RU2506543C1 - Sensor to monitor discrete levels of liquid with function of measurement of temperature and to monitor mass flow of liquid medium - Google Patents

Abstract

FIELD: measurement equipment.SUBSTANCE: invention relates to instrument making, namely, to discrete level metres, and may be used to monitor level and mass flow of fuel components during fuelling, consumption and storage in chemical, space and other industries. A sensor for monitoring of discrete liquid levels comprises a printed circuit board with an opening, on one side of which above the opening there is a sensitive element, made in the form of a heat insulating substrate with a film resistor (thermistor) placed on it a "dot" version to monitor the liquid level, and comprises a film resistor (thermistor) in a "dot" version for measurement of temperature of a surface liquid layer. The sensor also comprises an additional film resistor (thermistor) in a "dot" version for measurement of liquid surface layer temperature, at the same time the sensitive element for measurement of liquid temperature is made in the form of an additional heat insulating substrate with width of not more than 2 mm, where both thermistors are placed for measurement of liquid temperature, and is installed on the opposite side of the printed circuit board under the opening symmetrically to the sensitive element to monitor the level at the distance from 0.5 mm to 1.0 mm from the substrate with the thermistor used to monitor the level.EFFECT: higher accuracy of liquid medium temperature, in which level variation is monitored both as a sensor is submerged (fuelling), and also as a sensor is withdrawn from liquid (consumption, drainage), and expansion of functional capabilities of a device, making it possible to accurately determine mass flow of liquid medium.6 dwg

Description

The invention relates to instrumentation, namely to discrete level meters, and can be used to control the level and mass consumption of fuel components during refueling, consumption and storage in chemical, space and other industries.

A known liquid level control sensor (patent RU 2295115 C2, G01F 23/00, G01F 1/68, published March 10, 2007) comprising a housing with a printed circuit board and a thermistor on a substrate mounted on a printed circuit board. The printed circuit board is made in the form of a narrow (with an aspect ratio in the range 1: 3 ... 1: 5) thin plate, one short side of which is rigidly attached to the base of the case, and a hole with a diameter of 2 ... 4 times is made at the edge of the opposite non-fixed side a large width of the substrate with a thermistor placed above the hole and made of thin heat-insulating material in the form of a film, while the thermistor is made in the "point" form with dimensions (0.15 ... 0.5) mm × (0.15 ... 0.5) mm and a thickness of not more than 0.0005 mm. The thermistor is located at the bottom edge of the film.

The disadvantage of the sensor is the limitation of its functionality. The device does not allow monitoring the liquid level at the control points and at the same time measuring its temperature at these points, determining the mass flow rate of the liquid medium without using additional temperature or mass flow sensors.

In technical essence, of the known devices, the closest to the claimed device is a liquid level control sensor used in a control system that implements a method for monitoring discrete liquid levels that takes into account changes in liquid temperature (patent RU 2413184 C1, G01F 23/00, published 02.27.2011) . The sensitive element of each of the sensors of the system is made in the form of a heat-insulating substrate with a thermistor for measuring the liquid level and contains an additional thermistor placed symmetrically below the thermistor to measure the liquid level in the center of the substrate at a distance of no more than 2 mm. In this case, the thermistor used to determine the liquid level at the control point is located at the upper edge of the substrate, and an additional thermistor used to determine the temperature change of the upper liquid layer is located at the lower edge of the substrate. Both thermistors are connected to a measuring device.

In the technical solution protected by patent RU 2413184 C1, the use of a thermistor for temperature control, located under a thermistor designed to measure the level, and on the same substrate as it, allows you to control the temperature change and change the threshold value of the transition characteristic of the level thermistor signal depending on the temperature of the upper fluid layer, using the dependence of the resistance on the temperature of the thermistor and software control device. However, when these thermistors are located on the same substrate, the heated thermistor used to control the liquid level affects the thermistor to measure temperature due to heat exchange between the substrate and the thermistors, which significantly reduces the accuracy of measuring the temperature of the liquid surface layer at control points. Insufficient accuracy of temperature measurement does not allow to determine the exact mass flow rate of the liquid medium.

The specified device according to the patent RU 2413184 C1 is taken as a prototype.

The purpose of the invention is to increase the accuracy of measuring the temperature of a liquid medium, in which the level change is controlled both when the sensor is immersed (refueling) and when the sensor is removed from the liquid (discharge, discharge), and the device’s functionality is expanded to enable accurate determination of the mass flow rate of the liquid medium .

