A question came into me over at the Emerson Process Experts Facebook Fan Page:
Why are twin lead and single lead probes for guided wave radar used? And what are their advantages over each other?
I turned to Emerson’s Sarah Parker to help me address these questions. Here is Sarah’s response (with my embedded hyperlinks added):
There are 3 basic styles of GWR probes: Coaxial, single, and twin. Of these, the single and twin are available in both rigid and flexible forms [rigid single, flexible single, rigid twin, flexible twin]. The advantage of the coaxial probe is that it will not be impacted by nearby objects or narrow, restrictive nozzles. Plus, it provides a stronger signal, which may be necessary for low dielectric fluids.
The main disadvantage of coaxial probes is that they can get plugged easily with dirty or sticky fluids. The single lead probes work well in applications that tend to coat, but they can be impacted by nearby obstacles that act as false targets. The signal tends to be weaker than the other probes because it is more dispersed.
Twin probes provide a stronger signal than the single probes. Twin probes have spacers at regular intervals to maintain an equal distance between the probes for the entire length. These spacers become areas where materials will build up and cause false targets. This is similar to the coaxial probes, but may be easier to clean.
Choosing the correct probe can impact the long-range performance of the GWR. Consideration needs to be given to the installation, the dielectric properties of the material which impacts signal reflectivity, the overall distance to be measured and the coating or sticking properties of the fluid.