Guided Wave Radar (GWR), although a new technology relative to the industrial level market, has been used successfully in industrial applications for over a decade due to its superior performance, application flexibility, and immunity to changing process conditions. However, even with these benefits, and as is well known to experienced users of GWR technology, all applications are not created equal.
Although several factors can determine the likelihood of success when applying GWR to a level measurement application, most notable is the dielectric constant of the process medium. Process dielectrics range from that of water (very conductive) having a nominal dielectric constant of 80, to very light hydrocarbons (nonconductive) having dielectric constants in the range of 1.4 to 1.7. The effective dielectric constant can be even lower when certain process conditions like boiling, flashing or foaming occur, or when bulk solids are considered. The corresponding “GWR Reflection Coefficients” of these media, which are critical for reliably detecting the process level, range from about 80% for water to less than 5% for hydrocarbons like propane and butane.
GWR is a “contacting technology” because the GWR probe is in direct contact with the medium being measured. Since the signal is “focused” in or around the probe, the primary advantage of having the probe contacting the process medium is that very little energy is lost as the signal travels down the probe. Disadvantages include mechanical issues related to any contacting sensor (such as buildup) and the complications created in the matter of probe selection.