【2025 Level Gauges】The influence of the pressure and temperature of the medium being measured on the readings of radar level gauges
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This post was last edited by The one on 2025-11-22 10:53. Radar level gauges do not require air as a medium for transmitting microwaves; therefore, changes in the temperature of the medium have almost no effect on the speed of microwave propagation. However, the sensor and antenna parts of the radar level gauge are not resistant to high temperatures; therefore, the temperature of these parts 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 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 function properly in both vacuum and pressurized conditions. However, due to the structure 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. The following reply is for reference only.
The ultra-high-frequency centimeter waves emitted by radar level gauges propagate in a linear manner as spatial waves. When encountering the medium being tested, microwaves undergo reflection and refraction. The degree of reflection is related to the relative permittivity of the medium being tested. The higher the relative dielectric constant, the less loss in reflectivity. If the conductivity of the medium is greater than 10 mS/cm, all of the microwaves will be reflected back; otherwise, any medium will cause reflection and refraction, resulting in a reduction in the intensity of the effective reflected microwave signal.
The relative dielectric constant of a material is a physical quantity that characterizes the polarization of the medium; it is determined by the properties of the material itself, which is why different materials have different relative dielectric constants. Since an excessively low relative dielectric constant can cause effective signal attenuation in microwaves, each radar level gauge has a minimum relative dielectric constant. When selecting a radar level gauge, users must first consider the relative dielectric constant of the material in question to ensure proper operation of the gauge.
Different companies’ radar level gauges have varying requirements regarding the minimum relative dielectric constant, as the value of the dielectric constant is influenced by temperature and electromagnetic fields. Radar level gauges from different manufacturers have varying requirements regarding temperature and electromagnetic fields in terms of their structural design; as a result, their requirements for dielectric constant also differ, generally ranging from 1:5 to 2. However, as engineering experience with these products grows and the quality of the software technologies used improves, some companies’ radar level gauges are able to detect lower values of relative dielectric constant; as a result, they can even measure liquid hydrocarbons with a relative dielectric constant of only 1.2–1.9.
Due to the scattering and absorption of microwaves by liquid turbulence and foam, these phenomena also cause the microwave signal to attenuate, thereby affecting the proper operation of radar level gauges. For this reason, when selecting and installing radar level gauges, it is also necessary to take into account the turbulence and foam in the liquid.
If the liquid level range that the radar level gauge is intended to measure is small, meaning that the path length for the microwaves is short, then even if the microwave signal is attenuated, it can still be measured.