JPH04337422A - Liquid surface level detector - Google Patents

Abstract

PURPOSE:To obtain a liquid surface level detector of high reliability. CONSTITUTION:An electric potential V0 of a contact point of a reference voltage generating circuit B0, in which fixed resistance devices R10-R1n and a heat sensitive resistance device R20 or heat build-up heat sensitive resistance devices R21-R2n are connected in series, and electric potentials V1-Vn of a contact point of level detection circuits L1-Ln are input into comparators C1-Cn. A transistor of open collector circuit structure is arranged on the final stage of the comparators C1-Cn, and the transistor is turned ON correspondent to a detected liquid surface level. In the abovementioned structure, when the transistor of the comparators C1-Cn is turned ON correspondent to the number of the level detection circuits L1-Ln in the liquid, current correspondent to the liquid surface level runs in externally fixed resistance devices R1-Rn from a power source S3. The running current can be measured accurately by a pointer-type ammeter An in a fuel gauge for an automobile and so on.

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 using a heat-generating temperature-sensitive resistance element. The present invention can be applied to, for example, an automobile fuel gauge.

0002

2. Description of the Related Art Conventionally, fuel gauges for automobiles use a float to replace changes in fluid level with changes in contact position. The current flowing through the ammeter is changed through a resistance value that changes in accordance with the position of the contact, thereby changing the indicated position of the needle-type meter.

0003

SUMMARY OF THE INVENTION Such a fuel gauge for an automobile has a contact point for changing the resistance value, and there has been a problem of poor contact during long-term use of the contact point.

The present invention has been made to solve the above problems, and its purpose is to accurately drive needle-type gauges such as conventional automobile fuel gauges without using contacts. An object of the present invention is to provide a highly reliable liquid level detector.

[0005]

[Means for Solving the Problems] The structure of the invention for solving the above problems is such that a fixed resistance element and a heat-generating temperature-sensitive resistance element whose resistance value changes depending on temperature and generate heat when energized are connected in series. a level detection circuit, a board in which a plurality of the level detection circuits are connected in parallel in a direction in which the liquid level of the object to be measured changes, and the level detection circuit is arranged in the board;
Using a temperature-sensitive resistance element having almost the same temperature resistance characteristics as the temperature-resistance characteristic of the heat-generating temperature-sensitive resistance element of the level detection circuit,
A fixed resistance element having a resistance ratio substantially matching the resistance ratio of the fixed resistance element and the heat-generating temperature-sensitive resistance element of the level detection circuit, and whose sum of resistance values is sufficiently larger than the sum of their resistance values. and a reference voltage generation circuit in which the temperature-sensitive resistance element and the temperature-sensitive resistance element are connected in series, a potential at a connection point between the fixed resistance element of the reference voltage generation circuit and the temperature-sensitive resistance element is set as a reference potential, and each of the level detection circuits The potential at the connection point between the fixed resistance element and the heat-generating temperature-sensitive resistance element is set as the detection potential, the reference potential and the detection potential are input, and the transistor of the final stage open collector circuit configuration is selected depending on the magnitude of these potentials. a comparator arranged corresponding to the level detection circuit to turn on and off the level detection circuit; an external fixed resistance element connected in series to the collector of the transistor of the comparator; The present invention is characterized in that it has one indicating means connected between all other ends of the resistive elements and the power supply, and whose internal resistance is sufficiently smaller than that of the external fixed resistive element.

