Low-temperature liquid level measuring device and low-temperature liquid level measuring method

Abstract

A low-temperature liquid level measuring device is used for detecting the liquid level height of liquid at the temperature ranging from-250 DEG C to 0 DEG C in a liquid storage tank, the maximum liquid level height in the liquid storage tank is L0, and the low-temperature liquid level measuring device comprises N temperature-sensitive resistors and a circuit module. The N temperature-sensitive resistors are sequentially connected in series from top to bottom; the circuit module comprises a power supply unit and a voltage measuring unit, and the power supply unit is used for inputting current of which the voltage is first voltage UA to the N temperature-sensitive resistors; the voltage measuring unit is used for detecting a second voltage UB loaded to the uppermost temperature-sensitive resistor and detecting a third voltage UC loaded to N-1 temperature-sensitive resistors from top to bottom; the liquid level height L of the low-temperature liquid level is calculated according to the following formula: # imgabs0 #. The invention further provides a low-temperature liquid level measuring method. Compared with the prior art, the low-temperature liquid level measuring device and the low-temperature liquid level measuring method have the advantages that manual correction work can be reduced, and measuring precision and efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cryogenic liquid measurement, and in particular to a cryogenic liquid level measuring device and a cryogenic liquid level measuring method. Background Art

[0002] Compared with gases, liquids have the advantages of occupying less space, lower transportation cost risk, and less storage loss. Therefore, different means are often used in the existing technology to convert gases into cryogenic liquids for storage. For example, natural gas, nitrogen, hydrogen, etc. are often converted into cryogenic liquids such as liquefied natural gas, liquid nitrogen, and liquid hydrogen during storage and placed in liquid storage tanks.

[0003] However, if these cryogenic liquids leak during use, the liquid in the tank will quickly vaporize, causing the volume to expand, and then cause an explosion. Therefore, monitoring the liquid level status in the liquid storage tank is a top priority for ensuring safety in the storage and transportation of liquefied gas. To this end, the prior art provides a variety of devices and methods for measuring the liquid level in liquid storage tanks. Among them, the resistive cryogenic liquid level measuring device is widely used due to its simple structure and low price. The resistive cryogenic liquid level measuring device mainly utilizes the characteristic that the resistance of the sensor changes with temperature, detects the resistance value of each sensor separately and compares it, thereby determining the liquid level position, and then obtaining the height of the liquid level.

[0004] However, when using the resistive low-temperature liquid level measuring device, people found that its measured values ​​often have errors, and its reliability continues to decrease during use. Frequent manual calibration of the measuring device is required to ensure the accuracy of the measurement results, resulting in a huge workload. Summary of the invention

[0005] Based on this, the purpose of the present invention is to overcome the defects or shortcomings of the prior art and provide a low-temperature liquid level measuring device.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A low-temperature liquid level measuring device, used for detecting the liquid level height of a low-temperature liquid at -250°C to 0°C in a liquid storage tank, wherein the maximum liquid level height in the liquid storage tank is L0, comprises a thermistor and a circuit module;

[0008] The total number of the temperature-sensitive resistors is N, and the N temperature-sensitive resistors are arranged in series from top to bottom;

[0009] The circuit module includes a power supply unit and a voltage measurement unit. The power supply unit is used to input a current with a first voltage UA to N temperature-sensitive resistors. The voltage measurement unit is used to detect a second voltage UB applied to the uppermost temperature-sensitive resistor and a third voltage UC applied to the (N - 1) temperature-sensitive resistors from top to bottom. The liquid level height L of the low-temperature liquid is calculated according to the following formula:

[0010] Compared with the prior art, after the low-temperature liquid level measuring device of the present invention is set in the liquid storage tank, the accurate liquid level height of the low-temperature liquid can be obtained according to the number of temperature-sensitive resistors, the first voltage UA, the second voltage UB and the third voltage UC. Moreover, since the liquid level height is determined by the difference between the first voltage UA, the second voltage UB and the third voltage UC, the error of zero-point offset can be automatically offset, thus avoiding the manual calibration work of the low-temperature liquid level measuring device and improving the work efficiency.

