RU2550311C1 - Cryogenic liquid level meter - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: device for determination of level of cryogenic liquid consists of a sensor, analysis block and logger. The sensor is manufactured from a thin-walled dielectric plate installed vertically on the vessel base. By the height of the working area of the dielectric plate the measuring units coated with a thin layer of electric insulating material with high heat transfer factor are installed. Each measuring unit contains series connected sensing elements with identical resistance designed from a material with high thermistor sensitivity in the field of cryogenic temperatures, and located on identical distances from each other. The amount of sensing elements in all measuring units is identical.

EFFECT: improvement of accuracy of determination of level of cryogenic liquid in conditions of influence on measured medium of various disturbing effects.

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Description

The invention relates to cryogenic technology, in particular to cryogenic liquid level meters, and can be used in automated process control systems in cryogenic air separation plants.

A device for measuring the level of cryogenic liquid containing a sensing element is a sensor, a sensor housing and a secondary recording unit. The sensitive element of the high-temperature superconducting (HTSC) sensor is made of a flexible tape or wire HTSC conductor reinforced with silver. Sensitive element - the sensor can be U-shaped, zigzag or spiral configuration. The sensing element is located inside the dielectric housing or on the dielectric housing. A secondary recording unit is connected to the four external contacts of the HTSC conductor. One pair of external contacts is current. The second pair of internal ones is potential ones. A current ^is passed through the current contacts (I ⁺ , I ^- ), which heats a part of the HTSC conductor in a pair. This part will go into a normal (non-superconducting) state. The other part, which is in the liquid, will remain in the superconducting state. Since the level of superconductivity along the wire changes in accordance with the change in the level of the refrigerant, the voltage removed from the potential ends (U ⁺ , U ^- ) also changes (the transmitted current is constant). The magnitude of the voltage recorded by the secondary unit is inversely proportional to the level of refrigerant in the vessel, RF patent No. 2188397.

The main disadvantage of this device is the low measurement accuracy due to the influence of various perturbations on the medium being measured, the use of high-temperature superconducting materials for the manufacture of a sensitive element and the limitation of the measurement value in a meter and a half in height, due to difficulties encountered in the manufacturing process of an extended HTSC conductor.

The closest in combination of features is a device for measuring the level of cryogenic liquid based on discrete monolithic high-temperature superconductors, which consists of a sensor and a secondary recording unit. The sensor is a combination of sensitive high-temperature superconducting (HTSC) elements made of yttrium ceramics. HTSC elements are connected in series in a single circuit and are staggered along the length of the sensor inside or on top of the dielectric base. Chip resistors or a conductor made of high-resistance alloy are used as a heater. Heating elements are switched on sectionally or along the entire length of the sensor. A secondary recording unit is connected to the external contacts of the HTSC level gauge. One pair of external contacts is current. The second pair is potential. In addition to the measuring wires, heating conductors are connected to the sensor, which heat the section of sensitive elements, then the measuring current is passed through the current contacts (I +, I-) of the sensor, which determines which part of the HTSC level meter is in pair. The other part of the HTSC elements will remain in the superconducting state. Since the level of superconductivity along the sensor changes in accordance with the change in the level of the refrigerant, then the voltage removed from the potential ends (U +, U-) also changes (the transmitted current is a constant). The magnitude of the voltage recorded by the secondary unit is inversely proportional to the level of refrigerant in the vessel, RF patent No. 2187078.

The main disadvantages of the device under consideration include a significant dependence of the accuracy of measuring the level of cryogenic liquid on the magnitude of the introduced disturbances (pressure change, cryogenic liquid concentration, temperature), the use of high-temperature superconducting materials for the manufacture of sensitive elements.

The technical result is to increase the accuracy of measuring the level of cryogenic liquid under the influence of various disturbing influences on the medium being measured (pressure change in the tank, concentration of cryogenic liquid, temperature).

