JPS62251621A - Liquid level detector - Google Patents

Abstract

PURPOSE:To enable stable operation even when a source voltage varies and to accurately detect variation in liquid level by forming a resistor for indirect heating of a material which has a singular point in a positive resistance temperature coefficient (PTC) characteristic. CONSTITUTION:For example, the liquid level when a gasoline tank 22 contains gasoline 23 is L1. At this time, a sensor is in the gasoline 23, so heat generated by the PTC resistor 11 is radiated into the gasoline 23. Consequently, a negative resistance temperature coefficient (NTC) resistor 12 is held high in resistance, so a lamp P never turns on. Further, even if the source voltage rises, the temperature of the PTC resistor 11 is maintained almost at the curie point Tc, so the lamp P never turns on erroneously. When the liquid level drops to L2, the temperature of the NTC resistor 12 rises and the resistor decreases in resistance, so that the lamp P turns on. Then, even if the source voltage drops by variation, the temperature of the PTC resistor 11 is maintained almost at the curie point Tc and variation in liquid level is accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid level detector for detecting the liquid level of gasoline, kerosene, oil, water, or the like.

[Prior art]

BACKGROUND ART Various types of devices have been used to detect the liquid (gasoline) level in an automobile gasoline tank, the water level in a water tank, the liquid (oil) level in an oil tank, etc. Typical examples include those that use a float to mechanically swing the meter needle, and those that use a float with a magnet to operate a switch magnetically. In addition, in recent years, there have been systems that detect the change in resistance that appears when a sensor heated by energizing a resistor rises from the liquid to the liquid surface, and detects the liquid level based on this. For example, there are indirectly heated liquid level detectors and self-heating liquid level detectors.

FIG. 10(a) is a sectional view of a portion of the sensor of the indirectly heated liquid level detector. Indirect heater 1 made of carbon resistor etc.
The negative temperature coefficient of resistance (Nagative Te
mperature coefficient; hereinafter,
A resistor 2 having characteristics (simply referred to as NTC) is provided,
It is molded with resin 3. Now, when electricity is supplied to the indirect heater 1 from a heating circuit (not shown) via the lead wire 4, the NTC resistor 2 is heated by the generated heat. When the illustrated sensor is in the liquid, the heat from the indirect heater 1 is released into the liquid via the resin 3, so the temperature of the NTC resistor 2 does not rise much, resulting in a relatively high resistance. The current flowing through the lead wire 5 to a detection circuit (not shown) is small. However, when the sensor comes out of the liquid surface, the amount of heat dissipated decreases, and as a result, the temperature of the NTC resistor 2 rises and the resistance value decreases, so that it is connected to the detection circuit consisting of an amplifier, meter, etc. via the lead wire 5. More current flows. As a result, when the sensor comes out of the liquid level, the meter in the detection circuit takes a picture due to the action of an amplifier or the like, or a lamp, LED, etc. that is separately supplied with current lights up, and the liquid level is detected.

FIG. 10(b) is a sectional view of a portion of the sensor of the self-heating type liquid level detector. An NTC resistor 2 is connected to a metal case 6 provided with a large number of holes, and electricity is supplied from a power source (not shown) through the metal case 6 and lead wires 7. When this NTC resistor 2 is energized, it self-heats,
Therefore, the resistance value changes. Therefore, this change lights up a lamp or LED.

[Problems to be Solved by the Prior Art] According to the liquid level detector of the type shown in FIG. 10, the liquid level can be detected without using a float or the like.

However, in either case, when the voltage of the power source (power supply to the heating circuit) fluctuates, the amount of heat generated fluctuates accordingly, making accurate detection of the liquid level impossible. Particularly when this liquid level detector is used in a gasoline tank for an automobile, the power supply voltage varies between 8 volts and 15 volts, for example, with respect to the rated voltage of 12 volts.

Therefore, in the past, a constant voltage circuit was used in the heating circuit so that a constant voltage was supplied to the heat generating resistor of the liquid level detector. This has resulted in disadvantages such as the circuit becoming complicated and expensive, and failures occurring frequently.

