JPH09101190A - Liquid level detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clarify a cause for the occurrence of an error at the time of detecting liquid level. SOLUTION: Regarding the liquid level detector formed for causing the collector electrode of a photo transistor 14 to output a corresponding detection signal, depending on the existence of a liquid in an optical path between a light emitting diode 12 and a photo transistor 14, a light emitting diode D1 for signal level shift is connected in the forward direction across the collector electrode of the photo transistor 14 and the anode of the light emitting diode 12. Types of detection voltage are thereby made different from each other, depending on the normal status and the failure of the light emitting diode 12 or the photo transistor 14. Concurrently, the occurrence of a failure is judged, depending the presence or absence of light emission from the light emitting diode D1 for signal level shift.

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 various equipment such as a petroleum fan heater, and more particularly to a liquid level detector for detecting the liquid level of kerosene in an oil pan (or storage tank). Regarding the improvement of.

[0002]

2. Description of the Related Art Conventionally, a petroleum fan heater of this type has a liquid level detector for detecting the presence or absence of kerosene in a tank, and a photocoupler is used as the liquid level detector.

As shown in FIG. 10, this photocoupler connects a light emitting diode LED and a phototransistor PT to a power supply voltage VDD (for example, about 5V) via a connector C and current limiting resistors R1 and R2. It is a structure.

The input signal modes that this type of conventional photocoupler can give to the microcomputer M are only the High input signal mode and the Low input signal mode.

When the oil level of kerosene in the tank is above a certain reference for the position of the photocoupler, the light of the light emitting diode LED of the photocoupler passes through the spherical surface of the cover member and is diffused by kerosene or the like. Therefore, the phototransistor PT is not incident on the phototransistor PT without being returned to the outside, the phototransistor PT is off (with oil), and the High input signal of 5 V of the power supply voltage VDD is input to the microcomputer M through the resistor R2. To be done.

On the other hand, when the oil level of kerosene in the tank is lower than a certain reference with respect to the position of the photocoupler, the light of the light emitting diode LED of the photocoupler is reflected by the phototransistor PT on the spherical surface of the cover member. After reaching, the phototransistor PT is turned on (no oil), and a low input signal is input to the microcomputer M. The presence or absence of kerosene can be determined by the level of the input signal to the microcomputer M.

[0007]

However, if a failure occurs in the liquid level detector and its peripheral circuits, normal combustion may not be performed. Conventionally, as a failure that occurs in the liquid level detector, in addition to a failure of the photocoupler itself, such as a short-circuit (short circuit) or open (open) of the light emitting diode LED, a short (short circuit) or open (open) of the phototransistor, It is conceivable that the connection ends C1, C2, C3 of the connector C provided on the wiring path connecting the coupler and the microcomputer M are disconnected or the connection is defective. The disconnection or poor connection of the connector causes the following problems.

That is, for example, when the oil level of kerosene in the tank is lower than a certain level, the phototransistor PT
Is turned on, and the original input signal to the microcomputer M should be low level. However, the light emitting diode LED does not emit light when the connector C1 is disconnected, the phototransistor PT does not turn on when the connector C2 is disconnected, and the light emitting diode LED emits light when the connector C3 is disconnected. The phototransistor PT is not turned on. In this way, the connector C
If any of 1 to C3 is off, the power supply voltage VDD
(5V) is applied to the input terminal of the microcomputer M through the resistor R2, and the input signal becomes High level. Therefore, the microcomputer M recognizes the normal High input signal mode and erroneously determines that the oil level of kerosene in the tank is above a certain reference level.

As a result, the oil fan heater operates in the normal combustion mode even though there is almost no kerosene in the tank, and at this time, the pump has a small amount of kerosene with almost no kerosene in the tank. A large amount of air will be sent to the burner side. Therefore, the amount of air supplied into the burner becomes excessive and the pressure of the air increases, which may cause abnormal red combustion.

Further, in the above-mentioned conventional liquid level detector and its connecting circuit, as described above, whether the liquid level detector itself is out of order, or the connector is disconnected or the connection is defective is discriminated at the input signal level of the microcomputer M. Can not do it.

In addition, at the time of shipping inspection or maintenance / inspection, when an inspector or a service person determines a failure state, an auxiliary display means for visually confirming the failure state is provided. Is preferred.

Therefore, it is an object of the present invention to provide a liquid level detector capable of clarifying the cause of an abnormality at the time of liquid level detection.

