E-Zine February 2013
Capacitance level sensors have many sizes, lengths, shapes, and electrical properties to measure the level of the many varied materials that are located in vessels with widely varying geometry. Sanitary sensors are also available.
The most common sensor design incorporates a metal rod with an electrically nonconductive coating such as Teflon. When a conductive material covers the sensor, the transmitter measures the capacitance that is developed between the covered portion of the rod and the material.
A common sensor for non-conductive materials is a metal rod surrounded by a metal cylinder (with passages for the material to enter/exit the annulus). In these applications, the transmitter measures the capacitance developed between the rod and the cylinder as a result of non-conductive material filling of the annular space between the rod and cylinder.
Flexible sensors are available for longer lengths where the shipping and handling of rigid sensors tend to be problematic. The accuracy of flexible sensors is often inferior to that of rigid sensors.
Excerpted from The Consumer Guide to Capacitance and Radar Contact Level Gauges