The present invention has been made in view of the above points, and provides a liquid level detector that operates stably even when a fluctuating power supply voltage is directly supplied and can accurately detect changes in liquid level. This is what I am trying to do.

[Means for solving problems]

Positive Temperature Coefficient of Resistance
A first resistor (e.g. PTC ceramics) having a singular point (e.g. Curie point) in its characteristics (hereinafter simply referred to as PTC) and a second resistor having PTC or NTC characteristics are made of a material with good thermal conductivity. Adjacent via yF4 (eg metal). A heating circuit is connected to this first PTC resistor so that it can generate heat when energized, and a circuit (for example, a series circuit of a power supply and an LED) that detects a change in resistance due to temperature is connected to the second resistor. , as soon as the resistance of the second resistor decreases, for example, LE
Make sure D lights up.

[Effect]

When the first resistor is energized, it generates heat, which heats the second resistor. When this sensor is in the liquid, the second resistor does not reach a high temperature due to heat dissipation into the liquid, so the resistance value of the second resistor is maintained at a high resistance when NTC is detected. For example, the LED in the circuit does not light up. When the sensor comes out of the liquid surface, the heat dissipation decreases and the second resistor becomes hot, so the resistance value of the second resistor becomes NT
When it is C, the resistance becomes low, and the LED of the detection circuit lights up, for example. At this time, if the singular point (for example, the Curie point) on the resistance-temperature characteristic of the first resistor is set at a predetermined level (temperature), even if the power supply voltage fluctuates, the amount of current flowing, that is, the amount of heat generated, will decrease accordingly. It does not fluctuate, so there is no problem with liquid level detection.

[Embodiments] Several embodiments of the present invention will be described below with reference to FIGS. 1 to 9.

FIG. 1 is a basic circuit diagram of an embodiment of the present invention.

A power supply voltage V is supplied to a first resistor (hereinafter referred to as PTC resistor) 11 having PTC characteristics through lead wires 13a and 18b, and a second resistor having NTC characteristics body (hereinafter referred to as NTC resistor) 12
A series circuit including a display 13 including a lamp, an LED, etc. is connected in parallel to this PTC resistor 11.

The resistor elements 11, 12 are arranged as shown in cross section in FIG. 2 and in perspective view in FIG. That is, the PTC resistor 11 and the NTC resistor 12 are provided adjacently with a metal (for example, silver/palladium) layer 15 in between, and the resistor 11.1
Gold 5IN poles 16 and 17 are respectively formed on the other surface of 2. These are then molded with resin 3 such as epoxy resin.

FIG. 4 is a resistance/temperature characteristic diagram of the PTC resistor 11.

The resistance value (R>) increases with a positive coefficient as the temperature (T>) increases, and the resistance value increases rapidly when the temperature reaches around the Curie point (To). When the voltage rises, the resistance value increases rapidly, thus suppressing the increase in heat generation, that is, the temperature rise.On the other hand, when the power supply voltage is too low, setting the Curie point to an appropriate value will lower the resistance value. Therefore, the reduction in heat generation, that is, the temperature drop, can be suppressed.

Next, the specific operation will be explained with reference to FIG. Assume that when gasoline 23 is contained in gasoline tank 22, the liquid level is Ll in the figure. At this time, since the sensor is inside the gasoline 23, the heat generated from the PTC resistor 11 is released into the gasoline 23. Therefore, the temperature of the NTC resistor 12 does not rise above a certain level, and therefore the NTC resistor 12 is kept at a high resistance, so that the lamp P is not lit. Furthermore, even if the power supply voltage V fluctuates and becomes high, the temperature of the PTC resistor 11 remains at the Curie point. Since the lamp P is maintained nearby, the lamp P will not be erroneously lit.

When the liquid level drops to L2, it becomes difficult for the PTC resistor 11 to release heat. For this reason, the NTC resistor 12
The temperature rises, the resistance becomes low, and the lamp P lights up.