[0006]

[Operation] Each level detection circuit has a fixed resistance element and a heat-generating temperature-sensitive resistance element connected in series, and the reference voltage generation circuit has a fixed resistance element and a temperature-sensitive resistance element connected in series. A full bridge circuit is formed from the level detection circuit and the reference voltage generation circuit. Then, the potential at the connection point between the fixed resistance element and the heat-generating temperature-sensitive resistance element in the level detection circuit (detection potential), and the potential at the connection point between the fixed resistance element and the temperature-sensitive resistance element in the reference voltage generation circuit (reference potential) The two outputs are input to the comparators corresponding to the respective level detection circuits. The temperature resistance characteristic of the temperature sensitive resistance element of the reference voltage generation circuit is set to be approximately equal to that of the heat generating temperature sensitive resistance element of the level detection circuit. This can be easily realized by using the same element as the temperature-sensitive resistance element and the heat-generating temperature-sensitive resistance element of both circuits. Further, the resistance ratio between the resistance element of the reference voltage generation circuit and the temperature-sensitive resistance element is set to a value that substantially matches the corresponding resistance ratio of the level detection circuit. Therefore, even if the temperature of the liquid whose liquid level is to be measured changes over a wide range, the detection potential and the reference potential both change with similar temperature characteristics, so the potential difference between them does not change much. However, if the resistance ratio of the reference voltage generation circuit is completely equal to the resistance ratio of the level detection circuit,
Since the output of the comparator will become unstable, the resistance ratio between the two should be set to have a difference within a range that allows stable operation, taking into account the amount of resistance change in the heat-generating temperature-sensitive resistor element due to heat generated by energization of the level detection circuit. There is. Then, when the heat-generating temperature-sensitive resistance element of the level detection circuit changes from being in the liquid to being exposed in the air, the level detection circuit and the reference voltage generator are connected so that the detection potential changes beyond the reference potential. The resistance ratio with the circuit is set. As a result, the transistor of the open collector circuit configuration in the final stage of the comparator corresponding to the level detection circuit that changes from being submerged in the liquid to being exposed to the air is turned on from off as the liquid level changes. When the transistor of the comparator is turned on, a current flows from the power supply through the external fixed resistance element between the collector and emitter of the transistor. One indicating means whose internal resistance is sufficiently smaller than that of the external fixed resistance element is connected between the power supply and the external fixed resistance element. This indicating means measures the current flowing through the external fixed resistance element when the transistor of the comparator is turned on. That is, since the transistor has an open collector circuit configuration, the current flowing through the turned-on transistor does not affect other transistors. Therefore, the amount of current is proportional to the liquid level, and the liquid level can be known by the indicating means. On the other hand, the total resistance of the fixed resistance element and the temperature-sensitive resistance element of the reference voltage generation circuit is set to a large value, with the resistance ratio substantially matching the resistance ratio of the level detection circuit. Therefore, the value of the current flowing through the reference voltage generation circuit is small, and the amount of heat generated by the temperature-sensitive resistance element is small. Therefore, even if the temperature-sensitive resistive element of the reference voltage generation circuit is exposed to the air, the reference potential does not fluctuate much. Therefore, even in such a state, the output of each comparator will not be reversed, and an accurate liquid level will be detected.

[0007]

EXAMPLES The present invention will be explained below based on specific examples. FIG. 1 is an overall circuit diagram showing the electrical configuration of an automobile fuel gauge using a liquid level detector according to the present invention. R21 to R2n are exothermic temperature-sensitive resistance elements whose resistance values change depending on temperature. Well-known thermistors and platinum resistors can be used for these heat-generating temperature-sensitive resistance elements R21 to R2n. In this embodiment, a case is assumed in which platinum resistors whose resistance value increases as the temperature rises are used as the exothermic temperature-sensitive resistance elements R21 to R2n. Also, R20
The rate of resistance change due to temperature is the exothermic temperature-sensitive resistance element R
Like 21 to R2n, it is a temperature sensitive resistance element for temperature compensation with high specific resistance. Further, R10, R11 to R1n are fixed resistance elements having no temperature characteristics. The fixed resistors R11 to R1n and the heat-generating temperature-sensitive resistance elements R21 to R2n are connected in series, respectively, to form level detection circuits L1 to Ln. The fixed resistance element R10 and the temperature sensitive resistance element R20 are connected in series to constitute a reference voltage generation circuit B0. The temperature-sensitive resistance element R20 includes level detection circuits L1 to L.
A platinum resistor, which is the same element as the exothermic temperature-sensitive resistance elements R21 to R2n, is used. Therefore, the heat-generating temperature-sensitive resistance elements R21 to R2n and the temperature-sensitive resistance element R20 have the same temperature resistance characteristics. This reference voltage generating circuit B0 is a circuit for performing temperature compensation so that an accurate liquid level can be detected even if the temperature of the liquid changes. In addition, in order to detect the liquid level, a level detection circuit L1
-Ln, comparators C1-Cn are arranged, respectively. The final stage of each of the comparators C1 to Cn is a transistor having an open collector circuit configuration. . The inverting input terminals of these comparators C1 to Cn are respectively 1a to na, and the non-inverting input terminals are 1b to nb. Furthermore, comparators C1 to C
External fixed resistance elements R1 to Rn are connected in series to each of the external fixed resistance elements R1 to Rn, and the other ends of all of these external fixed resistance elements R1 to Rn are connected to the power source Se. An ammeter Am, which is an indicator and is a needle-type meter, is connected between the other ends of all of the external fixed resistance elements R1 to Rn and the power source Se.

