JPH09152366A - Detection apparatus for liquid level - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection apparatus by which a drop in the liquid level of the residual quantity or the like of an automobile fuel is detected and reported by a stable operation without a warning flicker in a warning boundary point at an irregular change in a liquid surface by means of an operating hysteresis characteristic by the linking operation of two thermistors with a simple circuit configuration. SOLUTION: A detection apparatus is constituted in such a way that a first thermistor 1 and a second thermistor 2 are grounded in two places corresponding to prescribed positions in which a drop in a liquid level inside a liquid container such as a tank or the like is to be alarmed, that the first thermistor 1 is electrified from a power supply E via a plurality of resistances 3, 4 and that the second thermistor 2 is electrified through a warning lamp 6 (a display element) by a transistor 5 whose base is connected to the connecting point of the resistances 3, 4. Then, a change in a resistance value at the warning level of the first thermistor 1 constitutes an electrifying condition to the second thermistor 2, and a stable lighting warning without the flicker operation of the warning lamp 6 is given by the operating hysteresis characteristic of a circuit as a whole by their linking operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detection device for detecting a decrease in liquid level by utilizing a change in resistance value due to a self-heating change in different heat radiation environments inside and outside the thermistor. .

[0002]

2. Description of the Related Art Conventionally, in this type of liquid level detecting device, the self-heating due to the heat radiation characteristic in the liquid of the thermistor in the environment outside the liquid is caused by the decrease of the remaining amount of fuel stored in the tank container or the water level of the cooling water. A change is detected and a display element such as a lamp is turned on to give an alarm.

In such a thermistor type liquid level detecting device, basically one liquid level change can be detected by providing one, but the liquid level (liquid level) is always changed or maintained flat. It is rarely used, and it is often used in a container installation environment such as a tank under vibration conditions or conditions in which the inclination changes, and in some cases it may be preliminarily stored in a plurality of connected containers.

For example, when detecting the remaining amount of gasoline in the fuel tank of an automobile, it is used in an environment in which the liquid level fluctuates due to running vibration of the vehicle, or it is connected to the main tank to preliminarily remove gasoline. It is used in a structure that includes a sub-tank that accommodates a part, and a flicker phenomenon occurs due to reciprocating in and out of liquid at the liquid level boundary position of the thermistor due to the frequency corrugation of the liquid level and irregular fluctuations.

Under such an environment, two thermistors are installed at detection points in a single container as a method for more accurate liquid level detection, or a thermistor is provided at each detection point of two containers. Installed so that at least one thermistor will issue an alarm under the condition that the resistance value changes due to the liquid exposure, and even if one thermistor is in the flickering environment, the detection output from the other thermistor prevents the flickering. This is dealt with by performing a so-called OR circuit processing.

[0006]

However, as described above, in the detection by simply ORing the detection outputs of the two thermistors, even if one of the thermistors is in the flickering state, the other thermistor outputs a stable output. If this occurs, an alarm without flicker phenomenon is possible, but it is necessary to prepare an individual circuit for detecting the change voltage for each thermistor, and further, the logic for the detection output of each thermistor detection circuit. A harmony processing circuit is required, and the circuit configuration becomes extremely complicated and expensive.

Further, even if only one of the thermistors outputs a stable output by OR detection of two thermistors, there is no cooperation effect of each, and the flicker prevention effect by the delay operation of each thermistor element is not provided. The flicker prevention effect with respect to the alarm activation of the entire circuit has a genkai, since it works only at the time of detection on an individual element basis.

An object of the present invention is to provide a liquid level detecting device having an extremely simple circuit configuration and capable of issuing an alarm with little flicker by the mutual effect of the thermistors.

[0009]

A first thermistor and a second thermistor, which are respectively disposed at predetermined two positions of a single container containing a liquid or at predetermined positions of at least two containers connected to each other, and a power source It is composed of at least two series resistors that conduct electricity to the first thermistor, and a transistor that is base-connected to a connection point of the series resistors and that conducts electricity from the power source to the second thermistor via a display element.

Further, the transistor is a PNP transistor, the emitter is connected to a power source, the collector is connected to the display element, and the base-emitter connection resistance is R1, and the base-first thermistor connection resistance is set. R2, the first thermistor resistance is Ra, and the base-emitter on-voltage of the transistor is VBE, then E · (R1 / (R1 + R2 + R
When a)) = VBE, the transistor is turned on and the second thermistor is energized via the display element.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION First and second thermistors are installed at two predetermined places where a liquid level alarm of a liquid container is to be made, and a power source supplies electricity to the first thermistor through a plurality of resistors and resistance connection is made. By connecting the display element to the second thermistor via the transistor base-connected to the point, the first thermistor is exposed to the outside of the liquid, and when the transistor conducts due to the resistance change due to self-heating, the second thermistor is passed through the display element. The thermistor is energized, and the energization current increases due to the change in the resistance value of the second thermistor exposed to the outside of the liquid, and the alarm is generated by the change to the lighting level of the display element. It becomes possible to detect the logical sum of the above, and a synergistic delay effect due to the energization of the thermistor in cooperation can be obtained, and a stable alarm becomes possible.

Further, by setting the resistance values of the plurality of resistors and the temperature change resistance characteristic of the thermistor, the delay condition due to the cooperation of the thermistors can be freely set, and the hysteresis characteristic can be obtained according to the use environment.