[0013]

In order to solve the above-mentioned problems, the invention described in claim 1 is, as shown in FIG. 5, whether liquid exists in the optical path between the light emitting diode 12 and the phototransistor 14. In the liquid level detector that outputs a corresponding detection signal from the collector electrode of the phototransistor 14 in accordance with the above, a signal level shifting light emitting diode D1 is provided in order between the collector electrode of the phototransistor 14 and the anode of the light emitting diode 12. It is configured by connecting in the direction.

According to the present invention, for example, the following operations are performed. When the liquid level detector is defective, for example, when the light emitting diode 12 is short-circuited, a current flows through the power source VDD, the collector electrode of the phototransistor 14, the signal level shifting light emitting diode D1, and the light emitting diode 12. At this time, since the light emitting diode 12 is short-circuited and its resistance value is zero, the voltage level of the detection signal becomes a value equal to the forward voltage drop generated in the signal level shifting light emitting diode D1, which is the same as the conventional ground level ( 0
V) does not hold. By associating this detection signal level state with the short circuit failure of the light emitting diode 12,
The cause of the abnormality can be distinguished.

On the other hand, the presence / absence of a current flowing through the light emitting diode D1 for signal level shifting, that is, the light emitting state is determined according to the conduction state (ON / OFF) of the light emitting diode 12, a short circuit failure, an open circuit failure, and the like. The signal level shifting light-emitting diode D1 also functions as a status indicator, and the presence / absence of the light emission is associated with each of the above operating states, so that the inspector or a service person can determine whether the liquid level detector is normal / abnormal or abnormal. Etc. can be visually announced. In this way, it is possible to clarify the cause of the abnormality or the like when the liquid level is detected.

According to the second aspect of the invention, as shown in FIG. 6, the collector electrode of the phototransistor 14 corresponds to the presence or absence of the detection liquid in the optical path between the light emitting diode 12 and the phototransistor 14. A liquid level detector for outputting a detection signal, comprising the light emitting diode 12
In the liquid level detector formed so that the phototransistor 14 is connected to the external circuit 26 via the connector 30, the connector connecting end 30b to which the collector electrode of the phototransistor 14 is connected and the anode of the light emitting diode 12 are connected. The signal level shifting light emitting diode D1 is connected in the forward direction to the connector connecting end 30a to which is connected.

According to the present invention, for example, the following operations are performed. Defective liquid level detector, eg light emitting diode 12
In the case of the short circuit failure, current flows through the paths of the power supply VDD, the signal level shifting light emitting diode D1, the connector connecting end 30a, the light emitting diode 12, the connector connecting end 30c, and GND. At this time, since the light emitting diode 12 is short-circuited and its resistance value is zero, the voltage level of the detection signal becomes a value equal to the forward voltage drop generated in the signal level shifting light emitting diode D1, and the GND level (conventional GND level ( It does not become 0V). By associating the detection signal level state with the short-circuit failure of the light emitting diode 12, the cause of the abnormality can be distinguished.

On the other hand, for signal level shifting depending on the conduction state (ON / OFF) of the light emitting diode 12, short circuit failure, open circuit failure, and connection (or contact) failure of the connector connection ends 30a and 30c. Since the presence / absence of a current flowing through the light emitting diode D1 is determined, that is, the light emitting state is determined, the light emitting diode D1 for signal level shift also functions as a status indicator, and the presence or absence of light emission is associated with each of the above operating states, Normal / abnormal of surface detector,
The inspector or a service person can be visually notified of the connection state of the connector, the content of the abnormality or the like by the issuing state of the issuing diode D1 attached to the external circuit installed at a position apart from the photo coupler. In this way, it is possible to clarify the cause of the abnormality or the like when the liquid level is detected.

According to a third aspect of the present invention, a liquid surface for outputting a corresponding detection signal from the collector electrode of the phototransistor 14 according to the presence or absence of the detection liquid in the optical path between the light emitting diode 12 and the phototransistor 14. The detector is configured by connecting the light emitting diode 12 and the phototransistor 14 to a detector such as the microcomputer 26 and the comparator 28 via connection ends 30a and 30b of the connector 30.

According to the present invention, the abnormality of the light emitting diode 12 and the phototransistor 14 and the detection signal can be directly detected by the detector such as the microcomputer 26 and the comparator 28.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings.

(I) Outline First, FIG. 1 shows an example of a petroleum fan heater to which the embodiment of the liquid level detector according to the present invention is applied, and the outline thereof will be described.

