Principle of Operations
The probe of the Pump Protection Switch forms one plate of a capacitance circuit, with the vessel wall making the second plate. The dielectric constant of the product between the probe and the vessel wall will cause a change of capacitance as the level approaches the probe. The change is detected, amplified and used to switch a relay for indication or control purposes. A special circuit is used to ignore product build-up between the sensing probe (active element) and guard, and also between the guard and vessel wall.

Primary Area of Application
The switch has immunity to build-up and monitor materials with a wide range of dielectric constants, so the system is applicable to a large variety of liquids.