RU2342640C1 - Liquid level control detector - Google Patents

Abstract

FIELD: physics; measurement.

SUBSTANCE: invention is related to instrument-making, namely, to discrete detectors of liquid level control and may be used in systems and instruments for control of liquid fuel level, in storage, fuelling and also in process of operation of engines that work on cryogenic fuel under rigid mechanical impact. Liquid level detector contains casing with printed circuit board, point sensitive element (thermistor) on substrate installed on printed circuit board, which is arranged in the form of narrow thin plate, one side of which is rigidly fixed to casing base, and at the edge of opposite non-fixed side, opening is provided with diameter that is 2...4 times more than width of substrate located above the opening and made from thin heat-insulating material, additionally three point thermistors are used, two of which are installed symmetrically on the front side of substrate at the distance of not more than 0.5 mm from the edge of substrate, and the other two - underneath on the opposite (screen) side with error of alignment that does not exceed 50 micrometer. Besides, in liquid level detector, substrate with thermistors passes through opening on printed circuit board, in which contact sites and connection conductors are installed, providing serial connection of thermistors installed one under another on substrate.

EFFECT: higher fast action and accuracy of liquid level detection, higher accuracy of liquid level change rate, both in case of fuelling and draining.

2 cl, 1 dwg

Description

The invention relates to instrumentation, namely to discrete sensors for monitoring the level of liquid, and can be used in systems and devices for controlling the level of liquid fuel, during storage, refueling, as well as during operation of engines using cryogenic fuel under severe mechanical stresses.

Known devices containing a sensing element (thermistor) made in the form of a cylindrical rod with wire leads (G. Wigleb. Sensors. M., Mir, 1989, p. 54) and in the form of a capsule with wire leads mounted on a ceramic board (Yu.V. Zaitsev et al. Semiconductor resistors in electronics. M., Energoizdat, 1988, p. 12).

The closest in technical essence is the liquid level control sensor according to patent No. 2295115 "Liquid level control sensor", priority date 02.07.2004, containing a sensing element (thermistor) located on a substrate mounted on a printed circuit board, which is attached to the base of the housing . The disadvantage of this device is the high heat capacity of the substrate, on the front side of which there is a thermistor, and a significant distance of the width of the heating zone along which the liquid level moves when the heated body of the thermistor is immersed or released. These shortcomings increase the error in level measurement at the control point and the delay time (edge) of the signal, which reduces the speed of determining the level.

The aim of the invention is to increase the speed and accuracy of determining the liquid level, as well as providing the possibility of increasing the accuracy of determining the rate of change of the liquid level both when refueling and when draining.

This goal is achieved by the fact that in the liquid level control sensor containing a housing with a printed circuit board and a point sensitive element (thermistor) on a substrate mounted on a printed circuit board, made in the form of a thin thin plate, one side of which is rigidly attached to the base of the housing, and the edges of the opposite loose side made a hole with a diameter of 2 ... 4 times the width of the substrate, placed above the hole and made of thin heat-insulating material, an additional three point is used x a thermistor, two of which are placed symmetrically on the front side of the substrate at a distance of not more than 0.5 mm from the edge of the substrate, and the other two below them on the opposite (screen) side with a registration error of not more than 50 μm. In addition, in the liquid level control sensor, the substrate with thermistors passes through the hole on the printed circuit board, on which the contact pads and connecting conductors are located, providing a serial connection of the thermistors located one below the other on the substrate.

Identified distinguishing features in the proposed combination were not found in previously known technical solutions, ensure the achievement of the goal and can be qualified as significant differences.

The invention is illustrated by drawings.

Figure 1. Substrate with four film thermistors placed on a) front and b) screen sides.

Figure 2. The electrical circuit of the film thermistors.

Figure 3. A substrate with film thermistors mounted on a printed circuit board, a) a top view, b) a side view, c) part of the board with the substrate installed.

