JPS5938522B2 - 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, may not be able to measure at close range, and have problems in terms of durability, so they are not suitable for detecting liquid levels in kerosene tanks, etc. It was inappropriate to use it.

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 the 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. Inside this long tube 1, three hemispherical floats are placed in a state of mutual interaction, and are made to move up and down within the long tube 1 according to the displacement of the liquid level A to be detected. 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.

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,
It has the advantage of being able to obtain stronger reflected light than direct reflected light from the liquid surface, being less sensitive to fluctuations in the liquid surface, and being less dependent 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, T 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 1,/12 and the distance L to the float 3, we obtained a characteristic that changes almost linearly as shown in FIG. Therefore, if the output ratio of the phototransistors 6 and 7 is 1 and /2, 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 10g11 and 10g12 of the amplifiers 8 and 9, and 11 is the output 10g of this amplifier 10.
, /12 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. Note that in order to eliminate the inconvenience 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 outputs 11, 1 of each phototransistor 6, 7
2 may be directly introduced into the division circuit and the ratio taken.O With the above configuration, the liquid level is 2.
It is obtained as the ratio between the outputs of the phototransistors 6 and 7, and does not depend on the absolute value of the phototransistor outputs like the detector shown in Figure 1, so even if there is dirt on the float 3, etc., it will hardly be affected. There is no.

This is clear from FIG. 8, which shows the relationship between the output ratio 11/2 and L when the reflective surface of the float 3 is painted black and when it is 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 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 tantalum but also in normal bright places.

This will lead to a wider range of uses for the detector. Thirdly, by changing the difference in the directivity angles of the two phototransistors, it is possible to change the rate of change in the output ratio of the phototransistors with respect to changes in the liquid level, as shown in FIG.

In the figure, a indicates that the directivity angle of the phototransistor 6 is ±
10 is a change curve of the output ratio 1,/12 when the directivity angle of the phototransistor 7 is ±30. Also, b indicates that the directivity angles of the phototransistors 6 and 7 are ±1σ and ±2, respectively.
This is a change curve for an output ratio of 11/12 when the power is 0. Therefore, if it is desired to make the rate of change of the output ratio of the phototransistor steeper with respect to a change in the liquid level, it is sufficient to increase the difference in the directivity angles of the two phototransistors. In this way, the output ratio changes greatly for a small change in the liquid level, so it is possible to accurately detect a small change in the liquid level. 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. Less susceptible to changes in reflectance due to dirt on the reflective surface of the float.

Therefore, the liquid level can always be detected accurately.

[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, 11/12 Characteristic diagram showing Fig. 7: Output 11 of phototransistors 6 and 7
, 12 is a block diagram showing an example of a circuit for obtaining 11/12 from Fig. 8. When the reflective surface of the Nifloat 3 is dirty,
Characteristic diagram showing the relationship between the liquid level and the output ratio of phototransistors 6 and 7 of 11/12 when painted black, Figure 9: Liquid level when changing the difference in directivity angle of phototransistors 6 and 7 FIG. 3 is a characteristic diagram showing the relationship between and an output ratio of 11/2. Symbol, 4: infrared light emitting diode, 6, 7: phototransistor.

Claims (1)

[Scope of Claims] 1. A long cylinder having a liquid inlet/outlet at its lower part, 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 float in the upper part of the long cylinder. A light emitting element and a plurality of light receiving elements having different directivities are arranged facing the float, the light from the light emitting element is reflected by the float, and the light reflected from the float is reflected by the plurality of light receiving elements. A liquid level detector that detects the light intensity of each light receiving element and continuously detects the position of the detected liquid level from the relative value between the outputs of each light receiving element. 2. The device according to claim 1, characterized in that the rate of change in the output ratio between the light receiving elements with respect to a change in the liquid level is made sharp by increasing the difference in directivity angle between the light receiving elements. Liquid level detector.