JPH09166476A - Liquid-level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid-level sensor by which a liquid level can be detected precisely with a simple configuration by detecting a collector output voltage at a PNP transistor whose base is connected to the collector of a phototransistor. SOLUTION: When liquid level is lowered and the prism reflecting face 31 of a liquid-level sensor is separated from a liquid, an optical coupling passage is formed across a light-emitting diode 2a and a phototransistor 2b, and incident light from the diode 2a is photoelectrically transduced by the phototransistor 2b. Since a transduced signal biases its base, the phototransistor 2b is turned on, and a current flows to its collector. A base current at an L-level flows to the base of a PNP transistor Q which is connected to it, and an output current is generated from its collector. On the other hand, when the reflecting face 31 is immersed in the liquid, the optical coupling passage is opened due to change in a refractive index, and the phototransistor 2b does not receive light so as to be turned off. As a result, the base of the transistor Q is set to an H-level, and no output is available from its collector. Consequently, on the base of whether an output from the collector of the transistor Q exists or not, the liquid level can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level sensor in which a prism and a photoelectric conversion element are combined.

[0002]

2. Description of the Related Art Generally, a fuel supply mechanism such as an oil fan heater is directly connected to a nozzle for injecting fuel toward a burner, a main body tank provided inside the main body, and a main body tank which can be detachably attached to the main body to supply fuel to the main body tank. It consists of a replenishing cartridge tank. Then, when the main body tank is emptied or is about to be emptied, the cartridge tank is taken out, fuel is put into the cartridge tank, and then the cartridge tank is attached to the main body again. Therefore, a liquid level detection sensor is attached to the main body tank in order to detect the presence or absence of fuel therein.

As shown in FIG. 4, a conventional liquid level sensor mounted on a tank has a reed switch 102 inside the stem 101 and two magnets 104 and 104 inside the float 103 via the stem 101, and leads. It was a float type that operates using the drive magnetic field of the switch. That is, in synchronization with the rise or fall of the liquid level, the magnet 104 together with the float 103 enters or leaves the drive magnetic field range of the reed switch 102, so that the contact of the reed switch 102 is turned on (solid line in the figure). Alternatively, the method is OFF (two-dot chain line in the figure) to detect the liquid level.

[0004]

However, in the case of the float type detecting device as described above, the contact resistance between the contacts increases due to wear, which may cause chattering or malfunction. In order to prevent this, it was necessary to devise a complicated control circuit for the fan heater body. Therefore, an object of the present invention is to provide a liquid level sensor that is less likely to cause chattering or malfunction even if the circuit of the fan heater main body is simplified.

[0005]

In order to achieve the object, a liquid level sensor of the present invention is based on a prism, a light emitting diode, and light emitted from the light emitting diode and incident through a prism reflecting surface. Comprises a phototransistor that is biased and a PNP transistor whose base is connected to the collector of the phototransistor.
It is characterized in that the collector output voltage of the NP transistor is used as the detection signal.

According to this liquid level sensor, when the prism reflection surface is out of the liquid, an optical coupling path is formed between the light emitting diode and the phototransistor, and incident light is photoelectrically converted by the phototransistor. Since the converted signal biases the base of the phototransistor, the phototransistor is turned on and a current flows through the collector. Therefore, the current biases the base of the PNP transistor to turn on the PNP transistor, and an output current is generated from the collector of the PNP transistor.

On the other hand, when the prism reflection surface is immersed in the liquid, the phototransistor does not receive light because the optical coupling path is opened due to the change in the refractive index. Therefore, the phototransistor is turned off and the collector of the PNP transistor is not output. Therefore, the collector output voltage can be used as the liquid level detection signal. Since the liquid level sensor of the present invention detects the liquid level based on the photoelectric effect of the photo reflector, no mechanical contact is required, and chattering or malfunction does not occur.

[0008]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the liquid level sensor of the embodiment, FIG. 2 is a schematic diagram showing a connection relationship between the liquid level sensor and a fan heater side control board, and FIG. 3 is a radial direction sectional view of the liquid level sensor.

