JP2000046630A - Liquid level detecting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level detecting element capable of preventing invasion of liquid surely, and capable of simplifying installment, and suitable for mass production. SOLUTION: A first light emitting/receiving part comprising a light emitting element 34 and a light receiving element 33, and a second light emitting/receiving part comprising a light emitting element 32 and a light receiving element 31 are arranged on a printed board 30 at prescribed intervals, and the printed board 30 is packaged in a case 41 comprising transparent material, to thereby arrange the first and the second light emitting/receiving parts in the case 41. When the exterior surface position of the case 41 corresponding to the second light emitting/receiving part on the upper stage is outside the liquid, emitted light from the light emitting element 32 is reflected on the exterior surface of the case 41, and the reflected light is received by the light receiving element 31 and a detection signal is outputted. Also, when the exterior surface position of the case 41 corresponding to the first and the second light emitting/ receiving parts on the upper and lower stages is outside the liquid, emitted lights from the light emitting elements 34, 32 are reflected on the case 41, and the reflected lights are received by the light receiving elements 33, 31 and detection signals are outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detector for optically detecting the presence or absence of a liquid such as water or kerosene.
For example, the present invention relates to a liquid level detector of a liquid level detecting device which is installed in a device such as an oil storage tank of a petroleum stove or a water tank of a water heater and detects the presence or absence of liquid in the device and the level of the liquid level.

[0002]

2. Description of the Related Art FIG. 11 shows an example of a conventional optical liquid level detector. Reference numerals 1, 2, and 3 denote lead terminals. The light-emitting element 4 is fixed to the end face 1a by a conductive adhesive so as to connect one electrode, and the light-receiving element 5 is similarly connected to the end face 3a of the lead terminal 3 by connecting the one electrode. It is fixed by an adhesive.

[0003] The other electrode of the light emitting element 4 and the light receiving element 5 is connected to the end face 2 a of the lead terminal 2 by the conductive wires 6 and 7.
It is connected to the. Note that one end of the lead terminals 1, 2, and 3, the light emitting element 4, the light receiving element 5, and the conductive wires 6 and 7 are provided inside a lens 8 having a hemispherical portion made of a transparent material.

The above liquid level detector supplies power to the lead terminals 1 and 2 to cause the light emitting element 4 to emit light. The emitted light diverges, and when the lens 8 is in contact with air, the ratio of the refractive index of the lens 8 to the refractive index of air is relatively large. Reflected at the boundary of
The reflected light at the position of the zenith 10 of the lens 8 enters the light receiving element 5.

When the lens 8 is in a liquid having a refractive index equal to or close to the refractive index of the lens 8, the emitted light is not reflected at the boundary between the lens 8 and the liquid, and The emitted light does not enter the light receiving element 5.

Therefore, by appropriately processing the photocurrent output from the light receiving element 5 based on the presence or absence of light incident on the light receiving element 5, it is possible to obtain a detection signal indicating whether the lens 8 is in contact with the liquid. Can be. In addition, it can be detected that the liquid level of the liquid is at the position of the lens 8 by the detection signal that changes when the liquid level of the liquid comes into contact with or separates from the zenith 10 of the lens 8.

FIG. 12 shows an example of a liquid level detector using such a liquid level detector. Reference numeral 20 denotes the liquid level detector described above. 21 is a liquid 22 to be detected
Is a lid provided on the upper part of the container 21. The lid 23 is provided with a holder 24, and the holder 24 is further provided with a liquid level detector 20 mounted with the lead terminal facing upward. 25 is a transfer pipe for transferring the liquid 22 in the container 21, and 26 is a pump for transferring the liquid.

The liquid level detector 20 is supplied with electric power by an attached electronic circuit device, and the detection signal is processed. Here, when the liquid level detector 20 is in the liquid, the output signal of the electronic circuit device responsive to the detection signal is H, and when the liquid level detector 20 is in the air, the output signal is L. .

The pump 26 is driven by the output signal H. Therefore, when the liquid 22 is sufficient in the container 21 and the liquid level detector 20 is submerged in the liquid,
The pump 26 is driven, and the liquid 22 in the container 21 is sent out of the container 21 through the transfer pipe 25.

