In many cases, through-air will be considered first as most people prefer a non-contact solution. Quality of the signal reflection is always the main consideration: mid-to-high dielectric media, little or no turbulence or foam, few false targets in the vessel, liquids that have a high propensity to coat, corrosive applications that demand noncontact. Larger vessels (>15-20 feet) or where headroom above the vessel is small are more easily outfitted with through-air.
Author - Bob Botwinski