JPH083437B2 - Continuous level gauge - Google Patents

Description

TECHNICAL FIELD The present invention detects and displays the amount of fuel of an automobile or the like by utilizing the fact that the degree of self-heating of a positive temperature coefficient thermistor differs between liquid and air. The present invention relates to a continuous liquid level meter which can continuously display changes in liquid level and has an improved detection element.

2. Description of the Related Art A positive temperature coefficient thermistor is a temperature sensitive resistor that has a property that its resistance value rapidly rises when the temperature rises above a certain temperature (Curie temperature), and is made of semiconductor ceramics or polymer materials. When a voltage is applied to the element to cause it to self-heat, the heating temperature differs between when the element is in the air and when it is in a liquid such as gasoline, and thus the resistance value is different. This can be used as a liquid level sensor.

A conventional liquid level meter of this type using a negative characteristic thermistor is in practical use. The structure is shown in FIG. In FIG. 5, reference numeral 1 is a sensing element using a rod-shaped negative characteristic thermistor, and 2 is a lead wire such as nickel fixed to the sensing element. Reference numeral 3 is an insulating plate, and 4 is a metal cylinder, which form a case.
Is fixed through. Reference numeral 5 is a lamp, in which the detection element 1 and a power source are connected in series.

In such a liquid level meter, when the sensing element 1 is in the air, the heat dissipation coefficient of the sensing element 1 becomes small, so that heat is easily generated and the temperature rises. Therefore, the resistance of the detection element 1 becomes small, the flowing current is large, and the lamp 5 is turned on.
Further, when the metal cylinder 4 is in the liquid, the liquid enters through the through hole a,
The sensing element 1 is immersed in the liquid. At this time, the heat of the detection element 1 is taken by the liquid, and the heat dissipation coefficient increases, so that the resistance of the detection element 1 increases and the current flowing through the circuit decreases, and the lamp 5 is turned off.

FIGS. 6 and 7 show another prior art example in which a plurality of negative characteristic thermistors shown in FIG. (For example, Japanese Utility Model Laid-Open No. 57-105930) Problems to be Solved by the Invention As described above, the conventional level gauge utilizes the fact that the amount of self-heating of the negative characteristic thermistor greatly differs in liquid and air. ,
The resistance value differs between liquid and air, and the lamp is turned on and off depending on the magnitude of the flowing current. Therefore, the presence or absence of liquid can be displayed with a very simple circuit. However, since there is only one sensing element, the only liquid level that can be displayed is whether the sensing element is in the liquid or in the air, and continuous changes in the liquid level could not be displayed. . Therefore, as described above, a structure using a plurality of sensing elements has been devised, but even with this, it is not possible to continuously display the amount of the liquid level only by displaying the liquid level stepwise.

In addition, since the negative characteristic thermistor is used for the detection element, the temperature of the detection element rises even when it is in the liquid when the ambient temperature rises, and the rise of the liquid temperature becomes large.

The present invention solves such a problem, and an object of the present invention is to provide an inexpensive continuous level gauge capable of displaying continuous changes in the liquid level with a simple structure.

Means for Solving the Problems In order to solve this problem, the present invention comprises a plurality of positive temperature coefficient thermistors having electrodes on opposite surfaces and two common electrode plates made of metal. A sensing element composed of two common electrode plates and two positive electrode thermistors which are fixed to each other with a gap therebetween so as to be electrically connected to the electrodes of the positive temperature coefficient thermistor. It is composed of a connected power source and a display device for the current flowing through the sensing element.

Operation The operation of this configuration will be described. Now, the positive temperature coefficient thermistor is a temperature-sensitive resistor whose resistance value rises rapidly above a certain temperature (Curie temperature) when the temperature rises. It is a mixture of barium titanate-based semiconductor ceramics and polymer resin with conductive powder. So you can create it. A voltage is applied to a sensing element that is configured by arranging a plurality of these PTC thermistors in a straight line at intervals and fixing metal common electrode plates from both sides so that they are electrically connected to the PTC thermistor electrodes. However, when the entire sensing element is in the air, the sensing element self-heats and reaches a thermal equilibrium at a certain temperature where the resistance increases. At this time, the current flowing through the circuit also stabilizes at a constant current.
The current value is displayed on the current display device. Also,
When the liquid level increases and is gradually immersed from the end of the sensing element, the temperature of the immersed positive temperature coefficient thermistor decreases,
The current increases accordingly as its resistance decreases. Furthermore, the electric current becomes maximum when the entire sensing element is immersed in the liquid. Even if the liquid level is between the adjacent positive temperature coefficient thermistors, the metal common electrode plate serves as a heat dissipation plate, so that the change in current is moderated and the current continuously changes. Thus, the current continuously changes according to the liquid level, and the value can be read by the current display device.

