E-Zine May 2013
There are a number of radar contact level measurement sensors available including dual-element, coaxial, and single-element sensors. Sanitary sensors are also available.
Dual-element sensors generally consist of two parallel rods separated by a spacer whereby one rod guides the radar signal to the surface of the material while the other rod guides the return signal to the transmitter. The coaxial sensor is a variation of the dual-element sensor where the concentric section takes the place of one of the rods.
Both dual-element and coaxial sensors are available in rigid or flexible designs. The accuracy of flexible sensors is generally inferior to that of rigid sensors. However, flexible sensors are generally often in longer lengths where the shipping and handling of rigid sensors tend to be problematic.
Single-element sensors emit radar energy near the base of the rod into the vapor space of the vessel. Some of the radar energy is absorbed by the material and returned to the transmitter via the rod. Materials with relatively high dielectric constants are generally required in order to obtain reflected signals that are sufficiently strong to achieve reliable measurement.
Excerpted from The Consumer Guide to Capacitance and Radar Contact Level Gauges