Sensor for monitoring liquid level

FIELD: physics.

SUBSTANCE: sensor for monitoring the level of a liquid has a housing and a printed-circuit board on which there is a substrate having one or two identical film resistors (thermistors) and contact pads (conductors). The printed-circuit board is in form of a plate, one short side of which is rigidly attached to the base of the housing and on the edge of the opposite free side there is a hole whose diameter is 2…4 times larger than the width of the substrate lying over the hole and made from thin heat-insulating material. Each film resistor (thermistor) is in 'point' form with dimensions in the range (0.15…0.5) mm • (0.5…0.5) mm and thickness not more than 0.0005 mm. The boundary surface between each film resistor (thermistor) and contact pads of the substrate (conductors) is in form of broken lines consisting of straight sections.

EFFECT: high mechanical strength of the structure.

3 dwg

 

The invention relates to instrumentation, namely, discrete sensors, level control, and can be used in systems and devices for monitoring the level of fuel storage, refueling, and also in the process of engine operation at cryogenic fuel under severe mechanical stress.

Known sensor and fluid level control (patent RU 2310173 C1, G01F 23/00, G01F 1/68, published 10.11.2007)containing heat insulating substrate mounted on a printed circuit Board made in the form of a narrow thin plate and is rigidly attached to the short side to the base of the sensor body, at the edge opposite to the loose side of the PCB made the hole, over which is placed a substrate with two thermistors in "the point" design. Moreover, as the substrate used thin film, and thermistors are located symmetrically at the upper and lower edges of the substrate at a distance of not more than 0.2-0.5 mm from the edge of the substrate, and the distance between thermistors is not more than 1.5 mm, the Disadvantage of this device is the low mechanical strength of the structure, due to the possible violations of the integrity of the connection of thermistor with the contact pads of the substrate, and a low yield because of the impact on the substrate surface defects in the manufacture of the device.

On the technical essence of the known devices closest to the claimed device is a sensor and fluid level control (patent RU 2295115 C2, G01F 23/00, G01F 1/68, published 10.03.2007), comprising a housing with a circuit Board and thermistor on the substrate mounted on the circuit Board. PCB is made in the form of narrow (with an aspect ratio in the range of 1:3...1:5) of a thin plate, one short side of which is rigidly secured to the base body, and at the edge opposite to the loose side of the completed hole diameter, 2...4 times larger width of the substrate with a thermistor, placed over the hole and made of a thin insulating material in the form of a film, while thermistor is made in the "point" of view with dimensions (0,15...0,5) mm × (0,15...0,5) mm and a thickness of not more than 0,0005 mm Thermistor is at the bottom edge of the film. The disadvantage of this sensor is the possibility of compromising the integrity of the connection conductor and a thermistor when the impact hammer liquid and the formation of microcracks, which impairs the mechanical strength of the device as a whole and can lead to failure of the level control system. The presence of defects in the film elements in the manufacture of the device also affects the yield of products.

The specified device according to patent RU 2295115 C2 is taken as a prototype.

The purpose of the invention is the enhancement of the mechanical strength of the structure by ensuring the integrity of the connection film resistor (thermoresistor is a) with pads of the substrate (conductors) and increasing the yield in the manufacture of the device.

This objective is achieved in that the control sensor of the liquid level, comprising a housing and a printed circuit Board, on which the substrate is placed on it by one or two identical film resistors (thermistors) and pads (conductors), printed circuit Board made in the form of a narrow plate, one short side of which is rigidly secured to the base body, and at the edge opposite to the loose side of the completed hole diameter, 2...4 times larger width of the substrate placed over the hole and made of a thin insulating material, and each film resistor (thermistor) built in "point" form with dimensions in the range (0,15...0,5)mm × (0,15...0,5)mm and a thickness of not more than 0,0005 mm, the boundary between each film resistor (thermistor) and the contact pads of the substrate (conductors) made in the form of broken lines, consisting of straight line segments.

The implementation of each interface between thermistor and a conductor in the form of a broken line consisting of straight line segments leads to an increase in the length of the boundary and thus to increase the adhesion of the conductor and a film resistor, ensuring the integrity of this compound when exposed hammer liquid that allows you to save preset resistance value of t is mortiser, necessary to control the liquid level, and improves the mechanical strength of the structure. In addition, increasing the clutch and the conductor film resistor reduces the influence of defects in the substrate, increasing the yield in the manufacture of sensors.

Identified a distinctive feature proposed in the aggregate, was not found in previously known technical solutions, ensures the achievement of this goal and can be regarded as a significant difference.

The invention is illustrated by drawings:

Figure 1 - sensor and fluid level control;

Figure 2 - the substrate with one film resistor (thermistor) (prototype);

Figure 3 - substrate with two film resistors (thermistors).

The proposed sensor and fluid level control (figure 1, a sensor with a single thermistor) includes a housing 1 and the circuit Board 2, on which the substrate 3 is placed on her film resistor (thermistor) 4 and pads (conductors) 5. Variant design with two identical thermistors 4. Circuit Board 2 is made in the form of a narrow plate, one short side of which is rigidly attached to the base 1, and at the edge opposite to the loose side made the hole 6 in diameter, 2...4 times larger width of the substrate 3. The substrate 3 is placed is above the opening 6 and is made of a thin insulating material. On the substrate 3 by vacuum deposition followed by photolithography deposited film resistor 4 titanium with copper pads 5. thermistor 4 is made in the "point" of the performance dimensions (heating area occupied by thermistor, made in the form of meander) in the range (0,15...0,5)mm × (0,15...0,5)mm and a thickness of not more than 0,0005 mm pads 5 of the substrate 3 through the contact pads of the printed circuit Board 2 are connected with wires 7 and are used to supply voltage to film thermistor 4.

