Capacitance Level Switch

A capacitance probe and the vessel wall form a capacitor whose value depends on what lies between them: air, a non-conductive liquid or a conductive one. As the product level rises along the probe, the capacitance changes and the electronics convert the change into a switch point or a continuous level signal. Modern electronics compensate for product build-up on the probe, so the technology works on adhesive, viscous and coating media where floats and forks foul.

Probes are rods for short ranges or cables for tall tanks, up to 32 m, in 316 stainless steel fully insulated with PTFE, PE or FEP for conductive and corrosive media, at process conditions to 64 bar and 200 °C. Mounting is top or side with threaded or flanged connections; gravity weights and tensioning springs keep cable probes straight, and weather covers and display modules are available.

Outputs are SPDT or DPDT contacts for switching, or 4–20 mA, HART, PROFIBUS PA and FOUNDATION Fieldbus for continuous measurement, so the same probe family serves both point and continuous level.

Applications are conductive and non-conductive liquids, adhesive and corrosive media and tall tanks in chemical, petrochemical, food, pharmaceutical, water treatment and general process industries. For a simple point level switch with no product dependence, see the vibrating fork level switch.