[0011] In one embodiment, the total number N of the temperature-sensitive resistors is N≥3, which increases the distribution density of the temperature-sensitive resistors in the liquid storage tank and further improves the measurement accuracy.

[0012] In one embodiment, it further includes a substrate made of a low-temperature resistant material, and the plurality of temperature-sensitive resistors are arranged on one side surface of the substrate, so as to facilitate the installation of the low-temperature liquid level measuring device into the liquid storage tank.

[0013] In one embodiment, the temperature-sensitive resistors are arranged at equal intervals from top to bottom, and the distance d between the temperature-sensitive resistors satisfies the relationship with the maximum liquid level height L0: To better judge the liquid level height of the low-temperature liquid.

[0014] In one embodiment, the temperature-sensitive resistor is made of a thermosensitive material with a negative temperature coefficient to achieve different resistances when located in gas and liquid.

[0015] In one embodiment, the temperature-sensitive resistor is arranged in the liquid storage tank; the circuit module is arranged outside the liquid storage tank to facilitate data display.

[0016] In addition, the present invention also correspondingly provides a low-temperature liquid level detection method, and its technical solution is as follows:

[0017] A low-temperature liquid level detection method for detecting the liquid level height of a low-temperature liquid in the range of -250°C to 0°C in a liquid storage tank, where the maximum liquid level height in the liquid storage tank is L0, includes the following steps:

[0018] Set N temperature-sensitive resistors arranged in series from top to bottom in the liquid storage tank, and input a current with the first voltage UA to the N temperature-sensitive resistors;

[0019] Obtain the second voltage UB across the topmost temperature-sensitive resistor and the third voltage UC across the top-down (N - 1) temperature-sensitive resistors;

[0020] Calculate the liquid level height L of the cryogenic liquid in the liquid storage tank through the following formula:

[0021] Compared with the prior art that separately detects the single-point resistance value, the cryogenic liquid level detection method of the present invention can obtain the accurate cryogenic liquid level height conveniently and quickly according to the number of detected temperature-sensitive resistors, the first voltage U A , the second voltage U B and the third voltage U C in combination with the maximum liquid level height L0 in the liquid storage tank. Moreover, since the liquid level height is determined by the differences between the first voltage UA, the second voltage UB, and the third voltage UC, it can automatically cancel the error of zero-point offset, thus avoiding the need for frequent manual calibration of the cryogenic liquid level measuring device and improving work efficiency.

[0022] In one embodiment, the method further includes the following steps:

[0023] Obtain the allowable error a% and deviation b% of the temperature-sensitive resistor, and set the function value

[0024] If the function value C ∈ [a% ± 5%], determine that the liquid storage tank is full or empty;

[0025] If the function value C ∈ [b% ± 5%], determine that the liquid storage tank is half-full and perform the calculation of the liquid level height L.

[0026] Thereby, the liquid level height of the cryogenic liquid in the liquid storage tank can be judged more accurately.

[0027] In one embodiment, the deviation b% is greater than or equal to twice the allowable error a%, increasing the deviation of the resistance value of the temperature-sensitive resistor in different states to better judge whether the corresponding temperature-sensitive resistor is in the liquid or in the gas.

[0028] In one embodiment, the method further includes the following steps: In the state that the liquid storage tank is full or empty, calculate and obtain the allowable error a% through the following formula: In the state that the liquid storage tank is half-full, calculate and obtain the deviation b% through the following formula: Thereby, the allowable error a% and the deviation b% can be accurately obtained.

[0029] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0030] Figure 1Schematic diagram of the overall structure of the low-temperature liquid level measuring device of the present invention;

[0031] Figure 2 Schematic diagram of the overall process of the low-temperature liquid level measuring method of the present invention;

[0032] Figure 3 Schematic diagram of the process for calculating the liquid level height L of the low-temperature liquid by the low-temperature liquid level measuring method of the present invention.