FIG. 2 is a detailed circuit diagram showing the output section of the above-mentioned automobile fuel gauge. The comparators C1 to Cn are composed of voltage comparing sections 11 to 1n and final stage transistors 21 to 2n having an open collector circuit configuration. Here, RAm is the internal resistance of the ammeter Am shown in FIG. 1, and this internal resistance RAm is assumed to be sufficiently smaller than the resistance values of the external fixed resistance elements R1 to Rn. Note that V is the voltage of the power source Se, and Vsat is the collector-emitter voltage when the transistors 21 to 2n are turned on.

FIG. 3 is a schematic diagram of a sensor section of an automobile fuel gauge. Reference numeral 100 designates a board on which the above-mentioned circuit is mounted, and the board 100 is fixed to a lid 101, and is connected to a reference voltage generating circuit B0 side consisting of a fixed resistance element R10 and a temperature-sensitive resistance element R20 with respect to liquid in a gasoline tank (not shown). Mounted for immersion. Further, 102 to 104 are the substrate 1
This is the connection terminal from 00 to the main body of the automobile fuel gauge. By the way, this liquid level detector takes advantage of the fact that the heat dissipation efficiency of the heat generated by energizing the platinum resistor differs greatly between when the platinum resistor is in the measuring liquid and when it is in the air. There is. The temperature rise due to heat generation in the platinum resistor is smaller when it is in liquid than when it is in air. Therefore,
The platinum resistor is initially present in the liquid, and as the liquid level falls and is exposed to the air, the temperature of the platinum resistor increases. The resistance value of a platinum resistor increases as the temperature rises. Depending on which platinum resistor's resistance value has changed, it can be determined which platinum resistor is exposed to the air, and the liquid level can then be detected.

[0010] The operation will be explained below, taking as an example the case where the exothermic temperature-sensitive resistance element R22 and the following made of a platinum resistor are in a liquid. The terminal voltages V1 and V2 of the heat-generating temperature-sensitive resistance elements R21 and R22 are the terminal voltage V0 of the temperature-sensitive resistance element R20.
The resistance value of fixed resistance element R10 is set in advance to be lower than . At this time, the final stage transistors 21 and 22 of the comparators C1 and C2 are turned on, and currents i1 and i2 flow through the external fixed resistance elements R1 and R2. The currents i1 and i2 are respectively (V-Vsat)/R1 when the external fixed resistance elements R1 and R2 have the same resistance value. Also, at this time, the terminal voltages V3 to Vn are the terminal voltages V0
Since the final stage transistors 23 to 2n of the comparators C3 to Cn are turned off, the current i3 to in becomes zero. Therefore, the current i flowing through the ammeter Am is i1 and i2
The total is 2(V-Vsat)/R1. here,
If the external fixed resistance elements R1 to Rn all have the same resistance value, as shown in FIG. 4, as the liquid level rises from the level detection circuit L1 to the level detection circuit Ln, the current flows through the ammeter Am. The current i increases in proportion to the number of level detection circuits 1, 2, . . . , n that are immersed. That is, the meter reading of the ammeter Am is accurately changed in accordance with the liquid level.

