JPS5938524B2 - 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 short distances, and they also have problems in terms of durability, so they are not used to detect liquid levels in kerosene tanks, etc. It was inappropriate.

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 plurality of light receiving elements with different directivities are provided at one end of a long tube, a float is placed inside the long tube, and the amount of light reflected from the float is detected by the light receiving element. The present invention is characterized in that the position of the liquid level to be detected is continuously detected from the relative value of the output of the light receiving element.

In explaining the present invention, a liquid level detector previously filed by the present applicant will be described below.

FIG. 1 shows a structural diagram of a liquid level detector.

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 is made to move up and down within the long tube 1 according to the displacement of the liquid level A to be detected. An infrared light emitting diode 4 and a phototransistor 5 are arranged at the upper end of the long tube 1.
are arranged in parallel facing the float 3.

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 tube 1, and travels in the opposite direction to reach the phototransistor 5. become.

In this case, the amount of light reaching 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 on the inner wall of the long cylinder 1. 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, in this liquid level detector, the light is reflected by the inner wall of the long cylinder 1, so the light from the light emitting diode 4 can be effectively used, and the light in the cross-sectional direction of the long cylinder 1 can be effectively used. Since the intensity distribution of the light emitting diode 4 and the phototransistor 5 become uniform, the requirement for accuracy regarding the mounting position and angle of the light emitting diode 4 and the phototransistor 5 can be relaxed, and as a result, variations in performance between individual detectors can be reduced.

Furthermore, since the light is reflected by the float 3,
This method has the advantage of being able to obtain stronger reflected light than direct reflection from the liquid surface, being less sensitive to fluctuations in the liquid surface, and not depending on whether the liquid is transparent or not.

However, the above configuration has a drawback in that the float 3, phototransistor 5, etc. are greatly affected by dirt.

In contrast, the present invention shown in FIGS. 2 and below has the advantage of not having such drawbacks.

In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals, so that most of the configuration of the level detector of the present invention is the same as that in FIG. 1. However, in the present invention, as shown in FIG. 3, a light emitting diode 4 and two phototransistors 6 and 7 are arranged at the upper end of the long tube 1 in a positional relationship that corresponds to the vertices of an equilateral triangle. The transistors 6 and 7 have different directivities as shown in FIG. With such a configuration, the light emitted from the light emitting diode and reflected by the float 3 will be incident on the phototransistors 6 and 7 at approximately equal rates; Since they have different directivities, each phototransistor 6,
The outputs 11 and 12 of 7 are as shown in FIG.

In other words, the rate of change of the output 11 with respect to the distance L to the float 3 of the phototransistor 6 with narrow directivity is clearly different from the rate of change of the output 12 with respect to the distance of the phototransistor 7 with wide directivity with respect to the distance to the float 3. . In addition,
The absolute value of the output of the phototransistors 6 and 7 depends on the type of element and has nothing to do with directivity. The directivity of each transistor 6, 7 is clearly expressed as the rate of change of the output with respect to the displacement of the float 3. As mentioned above, if the rates of change in the outputs of the two transistors 6 and 7 with respect to the displacement of the float 3 are different, then the distance to the float 3 should be known by taking these relative values.

Therefore, when we determined the relationship between the output ratio 11/12 and the distance L to the float 3, we obtained a characteristic that changes almost linearly as shown in FIG. 6. Therefore, if the output ratio of the phototransistors 6 and 7 is 11/12, the position of the float 3, that is, the liquid level can be determined from FIG. Next, an example of a circuit for obtaining the output ratio of phototransistors 6 and 7 is shown in FIG.