The above operation is continued, and the liquid 22 in the container 21 is
When the liquid level 22a drops to the liquid level 22b, the liquid level detector 2
0 is exposed to the air, the output signal becomes L, and the driving of the pump 26 is stopped. Therefore, the no-load operation of the pump 26 is prevented. Further, when the above liquid level detecting device is used in a petroleum stove combustion system, the supply of fuel is stopped and the fire is extinguished.

[0011]

In the above-mentioned liquid level detector, one end of the lead terminals 1, 2 and 3, the light emitting element 4 and the light receiving element 5, and the conductive wires 6 and 7 are embedded. In order to form the lens 8, the production is troublesome.

When the above-mentioned liquid level detector is mounted on a liquid level detecting device, it is necessary to separately prepare a mounting component having an electric connection portion of the lead terminals 1, 2, and 3. Therefore, production of this mounting component and its cost are required.

Further, in the above liquid level detector, liquid may enter from a gap between the lead terminal and the lens 8,
The light emitting element 4 and the light receiving element 5 may be damaged by the liquid that has entered.

In view of the above-mentioned circumstances, the present invention not only prevents the intrusion of liquid but also facilitates installation.
An object is to propose a liquid level detector suitable for mass production.

[0015]

According to a first aspect of the present invention, there is provided a liquid level detector for a liquid, such as water or kerosene, which comprises a light emitting element and a light receiving element. Is provided at a predetermined position on a printed circuit board, the printed circuit board is mounted in a container made of a transparent material, and the light emitting and receiving unit is disposed in the container, and the position of the outer surface of the container corresponding to the light receiving and emitting unit is in the liquid. When the light emitted from the light emitting element is transmitted through the container and the position of the outer surface of the container is outside the liquid, the light emitted from the light emitting element is reflected on the outer surface of the container. A liquid level detector characterized by detecting a liquid level from a change in the output of an element is proposed.

According to a second aspect of the present invention, first and second light emitting and receiving sections each including a light emitting element and a light receiving element are vertically elongated with the first light receiving and emitting section on the lower side and the second light receiving and emitting section on the upper side. The printed circuit board is provided at a predetermined interval, the printed circuit board is housed in a flat container made of a transparent material, and first and second light emitting and receiving units are disposed in the container. When the vertical position of the outer surface of the container corresponding to the light emitting / receiving unit or the position of the outer surface of the container corresponding to the second light emitting / receiving unit is out of liquid, the light emission of the first, second light emitting / receiving unit or the second light emitting / receiving unit Liquid level detection characterized in that the light emitted from the element is reflected on the outer surface of the container, and the liquid level is detected based on the output change of the light receiving element of the light receiving and emitting unit receiving the reflected light of the container due to the light emission of the light emitting element. Suggest a child.

In the light emitting and receiving unit according to the present invention, in addition to the configuration in which the light emitting element and the light receiving element are arranged to be parallel to the liquid surface of the liquid, a light shielding plate is provided between the light emitting element and the light receiving element. The light-emitting element and the light-receiving element may be configured so that the light emitted from the light-emitting element does not directly enter the light-receiving element, or the light-emitting element and the light-receiving element may be mounted on a small base material in advance, and the small base material may be provided on a printed circuit board.

[0018]

When the outer surface position of the container corresponding to the light emitting / receiving section is in the liquid, the refractive index of the liquid and the refractive index of the container are the same or similar. Emitted light passes through the container and radiates out of the container. From this, since light due to light emission of the light emitting element hardly enters the light receiving element, the output signal of this light receiving element becomes low level.

When the position of the outer surface of the container corresponding to the light emitting / receiving section comes out of the liquid into the air, since the refractive index of air and the refractive index of the container are different, the light emitted from the light emitting element is reflected by the outer surface of the container. . Therefore, the light emitted from the light emitting element is reflected by the container, and the reflected light is incident on the light receiving element, so that the output signal of the light receiving element becomes high level.

More specifically, if the liquid level of the liquid exceeds the position of the outer surface of the container corresponding to the light emitting / receiving section, the output of the light receiving element becomes low.
If the liquid level falls below the position of the outer surface of the container, the output of the light receiving element becomes a high level signal. As a result, the height of the liquid surface, that is, the amount of liquid in the liquid tank can be known from the output signal of the light receiving element.

