransistor 5 also decreases accordingly. It can be seen that it is reliably detected.In addition, in the same figure, float 6
A spherical one is used for this purpose, but there are no restrictions on the shape as long as the light from above is reflected in the same direction. The only disadvantage of the detector, which has many of the advantages mentioned above, is that if there is a large difference in the amount of light emitted above and below the liquid level, the dark current of the light receiving element such as a phototransistor, and the dynamic range of the amplifier circuit. Although it is relatively difficult to uniformly detect the liquid level due to the limit of , this can be easily solved by appropriately increasing the output of a light emitting element such as a light emitting diode. This goes further and makes it possible to substantially widen the liquid level detection range by increasing the light emitting element output. Note that the increase in the output of the light emitting element during this process can be thought of as follows: increasing the output of a single light emitting element as it is, or driving a plurality of light emitting elements in stages. In the latter case, the light emitting elements are turned on one by one as the liquid level becomes lower, that is, as the output of the light receiving element reaches a certain level or less. The drive circuit, amplifier circuit, liquid level display circuit, etc. connected to each of the infrared light emitting diode 4 as a light emitting element and the phototransistor 5 as a light receiving element may follow a conventional known circuit configuration.

In this case, if you use a microprocessor, you can downsize and
More preferable reliability and the like can be obtained. As described above, the present invention does not use any mechanical elements in the overall configuration of the detector, and also does not use large parts, so it can contribute to miniaturization.

Further, since the light emitting element and the light receiving element can be made of optical semiconductors that can be used semi-permanently, the reliability and longevity of the entire detector can be sufficiently increased. Furthermore, since no expensive parts are required, there is an effect that a cheaper product can be provided. Therefore, the liquid level detector according to the present invention is suitable for application to, for example, a kerosene tank of a domestic hot-air heater, which is required to be highly reliable, small, and inexpensive.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a liquid level detector according to an embodiment of the present invention, and FIG. 2 is a structural diagram of a modified embodiment thereof.

Claims (1)

[Claims] 1. A long cylinder having a liquid entrance/exit part at the bottom, a float placed in the long cylinder in a free state and moving up and down according to the displacement of the liquid surface to be detected, and a part facing the float arranged at the top of the long cylinder. A light-emitting element and a light-receiving element that emit the emitted light flux in a diffusing direction, the light from the light-emitting element is reflected by the float, and the light-receiving element detects the amount of light reflected from the float. A liquid level detector that continuously detects the position of the liquid level.