【2025 Level Gauges】Selection of Radar Level Gauge Antennas
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Radar level gauges can perform continuous measurement of different liquid levels. They are suitable for harsh environments such as high temperatures, steam, high dust levels, and volatile gases, as well as for situations with significant variations in dust, temperature, and pressure, where inert gases and steam are present. Radar level gauges can be classified into two types based on their operating principle: contactless and contact-type. 1. Contactless microwave level gauges use horn or rod antennas to transmit and receive microwaves; the gauge is installed at the top of the storage tank and does not come into contact with the medium being measured, with the microwaves traveling and returning through the space above the tank. It is easy to install and requires minimal maintenance, and it is not affected by factors such as the gas composition, dust, or temperature changes in the silo. 2. Contact-type microwave level gauges generally use metal wave guides (rods or steel cables) to transmit microwaves. The gauge is installed on the top of the tank, with the wave guide extending all the way to the bottom of the tank. The emitted microwaves travel downward along the outside of the wave guide; when they reach the surface of the material, they are reflected and return along the wave guide to the transmitter where they are detected.
The following response is for reference only. When a radar level gauge transmits microwaves, it does not require air as a medium for propagation; therefore, changes in the temperature of the medium have almost no effect on the speed of wave propagation. However, the sensor and antenna components of radar level gauges are not resistant to high temperatures; therefore, the temperature in these areas cannot be too high, otherwise they will not function properly. When using radar level gauges to measure high-temperature media, measures such as forced cooling with air or water are required to lower the temperature, or a distance must be maintained between the antenna horn and the highest liquid level to prevent the antenna from being affected by the high temperature. The operating temperature of storage tanks as measured by radar level gauges varies greatly among different manufacturers’ products; it is usually between -40 and 150°C, with some models capable of reaching 300°C.
Radar level gauges are also not affected by air density when transmitting microwave signals; therefore, they can operate properly in both vacuum and pressurized conditions. However, due to the structural characteristics of the level gauge, when the pressure inside the container rises to a certain level, the radar level gauge will experience significant measurement errors; therefore, this allowable pressure limit must not be exceeded. The requirements for the maximum operating pressure of storage tanks vary among different companies’ products as well.
Since the measurement principle of radar level gauges is related to the propagation properties of microwaves, characteristics of the material being measured such as the relative dielectric constant of the medium, turbulence in the liquid, and bubbles can cause attenuation of the microwave signal; in severe cases, this can even prevent the gauge from functioning.