This goal is achieved by the fact that the sensor controls discrete liquid levels, containing a printed circuit board with a hole, on one side of which a sensing element is installed above the hole, made in the form of a heat-insulating substrate with a film resistor (thermistor) placed on it in a “point” design for level control liquid, and the film resistor (thermistor) in the "point" design for measuring the temperature of the surface layer of the liquid contains an additional film resistor (thermistor) in "Point" design for measuring the temperature of the surface layer of the liquid, while the sensitive element for measuring the temperature of the liquid is made in the form of an additional heat-insulating substrate with a width of not more than 2 mm, on which both thermistors are located to measure the temperature of the liquid, and is installed on the opposite side of the circuit board under the hole symmetrically to the sensitive element for level control at a distance of 0.5 mm to 1.0 mm from the substrate with a thermistor used to control the level.

Improving the accuracy of measuring the temperature of the surface layer of the liquid at the points of control of level changes is carried out by implementing the following essential features.

The implementation of the sensing element for measuring the temperature of the liquid in the form of a separate additional heat-insulating substrate, on which there are two thermistors for measuring temperature, eliminates their heating from the substrate with a heated thermistor used to control the liquid level.

The location of the substrate, on which two thermistors for measuring temperature are placed, symmetrically under the substrate with a thermistor for measuring the level, makes it possible to control the temperature of the medium below and above the “point” sensing element that controls the liquid level at a distance of no more than 2 mm (the width of the substrate of the sensing element for temperature measurement). The design of the proposed sensor allows the measurement of the temperature of the medium directly in the area of the point of control of the liquid level, which eliminates the influence of the temperature distribution in the layers of the medium on the measurement results.

The distance from 0.5 mm to 1.0 mm between the substrates of two sensitive elements located above and below the hole of the printed circuit board is optimal, since with a closer arrangement of the substrates, the temperature of the heated thermistor for level measurement will affect the temperature rise of two thermistors for measurement temperature, and at a more distant distance, the temperature of the medium will not be determined in the region of the level control point.

In addition, the use of two thermistors for measuring temperature increases the reliability of the corresponding sensitive element of the proposed sensor.

For cryogenic liquids, accurate determination of the mass flow rate of a liquid medium is important. The use of the proposed sensor makes it possible to determine not only a change in the level (volume) both during refueling and during the discharge (discharge) of the liquid, but also to calculate the mass flow rate, since the change in the density of the liquid is a function of temperature. The exact values of the liquid temperature at the points of measurement of the level (volume) make it possible to determine the density of the liquid at the control points and, accordingly, the mass of the liquid and the change in mass (flow rate).

Identified distinctive 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 and photographic materials:

Figure 1 - printed circuit board with installed on it sensitive elements in assembled form;

Figure 2 is a drawing of the side of the printed circuit board with the sensor installed to determine the liquid level;

Figure 3 is a drawing of the opposite side of the printed circuit board with a sensor installed to determine the temperature of the liquid;

Figure 4 is a topological drawing of a sensor for measuring liquid level;

5 is a topological drawing of a sensing element for measuring liquid temperature;

6 is a sensor monitoring discrete fluid levels (in the housing).

The proposed sensor for monitoring discrete liquid levels contains a printed circuit board 1 (Fig. 1) with a hole 2. A printed circuit board 1 is a narrow plate, on one side of which (Fig. 1, Fig. 2) a sensing element 3 is installed above the hole 2 (Fig. 1). 2, Fig. 4), made in the form of a thin heat-insulating substrate 4 with a width of about 1 mm and a thickness of 0.1 mm, on which a film resistor (thermistor) 5 is placed to control the liquid level. The thermistor is made in the "point" version with dimensions of not more than 0.3 mm × 0.3 mm and a thickness of not more than 0.0015 mm. On the opposite side of the printed circuit board 1 (Fig. 1, Fig. 3) under the hole 2, a symmetrically sensitive element for level 3 control at a distance of 0.5 to 1.0 mm from the substrate 4 with a thermistor 5 used to control the level, a sensitive element 6 (figure 3, figure 5) for measuring the temperature of the liquid, made in the form of an additional thin heat-insulating substrate 7 with a width of 2 mm and a thickness of 0.05 mm, on which two film resistors (thermistors) 8 and 9 are placed to measure the temperature of the liquid environment at level control points. Thermistors are made in the "point" version with a total area of 1.5 mm × 2 mm and a thickness of not more than 0.0015 mm. The contact pads 10 of the printed circuit board 1 are connected by soldering to the contact pads 11 of the substrate 4 and to the contact pads 12 of the substrate 7 and provide the connection of the sensing elements 3 and 6 to the measuring device using the connecting wires 13 (FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5). To install the assembled circuit board in a container with liquid and protect the substrates 4 and 7 with thermistors 5, 8 and 9 from mechanical influences, the printed circuit board 1 is screwed through the mounting hole 14 and is fastened with one short side to the base of the sensor housing 15 (Fig. 6 )

A sensor for monitoring discrete liquid levels with the function of measuring temperature and controlling the mass flow rate of a liquid medium works as follows.

