JP2510524Y2 - Liquid level sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a liquid level sensor for detecting the liquid level of oil or the like.

[Conventional technology]

Conventionally, a liquid level sensor including a light emitting element and a light receiving element is configured, for example, as shown in FIG. In FIG. 2, the liquid level sensor 1 includes a light emitting element 2 such as an LED and a light receiving element 3 such as a photodetector, which are fixed downward, and both end surfaces thereof face upward with respect to the light emitting element 2 and the light receiving element 3, respectively. It is composed of a light guide 4 made of a transparent resin and bent into a substantially U-shape.

With such a configuration, when the light guide 4 is above the liquid surface to be detected, the light guide 4 is located in the air, so that the light guide 4 and the transparent resin forming the light guide 4 have the same refractive index. Since the difference from the refractive index of air is relatively large, the light emitted from the light emitting element 2 is emitted from the light guide 4
When the light travels in the inside of the light guide, the light is totally reflected at the boundary surface. Therefore, this light reaches the other end surface along the bent inside of the light guide 4, is emitted from the end surface, and is incident on the light receiving element 3. By appropriately processing the output signal of the light receiving element 3, it is detected that the liquid surface to be detected is below the light guide 4.

Here, when the liquid level rises and the light guide 4 comes to be located in the liquid, the light from the light emitting element 2 emits light because the difference between the refractive index of the transparent resin and the refractive index of the liquid is relatively small. When it encounters a boundary surface while traveling inside the light guide 4, it is refracted without being reflected there and emitted to the outside, and does not reach the light receiving element 3. As a result, it is detected that the liquid surface is above the light guide 4.

[Problems to be solved by the invention]

However, the liquid level sensor 1 configured in this way
However, since the light guide 4 is required, the cost is relatively high, and it is difficult to structurally reduce the size.

Therefore, a liquid level sensor 5 as shown in FIG. 3 is known. That is, in the liquid level sensor 5, the light emitting element 2 and the light receiving element 3 are mounted on the can stem 6, and the lens 7 is resin-molded with a transparent resin such as epoxy resin so as to cover the light emitting element 2 and the light receiving element 3. As in the case of the liquid level sensor 1 of FIG. 2, the light is emitted from the light emitting element 2 and reflected by the inner surface of the lens 7 by utilizing the change in the difference in refractive index between the air and the liquid. The received light is received by the light receiving element 3 to detect the liquid surface.

However, the liquid level sensor 5 configured in this way
In the case of (1), since the structure is a can stem, the cost is high, and the manufacturing process is complicated, so that mass production is difficult. In addition, since the light receiving element and the light emitting element are formed on the same surface, the process of being reflected from the inner surface of the lens 7 from the light emitting element to reach the light receiving element 3 is relatively long, which causes scattering from the resin forming the lens 7. Since light and light from the light emitting element 2 are directly incident on the light receiving element,
There is a problem in that the scattered light and the direct light become noise during liquid level detection, the S / N ratio becomes low, and thus the detection accuracy deteriorates.

In view of the above points, the present invention is configured so that light does not directly enter the light receiving element from the light emitting element and the S / N ratio is increased to improve the detection accuracy, and the size is small and the cost is low. It is intended to provide a liquid level sensor that is configured and can be mass-produced.

[Means and Actions for Solving Problems]

According to the present invention, the above object is to provide three lead frames extending substantially vertically and a first lead frame among the lead frames.
Light emitting element chip mounted on the upper end surface of the lead frame, a light receiving element chip mounted on the upper end surface of the second lead frame of the lead frame, and transparent so as to cover the light emitting element chip and the light receiving element chip. In a liquid level sensor including a lens formed by molding with a resin, the upper end surface of the lead frame for the light emitting element and the light receiving element for the light receiving element are arranged so that the light emitting element chip is located above the light receiving element chip. The lead frame is formed with a step on the upper end surface, and the width of the upper end surface of the light emitting element lead frame is set so that the light emitted from the light emitting element chip is defined by the upper end portion of the light emitting element lead frame. This is achieved by forming the light emitting device chip wider than the light emitting device chip so as to be cut off.

According to this invention, the light that is about to enter the light receiving element directly from the light emitting element is blocked by the upper end portion of the lead frame for the light emitting element chip, so that the light does not directly enter the light receiving element and the lead Since it is configured by attaching the light emitting element chip and the light receiving element chip to the upper end surface of the frame, it can be formed in a very small size which is substantially the same size as a conventional LED, etc., and at the inner surface of the lens from the light emitting element. Since the process of being reflected and reaching the light receiving element is relatively short, the scattered light incident on the light receiving element is significantly reduced, which increases the S / N ratio and improves the liquid level detection accuracy. Moreover, this liquid level sensor can be used with the conventional LE by simply changing the shape of the lead frame.
Since it can be manufactured in the manufacturing process of D, it becomes possible to mass-produce at low cost.

〔Example〕

The present invention will be described below based on the embodiments shown in the drawings.