The liquid level sensor 1 is an infrared light emitting diode 2a.
And a photoreflector 2 formed by integrating the phototransistor 2b, and the photoreflector 2
A tubular case 3 whose surface also serves as a prism reflection surface, a rubber cap 4 for sealing the opening of the case 3, and a case 3
Fixed inside the photo reflector 2 and other electronic parts (not shown) such as the PNP transistor Q shown in FIG.
Is mounted and connected to the kerosene tank (not shown).

The liquid level sensor 1 is powered by DC5V, which is the same as the operating power source of the microcomputer controlling the drive of the fan heater. The light emitting diode 2a has a rated value of 16 on the cathode side.
It is grounded via a current limiting resistor R1 of 0Ω and 1 / 4W. The phototransistor 2b is a light emitting diode 2
The emitter is a grounded type whose base is a current which is incident from a through the prism reflection surface and is photoelectrically converted, and its collector terminal is connected to the base terminal of a transistor Q having a base resistance of 4.7 kΩ. To the collector terminal of the phototransistor 2b, a current limiting resistor R2 having a rated value of 27 kΩ and 1/10 W is also connected in parallel with the transistor Q. Then, the anode of the light emitting diode 2a and the resistor R2
The other end and the emitter terminal of the transistor Q are connected and connected to a DC5V power source.

The sensor 1 has an optical coupling path between the light emitting diode 2a and the phototransistor 2b when the prism reflection surface 31 is released from the liquid, that is, when the liquid in the tank is reduced and the liquid level is lower than that of the sensor 1. And the incident light is photoelectrically converted by the phototransistor 2b. Since the converted signal biases the base of the phototransistor 2b, the phototransistor 2b is turned on and a current flows through the collector. Therefore, the base of the transistor Q becomes low level due to the current, and the base current flows,
An output current is generated from the collector of the transistor Q.

On the other hand, when the prism reflection surface 31 is submerged in the liquid, that is, when the liquid is supplied into the tank, the optical coupling path is opened due to the change in the refractive index, and thus the phototransistor 2
b does not receive light. Therefore, the phototransistor 2b is O
It becomes FF, the base of the transistor Q becomes high level, and it does not output from the collector. Therefore, the liquid level can be detected by the presence or absence of the output from the collector of the transistor Q.

Since the liquid level sensor of this embodiment detects the liquid level based on the photoelectric effect of the photo reflector, no mechanical contact is required, and chattering or malfunction does not occur. Further, since the float type liquid level sensor has two terminals, it is possible to connect it to the existing fan heater side control board to which the float type liquid level sensor is connected by adding a 0V terminal. Furthermore, since the sensor of this example is a signal output type, it can be directly input to a logic circuit such as a microcomputer. Therefore, the circuit configuration on the control board side is simple.

[0014]

As described above, according to the liquid level sensor of the present invention, the liquid level can be accurately detected with a simple structure.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a liquid level sensor according to an embodiment.

FIG. 2 is a schematic diagram showing a connection relationship between a liquid level sensor and a fan heater side control board according to an embodiment.

FIG. 3 is a radial cross-sectional view of the liquid level sensor.

FIG. 4 is an axial sectional view of a conventional liquid level sensor.

[Explanation of symbols]

 1 Liquid Level Sensor 2 Photo Reflector 2a Light Emitting Diode 2b Photo Transistor 3 Case 31 Prism Reflecting Surface 4 Cap 5 Substrate Q PNP Transistor

[Procedure amendment]

[Submission date] February 27, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0003

[Correction method] Change

[Correction contents]

Conventionally, liquid level sensors attached to the tank, the lead switch 102 to the internal scan Temu 101, the float 103 inside incorporate two magnets 104, 104 via the stem 101, using the driving magnetic field of the reed switch It was a float type that works by doing. That is, the float 10 is synchronized with the rise or fall of the liquid level.
Magnet 104 by exiting the entering or driving magnetic field range to the driving magnetic field range of the reed switch 102 with 3, the contacts of the reed switch 102 O N or in method of detecting a liquid surface I OF F and Do <br/> there were.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Fig. 4

[Correction method] Deleted

Claims (2)

[Claims] 1. A prism, a light emitting diode, a phototransistor whose base is biased by light emitted from the light emitting diode and incident through a prism reflection surface, and a PNP transistor whose base is connected to a collector of the phototransistor. And a collector output voltage of a PNP transistor as a detection signal. 2. The liquid level sensor according to claim 1, which is attached to a main body tank of an oil fan heater.