JPS6353423A - Fluid level sensor - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the detection of fluid levels within containers.

Description of the Prior Art Many systems have been invented to detect fluid levels in containers under various conditions. These include thermal fluid sensors, solid state devices and mechanical floating devices.

No. 4 discloses the use of a resistance wire in conjunction with a lamp indicator. , 3 6 1,0 3 8 and 3, 3 5
In No. 0,710, a capacitor sensor is used for fluid level detection. U.S. Patent No. 2,74
2.

No. 634 and No. 2,901,740 use a bridge circuit to detect changes in critical conditions. The floating device is covered by U.S. Patent No. 2.8011.5
It is used in the oil level display P5 disclosed in No. 17.

The fluid level sensor of the invention includes a heater or a deep needle portion adjacent to the pharyngeal tract and having a temperature-controlled circuit.

The temperature response circuit includes a plurality of thermistors wired within bridge wiring on the 11th surface of the board.

The heater circuit is constructed on one side of the substrate '7).

When the bridge and heater circuits are energized, the voltage on either of the bridges will be immersed.If the fluid pool being monitored is correct, only the lower part of the bridge will be immersed. Because fluids (ie, liquids) transfer heat faster than air, the immersed thermistor will be cooler and this will affect the relative output from the other side of the bridge. Also, if all the thermistors are immersed or suspended in air, a differential voltage will be generated. These relative voltages are available to a circuit that indicates to the operator that the fluid level is incorrect.

The sensing member of the probe includes a small, flat ceramic substrate with a thick film thermistor on one side and a heater in the form of an electrical circuit on the opposite side. The thermistor is connected to the switching circuit that controls the operation of the display means. It is being read. The components and switching circuitry may be integrated as part of the probe or metering float.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows an oil level detection device 1o. This universal oil level detection device ftlo includes a sealed three-pin (not shown) terminal connector 12, a cylindrical housing 14 containing electronic components inside, and an oil level detector 1i10 for mounting on the oil tank of an automobile. a threaded seal 16, a probe member 18 of a selected length, and a sensing member 20 mounted on the probe member 18.

In the configuration of this embodiment, the sensing member is a two-sided ceramic board 22 or approximately 0.132 cTrL (0.04 cTrL).
It is provided on a board with a thickness of 1 inch), and a detection circuit 24 in the form of a printed circuit is provided on one side of the point, and a heater circuit 26 in the form of a printed circuit is provided on the opposite side. The probe is molded and inserted into a high temperature thermoplastic (housing 14) along with terminals if necessary. Fired glass glaze coach ink
g 1a SS g laZ e COa tl n
g) 28 forms an anti-fishing membrane around the boat 922 and the circuit 24) 26;

Length 6.6C7n (2 inches) m 1.32CLrL
A (0.4 inch) board is large enough to integrate all the necessary circuitry for some applications, including the amplifier/switch circuits described below. The size of the boat 9: d is increased or decreased according to the physical separation of the electrical components.

As shown in FIG. ] plane includes the detection circuit 24. The detection circuit consists of four negative temperature coefficient thermistors 30, 3 wired in a parallel configuration by conductors 38.
2.34 and 36 included. Alternatively, the thermistors (eg, thermistors 30 and 36) may be ordinary resistors. Thermistors 30 and 34 are thermistors 32 and 36
Tilt substantially equidistant from one end of the board so that it is. Also, the first generation of thermistors are normally placed at a distance selected from each depending on the level of the fluid that determines the operating range. The heater circuits are arranged in a complicated manner so that all or one selected portion of the board is thereby heated. Alternatively, a positive temperature coefficient thermistor may be used for this purpose. In the second embodiment described here, the resistance may be about 10 to 500 Ω. A sufficient amount of heating is generated to induce a negative temperature coefficient thermistor i temperature on the opposite side of bow 1-'. The printed conductors on the heater side of the board are used to carry 2 amps, while the conductors on the detection circuit side carry 100 amps.
Milian is used to pass a. Each negative temperature coefficient (NTCJ) thermistor is between 5 and 20 ohms at room temperature and has a β value of about -3950.

The four NTC thermistors used in a particular bridge have the same temperature function as their resistance properties.

4 and 5 schematically show the bridge circuit 24. FIG. A comparison of FIG. 2 with this figure shows that conductor 38A provides current from the power source and conductor 38D is connected to ground. Conductors 38B and 38G are defined below.
It is used to measure the voltages ■a and ■b/.

The circuit 42 connected to the bridge functions like an amplifier/switch which (under certain conditions below) causes the operation of the indicator light 44. This circuitry may be integrated on board 22 or located separately therefrom. If the heater and sensing circuit and circuit 42 are not printed on the same alumina board, a standard PC board is used for this circuit. An indicator light is connected between the power supply and the emitter of the PNP transistor. When current flows from the emitter of this transistor through the collector to ground, the display will indicate a fluid level abnormality. The remainder of circuit 42 determines whether this has occurred. Zener diode Z1 protects transistor T3 from overvoltage conditions.

The conductive wire 38B is connected to the base of the PNP transistor T1 via a resistor R1 of IMΩ. A conductive wire 38C is connected to the emitter of this transistor Tl. The collector of transistor T1 is connected to ground and to the base of transistor T2 via resistors R2 and R3, respectively.

The collector of transistor T2 is directly connected to the base of transistor T3 through a resistor of Ω.

A 10KΩ resistor R5 is connected in series with resistor R4 and the lead from light 44. Diode D1 is provided to protect transistor T1 when Va becomes higher than Vb.

