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http://www.dhechina.com/ueditor/php/upload/image/20190723/1563865849300715.png Spherical tanks have excellent compressive strength; compared to cylindrical containers (i.e., conventional vertical storage tanks), at the same diameter and pressure level, their wall thickness is only half that of cylindrical containers, resulting in less steel being used； It has a large range, occupies less space, requires simple foundation work, and offers good cost-performance. It is one of the most commonly used storage tanks. In modern industrial enterprises, spherical tanks are primarily used for storing liquefied gases such as liquefied petroleum gas, liquid ammonia, and VCM monomer. These substances exist in gaseous form at normal temperature and pressure; to store them, they need to be converted into a liquid state by applying pressure and reducing temperature, which **improves storage efficiency**. At the same time, new requirements have been put forward for the selection of level gauges on spherical tanks. Firstly, the level gauge must be suitable for measuring over a wide range, and it must also have pressure resistance, so that changes in pressure inside the tank do not have a significant impact on its measurement stability and accuracy. Secondly, the impact of the purity, crystallinity, and impurity content of the medium on the level gauge measurement also needs to be considered. In addition, the feeding and discharging methods and speeds, as well as the impact of the medium’s volatility on level measurement, must also be considered. Therefore, it is advisable to consider level gauges whose impact of the aforementioned factors on the liquid level measurement of spherical tanks is minimal. 1. Servo level gauges http://www.dhechina.com/ueditor/php/upload/image/20190723/1563866498783084.png are mostly from imported brands, such as German E+H, Dutch Enraf, American Honeywell, and Japanese Tokyo Keiso. Advantages of Archimedes’ principle + electromagnetic principle: insensitive to pressure changes ； It features high precision, reaching ±0.5mm; when the measuring medium is pure and the feed and discharge speeds are low, it can be used as a metering-grade instrument ； Measurable multi-layer interfaces. Disadvantage: Requires an opening on the top of the tank ； It is necessary to obtain the medium density in real time; changes in density lead to changes in buoyancy, which in turn results in different depths of immersion of the float below the liquid surface, causing measurement errors ； A waveguide must be installed inside the tank, and the inner wall of this waveguide requires a high level of smoothness; otherwise, it will affect the movement of the float ； It is not suitable for measuring highly viscous media, as this may cause the float to get stuck inside the guide tube and break the connecting wire. 2. Radar level gauges: http://www.dhechina.com/ueditor/php/upload/image/20190723/1563866224536346.png. They operate on the principle of electromagnetic wave reflection; there are many brands available, both domestic and international, such as the imported brands Rosemount, VEGA, E+H, Siemens, etc ； Domestic brands such as Guda, Jier, HuiBo, DingHua, JingBo, and ShengBo. The advantages and disadvantages will be discussed in a separate article. 3. The magnetic flap level gauge operates on the principle of a communicating vessel; it has a simple structure, low technical complexity, and is easy to manufacture. There are many brands available both domestically and internationally, including WEKA and Kölner from Germany, IA from Germany as well, K-tek from the United States, Tokyo Keizō from Japan, along with hundreds of domestic brands. Advantages: Intuitive, easy to install, and low cost. Disadvantage: When the pressure inside the tank changes, there is a pressure imbalance between the inside of the tank and the pipe connecting it to the outside, resulting in measurement errors ； There was no remote level sensing; after improvements, multiple reed switches were used for remote detection. A certain distance was required between these reed switches, resulting in low accuracy in level measurement ； Connection flange holes, magnetic float balls; maintenance requirements increase when the medium being measured is dirty, and it is difficult to clean the tank during maintenance. 4. Sonar-type external level gauge – Principle of sonar echo ranging: http://www.dhechina.com/ueditor/php/upload/image/20190723/1563865775336996.png. Invented by Dinghua Electronics in 1990, sonar echo ranging is a technology that makes use of the propagation and reflection of sound waves within a medium; distance measurement is achieved by utilizing the relationships between time, speed, and distance. Currently, all the products are from domestic brands; there are around a dozen of them such as ELL from Dinghua Electronics, Lexun, Sichuang, Shengke, Huashun, Xunchuang, etc., and there is a significant difference in quality among them. Advantages: During installation and maintenance, no drilling is required, no heating is needed, the tank does not have to be emptied, and production can continue. Automatic calibration accuracy ； Unaffected by pressure inside the tank; maximum range of 30 meters ； Safe and reliable – Dinghua Electronics’ ELL sonar-type external level gauges achieve a safety integrity level of **certified SIL3. Disadvantage: Cannot measure liquid media with excessively high viscosity ； Liquids that produce a large number of bubbles or solid particles cannot be used ； Maximum measurement temperature range: -40～200 ℃. Given the current situation in China, most systems use a combination of two types among servos, radars, and external level gauges; a small number of spherical tanks employ dual-flange differential pressure level gauges, although these have lower precision and require more maintenance.