Embodiment FIG. 1 is a circuit diagram showing a continuous type level gauge according to an embodiment of the present invention, and FIG. 2 is a perspective view of a positive temperature coefficient thermistor used for its detecting element. In FIGS. 1 and 2, 6 is a positive temperature coefficient thermistor, and 7 is an electrode made of silver or the like provided on the surfaces facing each other. 8 is a common electrode plate such as a brass plate, between which the positive temperature coefficient thermistor 6 is 4
K, they are fixed at intervals. This fixation is performed by bonding the electrode 7 of the positive temperature coefficient thermistor 6 and the common electrode plate 8 with solder (not shown) or the like. Reference numeral 9 is a sensing element configured as described above, 10 is a power source, and 11 is an ammeter. Here, the common electrode plate 8 of the detection element 9, the power source 10 and the ammeter 11 are connected in series.

Since the heat dissipation coefficient is small when the entire sensing element 9 is in the air, the sensing element 9 self-heats and reaches thermal equilibrium at a high temperature. Therefore, the resistance value of the sensing element 9 becomes high, and the flowing current is the smallest. At this time, even if the position of the liquid surface is between the two adjacent positive temperature coefficient thermistors 6, the common electrode plate 8 serves as a heat radiating plate, so that the change in current is moderated and the current continuously changes. In this way, the current continuously changes according to the liquid level, and the value can be read by the ammeter 11 to know the liquid level. FIG. 3 is a graph showing these states, where the horizontal axis represents the liquid level, 0 indicates that the sensing element 9 is in the air, and 1 indicates that the entire sensing element 9 is in the liquid. The area a is a portion where the positive temperature coefficient thermistor 6 of the detection element 9 is in the liquid, and the area b is a position where the liquid level is not the positive temperature coefficient thermistor 6. As described above, the change of the current flowing according to the change of the liquid level is slightly different between the region a and the region b, but is almost a straight line.

FIG. 4 is a perspective view showing a sensing element used in another embodiment of the present invention. In FIG. 4, 12 is a positive temperature coefficient thermistor, and 13 is an electrode made of silver or the like provided on the surfaces facing each other. Reference numeral 14 is a common electrode plate made of a brass plate or the like, and the above positive temperature coefficient thermistors 12 are fixed between them at four intervals. This sticking is the electrode of the positive temperature coefficient thermistor 12.
This is performed by bonding 13 and the common electrode plate 14 with solder (not shown) or the like. Reference numeral c denotes a portion of the common electrode plate 14 to which the positive characteristic thermistor 12 is not fixed, and the width of the common electrode plate 14 in this portion is wider than the portion to which the positive characteristic thermistor 12 is fixed. Therefore, the function of the common electrode plate 14 as a heat radiating plate is more exerted, the change in the current when the liquid level changes in the portion c becomes larger than that shown in FIG. 1, and the change in the current is smooth as a whole. become.

EFFECTS OF THE INVENTION As described above, according to the present invention, a plurality of positive temperature coefficient thermistors are arranged at intervals as sensing elements and fixed by a common electrode plate that also serves as a heat dissipation plate. It is possible to inexpensively display continuous changes in liquid level with a small number of positive temperature coefficient thermistors without using it, and it is of great practical value without fear of overheating in the liquid.

[Brief description of drawings]

FIG. 1 is a block diagram showing a continuous level gauge according to an embodiment of the present invention, FIG. 2 is a perspective view of a positive temperature coefficient thermistor used therein, and FIG. 3 is a graph showing the operation thereof, FIG. Is a perspective view of a sensing element used in another embodiment of the present invention, FIG.
FIG. 6 and FIG. 7 are configuration diagrams showing conventional liquid level gauges. 6,12 …… Positive characteristic thermistor, 7,13 …… Electrode, 8,14 …… Common electrode plate, 9 …… Detecting element, 10 …… Power supply, 11 …… Ammeter.

Claims (2)

[Claims] 1. A plurality of positive temperature coefficient thermistors having electrodes on opposite surfaces, and two common electrode plates made of metal. The two common electrode plates are electrically connected to the electrodes of the positive temperature coefficient thermistor. In this way, a positive temperature coefficient thermistor is fixed between the two common electrode plates at a distance, and a sensing element, a power source connected to the sensing element,
A continuous liquid level gauge consisting of a display device for the current flowing through the sensing element. 2. The continuous liquid level gauge according to claim 1, wherein the width of the common electrode plate in a portion where the positive temperature coefficient thermistor and the common electrode plate are not in contact is larger than the width in a portion where they are in contact with each other.