How Are Storage Tank Levels Measured?

Measuring fluid levels in storage tanks is a critical part of operations at oil fields, refineries, manufacturing plants and other industrial sites. Accuracy and reliability are essential, particularly in the face of increasingly strict process control and custody transfer requirements. Below, we take a closer look at the different methods for measuring storage tank levels.

Sight glass

Sight glass is one of the simplest and oldest methods for measuring storage tank levels. While transparent windows do offer a general estimate of tank levels, they’re loaded with limitations. For example, clear materials are often weak and prone to failure. Build-up of scale and other debris can also obscure visibility.  

Floats

The float method uses a buoyant object to measure tank storage levels. A mechanical device is attached to the float to record its position and reveal tank levels.

Hydrostatic devices

Displacers, differential pressure transmitters and bubblers are all examples of hydrostatic devices used to measure storage tank levels.

Load cells

Also known as strain gauge devices, load cells use sensors to detect structural changes in a mechanical support bracket. The technology is based on the idea that the support bracket flexes as the force load changes. Data is then used to measure storage tank levels.

Magnetic level gauges

Magnetic level gauges use the same principle as floats, with the addition of magnets. The float is fitted with a set of magnets and placed in an auxiliary chamber attached to the storage tank. The float moves up and down according to fluid level and the attached magnets relay this information to a magnetised gauge.

Capacitance transmitters

These devices are based on the principle that process fluids usually have dielectric constants that are easily distinguishable from air. For example, the dielectric constant of diesel fuel is around 2.1 while the dielectric constant of air is 1.0. Capacitance transmitters measure storage tank liquid levels based on changes in capacitance.

Magnetostrictive level transmitters

This next-generation technology builds on the concept of magnetic level gauges. The transmitters measure torsional wave speeds to detect the float and calculate tank levels.

Ultrasonic level transmitters

Ultrasonic level transmitters are another cutting-edge solution. The technology uses ultrasound pulses to calculate the distance between a transducer device and the fluid surface.

Laser level transmitters

Laser transmitters are based on a similar principle to ultrasonic level sensors. Though instead of using ultrasound pulses, they rely on the speed of light. They’re ideal for opaque liquids, as well as slurries and viscous materials.

Above, we’ve covered some of the different methods used to measure storage tanks levels. For more information on other factors to consider, including preferred storage tank designs and materials, don’t miss ‘Storage Tanks for Oil & Chemicals - Everything You Need to Know’.