[0033] Explanation of reference numerals: 10, substrate; 20, thermistor; 20A, first thermistor; 20B, second thermistor; 20C, third thermistor; 20D, fourth thermistor; 30, circuit module; 31, voltage measurement unit; 32, power supply unit; 40, first electrode; 50, second electrode; 60, third electrode; 70, fourth electrode; 100, liquid storage tank. Detailed implementation manners

[0034] In view of the defect that the measured value often has errors and needs to be frequently calibrated during the use of the resistive low-temperature liquid level measuring device in the prior art, the applicant analyzed and studied the working principle and structure of the resistive low-temperature liquid level measuring device, and found that: since the resistive low-temperature liquid level measuring device works based on the characteristic that the resistance value changes with temperature, multiple sensors arranged along the height direction of the liquid storage tank are provided in the liquid storage tank. Since the resistances of the sensors in the gas and in the liquid are different, by respectively obtaining the resistance values of each sensor, it can be determined which sensors are in the gas and which sensors are in the liquid, and corresponding to the position of the uppermost sensor in the liquid, the liquid level height in the liquid storage tank can be determined.

[0035] However, the liquid volume in the liquid storage tank often changes, and the temperature in the tank fluctuates accordingly. The variable temperature environment causes the resistance value of the sensor to be continuously affected by temperature and undergo zero drift, resulting in the detection value = actual value ± drift error, thus leading to measurement errors, and it is necessary to frequently re-calibrate the zero points of each sensor manually to eliminate the errors.

[0036] In view of the above discovery, the applicant proposes a low-temperature liquid level measuring device, which changes the method of detecting the resistance value to judge the liquid level height in the prior art, and adopts the method of measuring two groups of voltage values and combining a simple algorithm to accurately obtain the liquid level height of the low-temperature liquid. Moreover, the drift errors can automatically cancel each other out during the combination of the two groups of voltage values, thereby overcoming the influence of the zero drift generated by the resistance value of the sensor affected by environmental factors on the measurement result and reducing the manual calibration work of the low-temperature liquid level measuring device. Moreover, different from the traditional method of performing multi-point resistance value measurement, the low-temperature liquid level measuring device of the present application can obtain the liquid level height of the low-temperature liquid by measuring two groups of voltage values, and this measurement method is accurate and fast.

[0037] Please refer to Figure 1 , the low-temperature liquid level measuring device of the present application is arranged in the liquid storage tank 100, and includes a substrate 10, a plurality of temperature-sensitive resistors 20 and a circuit module 30; the circuit module 30 includes a voltage measuring unit 31 and a power supply unit 32. The liquid storage tank 100 can store cryogenic liquids such as liquid nitrogen, liquefied natural gas, liquid oxygen, liquefied methane, etc., and the temperature range is: -250°C to 0°C

[0038] Among them, the substrate 10 is a plate made of low-temperature resistant materials, and the low-temperature resistant materials include polyimide (PI), polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), or metal, stainless steel, alloy, etc. plated with an insulating layer. The substrate 10 extends downward from top to bottom along the height direction of the liquid storage tank 100, and its length is at least equal to the maximum liquid level height L0 of the cryogenic liquid to be stored in the liquid storage tank 100. The substrate 10 can be arranged on the inner side wall of the liquid storage tank 100 or placed at the bottom of the liquid storage tank 100 to be fixed in the liquid storage tank 100.

[0039] A plurality of temperature-sensitive resistors 20 are arranged on one side surface of the substrate 10. A plurality of temperature-sensitive resistors 20 are arranged at intervals in sequence from top to bottom along the extending direction of the substrate 10 and are connected in series by wires, and the total number is N. The temperature-sensitive resistor 20 can be made of a negative temperature coefficient thermosensitive material, and the thermosensitive material includes a carbon-based material, and the carbon-based material includes carbon fiber, porous carbon or a carbon-based conductive paste formed by mixing the above materials with an organic polymer, and its resistance value decreases with the increase of temperature. In the full-tank or empty-tank state of the liquid storage tank, the allowable error of the resistance value consistency of the temperature-sensitive resistor 20 is a%. In the half-full state of the liquid storage tank, the deviation of the temperature-sensitive resistor 20 is b%, where b%≥2a%. Preferably, the temperature-sensitive resistors 20 are arranged at uniform intervals from top to bottom. The maximum liquid level height in the liquid storage tank is L0, and the relationship between the temperature-sensitive resistor spacing d and the maximum liquid level height L0 satisfies:

