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I. Overview: A radar level gauge is a level measurement instrument that utilizes microwaves to determine the level of liquids, particles, slurries, or solids in storage tanks, buffer tanks, wave stabilizers, and bypass pipes. It has the advantage of being unaffected by temperature, pressure, steam, as well as changes in the physical properties of the medium being measured. Over the years, it has been widely used in fields such as electricity, petrochemicals, metallurgy, and chemicals. Its features include: measurement is carried out using microwaves, it has a wide range of applications, and can be used for measuring the level of liquids, emulsions, molten materials, and other similar substances ； The medium under test can be flammable, explosive, highly corrosive, or substances under high temperature and pressure conditions. It features both digital and analog output options, and can be configured as a single unit or multiple units in a bus configuration, facilitating communication with the upper-level monitoring computer. It features intelligent processing capabilities, echo suppression, and strong interference resistance. The instrument has explosion-proof features and can be taken to the site for operation. The corrosion resistance requirements are met through the selection of different antennas. https://p26.toutiaoimg.com/origin/tos-cn-i-qvj2lq49k0/20a9608164dc4c979f5ea4b65ec41900?from=pc II. Working Principle and Characteristics The radar level gauge operates based on a \"top-down\" timing measurement principle, and it is used to determine the distance from the location where the probe is installed to the surface of the liquid. Its structure is very simple, mainly consisting of an instrument enclosure, process connections, and an antenna. Microwave pulses are emitted from the antenna toward the surface of the medium under test; the transmitted waves are reflected at the liquid surface, and these reflected waves are captured by the same antenna. Both the transmitted and reflected waves are sampled, and after signal processing, the distance D from the connection point of the process to the surface of the medium under test is determined. This distance D is proportional to the time taken by the microwave pulses to travel, that is, D = C*T2 (where C is the speed of light). Since the distance E from the process connection point to the zero level of the measured liquid level is known, the liquid level height L can be calculated as L = E – D. Typically, radar level gauges use microwave pulse signals with a operating frequency of 26 GHz; their measurement range can reach 30 M, and this range can be set arbitrarily within 30 M. It has a high level of intelligence, outputting a standard 4–20mA analog signal along with digital communication signals based on the HART protocol. For the current-output type, the lower liquid level measurement point E corresponds to an output of 4 mA, while the upper liquid level measurement point F corresponds to an output of 20 mA. For the digital output type, they correspond to 0% and 100% of the liquid level, respectively. By operating the display on-site, several parameters such as E.F. can be entered into the radar level gauge and stored in its internal EPROM; the radar level gauge then measures between the set values of E and F. III. Measurement System 1. Single-point measurement system The single-point measurement system is shown in the figure below: The radar level gauge is powered by a 24VDC two-wire system, and it can be configured on-site using an on-site operation display. Alternatively, an interface card is used to convert the analog signal generated by the radar level gauge into a digital signal, which is then sent to a higher-level monitoring PC for remote configuration. The measurement curve can be viewed on a PC, allowing one to identify any disturbances, determine their location and the extent of their impact. It is also possible to activate an automatic disturbance suppression function, thereby enhancing the reliability of the measurement accuracy. https://p26.toutiaoimg.com/origin/tos-cn-i-qvj2lq49k0/4ad623969267445aaae3ac30080fd345?from=pc 2. Multi-channel measurement system: The multi-channel measurement system is shown in Figure 3. The analog output signals from multiple radar level gauges are digitized and transmitted through interface modules and converters, before being connected to the upper-level monitoring bus system. The upper-level monitoring PC configures and transfers data with each radar level gauge via the bus, using the different address bits of the interface modules. https://p26.toutiaoimg.com/origin/tos-cn-i-qvj2lq49k0/f8b6ffd2b8dd4e21a6a6014f7bd71154?from=pc 3. Multi-channel digital measurement systems: In addition to the 4–20MA output mentioned above, radar level gauges can also be selected in models that come with digital output connectors. Connect the radar level gauge output to the field bus. Radar level gauges with digital outputs are used, which ensure high measurement accuracy during data transmission. Segment couplers are employed to electrically isolate the measurement bus from the output bus, thereby enhancing the system’s safety and resistance to interference. 4. Selection of the range for radar level gauges: Under normal circumstances, the range of a radar level gauge can be chosen based on the following three situations. 4.1 When the liquid surface in the tank is stable: For media with a dielectric constant of less than 1.4, the maximum range is 5M ； For dielectrics with a dielectric constant greater than 1.4 and less than 4, the maximum range is 10M ； For dielectrics with a dielectric constant greater than 4 and less than 10, the maximum range is 15M ； For liquids with a dielectric constant greater than 10, the maximum range is 30M. 4.2 When there are ripples on the liquid surface of the storage tank: For media with a dielectric constant of less than 1.4, the maximum range is 3M ； For dielectrics with a dielectric constant greater than 1.4 and less than 4, the maximum range is 5M ； For dielectrics with a dielectric constant greater than 4 and less than 10, the maximum range is 10M ； For liquids with a dielectric constant greater than 10, the maximum range is 15M. 4.3 When a wave-stabilizing tube is installed inside the storage tank or a bypass tube is installed outside the tank, since the microwaves emitted by the radar level gauge propagate downward along the tube walls with minimal energy loss, the maximum measurement range can be appropriately increased. IV. Installation Method: During installation, it is important to ensure that the central axis of the transmitting antenna is perpendicular to the surface of the medium being tested, and that there is at least a 20 CM distance between it and the tank walls. Avoid installing it at the center of the storage tank, as this will enhance false echoes. Try to avoid interference sources such as the feed inlet and agitator ； Try to avoid vibration, high-pressure cleaning, and lateral loads. Radar level gauges can be installed directly on the top of the tank using threads or flanges, or they can be mounted on the top of a guide wave tube or bypass pipe. Compared with traditional level gauges, it has the following advantages: easy installation and low installation costs. When used for measurement in the tank areas of refineries, it can be installed directly under the conditions of crude oil present, without the need to empty the tanks, thus saving time and costs ； Low maintenance costs, virtually maintenance-free, requires few spare parts, reduces labor intensity, and improves production efficiency ； Intelligent, high-precision, reliable in operation, and powerful in functionality. It features self-check, interference suppression, real-time display, checking of output current values, and artificial simulation of an output level gauge. Outputting digital signals enables communication and ensures system upgrades.