SCHE floating electrodes, available in Australia from Alvi Technologies are designed for use in pits, reservoirs, pump shafts and separator plants for liquids.
The SCHE floating electrode consists of an upper section and a lower section with the upper section incorporating an electrode holder and a rod electrode along with one control electrode and one earth electrode for alarm signalling. Alternatively, the rod electrode is also available with two control electrodes and one earth electrode for pre-alarm and main alarm. The lower section of the floating electrode is made up of four floats and stabilising plate.
SCHE floating electrodes normally float on conductive liquids such as water. The electrode is connected to an electrode relay, which supplies it with a low safety voltage. The height of the rod electrode is set in such a way that the two electrode rod tips are permanently under water. The position of the rod electrode can be shifted up or down based on the movement of the surface of the liquids.
Although the two electrode rod tips should be permanently under the liquid, they should be just below the surface of the liquid, so that when a conductive liquid (water for example) is overlaid by a non-conductive liquid (such as oil), a thin layer of the non-conductive liquid (oil) is sufficient to lift the electrode rod tips of the rod electrode from the conductive water layer into the non-conductive oil layer, interrupting the current flowing from the electrode relay via the rod electrode, and therefore activating an alarm.
For instance, if oil flows onto a still water surface following a leak, the exact setting of the rod electrode just below the surface of the water will ensure that an oil layer of approx. 3-10mm thickness is sufficient to interrupt the control current flowing via the rod electrode and activate the alarm.