In FIG. 1, the kerosene 5 stored in the oil pan 1 can be sent to the burner 3 by the pump 2. The fuel cartridge tank 4 is installed in the oil pan 1.

The fuel cartridge tank 4 has a valve 4
a is arranged, and kerosene 5 is successively supplied into the oil pan 1. In FIG. 1, the oil pan 1 is drawn larger than the fuel cartridge tank 4 for convenience of description.

The oil receiving tray 1 is provided with a liquid level detector 10, and the blower sends primary air and secondary air to the burner 3. If kerosene 5 in the oil pan 1
When the oil level decreases from L1 to L2 when the normal combustion operation is performed without knowing that, the pump 2 continues to suck the kerosene 5 and the oil pan 1
The air inside will also be inhaled. Eventually, the flame of the burner 3 extinguishes, but the problem is that kerosene and a large amount of air are sent into the burner 3, and the balance between air and kerosene is lost, resulting in an abnormal red fire. Therefore, it is necessary to surely notify the user that the kerosene in the oil pan 1 has become less than the predetermined amount.

FIG. 2 shows an example of a sectional structure of the liquid level detector 10 according to the present invention, FIG. 3 shows an equivalent circuit of an electric circuit of the liquid level detector 10, and FIG. 4 shows light emission as a light emitting element of the liquid level detector 10. Diode 12, phototransistor 1 as light receiving element
4, a transparent resin cover member 16 is shown.

As shown in FIG. 2, the liquid level detector 10 has three connection terminals 10a, 10b and 10c. FIG.
As shown in FIG. 3, the light emitting diode 12 and the phototransistor 14 that constitute the photocoupler 15 are mounted on the mounting plate 18, surrounded by the cover member 16, and mounted in the casing 19.

If the kerosene 5 is at the oil level L1, for example,
The light LT emitted from the light emitting diode 12 is diffused by the kerosene 5 and the cover member 16 and does not reach the phototransistor 14 as shown by the chain double-dashed line.
Is OFF.

On the other hand, when the kerosene 5 drops to the oil level L2, for example, the light LT emitted from the light emitting diode 12 is emitted.
Is reflected by the cover member 16 and reaches the phototransistor 14, as shown by the solid line, and the phototransistor 14 is turned on.

(II) First Embodiment FIG. 5 shows a liquid level detector 10 according to the first embodiment of the present invention.
An example of the electric circuit of is shown.

In FIG. 5, the power supply voltage VDD is connected to the anode of the light emitting diode 12 of the photocoupler 15 through the current limiting resistor R1, and the cathode of the light emitting diode 12 is grounded to GND. In addition, the power supply voltage VDD
To the collector electrode of the phototransistor 14 of the photocoupler 15 via the pull-up resistor R2, and the emitter of the phototransistor 14 is grounded to GND.

Between the anode of the light emitting diode 12 and the collector of the phototransistor 14, the light emitting diode D
1 is connected in the forward direction, that is, the cathode of the light emitting diode D1 is connected to the anode of the light emitting diode 12, and the anode of the light emitting diode D1 is connected to the collector of the phototransistor 14.

The connection point between the anode of the light emitting diode D1 and the collector of the phototransistor 14 is the output end of the liquid level detection signal, and this signal end is the microcomputer 26.
Is connected to the A / D conversion unit 28.

The current limiting resistor R1 is a resistor (for example, 150Ω) for passing a large current from the power supply VDD to the light emitting diode 12, and the pull-up resistor R2 is for passing a small current from the power supply to the phototransistor 14. Resistance (for example, 10 to 20 KΩ).

Next, the operation of the first embodiment will be described with reference to FIG. FIG. 7 illustrates the value of the input voltage to the microcomputer 26 for each embodiment and for each state (normal and abnormal).

The normal state shown in FIG. 7 is a state in which the light emitting diode (LED) 12 is not short-circuited or open-circuited and the phototransistor 14 is not short-circuited or open-circuited.

When the kerosene shown in FIG. 4 is filled up to the oil level L1 at this normal time, the light of the light emitting diode 12 is affected by the refractive index of the kerosene and the refractive index of the cover member 16, and the cover member 16
And does not reach the phototransistor 14. Therefore, in FIG.
4 is OFF, and the current from the power source is the pull-up resistor R2, the light emitting diode D1, and the light emitting diode 12
Flows along the path. Therefore, the forward voltage VF1 of the light emitting diode D1 (for example, 1.7 V, but 2 V for simplification of description) and the forward voltage VF2 of the light emitting diode 12 (also 2.0 V). The added output voltage value of 4.0 V is A of the microcomputer 26.
The data is input to the / D conversion unit 28, and the microcomputer 26
Judges that there is kerosene in the tank.