Furthermore, even if the power supply voltage decreases due to fluctuations, the temperature of the PTC resistor 11 remains at the Curie point T. Since it is maintained in the vicinity,
The lamp P will not be turned off accidentally.

Furthermore, in this embodiment, an NTC resistor 12 having a current capacity above a certain level is used as the resistor on the detection side, and since electricity is supplied to this through the lamp P, the heat generated by the PTC resistor 11 causes the NTC resistor to When 12 is heated to a certain extent, N
As the resistance of the TC resistor 11 decreases, the amount of current increases and self-heating begins. In this way, in this embodiment, the indirect heating method using the PTC resistor 11 and the NTC resistor 12 are used.
Since the self-heating system is also used, the following drawbacks of the conventional example shown in FIG. 10 can be solved.

That is, in the indirect heating type shown in Fig. 10 (a), the indirect heating heater 1
It is necessary to increase the amount of heat generated by the
(The capacitance of the resistor 2 is small), so there was a risk that a small change in potential would cause a large change in temperature, or that it would catch fire due to overheating. However, in this embodiment, if the NTC resistor has a relatively large current capacity and starts to self-heat after being indirectly heated to a certain extent, the above-mentioned drawback is solved. In addition, with the self-heating type shown in Figure 10(b), it is difficult to increase the self-heating amount when the liquid temperature is low (for example, when used in winter or in a cold region), and for this reason, the liquid level may not be detected. there were. However, in this embodiment, the NTC resistor 12
Since the liquid level is indirectly heated by the PTC resistor 11 up to a temperature at which self-heating is possible, the liquid level can be accurately detected even in a low temperature state.

The present inventors conducted the following experiment in order to investigate the performance of the embodiment shown in FIG. That is, in FIG. 1, ceramics with a Curie point of 120°C is used as the PTC resistor 11, a resistance material with a resistance value of 400'C at 100°C is used as the NTC resistor 12, and a 12V, 3.4W resistor is used as the display 13. I used a light bulb. Then, the power supply voltage (DC) was changed from 8 volts to 16 volts, and -4
The liquid level from 0'C to +80'C was detected. As a result, it was confirmed that the liquid level could be detected within these ranges without any problems.

FIG. 6 is a sectional view showing a modification of a portion of the sensor of the embodiment shown in FIGS. 1 to 5 above. If the metal plate 20 is interposed between the resistors 11 and 12 as shown in FIG. If the resin 3 is housed in the metal case 21 as shown in FIG. In addition, if a heat insulating material 21- is provided on the outer surface of the PTC resistor 11 as shown in FIG. 6(C),
Heat from the PTC resistor 11 can be prevented from being released into the liquid, and therefore the energy consumption of the liquid level detector can be reduced.

FIG. 7 shows another modification of a portion of the sensor of the embodiment shown in FIGS. 1-5. As shown in a sectional view in FIG. 7(a) and in a perspective view in FIG. 7(b), the resistor 11
．． 12 into a cylindrical shape and a metal mold ti25,2 between them.
6.27, the heat generation of the PTC resistor 11 can be reduced to N.
It can be efficiently transmitted to the TC resistor 12, and the NT
Heat can be efficiently radiated from the C resistor 12 into the liquid. Therefore, it is possible to simultaneously reduce current consumption and speed up liquid level detection.

FIG. 8 is a perspective view showing a portion of a sensor according to a second embodiment of the present invention. A rod-shaped PTC resistor 11 is provided on one surface of a heat-insulating insulating rod 31 with a metal layer 16 interposed therebetween.
An island-shaped NTC resistor 12 is placed on one surface of 1 with a metal layer 15 interposed therebetween.
Provide multiple. Then, lead wires 188 to 18G are wired and molded with resin (not shown).

FIG. 9 shows the state of use of the second embodiment.

Insert the sensor into the tank 22 and insert the sensor S1. S
2. Lamps P1.S3 respectively. P2.

Connect P3. Now, the liquid level of gasoline 23 in tank 22 is rising. In the above example, all sensors 81 to S3 are in gasoline. For this reason, the amount of heat dissipated is large, so NTC
Both resistors 12 are kept at a low temperature, so that the lamp P1
~P3 does not light up.