In the technical solution protected by patent RU 2295115 C2 and adopted for the prototype sensor, a fluid level control includes a substrate 8 (figure 2) with thermistor 9 and the pads 10, with each boundary 11 between thermistor 9 and the pads 10 are made in the form of a short straight line segment that reduces the mechanical strength of the structure and reduces the yield in the manufacture of devices. Unlike the prototype of the proposed sensor and fluid level control interface 12 between the resistors 4 and pads (conductors) 5, deposited on a substrate 3 made in the form of broken lines, consisting of straight line segments (figure 3). Figure 3 presents the design variant with two identical thermistors.

The sensor and fluid level control works follow the way.

By wire 7 (Fig 1) on PCB pad 2 and pad 5 of the substrate 3 and thermistor 4 direct voltage. Under the action of electric current is the self-heating thermistor 4, its resistance increases and thermal balance is established, during which the temperature and the resistance of thermistor 4 is constant and determined by the heat dissipation in the medium (liquid or gas above the liquid), which placed the sensor.

When immersed in the liquid or retrieved from thermistor 4 heat balance is disturbed, the temperature of thermistor 4 is decreased or increased by changing the heat transfer in the environment, the resistance of thermistor changes.

Thus, by controlling the resistance value of thermistor 4, it is possible to determine the moment of transition of thermistor 4 border "liquid - gas" and, accordingly, the height of the liquid level. Similarly operates the sensor and fluid level control with two identical film resistors (thermistors) 4.

Control sensor liquid level contains a substrate on which the film elements of different thickness: copper pads (conductors) have a thickness of 1÷2 μm, and a titanium film resistor is about 0.1 μm. When exposed to vibrograf directed perpendicular to the surface is rnost substrate, under the pressure of the fluid, the substrate is deformed and effort is transmitted to the film resistor and the contact pads of the substrate, which leads to the appearance of microcracks, which violate the integrity of the film elements and reduce the adhesion of the conductor and a film resistor (thermistor).

As a result of executing each of the interface between the film resistor (thermistor) and pads (conductors) in the form of broken lines, consisting of straight line segments (figure 3), but not in the form of a short straight line segment, as in the prototype (figure 2), the length of the boundary increases in 4÷5 times and, accordingly, increases the traction surface of a film resistor with conductors and increases the mechanical strength of the structure.

In the process of making the device thin titanium film thickness of about 0.1 μm is applied on a thin substrate with a thickness of 20-100 μm, on the surface of which there are microdefects, which have an impact on the surface of the deposited titanium layer and lead to marriage in the manufacture. The increase of the boundary between thermistor and the conductors can reduce the influence of defects in the substrate on the integrity of the deposited layers and to increase the yield.

Thus, the proposed design of the device (with one or two identical thermistors) ensure the AET goal, namely:

- increasing the mechanical strength of the structure by ensuring the integrity of the connection film resistor (thermistor) with contact pads of the substrate (conductors);

- increasing the yield in the manufacture of the device.

The sensor control liquid level, comprising a housing and a printed circuit Board, on which the substrate is placed on it by one or two identical film resistors (thermistors) and pads (conductors), while PCB is made in the form of a narrow plate, one short side of which is rigidly secured to the base body, and at the edge opposite to the loose side made a hole diameter of 2 - 4 times larger width of the substrate placed over the hole and made of a thin insulating material, and each film resistor (thermistor) is made in the "point" of view with dimensions the range(0,15 - 0,5) · (0,15 - 0,5) mm and a thickness of not more than 0,0005 mm, characterized in that the boundary between each film resistor (thermistor) and the contact pads of the substrate (conductors) made in the form of broken lines, consisting of straight line segments.



 

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, where h is the level of the liquid in the reservior; CA is capacitance of the double-electrode capacitive liquid level sensor; CB is overall capacitance of the double-electrode capacitive liquid level sensor connected in parallel to the capacitive sensor of dielectric properties; A, B and D are structural parametres of the double-electrode capacitive liquid level sensor and capacitive sensor of dielectric properties. The device for measuring liquid level has a double-electrode capacitive liquid level sensor made in form of a coaxial capacitor, and two cylindrical electrodes. The lower end of the inner electrode of the double-electrode capacitive liquid level sensor is connected to one of the electrodes of the capacitive sensor of dielectric properties through the closing contact of a reed relay, and the lower end of the outer electrode of the double-electrode liquid level sensor is connected to the second electrode of the capacitive sensor of dielectric properties.

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FIELD: physics.

SUBSTANCE: sensor for monitoring the level of a liquid has a housing and a printed-circuit board on which there is a substrate having one or two identical film resistors (thermistors) and contact pads (conductors). The printed-circuit board is in form of a plate, one short side of which is rigidly attached to the base of the housing and on the edge of the opposite free side there is a hole whose diameter is 2…4 times larger than the width of the substrate lying over the hole and made from thin heat-insulating material. Each film resistor (thermistor) is in 'point' form with dimensions in the range (0.15…0.5) mm • (0.5…0.5) mm and thickness not more than 0.0005 mm. The boundary surface between each film resistor (thermistor) and contact pads of the substrate (conductors) is in form of broken lines consisting of straight sections.

EFFECT: high mechanical strength of the structure.

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