In addition, since a current flows through the light emitting diode 12 of the photocoupler 15 under normal conditions, the light emitting diode D1
A current also flows therethrough, and therefore the light emitting diode D1 is always in a light emitting state. By utilizing this fact, by arranging the light emitting diode D1 at a position on the control board where it can be easily viewed, the light emitting diode D1 acts as an operation state indicator, and therefore, the light emitting state of the light emitting diode D1 causes the factory to operate. An inspector or a service person in the market can easily visually recognize that the liquid level detector is “normal”.

On the other hand, when the kerosene is reduced to the oil level L2 as shown in FIG. 4 during normal operation, the light emitting diode 1
The light 2 is reflected inside the sensor and is reflected by the phototransistor 14
To reach. Therefore, in FIG. 5, the phototransistor 14 is turned on, and the current from the power supply VDD drops to GND. As a result, A / of the microcomputer 26
The D converter 28 has a collector of the phototransistor 14
The emitter-to-emitter voltage VCE (about 0.2V = 0V) is input, and the microcomputer 26 determines that "there is no kerosene in the tank".

In the "no kerosene" state, the anode potential of the light emitting diode D1 becomes 0V, so the issuing diode D1 does not light up, and the non-lighting state causes an inspector in a factory or a service in the market. The operator can easily visually recognize that the liquid level detector is “normal”.

The above description is for the case where both the light emitting diode 12 and the phototransistor 14 are normal.

Next, an explanation will be given of an abnormal condition when the kerosene 5 is present in the tank 1 of FIG. The abnormal state is a case where the light emitting diode 12 has a short circuit failure or an open circuit failure, or the phototransistor 14 has a short circuit failure or an open circuit failure.

There is kerosene 5 in the tank 1 up to the oil level L1,
When the light emitting diode 12 has a short circuit failure, a current flows through the path of the power supply VDD, the pull-up resistor R2, the voltage drop light emitting diode D1, the light emitting diode 12, and GND. At this time, the light emitting diode 12 does not emit light, and the phototransistor 14 is OFF. Therefore, the light emitting diode D
Only the forward voltage VF1 (2.0 V) of 1 is input to the A / D conversion unit 28 of the microcomputer 26 as an input voltage.

When the kerosene 5 is in the tank 1 up to the oil level L1 and the light emitting diode 12 fails to open, the light emitting diode 12 does not emit light and the phototransistor 14 is turned off.
It is. Moreover, since the current path of the light emitting diode D1 is also cut off, the power supply voltage VDD (5V) is input to the A / D conversion unit 28 of the microcomputer 26 as an input voltage.

Further, if kerosene 5 is in the tank 1 up to the oil level L1 and the phototransistor 14 is short-circuited, G
The signal of the ND potential level is A of the microcomputer 26.
It is input to the / D conversion unit 28.

Next, a description will be given of an abnormal state when the oil level of kerosene 5 is L2 in the tank 1 of FIG. 2 and there is no kerosene 5.

Even when there is no kerosene 5 in the tank 1, as in the case where the kerosene 5 exists in the tank 1 described above,
When the light emitting diode 12 has a short circuit failure, only the forward voltage VF1 (2.0 V) of the light emitting diode D1 is input to the A / D conversion unit 28 of the microcomputer 26 as an input voltage.

Further, when the light emitting diode 12 has an open circuit failure, the power supply voltage VDD (5V) changes to the microcomputer 2
6 is input as an input voltage to the A / D conversion unit 28.

Further, when the phototransistor 14 is short-circuited, the zero level is A of the microcomputer 26.
The voltage is input to the / D converter 28 as an input voltage.

As described above, according to the present embodiment, due to the presence of the light emitting diode D1 which is the signal level shifting means, the output signal level when the presence or absence of kerosene is detected and the output signal level when the liquid level detector is defective. And can be different. As a result, the signal level of the detection signal obtained from the signal output terminal of the photodiode 14 varies depending on the cause of the abnormality, so that the cause of the abnormality at the time of detecting the liquid level can be clarified.

In addition, in a normal state, the light emitting diode 12 does not emit light, so that the light emitting diode D1 is in a non-light emitting (off) state. By utilizing this fact, the light emitting diode D1 is arranged on the control board at a position where it can be easily viewed, so that an inspector in a factory or a service person in the market can change the liquid level detector depending on the light emitting state of the light emitting diode D1. It is easy to visually recognize that is "normal".

It should be noted that although the light may be emitted exceptionally, the light emitting state of the light emitting diode D1 is an auxiliary notification means to the inspector or the service person, and the final judgment as to whether or not there is an abnormality is made by the microcomputer. At 26, the safety is ensured because it is performed by the input signal to the A / D converter converter 28.

(II) Second Embodiment FIG. 6 shows a second embodiment of the liquid surface detector 10 according to the present invention. In FIG. 6, the first embodiment (FIG. 5)
Elements that are the same as or equivalent to the constituent elements are given the same reference numerals and described below.

The present embodiment shows an application example of the present invention when the liquid level detector 10 shown in the first embodiment is connected via a connector 30. Such an aspect
It is often used in actual assembly.

The connector 30 has three connecting ends 30a, 3
It has 0b and 30c. The connection end 30a electrically connects the anode of the light emitting diode 12 and the current limiting resistor R1. The connection end 30b electrically connects the collector electrode of the phototransistor 14 and the pull-up resistor R2.
0c electrically connects the cathode of the light emitting diode 12 and the emitter electrode of the phototransistor 14 to the ground. The light emitting diode D1 as a voltage drop means is provided on the external circuit side of the photocoupler 15 with the connection terminals 30a, 3a.
0b, the anode of the light emitting diode D1 is connected to the collector electrode of the phototransistor 14, and the cathode of the light emitting diode D1 is connected to the anode of the light emitting diode 12.

Next, the operation of the second embodiment will be described.

When both the light emitting diode 12 and the phototransistor 14 are normal as shown in FIG. 7, the value of the input voltage to the microcomputer 26 is as shown in FIG.
It is the same as the normal case of the principle diagram of.

In addition, regardless of the presence or absence of kerosene in the tank, in the case of an abnormality in which the light emitting diode (LED) 12 has a short circuit failure or an open circuit failure, or the phototransistor 14 has a short circuit failure or an open circuit failure, the microcomputer 26 is instructed. The value of the input voltage is the same as in the abnormal case of FIG.

However, in this embodiment, regardless of the presence or absence of kerosene in the tank, as shown in FIG.
The case where any of the connection ends 30a, 30b, 30c of No. 1 has a poor connection or a bad contact is added as an abnormal state.

Connection end (NO. 1) 30a of the connector 30
If the light emitting diode 12 has a poor connection or a poor contact, the light emitting diode 12 is in the same open circuit condition and the phototransistor 14 is OFF. Therefore, the power supply voltage (5
V) is an A / D conversion unit 28 of the microcomputer 26
Input as an input voltage.

The connection end of the connector 30 (NO. 2)
When the connection or the connection failure occurs in 30b, the forward voltage VF1 (2.0V) of the light-emitting diode D1 and the forward voltage VF2 (for example, 2.0V) of the light-emitting diode 12 are added, and the voltage value of 4 points is 0V. Computer 2
6 is input as an input voltage to the A / D conversion unit 28.

Further, the connection end of the connector 30 (NO.
3) If the connection or contact failure of 30c occurs, the light emitting diode 12 becomes the same as the open failure,
The power supply voltage (5V) is A / of the microcomputer 26.
The voltage is input to the D conversion unit 28 as an input voltage.

(III) Third Embodiment FIG. 8 shows a liquid level detector according to a third embodiment of the present invention.

In this embodiment, the anode of the light emitting diode 12 of the photocoupler 15 is connected to the connection terminal (N) of the connector 30.
O. 1) 30a, and the collector terminal of the phototransistor 14 is connected to the connector 30 (NO. 2) 30b.
By connecting the detection signal voltages obtained at the connection ends 30a and 30b to each other, the failure detection of the photocoupler 15 and the connection failure or contact failure of the connector 30 are determined. Although not shown, the comparison of the detection signals is performed by software by a comparison program in the microcomputer 26 after being converted into a digital signal by the A / D converter 28, or by hardware using a comparator. It is processed.

FIG. 9 shows an example of the microcomputer input voltage in this embodiment similar to FIG.

According to the above configuration, it is possible to detect a failure of the photocoupler 15 or a connection failure of the connector with an extremely simple configuration.

In the above description of each embodiment, the liquid level detector applied to the oil fan heater is described as an example, but the invention is not limited to this, and the forced air supply / exhaust type hot air heater, the oil boiler, It goes without saying that the present invention can be applied to devices in other areas and fields such as automobile fuel gauges and silicon oil gauges such as copy machines.