When the liquid level of gasoline reaches Ll, the sensor S1 comes out from the liquid level. For this reason, the amount of heat dissipated by the NTC resistor 11 of the sensor S1 decreases, and therefore the resistance decreases due to the temperature rise, and the lamp P1 lights up.

Similarly, when the liquid level reaches L2, lamps P1 and P turn on, and when the liquid level reaches L3, all lamps P1 to P3 turn on, and as a result, the liquid level can be detected and displayed digitally. .

The present invention is not limited to the above embodiments, and various modifications are possible. For example, the structure of a portion of the sensor is not limited to the one shown in the drawings, and any structure may be used as long as two resistors are adjacent to each other with a material having good thermal conductivity interposed therebetween. Further, the resistor on the detection side is not limited to NTC, but may be PTC. However, when using PTC, you cannot expect a decrease in resistance and self-heating when the temperature rises, so lamps,
Although it is not possible to connect LEDs or the like in series and turn them on, the signal can be detected using an amplifier, comparator, etc. and easily displayed on a meter or the like.

In general, the present invention can be used not only for liquid level detection but also for temperature detection. That is, since the amount of heat radiated from the sensor changes according to changes in the environmental temperature, lighting of the lamp, etc. can be controlled in the same manner as in the above embodiment.

〔Effect of the invention〕

As described above, in the present invention, the resistor for indirect heating is formed of a material that has a singular point in PTC characteristics, so even when the power supply voltage fluctuates, the liquid level can be accurately determined without using a low voltage circuit. A liquid level detector capable of detection is obtained. Furthermore, if a material having NTC characteristics is used for the resistor on the detection side, self-heating can be expected when the temperature rises, and therefore stable operation can be achieved with an extremely simple circuit even in a low-temperature environment.

[Brief explanation of drawings]

Figure 1 is a basic circuit diagram of the first embodiment, Figure 2 is a circuit configuration diagram showing a part of the sensor in cross section, Figure 3 is a perspective view of part of the sensor, and Figure 4 is the resistance/temperature of the PTC resistor. Characteristic diagram,
FIG. 5 is an explanatory diagram of the usage state of the first embodiment, FIG. 6 is a sectional view of a modified example of a part of the sensor according to the first embodiment, and FIG.
The figure is a sectional view of a portion of a sensor according to a modification of the first embodiment, and FIG. 8 is a perspective view of a portion of a sensor of the second embodiment.
FIG. 9 is an explanatory view of the second embodiment in use, and FIG. 10 is a sectional view of a portion of a conventional sensor. 1...Indirect heater, 2,12...NTC resistor,
3...Resin, 4,5.7.18a ~18G-...Lead wire, 6.21...Metal case, 11...PTC
Resistor, 13... Indicator, 15... Metal layer, 16,
17.25-27...metal electrode, 20...metal plate,
21--Insulation material, 22-Gasoline tank, 23
...gasoline, 81-S3...sensor, P1-P
3...Lamp. Applicant's agent Yoshi Hase Resin 1 Figure 2 Figure 4 Figure 5
Figure 6 (a) (b)
(c) Figure 7 (a) (b) Figure 8 Figure 9
Figure 10 (a) (b)

Claims (1)

[Claims] 1. A first resistor having a singular point in positive resistance temperature characteristics, and a positive or negative resistor provided adjacent to the first resistor through a material with high thermal conductivity. a second resistor having a resistance-temperature characteristic; a heating circuit that heats the first resistor by applying current; and a detection means that detects a change in electrical resistance of the second resistor. Detector. 2. The liquid level detector according to claim 1, wherein the first resistor is made of ceramic having a Curie point in a positive resistance temperature characteristic. 3. The second resistor is made of ceramics having negative resistance-temperature characteristics, and the detection means includes a power supply that energizes the second resistor, and a display element connected in series to the second resistor and the power supply. A liquid level detector according to claim 2, comprising: