JPS62162926A - Continuous level gage - Google Patents

Abstract

PURPOSE:To prevent overheating in a liquid and to reduce consumption electric power by using a long-sized positive characteristic thermistor as a detecting element and covering the circumference with a heat insulator leaving a part and making it possible to indicate a continuous change of a liquid level with simple constitution. CONSTITUTION:The detecting element 6 consisting of the long-sized positive characteristic thermistor is covered by the heat insulator 8 such as insulating resin leaving only the surface of an electrode 7 of one side. In this way, when the element 6 is dipped in the liquid such as gasoline, a surface area of the element 6 which comes in direct contact with the liquid is reduced and heat radiation in the liquid is reduced, by which the resistance is made high and the consumption electric power is reduced. Further, an electric current value of the element 6 is changed in a straight line as the element 6 is dipped in the liquid and the change of the liquid level can be continuously indicated by reading the electric current change.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention detects and displays the amount of fuel in automobiles, etc. by utilizing the fact that the degree of self-heating of a positive temperature coefficient thermistor differs between in liquid and in air. , relates to a continuous liquid level gauge that can continuously display changes in liquid level.

Conventional technology A positive temperature coefficient thermistor is a temperature-sensitive resistor that has the property of rapidly increasing its resistance when the temperature rises above a certain temperature (Currie temperature), and is made of semiconductor ceramics or polymer materials. When a voltage is applied to this element to generate self-heating, the temperature is different when the element is in the air and when it is in a liquid such as gasoline, and the resistance value is different. It can be used as

Conventional liquid level needles of this type that use a negative characteristic thermistor have been put into practical use. FIG. 8 shows its configuration. 8th
In the figure, numeral 1 is a sensing element made of a rod-shaped negative characteristic thermistor, and numeral 2 is a lead wire made of nickel or the like fixed thereto. Reference numeral 3 indicates an insulating plate, and 4 indicates a metal tube, which together constitute a case, to the center of which the detection element 1 is fixed via a lead wire 2. 5 is a lamp, to which the detection element 1 and a power source are connected in series.

In such a liquid level needle, when the sensing element 1 is in the air, since the heat dissipation coefficient of the sensing element 1 is small, it is easy to generate heat and the temperature becomes high. Therefore, the resistance of the sensing element 1 becomes small, the current flowing becomes large, and the lamp 5 lights up. Further, when the metal cylinder 4 is in the liquid, the liquid enters through the through hole a, and the sensing element 1 is immersed in the liquid. At this time, the heat of the sensing element 1 is taken away by the liquid, and the heat dissipation coefficient increases, so the sensing element 1
The resistance increases and the current flowing through the circuit decreases,
9 and 10 show yet another conventional example in which a plurality of negative characteristic thermistors shown in FIG. 8 are used to display changes in the liquid level in stages. (Jitsukai Sho 57-105930
Problems to be Solved by the Invention Conventional liquid level needles take advantage of the fact that the amount of self-heating of a negative characteristic thermistor is significantly different between liquid and air, and the resistance value is different between liquid and air. The lamp is turned on and off depending on the magnitude of the current flowing through it. Therefore, the presence or absence of liquid can be displayed using a very simple circuit. However, since there is only one sensing element, the liquid level that can be displayed is only one point, whether the sensing element is in the liquid or in the air, and changes in the liquid level cannot be displayed continuously. Ta.

Therefore, a structure using a plurality of sensing elements has been devised, but even this can only display the liquid level in stages, but cannot continuously display the amount of liquid level.

In addition, since a negative characteristic thermistor is used as the detection element,
As the ambient temperature rises, the temperature of the sensing element rises even when it is submerged in liquid, making the rise in liquid temperature more difficult.

Means for Solving the Problem In order to solve this problem, the present invention uses a long sensing element consisting of a positive temperature coefficient thermistor fixed so that the immersion length changes as the liquid level changes. , consisting of a power supply connected in series to the sensing element and a display device for the current flowing through the series circuit, and the direction of the line connecting both electrodes of the sensing element is parallel to the liquid level, and the sensing element is All but one part is covered with insulation.

Effect The effect of this configuration will be explained. First, a positive temperature coefficient thermistor is a temperature-sensitive resistor whose resistance value increases rapidly when the temperature rises above a certain temperature (Currie temperature), and is made of barium titanate-based semiconductor ceramics or a polymer resin mixed with conductive powder. It can be created using things like When a voltage is applied to a long sensing element made of this positive temperature coefficient thermistor and the entire sensing element is in the air, the sensing element self-heats, its resistance increases, and it reaches thermal equilibrium at a certain temperature. At this time, the current flowing through the circuit also stabilizes at a certain constant current. The current value is displayed on a current display device. Then, as the liquid level increases and the sensing element is gradually immersed from the end, the temperature of the immersed part becomes lower and the resistance of that part becomes smaller. Then, since the resistance of a portion of the sensing element decreases, the current increases accordingly. On the other hand, when the entire sensing element is immersed in the liquid, the current becomes the largest. In this way, the current changes continuously depending on the liquid level, and its value can be read on the current display device. Also, if the line connecting both electrodes of the sensing element is made perpendicular to the liquid level, the part of the sensing element in the air and the part in the liquid will be connected in series, and the resistance value of the part in the air will be becomes high, the voltage is concentrated there, and no voltage is applied to the part in the liquid. Therefore, the line connecting both electrodes of the sensing element needs to be parallel to the liquid level.

In addition, since the area around the sensing element is covered with insulation material except for a part, the actual heat dissipation area is small, so even if the sensing element is large in shape, it generates less heat and consumes less power. .

Embodiment FIG. 1 is a schematic configuration diagram showing a continuous liquid level needle according to an embodiment of the present invention, and FIG. 2 is a sectional view of a sensing element portion taken in a plane parallel to the liquid level. 6 is a sensing element consisting of a positive characteristic thermistor, for example, with a resistance value of 10Ω at room temperature and a Curie temperature of 60°C.
'C, the shape is a long plate with a thickness of 1ffff, a width of 2 Mill, and a length of 10Qffff. This sensing element 6 is mounted so that the length of immersion changes as the liquid level changes. T is an electrode made of baked silver or the like provided on both sides, and the sensing element 6 is fixed so that the direction of the line connecting the electrodes on both sides is parallel to the liquid level. Reference numeral 8 denotes a heat insulating material such as an insulating resin, which covers only one electrode surface of the detection element 6 made of the positive temperature coefficient thermistor.

9 is a power supply connected in series to the detection element 6, 12v11o
is an ammeter that displays the current flowing through the sensing element 6.

Now, when the entire sensing element is in the air, the heat dissipation coefficient is small, so the sensing element self-heats and reaches thermal equilibrium at a high temperature. Therefore, the resistance value of the sensing element becomes high and stable.

The current at this time was 100 mm. Conversely, when the entire sensing element is submerged in gasoline, the resistance is low and the current is 40
It was 0mA.

However, if the sensing element is immersed sequentially from the end, the current value changes approximately linearly from 100 mA to 400 mm.

In this way, with a very simple configuration and without using a special amplification circuit, changes in liquid level can be continuously indicated simply by reading changes in current. Furthermore, since a positive temperature coefficient thermistor is used, it has a self-temperature control function, and the surface temperature of the sensing element remains almost constant even when the ambient temperature rises, and does not overheat. Furthermore, since the sensing element is covered with a heat insulating material except for a part, the surface area that comes into direct contact with the liquid is small even if it is submerged in the liquid. Therefore, even if the sensing element itself has a large shape, less heat is dissipated in the liquid, resulting in higher resistance and lower power consumption. These conditions are shown in FIG. Third
In the figure, "B" shows the state of current generated by the detection element of the present invention, and "B" shows the state of current when a detection element made of a positive temperature coefficient thermistor of the same shape is used without using a heat insulating material.

4 and 5 a and 5 b show another embodiment of a detection element using a positive temperature coefficient thermistor. FIG. 5 is a perspective view of a sensing element constructed using the present invention, and FIG. 5 is a sectional view thereof. 11 is a positive temperature coefficient thermistor, and 12 is an electrode made of baked silver or the like attached to both main surfaces thereof. Reference numeral 13 denotes a common electrode such as a brass plate, to which a plurality of the positive temperature coefficient thermistors 11 are tightly attached in parallel with each other by soldering or the like (not shown). Reference numeral 14 denotes a heat insulating material made of insulating resin such as phenol, which covers all but a portion of the sensing element consisting of a plurality of positive temperature coefficient thermistors. In addition, in FIG. 5, the heat insulating material 14 is shown by a dotted line so as not to complicate the drawing.

Generally, ceramics such as positive temperature coefficient thermistors are brittle and it is difficult to create a long shape as used in the present invention, but if the sensing element is configured as shown in Figure 6, , a small-sized positive temperature coefficient thermistor can be used, yield is high, and long sensing elements can be easily produced.0 Figure 6 shows that temperature compensation can be used in a wide temperature range with a simple configuration. This is another embodiment of the present invention.

Reference numeral 15 denotes a sensing element consisting of a long positive temperature coefficient thermistor, and as described above, its resistance value changes depending on the length of immersion in the liquid. Similarly, numeral 16 is a temperature compensation element using a positive temperature coefficient thermistor, which is always in the liquid or in the air, or has a large shape to almost eliminate the difference in heat generation between the liquid and the air, and its resistance is proportional to the ambient temperature. It was decided only by

17 is a crossed coil ratio meter. This crossed coil ratio meter 17 uses two crossed coils and can display the ratio of currents flowing through the two coils. A current flowing to the sensing element 16 is passed through one coil C1, and a current flowing to the temperature compensation element 16 is passed through the other coil C2.

Here, if a temperature compensation element is not used, the current flowing through the sensing element differs greatly between the liquid and the air, but it also varies depending on the ambient temperature, making it difficult to display the liquid level with only the current value over a wide temperature range. Met. In FIG. 6, 18 is a magnetic material such as iron, and 19 is a pointer.

In the embodiment shown in FIG. 6, a temperature compensation element is used, and the ratio of the current flowing through the sensing element and the current flowing through the temperature compensation element is kept constant even if the ambient temperature changes as long as the liquid level is constant.
This makes it possible to display the liquid level over a wide temperature range. However, if you use a crossed coil ratio meter to display the ratio of the currents flowing through both, you can easily and inexpensively display the ratio of the currents.

FIG. 7a shows the state of the current 11 flowing through the sensing element when no temperature compensation element is used, and it can be seen that the characteristics change greatly depending on the ambient temperature. On the other hand, FIG. 7 shows the ratio i+/i2 of currents 12 and 11 flowing through a temperature compensating element. in this case,
12/i is determined only by changes in the liquid level, regardless of the ambient temperature.

In this embodiment, only the plate-shaped sensing element and the one joined by solder are shown as the sensing element, but the sensing element may be rod-shaped, film-shaped, or thin-film shaped. In addition, a fixed resistor may be appropriately inserted into the series circuit. Effects of the Invention As described above, the present invention uses a long positive temperature coefficient thermistor as a sensing element, and the surrounding area is covered with heat insulating material except for a part. By covering it with a liquid, it is possible to display continuous changes in the liquid level with a simple configuration without using a special amplifier circuit, and there is no risk of overheating in the liquid, and it has great practical value with low power consumption. It is what it is.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a continuous liquid level needle according to an embodiment of the present invention, FIG. 7a and 7b are graphs for explaining the operation of the present invention, and FIGS. 8, 9, and 10 are a schematic configuration diagram and a circuit diagram showing a conventional liquid level needle, respectively. 6.15...Detection element, 7,12...
Electrode, 8゜14...Insulating material, 9...Power supply, 1o...Ammeter, 11...Positive characteristic thermistor. Name of agent: Patent attorney Toshio Nakao and 1 other person6-
& Taro wood - Fig. 1 7-9 Plum δ - - JFZT wood / θ-1 + 91↑ Fig. 2 Fig. 6 Fig. 7

Claims (2)

[Claims] (1) A long sensing element consisting of a positive temperature coefficient thermistor fixed so that the immersion length changes as the liquid level changes, a power supply connected in series to the sensing element, and a The direction of the line connecting both electrodes of the sensing element is parallel to the liquid level, and the cross-sectional shape of the sensing element in the liquid level direction is almost uniform, and the sensing element is uniform. A continuous liquid level gauge whose surroundings are covered with insulation material except for the upper part. (2) A continuous liquid level gauge according to claim 1, which uses detection elements consisting of a plurality of positive temperature coefficient thermistors connected in parallel and each of which is substantially closely fixed.