[0013]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. First, two positions, which are equal to each other in plan or liquid quantity, are located at arbitrary positions in a liquid container, which is a fuel tank, where a residual quantity alarm is desired. The thermistor 1 and the second thermistor 2 are installed, and one terminal of the first thermistor 1 is grounded and the other terminal is connected to the power source E side.

A plurality of resistors 3 and 4 are connected in series on the power source E side of the first thermistor 1, and current is set through the resistors 3 and 4 while conducting current is set.
A PNP transistor 5 is connected at the connection point of the resistors 3 and 4 to the base. The emitter of the transistor 5 is connected to the power supply E, and the collector is grounded at one end via an alarm lamp 6 which is a display element. Second thermistor 2
It is connected to the.

Here, the resistance values of the resistors 3 and 4 are represented by R1 and R
2, the first thermistor resistance value is Ra, and the base-emitter on-voltage of the transistor 5 is VBE, the second thermistor due to the ON operation of the transistor 5 at E · (R1 / (R1 + R2 + Ra)) = VBE The energization condition to 2 can be freely changed by setting each resistance value, and the operation hysteresis due to the time characteristic of the resistance change of the first and second thermistors 1 and 2 can be arbitrarily set.

That is, as shown in the time axis change characteristic of the thermistor resistance value of FIG. 2, if both thermistors 1 and 2 are exposed to the outside of the liquid due to the liquid level lowering to the alarm level, the power is supplied through the resistors 3 and 4. Self-heating due to energization from E occurs (in the liquid, heat dissipation to the liquid is large and temperature rise due to self-heating is suppressed, but heat dissipation outside the liquid is reduced, resulting in temperature rise due to self-heating) The resistance value gradually decreases as the temperature rises.

When the decrease in the resistance value due to the increase in self-heating reaches the ON level of the transistor 5 according to the above equation, the conduction of the transistor 5 causes the second thermistor 2 to be energized via the warning lamp 6, but the second thermistor. Since 2 is also exposed to the outside of the liquid at this time and has no heat dissipation effect, the temperature gradually rises due to self-heating, and its resistance value decreases.

The warning lamp 6 does not light up because the resistance value of the thermistor 2 is large and the amount of current required for lighting is not supplied at the initial stage of turning on the transistor 5, but it does light up due to an increase in the amount of power supply due to the decrease in the resistance value of the thermistor 2. Leading to. This lighting timing is determined by its own threshold level due to the resistance value change of the thermistor 2. However, regarding the lighting switching imperfection due to the slow change of the energization current, a threshold change point such as a Zener diode is clear in the circuit. This can be solved by connecting the elements. As the display element 6, a light emitting diode may be used instead of the lamp, but in this case, the light emitting current emits a small amount of light, so that the light emitting timing is adjusted by connecting a fixed resistor in series to adjust the current. Can be set.

The above alarm operation is apparent from the change characteristic of FIG. 2, but as described above, the second thermistor 2 is not activated until the second thermistor 2 is turned on by the change in the resistance value of the first thermistor 1. Since the resistance value changes due to energization and the lighting of the alarm lamp 6 is controlled for the first time, a relatively large time delay exists between them and the alarm liquid level boundary level of the thermistors 1 and 2 is increased. Even when an instability such as in-liquid or out-of-liquid reciprocation due to vibration is detected, the change does not immediately appear as an energization change to the alarm lamp 6, and the operation hysteresis at this boundary point is set to be relatively large, and flicker occurs. This enables stable alarm operation without any problems. In addition, resistors 3 and 4
Since the energizing current to the thermistor 1 can be set by setting the resistance value of, if the heat generation response at the alarm point is changed by this energizing amount, the on timing of the transistor 5 can be freely set, and the hysteresis of the entire circuit can be set. The characteristics can be adjusted arbitrarily.

[0021]

As described above, according to the present invention, the detection structure by the cooperative action of the two thermistors 1 and 2 enables
With a very simple circuit configuration, it is possible to add a large hysteresis to the unstable detection operation due to the fluctuation of the liquid level at the alarm level, thereby delaying the transmission of the detection fluctuation to the alarm operation and suppressing the alarm flickering phenomenon. It becomes possible to provide a stable alarm operation. .

Further, it is extremely easy to freely set the delay time of the entire circuit, that is, the hysteresis width by setting the resistance values of the resistors 3 and 4, and it is possible to freely set the liquid level detection in accordance with the usage environment and the required accuracy. Therefore, a liquid level detection device having a very wide range of use can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a liquid level detecting device according to the present invention.

FIG. 2 is an explanatory diagram of alarm actuation characteristics in the liquid level detection device of the present invention.

[Explanation of reference numerals] 1 first thermistor 2 second thermistor 3,4 resistance 5 transistor (PNP transistor) 6 alarm lamp (display element) E power supply

Claims (2)

[Claims] 1. A first thermistor and a second thermistor which are respectively arranged at predetermined two positions of a single container containing a liquid or at respective predetermined positions of at least two containers connected to each other, and a first power source to the first thermistor. A liquid level detecting device comprising: at least two series resistors for energizing a thermistor; and a transistor which is base-connected to a connection point of the series resistors and energizes the second thermistor from the power source through a display element. 2. The transistor is a PNP transistor, the emitter is connected to a power source, the collector is connected to the display element, the base-emitter connection resistance is R1, and the base-first thermistor connection resistance is set. R
2, the first thermistor resistance is Ra, and the base-emitter on-voltage of the transistor is VBE,
E · (R1 / (R1 + R2 + R
2. The liquid level detecting device according to claim 1, wherein the transistor is turned on when a)) = VBE and is energized to the second thermistor through the display element.