[0011]

Effects of the Invention The present invention provides a level detection circuit in which a fixed resistance element and a heat-generating temperature-sensitive resistance element are connected in series, and a temperature resistance characteristic of the fixed resistance element and the heat-generating temperature-sensitive resistance element of the level detection circuit is almost the same. The liquid level is detected by the output of a full bridge circuit including a reference voltage generating circuit connected in series with a temperature sensitive resistance element having the following characteristics. Therefore, the liquid level can be accurately detected without the influence of environmental temperature. Further, a transistor having an open collector circuit configuration is disposed at the final stage of the comparator disposed corresponding to the level detection circuit. The transistor is then turned on in response to the detected liquid level. When the transistor of the comparator is turned on, current flows from the power supply through an external fixed resistance element connected in series to its collector. Thereby, the current flowing through the transistors of these comparators can be increased accurately in accordance with the number of level detection circuits in the liquid. This current is measured by one indicating means whose internal resistance is sufficiently lower than that of the external fixed resistance element. As a result, the liquid level detector of the present invention can accurately drive a needle-type indicator such as a conventional automobile fuel gauge, which is an indicating means, in accordance with the liquid level without using any contacts.

[Brief explanation of drawings]

FIG. 1 is an overall circuit diagram showing the electrical configuration of an automobile fuel gauge using a liquid level detector according to a specific embodiment of the present invention.

FIG. 2 is a circuit diagram showing in detail the output portion of the circuit of FIG. 1;

FIG. 3 is a schematic diagram showing the configuration of an automobile fuel gauge using the liquid level detector according to the same embodiment.

FIG. 4 is a characteristic diagram showing the relationship between current values corresponding to increases in liquid level according to the same embodiment.

[Explanation of symbols]

B0 - Reference voltage generation circuit L1 - Ln - Level detection circuit C1 - Cn - Comparator R1 - Rn - External fixed resistance element R10 - R1n - Fixed resistance element R2
0-Temperature-sensitive resistance element R21~R2n-Exothermic temperature-sensitive resistance element Am-Ammeter Se-Power supply

Claims (1)

[Claims] 1. A level detection circuit in which a fixed resistance element and a heat-generating temperature-sensitive resistance element whose resistance value changes depending on temperature and which generates heat when energized are connected in series; A plurality of boards arranged in parallel connection in the direction in which the surface level changes, and a board arranged on the board,
Using a temperature-sensitive resistance element having almost the same temperature resistance characteristics as the temperature-resistance characteristic of the heat-generating temperature-sensitive resistance element of the level detection circuit,
A fixed resistance element having a resistance ratio substantially matching the resistance ratio of the fixed resistance element and the heat-generating temperature-sensitive resistance element of the level detection circuit, and whose sum of resistance values is sufficiently larger than the sum of their resistance values. and a reference voltage generation circuit in which the temperature-sensitive resistance element and the temperature-sensitive resistance element are connected in series, a potential at a connection point between the fixed resistance element of the reference voltage generation circuit and the temperature-sensitive resistance element is set as a reference potential, and each of the level detection circuits The potential at the connection point between the fixed resistance element and the heat-generating temperature-sensitive resistance element is set as the detection potential, the reference potential and the detection potential are input, and the transistor of the final stage open collector circuit configuration is selected depending on the magnitude of these potentials. a comparator arranged corresponding to the level detection circuit to turn on and off the level detection circuit; an external fixed resistance element connected in series to the collector of the transistor of the comparator; 1. A liquid level detector comprising one indicating means connected between all other ends of the resistive elements and a power source and having a sufficiently smaller internal resistance than the external fixed resistive element.