[0040] The N temperature-sensitive resistors 20 are continuously printed into a film by a printing process and fixed to the substrate 10. The number of the N temperature-sensitive resistors 20 can be set according to the height of the liquid storage tank 100, the measurement height accuracy, etc., which is not limited here, but it can be understood that as the height of the liquid storage tank 100 increases, the number of required temperature-sensitive resistors 20 will increase, the spacing between the temperature-sensitive resistors 20 will decrease, and the measured liquid level accuracy will increase. Therefore, preferably, the total number N of the temperature-sensitive resistors 20≥3.

[0041] In this embodiment, the temperature-sensitive resistor 20 includes a first temperature-sensitive resistor 20A, a second temperature-sensitive resistor 20B, a third temperature-sensitive resistor 20C, and a fourth temperature-sensitive resistor 20D. Along the arrangement direction of the temperature-sensitive resistor 20 from top to bottom, the first temperature-sensitive resistor 20A is the first temperature-sensitive resistor, located at the top and close to the top of the liquid storage tank 100; the second temperature-sensitive resistor 20B is adjacent to the first temperature-sensitive resistor 20A, located directly below the first temperature-sensitive resistor 20A, and is the second temperature-sensitive resistor; the fourth temperature-sensitive resistor 20D is located at the bottom, close to the bottom of the liquid storage tank 100, and is the Nth temperature-sensitive resistor; the third temperature-sensitive resistor 20C is adjacent to the fourth temperature-sensitive resistor 20D and is located directly above the fourth temperature-sensitive resistor 20D, and is the (N - 1)th temperature-sensitive resistor.

[0042] The voltage measurement unit 31 and the power supply unit 32 are located outside the liquid storage tank 100. Preferably, the voltage measurement unit 31 and the power supply unit 32 are close to the top of the liquid storage tank 100. The two ends of the plurality of series-connected temperature-sensitive resistors 20 are respectively electrically connected to the positive and negative electrodes of the power supply unit 32 to form a power supply loop, and the power supply unit 32 inputs a first voltage UA to the plurality of series-connected temperature-sensitive resistors 20. One end of the voltage measurement unit 31 is electrically connected to the zero line of the power supply unit 32, and the other end is electrically connected between the first temperature-sensitive resistor 20A and the second temperature-sensitive resistor 20B, thereby forming a first loop in parallel with the first temperature-sensitive resistor 20A to detect the second voltage U applied to the first temperature-sensitive resistor 20A. B At the same time, one end of the voltage measurement unit 31 is electrically connected to the zero line of the power supply unit 32, and the other end is electrically connected between the third temperature-sensitive resistor 20C and the fourth temperature-sensitive resistor 20D, thereby forming a second loop in parallel with the temperature-sensitive resistors 20 between the first temperature-sensitive resistor 20A and the third temperature-sensitive resistor 20C to detect the third voltage U applied to the N - 1 temperature-sensitive resistors 20 between the first temperature-sensitive resistor 20A and the third temperature-sensitive resistor 20C. C That is, the third voltage U C is the total voltage applied to all the temperature-sensitive resistors 20 above the fourth temperature-sensitive resistor 20D.

[0043] Furthermore, the voltage measurement unit 31 is provided with a data processing module and a display screen, which can perform arithmetic processing on the detected voltage value and directly display the magnitude of the liquid level height L of the low-temperature liquid in the liquid storage tank 100.