In the liquid level detector of the second invention, after the liquid level is detected by the upper light receiving / emitting section, the liquid level can be detected again by the lower light receiving / emitting section. That is, by detecting the liquid level in the upper light receiving / emitting unit, a detection signal indicating that the liquid has decreased is output, and a display prompting the replenishment of the liquid can be performed. When the liquid level is detected by the lower light emitting / receiving unit, it is detected that the liquid has not been replenished, and processing such as stopping the operation of the device is performed based on the detection signal.

[0022]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a front view of the liquid level detector.
The case 41 is partially cut away. FIG. 2 shows FIG.
FIG. 4 is a cross-sectional view taken along the line AA of FIG. As shown in FIGS. 1 and 2,
Reference numeral 30 denotes a printed circuit board on which copper foils 30a, 30b, and 30c of a predetermined shape are provided.

At one end (the lower part in the drawing) of the printed circuit board 30 and a part of the copper foil 30a which is a predetermined middle part,
On the other hand, light receiving elements 31 and 33 such as phototransistors are fixed with a conductive adhesive so that the electrodes are in contact with each other. The other electrodes of the light receiving elements 31 and 33 are connected to conductive lines 35 and 37, respectively.
The wiring is provided at a predetermined position of the copper foil 30b.

At two places of the copper foil 30b corresponding to the two light receiving elements 31 and 33, light emitting elements 32 and 34 such as LEDs are made of a conductive adhesive so that one of the electrodes is in contact therewith. It is stuck. Further, the other electrodes of the light emitting elements 32 and 34 are wired at predetermined positions of the copper foil 30c by the conductive lines 36 and 38.

Further, between the light receiving element 31 and the light emitting element 32 and between the light receiving element 33 and the light emitting element 34, light shielding plates 3 are provided so that the light emitted from the light emitting element does not directly enter the light receiving element.
9 and 40 are provided. As described above, the printed circuit board 3 provided with the first and second two light receiving / emitting portions constituted by the light receiving element 33 and the light emitting element 34 and the light receiving element 31 and the light emitting element 32
Reference numeral 0 denotes a flat case 41 which is formed of a transparent material while leaving the other end (the upper part in the drawing), and is provided between the printed circuit board 30 and the case 41 (space). A transparent resin material 42 having substantially the same refractive index is filled.

The liquid surface detector configured as described above supplies power to the copper foils 30b and 30c of the printed circuit board 30 and
2, 34 emit light. FIG. 2 shows a part 43 of a light beam emitted by the light emitting element 34 forming the first light emitting / receiving unit. Since the refractive index of the case 41 is larger than the refractive index of air when the liquid level detector is in the air, the light beam 43 has a surface 41a of the case 41 as shown by a light beam 43a.
And is incident on the light receiving element 33.

When the liquid level detector is in the liquid, the refractive index of the liquid and the refractive index of the case 41 are the same or close to each other. The light is not reflected by the surface 41 a of the negative electrode 41, is emitted outside, and does not enter the light receiving element 33. That is, when the liquid level detector comes out of the liquid into the air, a photocurrent is generated in the light receiving element 33, and this photocurrent is extracted from the copper foils 30a and 30b.

By appropriately processing the presence or absence of the photocurrent, a detection signal corresponding to the presence or absence of the liquid can be obtained. In addition,
Since the light emitted from the light emitting element 34 is shielded by the light shielding plate 40 and does not directly enter the light receiving element 33, the SN ratio is improved.

The function of the first light emitting / receiving section constituted by the light emitting element 34 and the light receiving element 33 has been described above. The function of the second light receiving / emitting section constituted by the light emitting element 32 and the light receiving element 31 is also the first. The description is omitted because it is the same as the light emitting / receiving section.

FIG. 3 shows an example in which the above-mentioned liquid level detector is used for a stove. Reference numeral 51 denotes a container for storing kerosene, and reference numeral 52 denotes kerosene. Reference numeral 53 denotes a lid of the container 51. The lid 53 has a first light emitting / receiving unit 50a and a second light emitting / receiving unit 50a.
The liquid level detector 50 provided with b is attached via the holder 54. 55 is a pipe for transferring kerosene,
The end of the pipe 55 is provided with a burner or a vaporizer. 56 is a pump for pumping kerosene to a burner or a vaporizer.