The technical result is achieved due to the fact that in the device for measuring the level of cryogenic liquid, consisting of a sensor installed in the tank and a recorder, the sensor is made of a thin-walled dielectric plate with a height of H = H ₁ + H ₂ , where H ₁ is the height of the sensor’s working area, h ₂ - height of the mounting area of the sensor, installed vertically on the basis of the container on which the measuring units N≥3 with inputs for connection to a power supply, coated with a thin layer of electrically insulating material with a high coefficient teplopered moreover, each measuring unit contains M series-connected sensitive elements of the same resistance made of a material having a high thermistor sensitivity in the region of cryogenic temperatures and located at a distance h * (N (m-1) + n) from the lower edge of the dielectric plate where h = H ₁ / (M * N + 1) is the measurement step, n = 1 ... N, m = 1 ... M and an analysis unit is additionally introduced, N inputs of which are connected to the corresponding sensor outputs, and the output of the analysis unit is connected to the input of the registrar.

The invention is illustrated in figure 1, which shows an embodiment of a sensor with three measuring units,

 where 1 is the dielectric plate;

2 - measuring unit;

3, 4, 5 - sections determining the position of the liquid level;

a _nm is the sensitive element, where n = 1 ... N, N is the number of measuring units; m = 1 ... M, M is the number of sensitive elements in the measuring unit;

H ₁ - the height of the working area of the sensor;

H ₂ - the height of the mounting area of the sensor;

h is the measurement step.

A current of a fixed value is passed through all N measuring blocks, slightly heating the sensitive elements a _nm that are part of each measuring block. Assume that the liquid level in the vessel corresponds to the level indicated by section 3. With this level of cryogenic liquid in the vessel, the first three elements a ₁₁ , a ₁₂ , a _{13 of the} first measuring unit 2.1 are present. For the remaining measuring units, only the first two elements are in the liquid. In the second measuring unit 2.2, the sensitive elements a ₂₁ and a ₂₂ are in the liquid, and in the third measuring unit 2.3 there are a ₃₁ and a ₃₂ elements. The temperature of the elements in the liquid is lower than the temperature of the elements located above the liquid due to the higher thermal return. Accordingly, the resistance of these sensitive elements is different from the resistance of the sensitive elements located above the liquid. The result of comparing the voltage values on all measuring blocks shows that the voltage value taken from the outputs of the 2nd and 3rd blocks is the same, since these measuring blocks have the same number of sensitive elements in the liquid, equal to 2, and the first measuring block the voltage value will be different from the others, since this measuring unit has three sensing elements in the liquid, i.e. U ₁ ≠ U ₂ = U ₃ . Considering the result of comparing the voltage values on the measuring units during the process of increasing the level of cryogenic liquid from the moment of its complete absence, we determine the level of cryogenic liquid corresponding to the mark located between the third sensitive element a _{13 of the} first measuring unit 2.1 and the third sensitive element a _{32 of the} second measuring unit 2.2.

Figure 2 presents a structural diagram of a device for determining the level of cryogenic liquid,

 where 6 is the sensor;

7 - analysis unit;

8 - the registrar.

The sensor 6 consists of a base made of a thin-walled dielectric plate of height H = H ₁ + H ₂ , which is located vertically on the base of the tank. N≥3 measuring units are located in the working area of the base, each of which contains M series-connected sensitive elements a _nm , where n = 1 ... N, m = 1 ... M, of the same resistance, having high thermistor sensitivity in the cryogenic temperature range. The measuring units are coated with a thin layer of electrical insulation material with a high heat transfer coefficient, which provides reliable thermal contact between the cryogenic liquid and the sensitive elements. The number of sensitive elements in the measuring unit is determined depending on the number of measuring units, sizes sensitive elements, measuring the level height corresponding to the height H of the working area of the sensor ₁ and the necessary measurement steps h = H ₁ / (M * N + 1). Sensing elements are located at a distance equal to h * (N (m-1) + n) from the lower edge of the sensor base.

The analysis unit 7 is intended for measurement with a specified interval of voltage values on the measuring units, their processing, comparison and subsequent transmission of information about the level of cryogenic liquid to the recorder. The analysis unit has N inputs connected to the corresponding outputs of the sensor 6, and one output connected to the input of the recorder 8.