[0044] Further, the low-temperature liquid level measuring device further includes a first electrode 40, a second electrode 50, a third electrode 60, and a fourth electrode 70. One end of the first electrode 40 is connected to the voltage measuring unit 31, and the other end is connected between the third temperature-sensitive resistor 20C and the fourth temperature-sensitive resistor 20D; one end of the second electrode 50 is connected to the voltage measuring unit 31, and the other end is connected between the first temperature-sensitive resistor 20A and the second temperature-sensitive resistor 20B; the third electrode 60 is connected between the neutral line of the power supply unit 32 and the first temperature-sensitive resistor 20A; one end of the fourth electrode 70 is connected to the voltage input line of the power supply unit 32, and the other end is connected to the fourth temperature-sensitive resistor 20D. The setting of the first electrode 40, the second electrode 50, the third electrode 60, and the fourth electrode 70 facilitates wiring and conduction, and can also be used as a data interface for data transmission.

[0045] Please refer to Figure 2 , based on the above structure of the low-temperature liquid level measuring device, the present application also provides a low-temperature liquid level measuring method, which includes the following steps:

[0046] Step S10: Set the above low-temperature liquid level measuring device including N temperature-sensitive resistors 20 in the liquid storage tank 100, the maximum liquid level height L0 of the low-temperature liquid in the liquid storage tank 100, and input a current with the first voltage UA to a plurality of series-connected temperature-sensitive resistors 20 through the power supply unit 32.

[0047] Step S20: Obtain the second voltage UB loaded on the first temperature-sensitive resistor 20A and the third voltage UC loaded between the first temperature-sensitive resistor 20A and the third temperature-sensitive resistor 20C through the voltage measuring unit 31.

[0048] Step S30: Calculate the liquid level height L of the low-temperature liquid according to the first voltage UA, the second voltage UB, the third voltage UC, the total number N, the maximum liquid level height L0, and the following formula: Wherein, the liquid level height L of the low-temperature liquid is the distance from the bottom of the liquid storage tank 100 to the liquid level stored therein.

[0049] Specifically, please refer to Figure 3 , step S30 further includes the following steps:

[0050] Step S31: Obtain the allowable error a% of the temperature-sensitive resistor 20, the deviation b% of the temperature-sensitive resistor 20, and the function value C.

[0051] Wherein, let the function value And the allowable error a% and the deviation b% can be obtained through experiments or detections.

[0052] During the initial calibration, when the liquid storage tank 100 is full or empty, the first voltage UA, the second voltage UB, and the third voltage UC are detected, and the allowable error a% is calculated through the following formula, and the allowable error a% is stored as a fixed value in the circuit module 30:

[0053] During the initial calibration, when the liquid storage tank 100 is half full, the first voltage UA, the second voltage UB, and the third voltage UC are detected, and the deviation b% is calculated through the following formula, and the deviation b% is stored as a fixed value in the circuit module 30:

[0054] Therefore, the allowable error a% and the deviation b% are determined by the characteristics of the thermistor 20 and are constant values.

[0055] Step S32: Determine whether the function value C and the allowable error a% satisfy the following relationship: C = a% ± 5%; if so, determine whether the liquid storage tank 100 is full or empty; if not, go to step S33.

[0056] Step S33: Determine whether the function value C and the deviation b% satisfy the following relationship: C = b% ± 5%; if so, determine that the liquid storage tank 100 is half full and execute step S34; if not, determine that there is an error, including errors such as a break in the circuit, and the circuit needs to be detected.

[0057] Step S34: According to the first voltage U A 、the second voltage U B 、the third voltage U C 、the number N of the thermistors 20 and the highest liquid level L0, calculate the liquid level height L of the cryogenic liquid in the liquid storage tank 100.

[0058] When the liquid in the liquid storage tank 100 is in a half-full state, assume that n of the N thermistors 20 are below the liquid level and their resistance values are all the first resistance value, then N - n thermistors 20 are above the liquid and their resistance values are all the second resistance value. At this time, the first voltage U A 、the second voltage U B 、the third voltage U C satisfy the following relationship:

[0059] U A =(N - n)U B +n(U A -U C )

[0060] Thus, we get:

[0061]

[0062] Also according to:

[0063] Wherein: L is the liquid level height of the cryogenic liquid, n is the number of the temperature-sensitive resistors 20 below the liquid level, N is the total number of the temperature-sensitive resistors 20, and L0 is the highest liquid level of the cryogenic liquid in the liquid storage tank 100.