The circuit 42 turns on the indicator light 4.1 only when Jb exceeds Va by a predetermined pressure. F: Let'a. Therefore, transistor T1 has a threshold voltage below which it does not become conductive. This voltage ranges from 0.05 to 1.0 μ.

If all four thermistors are exposed to air (such as in a low fluid level condition), the bottom edge of the board (which holds thermistors 32 and 36) will heat up more than the top edge, causing the voltage to drop. Vb exceeds voltage Va. Therefore, thermistors 32 and 36 will be hotter than thermistor 30 and thermistor 34 creating a potential difference across the bridge. Current flows through transistors T1 and T2, making transistor T3 conductive. When operated in this manner, transistor T3 allows current to flow through indicator light 44 to ground. That is, the display light 44
is conductive.

If the fluid level is within an acceptable range, thermistors 30 and 34 are in air and only thermistors 32 and 36 are immersed in the fluid. This causes thermistors 32 and 36 to be cooler than thermistors 30 and 34 because heat is absorbed more quickly by the fluid than by air. Therefore, Va
is held at Vb, and no stain current flows through the transistor T1.

Under these conditions, indicator light 44 is not activated.

The circuit 42 may be modified to provide a signal if the container overflows. Under this condition, all four NTC thermistors are immersed in fluid (liquid). Heater circuit 26
has less influence than when all these thermistors are suspended in the air. As shown graphically in FIG. 5, Vb slightly exceeds Va. low,
Substantially different voltages are generated under normal and high fluid levels, and circuit 42 may be used to generate signals under both low and high fluid levels.

Alternatively, different signals may be generated to distinguish between low and high levels.

If necessary and desirable, multiple thermistors may be used to indicate multiple liquid levels. By integrating the circuit 42 within the housing 14 or on the board 22, a complete sensing device can be provided that only needs to be connected to a power source and an indicator lamp.

This can greatly simplify the device. The sensing member 20 may be disposed within a cylindrical container to provide accurate readings within the turbulent fluid.

Regarding possible variations of the invention, the indicator light sends a pulse:M modulated signal to the computer of the motor vehicle:
(May be omitted along with resistors R4, R5 and transistor T3, whereby specific messages are monitored for specific fluid levels (e.g. crankcase oil, transmission fluid, brake fluid, coolant) information can be displayed on the dash board of the vehicle.

Maintaining certain fluid levels (such as transmission fluid) is critical to the operation of a vehicle, and signals from a circuit cause a pump to direct fluid from the pump or other backup equipment to where it is needed. : Used.

[Brief explanation of drawings]

Figure 1 is yong? Perspective Z of the device for detecting the fluid level in the unit. Figure 2 is an enlarged plan view of four thermistor bridge circuits provided on a thin ceramic substrate. FIG. 3 is a schematic diagram of a four thermistor bridge circuit connected to a fluid level indicating circuit. FIG. 4 is a schematic diagram of the bridge circuit, adjacent heater circuit, and display circuit. FIG. 5A is a graph showing voltages on both sides of the bridge circuit under various conditions. FIG. 5B is a diagram illustrating the signals provided by the display circuit under various fluid level conditions. (5 other people)

Claims (8)

[Claims] (1) a thin and flat thermally conductive substrate having a probe section, a first end surface on which the probe section is provided, and a second end surface opposite to the first end surface; a bridge circuit arranged including first, second, third and fourth thermistors (30, 32, 34, 36), said two thermistors (32, 36) being in a fluid; while the other two
The two thermistors (32, 36) are relatively closer to the second end face of the substrate than the other thermistors (30, 34) such that one thermistor (30, 34) is left out of the fluid. heater means for heating the entire substrate and the four thermistors; a first pair connected to the bridge circuit for connecting the bridge circuit between a power source and ground; a second pair of conductors connected across the bridge circuit for connection to a detection circuit, wherein the heater means is activated and the substrate containing the four thermistors is completely removed. When exposed to air, the second end surface of the substrate and the two thermistors (32, 36) located relatively close to the second end surface and the other two thermistors. (2) a detection circuit connected between the second pair of conductors, the detection circuit comprising: a first PNP transistor; and a detection circuit connected to the base of the first PNP transistor; one conductor of the pair of conductors; another conductor of the second pair of conductors connected to the emitter of the first PNP transistor; a second NPN transistor; The collector of the first PNP transistor is connected to the second
a power supply; an indicator connected between the power supply and ground; a third transistor for controlling operation of the actuator; and the second NPN transistor. The collector of
2. A fluid level sensor according to claim 1, wherein the fluid level sensor is connected to a transistor of the present invention. (3) The liquid level sensor according to claim (1), wherein all of the four thermistors are negative temperature coefficient thermistors. 4. The fluid level sensor of claim 3, wherein all of the thermistors provide substantially the same resistance at room temperature and vary in resistance substantially in the same manner as a function of temperature change. (5) the substrate is a planar non-metallic board having a first side surface and a second side surface, the bridge circuit is disposed on the first side surface of the substrate, and the heater means is located on the second side surface of the substrate;
A fluid level sensor according to claim 1, which is arranged on a side surface of the fluid level sensor. (6) The fluid level sensor according to claim (1), wherein the substrate, the bridge circuit, and the heater means are cased with a thin glass film. (7) A fluid level sensor according to claim 1, wherein the two thermistors (36, 32) are at substantially equal distances from the second end surface of the substrate. (8) The substrate, the bridge circuit, and the heater means are housed in a thin glass membrane casing.
) Fluid level sensor described in section 2.