In another non-mechanical sensor called pneumatic fluid level sensor, changes in the pressure of the column of air above the fluid level activates a float level switch. Pneumatic sensors are especially useful when non-contact with the fluid is a necessity: these fluids may be hazardous, corrosive, or highly viscous.
In a conductive fluid level sensor, the fluid level is measured when the electroconductive fluid touches the corrosion- and abrasion-resistant electrodes or probes at the same time to complete an electric circuit. The less electroconductive the fluid, the more power is needed. But overall, the voltage and current involved are relatively low and hence safe. The advantage of this kind of sensor is that it doesnt involve moving parts and is easy to install.
In capacitive sensors, the sensors are electrodes (in a dielectric, e.g., the fluid) that detect changes in capacitance between the conducting plates immersed in the fluid. A detection circuit (the capacitance bridge) allows the capacitance variation to be measured continuously. The change in capacitance is correlated with the fluid level. As the level increases and fills up more of the gap between the plates, the capacitance increases and is detected by the sensor. Like conductive fluid level sensors, it is rugged and has no moving parts. A problem would be static charge from friction that may cause a spark. Debris can also build up around the plates, reducing their effectiveness. Such problems can be countered by good design and sufficient static grounding.