Level Sensors

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

Pressure Sensor.jpg

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.PNG

Type

Pressure sensor  

Accuracy

Fair. 10-20mm for 5m tank.

Suitable For

Most liquids including water, fuels, chemicals

Pros

Inexpensive, easy installation

Cons

Contacts liquid, has a cable, may require calibration for non standard liquid densities

ultrasonic sensor.jpg

Ultrasonic Sensor

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

ultrasonic level sensor open tank.PNG

Type

Distance sensor

Accuracy

Excellent. 1-2mm for 5m probe

Suitable For

Most liquids, non enclosed tanks/water bodies, liquid surface must be clear of obstruction

Pros

Non contact, compact, low power, accurate, does not need calibration, no moving parts

Cons

More fiddly installation than pressure sensors, susceptible to condensation on the sensor surface in enclosed tanks, minimum distance from sensor to liquid 

radar level sensor.PNG

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 level sensor diagram with foam.PNG

Type

Distance Sensor

Accuracy

Excellent. 1mm for 5m probe

Suitable For

All liquids, all tank configurations, can handle surface foam and particulates in air

Pros

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

Cons

Expensive, more power required compared to other sensor types, more fiddly installation than pressure sensors

Pressure Transducer cabled.PNG

Pressure Transducer

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

pressure transducer sensor.PNG

Type

Pressure Sensor

Accuracy

Fair, 10-20mm for 5m tank.

Suitable For

Most liquids including fuels, chemicals, pressure pipe installation only (tank offtakes) 

Pros

Inexpensive, no cables in liquid, insensitive to condensation/liquid foam/turbulence/tank obstructions, no minimum sensor distance, not installed on top of tank

Cons

Requires access to tank pipe offtake