The liquid level when the kerosene 52 is sufficient in the container 51 is indicated by 52a. In this state, both the first light receiving / emitting unit 50a and the second light receiving / emitting unit 50b are in kerosene. At this time, an indication that kerosene is sufficiently in the container is displayed on a display device (not shown) based on the detection signal from the first light emitting / receiving unit 50a. Alternatively, an operation such as stopping the driving of the kerosene supply device is performed.

Next, when the kerosene is consumed and the liquid level reaches the position indicated by 52b, the second light emitting / receiving section 50b is exposed to air, and the second light receiving / emitting section 50b detects the kerosene at its detecting section. Is detected. Based on the detection signal output by this detection, the display device performs a display urging the supply of kerosene. Alternatively, an operation such as driving a kerosene supply device is performed.

The liquid level 52c indicates a state in which kerosene is not replenished for some reason and kerosene consumption continues even if the second light receiving / emitting unit 50b detects that kerosene is not detected by the detection unit. I have. In this state, the first light emitting / receiving section 50a is also exposed to the air, and the first light emitting / receiving section 50a detects that there is no kerosene in its detecting section, and the drive of the pump 56 is performed by a detection signal based on the detection. Stopped.

Therefore, no-load operation of the pump is prevented. In addition, when the amount of kerosene decreases, air may be mixed into kerosene. However, such abnormal combustion by kerosene can be reliably prevented, and safety can be secured.

As described above, the first light emitting / receiving section 5
The liquid level detector provided with a detection unit for detecting the amount of kerosene and a second light receiving / emitting unit 50b prompts replenishment when kerosene is reduced to a certain amount. The function of the device can be enhanced by stopping the operation or the like.

FIGS. 4 and 5 show a light emitting / receiving device 61 shown as another configuration example of the light emitting / receiving unit provided in the present liquid level detector.
Is a front view, and FIG. 5 is a side view. In these drawings, reference numeral 60 denotes a small printed circuit board (base material) having a small area which can be mounted on the printed circuit board 30 shown in FIG.
0a, 60b, 60c, and 60d are provided. 31
Is a light receiving element similar to that shown in FIG. 1, and 32 is a light emitting element similar to that shown in FIG.

At a predetermined position of the copper foil 60a, a light receiving element 31 is fixed with a conductive adhesive so as to connect one electrode. The other electrode of the light receiving element 31 is wired at a predetermined position of the copper foil 60b by a conductive line 35.

At a predetermined position of the copper foil 60d, a light emitting element 32 is fixed with a conductive adhesive so as to connect one electrode, and the other electrode of the light emitting element 32 is connected with a conductive wire 36 to the copper foil 60d.
It is wired at a predetermined position of c. Further, a light shielding plate 39 is provided between the light receiving element 31 and the light emitting element 32. The light receiving element 31, the light emitting element 32, and the conductive wires 35 and 36 are embedded in a transparent package 62.

FIG. 6 shows a state where the two light receiving / emitting devices 61 (A, B) configured as described above are mounted on a printed board 65. Here, the light receiving / emitting device 61 of A is a first light receiving / emitting device, and the light receiving / emitting device 61 of B is a second light receiving / emitting device.

The printed board 65 has a copper foil 6 of a predetermined shape.
5a, 65b and 65c are provided. To the copper foil 65a, a copper foil 60c of the light emitting and receiving device 61 of A and a copper foil 60c of the light emitting and receiving device 61 of B are respectively fixed by a conductive adhesive or soldering.

The copper foil 65b includes the copper foil 60b and the copper foil 60d of the A light emitting / receiving device 61 and the copper foil 60d of the B light emitting / receiving device 61.
b, the copper foil 60d, and the copper foil 65c, the copper foil 60a of the light emitting / receiving device 61 of A and the copper foil 6 of the light emitting / receiving device 61 of B.
0a are similarly fixed by a conductive adhesive or soldering. The printed circuit board 65 on which the light receiving and emitting devices 61 A and B are mounted is the same as the case 41 shown in FIG.
The space (space) between the printed board 65 and the case 41 is filled with the transparent resin material 42.

FIG. 7 is a wiring diagram showing the electrical connection of the present liquid level detector, wherein L1 and L2 are the light emitting elements 32 and 34 described above.
And are connected in parallel. However, a configuration in which they are connected in series may be used. P1 and P2 are phototransistors as the light receiving elements 31 and 33, which are connected in parallel.