From a controlled source of constant voltage through wires 13 to the contact pads 10 of the printed circuit board 1 and the contact pads 11 of the substrate 4 and further to the thermistor 5 used to control the liquid level, a supply voltage is supplied. Under the influence of an electric current (heating current of about 20 mA), the thermistor 5 self-heats up, its resistance increases and a heat balance is established at which the temperature and resistance of the thermistor 5 are constant and are determined by the heat transfer to the medium in which the sensor is placed. As a result of heating, the temperature of the thermistor 5 is higher than the ambient temperature (gas) by 40-50 degrees. When the thermistor 5 is immersed in or removed from the liquid, the phase state of the medium changes, the heat balance is violated, the temperature of the thermistor 5 decreases or increases due to a change in the thermal conductivity of the medium, which leads to a change in the resistance of the thermistor and a change in voltage in the diagonal of the balanced bridge of the measurement circuit, i.e. a change in the voltage supplied to the measuring device, providing a comparison of the measured voltage with a threshold voltage. If the signal in the diagonal of the balanced bridge is less than the threshold value, then the sensing element 3 is in the liquid. When the liquid is consumed, the level decreases, the thermistor 5 crosses the liquid-gas boundary, the signal in the diagonal of the balanced bridge increases and becomes larger than the threshold. Thus, by controlling the resistance value of the thermistor 5, the moment of the transition of the liquid-gas or gas-liquid boundary by the thermistor 5 and, accordingly, the height of the liquid level (liquid volume) are determined.

At the same time, in the region of the liquid level control point, the temperature of the surface liquid layer is measured, which varies in the layers of the medium under the influence of various factors. From a controlled source of constant voltage through wires 13 to the contact pads 10 located on the opposite side of the circuit board 1, and the contact pads 12 of the substrate 7 and further to the thermistors 8 and 9 used to measure the temperature of the liquid, a supply voltage is supplied whose magnitude is insufficient for self-heating thermistors 8 and 9 (heating current no more than 1 mA), but provides a mode for measuring the temperature of the liquid. The temperature of thermistors 8 and 9 and the environment are the same. When the temperature of the liquid medium changes, the resistances of the thermistors 8 and 9 change and, accordingly, the signal values in the diagonals of balanced bridges change. Using the resistance values of the thermistors 8 and 9 of the sensing element 6 located in the liquid, the temperature of the surface layer of the liquid is determined at two points between which the thermistor 5 is located, and its average value for the region of the level control point is calculated.

The value of the initial resistance of thermistors 8 and 9 at a normal ambient temperature (15-20ºС) is not less than 500 Ohms and exceeds the resistance of thermistor 5 of the sensing element 3 used for level control, as well as the resistance of the thermistor for measuring temperature according to the prototype RU 2413184 C1, not less than four times, which further increases the accuracy of measuring the temperature of the liquid medium.

The high accuracy of determining the temperature of the liquid allows us to more accurately determine the density of the liquid at these points, which is a function of temperature, from the obtained values of the temperature of the surface layer of the liquid at the control points of level measurement. The values of the liquid level (volume) measured by the sensor and the obtained values of the liquid density at the control points make it possible to determine the mass of the liquid at the level control points and, accordingly, to calculate the maximum change in its mass (flow rate) for different liquid levels, which is especially important for level control mass flow of fuel components during refueling, consumption and storage.

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

- improving the accuracy of measuring the temperature of the liquid medium, in which the level change is controlled both when the sensor is immersed (refueling), and when the sensor is removed from the liquid (consumption, discharge);

- expanding the functionality of the device, allowing accurate determination of the mass flow rate of the liquid medium.

The combination of the function of the sensor for monitoring discrete liquid levels with the function of measuring temperature and controlling the mass flow rate of the liquid medium in the same overall dimensions eliminates the need for additional sensors to more accurately measure the temperature and mass flow rate of the liquid to achieve this goal.

Claims (1)

A discrete liquid level control sensor containing a printed circuit board with an opening, on one side of which a sensing element is installed above the opening, made in the form of a heat-insulating substrate with a film resistor (thermistor) placed on it in a “point” design for monitoring the liquid level, and a film resistor ( thermistor) in the "point" version for measuring the temperature of the surface layer of the liquid, characterized in that it contains an additional film resistor (thermistor) in the "point" version temperature measurement of the surface layer of the liquid, while the sensitive element for measuring the temperature of the liquid is made in the form of an additional heat-insulating substrate with a width of not more than 2 mm, on which both thermistors are located to measure the temperature of the liquid, and is installed on the opposite side of the printed circuit board under the hole to the symmetrically sensitive element for level control at a distance of 0.5 mm to 1.0 mm from the substrate with a thermistor used to control the level.

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