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