【2025 Level Gauges】The influence of the properties of the medium being measured on radar level gauge measurements
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This post was last edited by The one on 2025-11-22 at 14:24. 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 signals; in severe cases, the gauge may not function at all.
The ultra-high-frequency centimeter waves emitted by radar level gauges propagate in a straight line in the form of 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 waves 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.