R1 is a load resistance for converting the photocurrents of P1 and P2 into a voltage. R2 is a stable resistor for stabilizing the currents of L1 and L2. In addition, R1, R2
Is an external resistance, but may be incorporated in the present liquid level detector. The circuit terminals V and O are connected to a power supply. The power supply voltage is E. A detection signal is output to the circuit ends S and O.

Here, the first and second light emitting / receiving sections of the present liquid level detector are both in the air, and further provided in the first light emitting / receiving section when the value of the load resistance R1 is set to zero. saturation photocurrent of the light receiving element P1 and i _1, the saturation photocurrent of the light receiving element P2 having a second light receiving and emitting unit and i _2.

When E, R, i ₁ and i ₂ have the following relationships, a good detection signal with high resolution can be obtained. E> R1 (i ₁ + i ₂ )

Here, the above equation is solved for R1, and further, the following relational expression is obtained by inserting conditions for obtaining a detection signal. 0 <R1 <E / (i ₁ + i ₂ )

When the load resistance R1 according to this relational expression is used, the photocurrents i ₁ and i ₂ of P1 and P2 are zero or a very small current when the liquid level of the kerosene 52 shown in FIG. Therefore, the value Sa of the detection signal becomes equal to the power supply voltage E or E.

[0048] In the position indicated by the 52b position similarly liquid surface, the light current _{i 2} flows through the P2, the photocurrent _{i 1} of P1 is zero. Therefore, the value Sb of the detection signal is as follows: Sb = Ei ₂ × R1.

[0049] Further, when the position of the liquid surface is in the position shown by 52c, since the photocurrent _i 1, _{i 2} flows in each of P1, P2, the value Sc of the detection signal, Sc = E-R1 (i ₁ + i ₂ ).

The values Sa, Sb, Sc of the above detection signals are used as signals for controlling the operation of a device such as a stove, but the number of wires to the control circuit may be three, and the present liquid level detector can be simplified. Can be used.

8 and 9 show a light emitting / receiving device 71 showing another example of the structure of the light emitting / receiving unit provided in the present liquid level detector. FIG. 8 is a front view, and FIG. 9 is a side view. FIG. 10 is a sectional view taken along line BB in FIG.

In this light emitting / receiving device 71, a concave portion 70b, 70c divided into two by a partition portion 70a is formed in a case (base material) 70, and a lead is provided at the bottom of one concave portion 70b.
One side of the lead terminals 72 and 73 and one side of the lead terminals 74 and 75 are provided at the bottom of the other concave portion 70c. In addition, the partition part 70a serves as a light shielding plate part.

Then, at one end of the lead terminal 72,
The light receiving element 31 is provided so as to connect one electrode, and the other electrode of the light receiving element 31 is connected to one end of a lead terminal 73 by a conductive wire 35.

The light emitting element 32 is provided at one end of the lead terminal 74 so as to connect one electrode, and the other electrode of the light emitting element 32 is connected to the lead terminal 75 by the conductive wire 36. It is connected to one end.

Further, the light receiving element 31, the light emitting element 32, one side of the lead terminals 72, 73, 74 and 75, the conductive wire 3
The two concave portions 70b and 70c are filled with the resin material 76 so that the layers 5 and 36 are embedded in the transparent resin material 76.

The light emitting / receiving device 71 thus configured is provided with two light emitting / receiving devices 71 (A, B) having the same configuration, and thus is similar to the light emitting / receiving device 61 (A, B) shown in FIG. A liquid level detector can be formed by mounting the printed circuit board 65 and electrically connecting each lead terminal to the printed circuit board 65.

Although the embodiment of the present invention has been described above, the liquid level detector of the present invention employs the ratio of the refractive index of the case 41 to the refractive index of air and liquid (kerosene or the like) to be detected. The value of the detection signal is obtained using the fact that the reflectance of the boundary surface is determined by the angle of incidence of light on the boundary surface.

Therefore, for example, kerosene and water have different refractive indices, so that it is possible to discriminate kerosene and water by appropriately processing the value of the detection signal. Therefore, the second light emitting / receiving unit 50b of the liquid level detector 50 shown in FIG.
If the first light emitting / receiving unit 50a detects water, it is known that water has entered the container 51, and it is possible to take measures such as draining water before operating the stove.