[0068]

As described above, according to the first aspect of the present invention, the signal level shifting light emitting diode is connected in the forward direction between the collector electrode of the phototransistor and the anode of the light emitting diode. With this configuration, when the liquid level detector is defective, the voltage level of the detection signal is shifted by the signal level shifting light emitting diode, and by correlating this detection signal level state with the short circuit failure of the light emitting diode or phototransistor. The cause of abnormality can be distinguished. The light emitting state of the light emitting diode for signal level shift is determined according to the conduction state of the light emitting diode of the photocoupler or the phototransistor, the short circuit failure, the open circuit failure, etc. By associating with each other, the normality / abnormality of the liquid level detector, the content of the abnormality, etc. can be visually notified to the inspector, service person, or the like. In this way, it is possible to clarify the cause of the abnormality or the like when the liquid level is detected.

According to the second aspect of the present invention, a light emitting diode for signal level shifting is provided between the connector connecting end to which the collector electrode of the phototransistor is connected and the connector connecting end to which the anode of the light emitting diode is connected. Since the connection is made in the forward direction, when the liquid level detector is defective, the detection signal voltage level is shifted by the signal level shifting light emitting diode D1, and this detection signal level state and the light emitting diode, phototransistor or By associating with the connection state of the connector, the cause of the abnormality can be distinguished. On the other hand, the presence or absence of light emission is associated with each of the above operating states according to the conduction state (ON / OFF) of the light emitting diode, the state of short circuit failure, the state of open circuit failure, and the presence or absence of connection (or contact) failure of the connector connection end. Depending on whether the liquid level detector is normal / abnormal, the connection status of the connector, or the content of the abnormality, the inspector, service person, etc. can check the light emission state of the light emitting diode D1 attached to the external circuit installed at a position apart from the photo coupler. Can be visually announced. In this way, it is possible to clarify the cause of the abnormality or the like when the liquid level is detected.

According to the third aspect of the invention, the abnormality of the light emitting diode and the phototransistor and the detection signal can be directly detected by the detector such as the microcomputer and the comparator.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a petroleum fan heater including a liquid level detector of the present invention.

FIG. 2 is a vertical sectional view showing a structural example of a liquid level detector according to the present invention.

FIG. 3 is an equivalent circuit diagram of a photocoupler.

FIG. 4 is an enlarged view of a photocoupler portion of the liquid surface detector according to the present invention.

FIG. 5 is an electric circuit diagram showing a first embodiment of a liquid level detector according to the present invention.

FIG. 6 is an electric circuit diagram showing a second embodiment of the liquid surface detector according to the present invention.

FIG. 7 is an explanatory diagram showing an example of an input voltage of the microcomputer in the first and second embodiments.

FIG. 8 is an electric circuit diagram showing a third embodiment of the liquid level detector according to the present invention.

FIG. 9 is an explanatory diagram showing an example of an input voltage of the microcomputer according to the third embodiment.

FIG. 10 is a diagram showing a conventional liquid level detector.

[Explanation of symbols]

 5 Kerosene (liquid) 10 Photocoupler (sensor) 12 Light emitting diode (light emitting element) 14 Photodiode (light receiving element) 26 Microcomputer (detector) 28 A / D converter 30 Connector 30a, 30b, 30c Connector connection end D1 Light emitting diode (Signal level shift means)

Continuation of front page (72) Inventor Tadashi Yamaguchi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A liquid level detector that outputs a corresponding detection signal from the collector electrode of the phototransistor according to the presence or absence of liquid in the optical path between the light emitting diode and the phototransistor, wherein the collector electrode of the phototransistor is A liquid level detector characterized in that a light emitting diode is connected in a forward direction between an anode of the light emitting diode and the anode. 2. A liquid level detector which outputs a corresponding detection signal from a collector electrode of the phototransistor according to the presence or absence of a detection liquid in an optical path between the light emitting diode and the phototransistor, wherein In a liquid level detector in which a phototransistor is connected to an external circuit via a connector, a connector connection end to which a collector electrode of the phototransistor is connected and a connector connection end to which an anode of the light emitting diode is forwardly connected A liquid level detector characterized in that a light emitting diode is connected therebetween. 3. A liquid level detector that outputs a corresponding detection signal from the collector electrode of the phototransistor according to the presence or absence of a detection liquid in the optical path between the light emitting diode and the phototransistor, A liquid level detector characterized in that a phototransistor is connected to a detector such as a microcomputer or a comparator via a connector.