[0064] It can be obtained that:

[0065]

[0066] Therefore, substituting the measured first voltage UA, the second voltage UB, the third voltage UC, the number N of the temperature-sensitive resistors 20, and the maximum liquid level height L0 can obtain the liquid level height L.

[0067] In the above liquid level measurement method, the liquid level height L is calculated by using the voltage difference, and the offset value can be automatically cancelled, avoiding the error caused by the offset of the resistance value when directly measuring a single resistance value.

[0068] Compared with the prior art, the cryogenic liquid level measurement device and the cryogenic liquid level measurement method of the present invention have the following advantages:

[0069] 1. It can reduce the work of manual correction and improve work efficiency;

[0070] 2. The detection speed of the cryogenic liquid level height in the liquid storage tank is fast and the accuracy is high;

[0071] 3. The structure is simple, easy to implement, and has wide applicability.

[0072] The above embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A low-temperature liquid level measuring device, used to detect the liquid level of a low-temperature liquid at -250°C to 0°C in a liquid storage tank, wherein the maximum liquid level in the liquid storage tank is L0, characterized in that: include: The total number of thermistors is N, and the N thermistors are arranged in series from top to bottom; The circuit module includes a power supply unit and a voltage measuring unit, wherein the power supply unit is used to input a current having a first voltage UA to the N temperature-sensitive resistors; the voltage measuring unit is used to detect a second voltage UB loaded on the top temperature-sensitive resistor and a third voltage UC loaded on (N-1) temperature-sensitive resistors from top to bottom; the liquid level L of the low-temperature liquid level is calculated according to the following formula:

2. The low-temperature liquid level measuring device according to claim 1, characterized in that: The total number N of the temperature-sensitive resistors is ≥3.

3. The low-temperature liquid level measuring device according to claim 1, characterized in that: It also includes a substrate made of low-temperature resistant material, and the plurality of temperature-sensitive resistors are arranged on a side surface of the substrate.

4. The low-temperature liquid level measuring device according to claim 1, characterized in that: The temperature-sensitive resistors are arranged at equal intervals from top to bottom, and the temperature-sensitive resistor interval d and the maximum liquid level height L0 satisfy the relationship:

5. The low-temperature liquid level measuring device according to claim 1, characterized in that: The temperature sensitive resistor is made of a thermal sensitive material with a negative temperature coefficient.

6. The low-temperature liquid level measuring device according to claim 1, characterized in that: The temperature-sensitive resistor is arranged in the liquid storage tank; and the circuit module is arranged outside the liquid storage tank.

7. A low-temperature liquid level detection method, used to detect the liquid level height of a low-temperature liquid at -250°C to 0°C in a liquid storage tank, wherein the maximum liquid level height in the liquid storage tank is L0, characterized in that: The following steps are involved: N temperature-sensitive resistors are arranged in series from top to bottom in the liquid storage tank, and a current having a voltage of the first voltage UA is input to the N temperature-sensitive resistors; Obtaining a second voltage UB loaded on the top temperature-sensitive resistor and a third voltage UC loaded on (N-1) temperature-sensitive resistors from top to bottom; The liquid level L of the cryogenic liquid in the liquid storage tank is calculated by the following formula:

8. The low-temperature liquid level detection method according to claim 7, characterized in that: The following steps are also included: Get the allowable error a% and deviation b% of the temperature sensitive resistor, and set the function value If the function value C∈[a%±5%], it is determined whether the liquid storage tank is full or empty; If the function value C∈[b%±5%], the liquid storage tank is judged to be half full, and the liquid level height L is calculated.

9. The low-temperature liquid level detection method according to claim 8, characterized in that: Also includes: The deviation b% is greater than or equal to twice of a%.

10. The low-temperature liquid level detection method according to claim 8, characterized in that: The following steps are also included: When the liquid storage tank is full or empty, the allowable error a% is calculated by the following formula: When the liquid storage tank is half full, the deviation b% is calculated by the following formula:

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