The proposed liquid level control sensor contains: a heat-insulating thin substrate 1 (Fig. 1), on which are film resistors with the same structural and electrical characteristics (R1 and R2 on the front side, R3 and R4 on the screen). The substrate 1 (figure 3) passes through the hole 3 (figure 3) of the printed circuit board 2 (figure 3) and is soldered to the contact pads located on the front and screen sides of the printed circuit board. The hole 4 (figure 3) is intended for mounting the circuit board to the flange of the housing. Connecting wires 5 (figure 3) are connected to the pads 6 of the printed circuit board 2 (figure 3).

The film thermistors R1, R2, R3 and R4 located on the substrate 1 are connected using printed conductors in accordance with the electrical circuit shown in figure 2.

The level control sensor operates as follows.

Through the connecting conductors 5 (Fig. 3) to the contact pads 6 of the printed circuit board 2 (Fig. 3) and then to the thermistors R1, R2 and R3, R4 (Fig. 1 and Fig. 2) a constant voltage is applied, under the influence of an electric current self-heating of thermistors, their resistance increases and a heat balance is established at which the temperature and resistance of the thermistors are constant.

When immersed in a liquid or when a level sensor is removed from a liquid, the heat balance is violated, the temperature and resistance of the thermistors R1, R2, R3, R4 decreases or increases due to a change in the heat capacity of the medium.

The time the temperature and resistance of thermistors change depends on the rate of change of the liquid level and the distance of the width of the heating zone (the area occupied by the thermistor) along which the level moves.

The error in level measurement at control points with decreasing width of the heating zone also decreases.

The introduction of additional thermistors, their symmetrical placement on the substrate 1 at a distance of not more than 0.5 mm from the edge of the substrate and the location of the thermistors under each other with an error of not more than 50 μm on the screen and front sides of the substrate 1 allows, by reducing the area occupied by the thermistors on the front and screen sides, 1.5–2 times reduce the heating zone compared to the location of the thermistor on one side, while maintaining the resistance value of the thermistors, in addition, the temperature of the thermo ezistorov because of mutual heating and resistance change upon transition from one state to another, the delay time is reduced by increasing the steepness of the edges.

The use of a thin substrate, on the front and screen sides of which there are thermistors, does not allow for a series connection of R1 with R3, as well as R2 with R4. The series connection of resistors R1 with R3 and R2 with R4 is ensured by passing the substrate through the hole of the printed circuit board, connecting the contact pads of the substrate located on the screen and front sides, respectively, with the contact pads located on the front and screen sides of the printed circuit board and connecting conductors located on printed circuit board. Reducing the heat capacity of the structure and reducing the length of the path that the liquid level passes through the heating zone, on which the self-heated bodies of two thermistors are located, are located one below the other, they can reduce the delay time (increase the steepness of the fronts) and more accurately determine the rate of change of the liquid level.

The use of four thermistors, two of R1 and R3 of which are connected in series and located one below the other on one edge of the substrate, and the other two R2 and R4 are connected in series and located one below the other on the substrate edge (Fig. 2), allows you to determine the rate of change of level liquid as the ratio of the distance between the centers of the thermistors R1 and R2 or R3 and R4 located on the edges of the substrate, and the time between the edges of the measured voltage, determined by the change in the resistances (temperature) of the thermistors.

Thus, the proposed design ensures the achievement of the goal:

- improving the accuracy of determining the level at the control point and speed both when immersed in a liquid, and when removing the level control sensor from the liquid;

- provides the ability to determine the speed of level measurement both when refueling and when draining.

Claims (2)

1. A liquid level control sensor comprising a housing with a printed circuit board and a point sensing element (thermistor) on a substrate mounted on a printed circuit board made in the form of a narrow thin plate, one side of which is rigidly attached to the base of the housing, and at the edge of the opposite non-fixed side made a hole with a diameter of 2 ... 4 times the width of the substrate placed above the hole and made of thin heat-insulating material, characterized in that it additionally uses three point thermistor , Two of which are placed symmetrically on the front side of the substrate at a distance of not more than 0.5 mm from the substrate edge, and the other two on the opposite underneath (screen) side of the combination with the error not more than 50 microns. 2. The liquid level control sensor according to claim 1, characterized in that the substrate with thermistors passes through an opening on the printed circuit board, on which there are contact pads and connecting conductors that provide serial connection of thermistors located one below the other on the substrate.

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