Learn about tank level sensors

Overview

There are a number of sensor options for automatically sensing liquid levels. Below we layout the fundamentals of each.

Submersible pressure level sensor

A cabled sensor is immersed and sits at the bottom of the liquid. An internal diaphragm in the sensor is deformed in proportion to the pressure of liquid above.

Submersible pressure level sensor
  
Submersible pressure level sensor in tank

 

Accuracy Suitable for Pros Cons
Fair. 10-20mm for 5m tank. Most liquids including water, fuels, chemicals. Inexpensive, easy installation. Contacts liquid, has a cable, may require calibration for non standard liquid densities.

Ultrasonic sensor

Emits a sound pulse which reflects off the liquid surface then measures the time taken for the echo to return to the sensor.

Ultrasonic sensor
  
Ultrasonic sensor in tank

Accuracy Suitable for Pros Cons
Excellent. 1-2mm for 5m probe. Most liquids, non- enclosed tanks/water bodies, liquid surface must be clear of obstruction. Non-contact, compact, low power, accurate, does not need calibration, no moving parts. More fiddly installation than pressure sensors, susceptible to condensation on the sensor surface in enclosed tanks, minimum distance from sensor to liquid.

Radar Sensor

Emit a microwave beam which is reflected off the liquid surface subtly changing the frequency, and this is used to measure the distance between the sensor and liquid surface. 

Radar sensor  Radar sensor in tank

Accuracy Suitable for Pros Cons
Excellent. 1mm for 5m probe. All liquids, all tank configurations, can handle surface foam and particulates in air. Non-contact, accurate, insensitive to condensation or buildup on sensor, insensitive to liquid surface foam, no minimum sensor distance, can be installed near tank walls, no moving parts. Expensive, more power required compared to other sensor types, more fiddly installation than pressure sensors.

Pressure Transducer

Works the same as the submersible level pressure sensor but installed into a liquid pressure pipeline after the tank offtake/shut-off valve and not in the tank.  

Pressure transducer Pressure transducer in tank 

 

Accuracy Suitable for Pros Cons
Fair, 10-20mm for 5m tank. Most liquids including fuels, chemicals, pressure pipe installation only (tank offtakes). Inexpensive, no cables in liquid, insensitive to condensation/liquid foam/turbulence/tank obstructions, no minimum sensor distance, not installed on top of tank. Requires access to tank pipe offtake.
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