When detecting fluid levels through a tank, which type of proximity sensor would be used?

• A. Inductive
• B. Photoelectric
• C. Unshielded capacitive
• D. Shielded capacitive

Answer: (C)

Capacitive sensing detects changes in capacitance caused by the dielectric material surrounding the sensor. When measuring fluid level through a tank, the liquid’s dielectric constant changes the amount of capacitance as the height of liquid changes. Placing a sensor on the outside of a non-metallic tank works well because the electric field can penetrate the tank wall and interact with the liquid inside.

Unshielded capacitive sensors have a broader sensing field, which makes them more effective for detecting changes through a wall and into the liquid. Shielded capacitive sensors confine the field to the immediate sensing area, which improves selectivity in cluttered environments but reduces sensitivity when sensing through a wall. Inductive sensors detect metal targets, not liquids, and photoelectric sensors require a clear optical path and are less reliable with opaque liquids or complex tank geometries.

So, for detecting fluid level through a tank, the unshielded capacitive sensor is the best choice.