In the figure, 8 and 9 are known logarithmic amplifiers, 10 is a differential amplifier for taking the ratio of the outputs 10gI, 10g12 of the amplifiers 8 and 9, and 11 is the output 10g of this amplifier 10.
It is an inverse amplifier that converts 11/I2 to 11/12. The reason why logarithmic amplifiers 8 and 9 are used in this circuit is that the output range of phototransistors 6 and 7 is extremely wide, ranging from one to three digits, depending on whether the liquid level is high or low. In addition,
In order to eliminate the disadvantage of widening the output range, the output of the light emitting diode 4 may be increased as appropriate depending on the liquid level. Moreover, the output 1 of each phototransistor 6, 7,
12 may be directly introduced into the division circuit and the ratio thereof may be calculated. With the above configuration, the liquid level can be obtained as the ratio between the outputs of the two phototransistors 6 and 7, and does not depend on the absolute value of the phototransistor outputs like the detector shown in FIG. Even if the float 3 etc. is dirty, it will hardly be affected by it. This is clear from FIG. 8, which shows the relationship between the output ratio 11/12 and L when the reflective surface of the float 3 is painted black and when it is not painted black. However, in the liquid level detector described above, information regarding the liquid level is obtained from the reflected light from the float surface. Therefore, if light other than the reflected light from the float surface reaches the light receiving elements 6 and 7, this becomes noise light. A particular problem arises when the light from the light emitting element 4 is diffusely reflected on the inner wall of the long tube and directly reaches the light receiving elements 6 and 7. Since the amount of reflected light from the float 3 becomes small, it cannot be ignored. Therefore, as shown in FIG. 6, when L becomes large, the output ratio 11/12 becomes saturated and does not change. Therefore, in the present invention, in order to make this measurable distance as large as possible, the reflectance of the inner wall of the long cylinder especially near the light emitting/receiving elements 6 and 7 is made smaller than the reflectance of other inner wall portions.
The effect obtained by doing this is shown in FIG. In the figure, the dotted line indicates a case where the inner wall of the long cylinder has a uniform reflectance as in FIG. 6, and the solid line indicates a case where the reflectance of the inner wall near the light emitting/receiving element is reduced. In addition to the above-mentioned 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 float are placed inside a long cylinder, simply installing a filter at the liquid entrance and exit port prevents the intrusion of dust and the like, making the interior less likely to get dirty.

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

This will lead to a wider range of uses for the detector. As mentioned above, the liquid level detector of the present invention has the following advantages.

Since it is hardly affected by changes in the emission intensity of one light emitting element, voltage fluctuations and temperature characteristics of the light emitting element can be ignored.

2.It is less susceptible to changes in reflectance due to dirt on the reflective surface of the float, and the measurable range can be increased.

Therefore, the liquid level can always be detected accurately and over a wide range.

[Brief explanation of the drawing]

Fig. 1: Structural diagram of a conventional liquid level detector, Fig. 2: Structural diagram of a liquid level detector of the present invention, Fig. 3: Top view of Fig. 2, Fig. 4: Orientation of phototransistor. Diagram showing the characteristics, Figure 5: Characteristic diagram showing the relationship between the liquid level and the outputs of the phototransistors 6 and 7, Figure 6: Relationship between the liquid level and the output ratio of phototransistors 6 and 7 of 1/12 Characteristic diagram showing Fig. 7: Outputs 1, , of phototransistors 6 and 7.
A block diagram showing an example of a circuit for obtaining 11/2 from 12,
Figure 8: Liquid level and phototransistor 6 when the reflective surface of float 3 is dirty and painted black
, 7, and the output ratio 11/12. Figure 9: The relationship between the liquid level and the output p ratio 1/2 when the reflectance near the light emitting diode 4 and phototransistors 6 and 7 is changed. Characteristic diagram showing the relationship.

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 plurality of light receiving elements having different directivity, the light from the light emitting element is reflected by the float, and the quantity of light reflected from the float is detected by each of the plurality of light receiving elements. In a liquid level detector that continuously detects the position of the liquid surface to be detected from the relative value between the outputs of each light receiving element, the reflectance of the inner wall of the long cylinder around the light emitting element and the light receiving element is reduced. A liquid level detector characterized by: