SLW conductivity level switch is based on the principle of measuring level through the electrical properties of the process material. As the name suggests, conductivity based level switches and sensors sense the level of water or other conductive liquids that have free ions.
These switches are successfully used in processing plants for conductive liquids of conductivity not less than 25μ Siemens.
A low AC voltage is applied between the probe electrode and the tank wall (or reference electrode in case of insulated tank). When the liquid comes in contact with the electrode tip, a conductive path is established between the sense electrode and the tank wall / reference electrode. This current is sensed, amplified and made to operate a relay whose contacts in turn can be used for annunciation / control.