Which sensor type is commonly used to sense through a tank wall for non-metallic contents?

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

Answer: (B)

Unshielded capacitive sensing is the approach that works best for sensing through a tank wall when the contents are non-metallic. Capacitive sensors detect level by measuring changes in capacitance between their electrode and the liquid, which depends on the dielectric difference between air, the wall, and the liquid. When the wall is non-metallic, the electric field can pass through it and interact with the liquid inside, so changes in the liquid level alter the overall capacitance.

Using an unshielded design maximizes how far the electric field extends beyond the sensor into the wall and into the liquid, giving good sensitivity for through-wall, non-metallic contents. Shielded capacitive sensors place a grounded shield around the sensing element, which helps against external noise but also reduces the field’s reach through the wall, making through-wall measurement less effective. Inductive sensors depend on metal targets and aren’t suitable for sensing non-metallic contents through a wall, and ultrasonic sensing, while possible, is generally less direct for through-wall level measurement in non-metallic tanks and can be affected more by wall material and thickness.

So, the commonly used choice in this scenario is unshielded capacitive sensing.