The device operates as follows: a current is supplied to the N inputs of the sensor 6, which heats the sensitive elements. In the absence of cryogenic liquid in the tank, the voltage value taken by the analysis unit 7 from the outputs of all N measuring units is the same. With an increase in the level of cryogenic liquid in the tank above the location of the first sensitive element of the first measuring unit a ₁₁ (section 4), the temperature of the sensitive element will decrease due to a higher heat transfer from its surface to the liquid. As a result of lowering the temperature of the sensitive element, its resistance will decrease. As a result of a change in the resistance of the sensitive element, the voltage value taken from the contacts of the first measuring unit 2.1 will change. The analysis unit, comparing the voltage values at all measuring units, determines that the voltage value has changed at the first measuring unit, and has remained unchanged at the other ones, which corresponds to an increase in the level of cryogenic liquid by h equal to the location of the sensitive element a _{11 of the} first measuring unit. A further increase in the level of cryogenic liquid above the location of the first sensitive element of the second measuring unit a ₂₁ (section 5) leads to a change in the magnitude of the voltage taken from the contacts of the second measuring unit. The result of comparing the voltage values at this stage shows that the voltage value taken from the contacts of the second measuring unit changed and became equal to the voltage value at the first measuring unit, and remained unchanged at the third, which corresponds to a 2h increase in the level of cryogenic liquid in the tank.

The measuring blocks of the sensor can be made of a set of resistors connected in series with each other, or of wire threads, with the resistor playing the role of the sensing element in the first case, and the coil of wire in the second. Measuring blocks made of a set of resistors can be located on a dielectric plate both on one vertical axis or on several, depending on the design dimensions of the sensor and sensitive elements.

The device for determining the level of cryogenic liquid can significantly reduce the measurement error arising as a result of changes in pressure in the tank and the concentration of cryogenic liquid, which ultimately leads to a change in its temperature. This is achieved due to the fact that the level is determined not by the actual value of the voltage change at the outputs of the measuring units, but by the ratio of these values relative to each other. Accordingly, in the event that any disturbing effect is introduced into the measured medium, this effect will be equally applied to all measuring units and the ratio of the voltage values on the measuring units, which was before the changes were made to the measured medium, will remain the same after the influence given disturbing influences.

The characteristics indicated in the characterizing part of the formula allow us to consider the proposed technical solution as meeting the “novelty” criterion. Since the combination of features of the distinctive and restrictive parts is not known from the scientific, technical and patent literature, the device meets the criterion of "inventive step".

The device is capable of measuring the level of cryogenic liquid under conditions of strong disturbances in the composition of the measured liquid, temperature and pressure, which makes this device advantageous in comparison with analogues. The use of sensitive elements made of thermistor material makes the device more accessible for use. The simplicity of the sensor design ensures its high reliability.

The specified device can be manufactured at enterprises of the Russian Federation, which meets the criterion of "industrial applicability".

Claims (1)

A device for determining the level of cryogenic liquid, consisting of a sensor installed in the tank and a recorder, characterized in that the sensor is made of a thin-walled dielectric plate with a height of H = H ₁ + H ₂ , where H ₁ is the height of the sensor’s working area, N ₂ is the mounting height zone of the sensor mounted vertically on the basis of the capacitance, on which N≥3 measuring units with inputs for connecting to the power supply, covered with a thin layer of electrical insulation material with a high heat transfer coefficient, are located, with each meter ny block contains M series connected sensing elements of equal resistance, made of a material having a high thermistor sensitivity at cryogenic temperatures, and arranged at a distance h * (N (m-1) + n) from the bottom edge of the dielectric plate where h = H ₁ / (M * N + 1) is the measurement step, n = 1 ... N, m = 1 ... M, and an analysis block is additionally introduced, N inputs of which are connected to the corresponding outputs of the sensor, and the output of the analysis block is connected to the input of the recorder.

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