Measuring tank level with ultrasound, from above or from outside
, 5 min read
A top-mounted ultrasonic sensor measures the distance down to the liquid surface and subtracts it from the tank height. An externally mounted sensor is pressed against the outside of the tank bottom and measures the liquid column through the wall, so the tank is never opened or drilled.
Top mounting
Mount the sensor vertically above the liquid, away from the inlet stream, ladders and the tank wall, so the beam reaches only the surface. Keep the full-tank level outside the blind zone. Foam, heavy condensation and strong vapour weaken the echo; a narrow-beam sensor helps in tall, narrow tanks.
External mounting through the wall
An external sensor couples ultrasound through the tank bottom with a coupling pad or gel. The pulse travels up through the liquid and reflects off the surface. Because nothing touches the contents, it suits sealed, pressurised and hazardous tanks such as LPG cylinders, fuel tanks and chemical containers. The wall must be solid, and the liquid must carry sound well.
Waste bins and solids
Fill-level sensors under the bin lid measure the distance to the waste and report percent full over a low-power network. Uneven heaps reflect sound irregularly, so sensors average several readings and use a wide beam.
Alternatives
- Submersible pressure level transmitters, when the tank can take a probe and foam or vapour block ultrasound
- Radar level sensors for very tall silos and difficult vapours
- Float switches for simple high and low alarms