In implementing the present invention, the light emitting element 3
When an infrared light emitting element, an ultraviolet light emitting element, or the like is used as 2 and 34, the case 41 and the synthetic resin material 4 shown in FIGS.
2, the package 62 shown in FIGS. 4 and 5 uses a transparent material for the emission wavelength. Further, in the above description, the air is not limited to the actual air, but may be a gas such as nitrogen, or may be a medium having a refractive index smaller than the refractive index of the liquid to be detected.

[0060]

As described above, the liquid level detector according to the present invention comprises:
Since the light emitting and receiving unit including the light emitting element and the light receiving element is provided at a predetermined position on the printed circuit board, and the printed circuit board is provided in a container made of a transparent material, and the light receiving and emitting unit is disposed in the container, The liquid level detector is easy to produce, suitable for mass production, and is advantageous for low cost.

Further, since this liquid level detector can be attached with a part of the container as an attaching portion, it can be easily attached without using any attaching parts and the like, and the intrusion of the liquid can be surely prevented. It becomes a liquid level detector.

[Brief description of the drawings]

FIG. 1 is a partially cutaway simplified front view of a liquid level detector of the present invention.

FIG. 2 is a cross-sectional view of the liquid level detector taken along the line AA in FIG.

FIG. 3 is an explanatory diagram for explaining a use state of the liquid level detector.

FIG. 4 is a front view of a light emitting and receiving device showing another configuration example of the light emitting and receiving unit provided in the liquid level detector.

FIG. 5 is a side view of the light emitting and receiving device shown in FIG.

FIG. 6 is a front view in which the light emitting and receiving device shown in FIGS. 4 and 5 is mounted on a printed circuit board.

FIG. 7 is a circuit diagram for explaining the operation of the liquid level detector.

FIG. 8 is a front view of a light emitting and receiving device showing another configuration example of the light emitting and receiving unit provided in the liquid level detector.

9 is a side view of the light emitting and receiving device shown in FIG.

FIG. 10 is a sectional view taken along line BB in FIG. 8;

FIG. 11 is a simplified front view showing the configuration of a conventional liquid level detector.

FIG. 12 is an explanatory diagram for explaining a use state of a conventional liquid level detector.

[Explanation of symbols]

30, 65 Printed circuit board 30a, 30b, 30c, 65a, 65b, 65c Copper foil 31, 33 Light receiving element 32, 34 Light emitting element 35, 36, 37, 38 Conductive wire 39, 40 Light shield plate 41 Case 42 Transparent resin material 60 Small printed circuit board 61, 71 Light emitting / receiving device

Claims (5)

[Claims] In a liquid level detector for a liquid such as water or kerosene, a light receiving / emitting unit including a light emitting element and a light receiving element is provided at a predetermined position on a printed board, and the printed board is mounted in a container made of a transparent material. The light emitting / receiving section is disposed in a container, and when the outer surface position of the container corresponding to the light receiving / emitting section is in the liquid, the light emitted from the light emitting element transmits through the container, and the outer surface position of the container is out of the liquid. A liquid level detector configured to reflect light emitted from the light emitting element on an outer surface of the container, and detect a liquid level from a change in output of a light receiving element that receives the reflected light from the container due to light emission of the light emitting element. 2. A first and a second light emitting element and a light receiving element.
The first light receiving / emitting section is located on the lower side, and the second light receiving / emitting section is located on the upper side at a predetermined interval on a vertically long printed circuit board. And the first and second light emitting and receiving sections are disposed inside the container, and correspond to the vertical position of the outer surface of the container corresponding to the first and second light emitting and receiving sections or the second light receiving and emitting section. When the position of the outer surface of the container is outside the liquid, the light emitted from the first and second light emitting / receiving units or the light emitting elements of the second light emitting / receiving unit is reflected on the outer surface of the container. A liquid level detector characterized in that the liquid level is detected based on a change in output of a light receiving element of the light receiving / emitting unit that receives light. 3. The liquid level detector according to claim 1, further comprising a light emitting / receiving section in which a light emitting element and a light receiving element are arranged in parallel with the liquid surface of the liquid. 4. A light-shielding plate is provided at a position on a printed circuit board between a light-emitting element and a light-receiving element.
Or the liquid level detector described in 2. 5. The liquid level detector according to claim 1, wherein the light emitting element and the light receiving element are provided on a small base, and the small base is arranged on a printed circuit board.