FIG. 1 shows an embodiment of a liquid level sensor according to the present invention. The liquid level sensor 10 includes three lead frames 11, 12 and 13 extending substantially vertically and A light emitting element chip attached to the upper end surface 11a of the first lead frame 11, for example, an LED chip 14, and a light receiving element chip attached to the upper end surface 12a of the second lead frame 12, for example, a photodetector chip 15, and the LED.
The lens 16 is formed by potting a transparent resin such as an epoxy resin so as to cover the upper ends of the chips 14 and 15 and the lead frames 11, 12 and 13.

In this case, the upper end surfaces 11a and 12a of the lead frames 11 and 12 are
As shown in FIG. 1, it is formed with a step,
The upper end surface 13a of the lead frame 13 is
It is formed in two steps according to a and 12a. Further, as is clear from FIG. 1, the upper end surface 11 a of the light emitting element lead frame 11 is wider than the LED chip 14. As a result, the light emitted from the LED chip 14 does not directly enter the photodetector chip 15, and the lead frames 11, 1
It is designed to be shut off by the upper end of 3. The tip of the third lead frame 13 may be formed with two steps as shown in the figure, and the light emitting element chip 14 may be placed on the higher side. Separately from this, the photodetector chip 15 may be placed on the lower side of the step. In that case, the first lead frame 11 serves as a common electrode in the former example, and the second lead frame 12 serves as a common electrode in the latter example.

In addition, the LED chip 14 and the photodetector chip 15 described above.
Are fixed to the upper end surfaces 11a and 12a by conductive bonding or the like and electrically connected to the lead frames 11 and 12, and are wire-bonded to the upper ends of the third lead frames 13, respectively. .

The liquid level sensor 10 according to the present invention is configured as described above, and the third lead frame 13 is used as a common electrode through the lead portions (not shown) below the three lead frames 11, 12, and 13. When power is supplied to the first lead frame 11, the LED chip 14 emits light, and the light emitted from the LED chip 14 is such that the light directly going to the photodetector 15 is blocked by the upper ends of the lead frames 11 and 13. Because it is done
Only the light emitted from the LED chip 14 and reflected by the inner surface of the lens 16 can enter the photodetector 15.

When the liquid level sensor 10 is used, the liquid level sensor 10 is turned upside down and attached appropriately. When the lens 16 is located above the liquid level to be detected, the lens 16 is in the air, Since the difference between the refractive index and the refractive index of air is relatively large, the light from the LED chip 14 hits the inner surface of the lens 16 and is totally reflected, and enters the photodetector 15, so that the liquid surface is below the lens. Can be detected.

On the other hand, when the liquid surface to be detected is above the lens 16, the lens 16 is located in the liquid, and therefore the difference between the refractive index of the lens 16 and the liquid around it is relatively small, so that the LED When the light from the chip 14 hits the inner surface of the lens 16, it is refracted without being totally reflected and is emitted to the outside, whereby the photodetector 15 has an LED chip 14
Almost no light is incident and it can be detected that the liquid surface is above the lens 16.

As described above, according to the present invention, the upper end surface of the lead frame for the light emitting element and the lead frame for the light receiving element are arranged so that the light emitting element chip is located above the light receiving element chip. The light emitted from the light emitting element chip is blocked by the upper end of the light emitting element lead frame, and the width of the top surface of the light emitting element lead frame is cut off. As described above, since the light emitting element chip is made wider than the light emitting element chip, the light directly entering the light receiving element from the light emitting element is blocked by the upper end portion of the light emitting element chip lead frame. There is no direct light incident on.

In addition, since it is configured by attaching the light emitting element chip and the light receiving element chip to the upper end surface of the lead frame, it can be formed in a very small size which is substantially the same size as a conventional LED, etc. Due to the relatively short travel of the light reflected by the inner surface and reaching the light receiving element, the scattered light entering the light receiving element is significantly reduced, which increases the S / N ratio and improves the liquid level detection accuracy. It will be.

Moreover, since the liquid level sensor can be manufactured in the conventional LED manufacturing process only by changing the shape of the lead frame, it can be mass-produced at low cost.

Thus, according to the present invention, the light-emitting element is configured so that light does not directly enter the light-receiving element, and the S / N ratio is increased to improve the detection accuracy, and the size and cost are reduced. An extremely excellent liquid level sensor that can be obtained and mass-produced can be provided.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of a liquid level sensor according to the present invention. 2 and 3 are schematic views showing an example of a conventional liquid level sensor. 10 …… Liquid level sensor; 11 …… First lead frame; 12…
… Second lead frame; 13 …… Third lead frame;
11a, 12a, 13a …… Upper surface; 14 …… LED chip; 15 …… Photo detector; 16 …… Lens.

Claims (1)

(57) [Scope of utility model registration request] 1. A lead frame comprising three lead frames extending substantially vertically, a light emitting element chip attached to an upper end surface of a first lead frame of the lead frames, and a second lead frame of the lead frames. A liquid level sensor including a light-receiving element chip attached to the upper end surface of the light-receiving element, and a lens formed by molding with a transparent resin so as to cover the light-emitting element chip and the light-receiving element chip. A step is formed between the upper end surface of the lead frame for the light emitting element and the upper end surface of the lead frame for the light receiving element so as to be located above the chip, and on the lead frame for the light emitting element. The width of the end face is adjusted so that the light emitted from the light emitting element chip is blocked by the upper end of the lead frame for the light emitting element. A liquid level sensor characterized by being formed wider than the top.