Mass type liquid level meter - the latest technology of low temperature medium li

2018.07.17

ⅠOverview of traditional liquid level measurement methods for low temperature medium
1. Float level meter
It only can be used in small vertical cryogenic containers, such as Dewar and mini cans. This type of liquid level gauge has simple structure, low cost, but poor measurement accuracy and easy failure, and needs frequent replacement.
2. Servo type or radar type liquid level gauge
Only used on large storage tanks under atmospheric pressure. The liquid level gauge can measure the density in different height direction accurately. But the structure is complex, the cost is too high, suitable for high value storage tank.
3.Capacitance level meter
Currently, it is only used in LNG vehicle bottles and has the potential to be used in other cryogenic containers. The liquid level gauge of this principle is suitable for use in horizontal containers. Its accuracy is higher than that of differential pressure type liquid level gauge, but it is still affected by the change of medium composition and temperature.
4.Differential pressure type liquid level gauge
This is a liquid level gauge widely used in the cryogenic industry. Its principle is to measure the tiny static pressure difference between the gas phase and the liquid phase and convert it into liquid level height. Obviously, the accuracy of this principle is affected by the change of medium composition and temperature, and the precondition of stable operation is the stability of pressure and the calm of liquid level. In the tank fluid filling and unloading operations or tank shaking, differential pressure type liquid level gauge can not work normally, and sometimes damage the differential pressure level gauge sensor and micro pressure gauge. False liquid level, ice plugging and leakage are unavoidable troubles of differential pressure liquid level gauge.
5. Mass type liquid level meter
It is a new product just appeared in recent two years, it overcomes the shortcomings of the above four liquid level gauge, can be widely used in all kinds of cryogenic medium containers. The following is a comprehensive introduction to the liquid level gauge.

Ⅱ What is a mass level meter?

Mass level meter is a kind of low temperature medium measuring instrument innovated and developed by DeleeTech (Beijing DeleeTech Measurement and Control Tech. Co., Ltd). It can directly and accurately measure and display the quality of low temperature medium in the tank in real time (it can also display the mass percentage), and the measurement result is not affected by the change of medium composition and temperature. The liquid level meter is composed of mass sensor, coaxial cable, electrode extractor, armoured cable, transmitter with LCD, etc.

Ⅲ Performance characteristics of mass type liquid level gauge
1. The measurement accuracy is much higher than the differential pressure type liquid level gauge, which is convenient for the business management of income, sales and inventory, and can be used as a reference for distribution and settlement;
2. Easy to realize electric signal transmission, with direct output interface, no need to install transmitter separately;
3. Good stability. It is not affected by the change of composition and temperature, and can display the liquid level in real time under the condition of fluctuation of liquid level and pressure.
4.There is no need to do any operation in use, and there is no risk of damage to the instrument due to wrong operation, which meets the requirements of real-time measurement. And differential pressure level meter in use need correct operation, such as the operation is not in accordance with the the operation of the order "open balance valve, then open phase pipe (low voltage side) and liquid phase pipe(high side) valve, then close the balance valve, waiting for instrument data stability, and read data", it will have the risk of damage to the instrument or waiting for a long time to read data.
5. High reliability. There is no such weak movable elements as bellows, diaphragms, springs, connecting rods and Bourdon pipes on differential pressure level meters, so the mass level meters are shock-resistant and have a long service life, especially suitable for use on mobile containers such as tank cars, containers and dewar bottles.
6.The mass level meter does not have a pressure tube, so there will be no false liquid level. Differential pressure level meter requires gas phase and liquid phase pressure tube. The indirect measurement principle determines that false liquid level will be generated in the circulation of the liquid filling and using, which will interfere with the operator's correct reading of the liquid level data.
7. There is no risk of failure such as ice plugging or leakage. The mass gauge has no gas-phase or liquid-phase pressure tubes, no needle valves or globe valves, so there is no risk of failure such as ice plugging or leakage. However, the diameter of the gas-phase and liquid-phase pressure pipe of the differential pressure level gauge is very small, and there are several needle valves and globe valves with them, and there are connection ports between them, which are easy to cause ice blocking or leakage, thus causing the failure of the differential pressure level gauge and other problems.
8. Large screen, wide temperature liquid crystal design, IP67 waterproof structure, keyless technology, meet the all-weather outdoor environment conditions.
9. Anti-interference circuit, intrinsically safe and explosion-proof design, with flameproof case, suitable for complex electromagnetic environment and explosion-proof environment.

Ⅳ Measurement accuracy of mass type liquid level meter
By carrying out comparative test. The measurement accuracy is between 0.2% FS and 2.0% FS.
Within the range of 15% ~ 100% liquid level, the measurement accuracy is not less than 0.5% FS.
Taking the 195L Dewar as an example, it was found that the maximum absolute error value did not exceed 1.5kg in the 6 test comparisons of liquid nitrogen filling to full cylinder through weighing comparison tests conducted by several enterprises.

Ⅴ What are the functions of the mass level meter
◎ The quality or mass percentage in the tank can be directly displayed on the spot;
◎ It can keep working for 3 ~ 5 years with its own power supply;
◎ It can provide the position information and running track of the equipment;
◎ It can output 4 ~ 20mA signal or 485 signal, and can output GPRS signal wirelessly.
◎ It can be adjusted locally or remotely;
◎ It can diagnose the fault by itself;
◎ The alarm limit of high and low liquid level can be set;
◎ The measuring medium can be changed;
◎ It can realize two-way communication.

Ⅵ Applicable medium and type of equipment for mass level meter
Mass level gauge is suitable for liquefied natural gas (LNG), liquid oxygen, liquid argon, liquid nitrogen, carbon dioxide and other media, widely used in low temperature storage tanks, ISO tank, road tanker, Dewar, mini tank, marine tank, pipeline, pump pool and other equipment.

Ⅶ Working principle of mass type liquid level meter
The new RF impedance circuit and vector measurement method are adopted, and the working principle is as follows:
Above, imaginary part reflected with the capacitance parameter of liquid level, the real component reflects conductance parameters related to medium temperature, high frequency signal through the launch and receive the echo, and then by the embedded microcontroller processor after operation of multiple parameters, is not dependent on temperature changes in temperature compensation coefficient and no changes over medium composition of the medium component compensation coefficient, finally get tank of the quality of the accurate numerical synthesis, and on the basis of the principle of developing the latter level gauge. The digital display can directly display the mass (or volume percentage or mass percentage) of the media in the tank. The technology has been used in LNG tanker in 2014. The measurement accuracy is not affected by the fluctuation of liquid level, the change of medium composition, or the change of medium temperature.

Ⅷ How to install the mass level meter?
In the manufacture of cryogenic containers, the mass level gauge is installed and debugged by the equipment manufacturer, and the user does not need to do any installation or debugging work. The installation diagram of the equipment manufacturer is as follows:
1. Installation of mass level gauges for Dewar or mini cans

2. Installation of mass level gauges for horizontal and vertical tanks