Measuring Level and Volume of Solids

Level measurement is one of the mainstays for the process industries. As technology has advanced over the years from manual measurements including dipsticks, site glasses and tapes to automatic measurement—these advancements have led to improved control, safety, and inventory management.

Emerson's Mark Menezes

Mark Menezes
Measurement Business Manager

Solids-MeasurementLevel and volume measurements of solids pose a unique challenge since the level may have peaks and valleys.

Emerson’s Mark Menezes wrote a Canadian Process eNews article, Solids Measurement Applications-Level or Volume on ways to address these measurements.

Mark describes the difficulty in these measurements:

While the level at one location in the vessel may be (say) 50%, directly underneath the filling point it may be 100%, so additional material cannot be added and the vessel is effectively “full”. Directly over the emptying point, the level may be 0%, so material cannot be removed and the same vessel is effectively “empty” (operators describe this as a “rat hole”). Average level can be anywhere between 0-100%, so it is impossible to judge how much material is actually in the vessel.

The key is to know maximum level, minimum level and total volume. Technologies for measuring solids volume are:

…radar, ultrasonic and sonic (acoustic).

Mark highlights the strengths and gaps of each technology:

Radar provides very fast response to changes in level, making it suitable for closed loop process control and safety applications. The speed of radar is unaffected by changes in the vapor space – humidity, temperature, composition or pressure/vacuum – providing better accuracy than speed-of-sound technologies. With appropriate heating or purging, radar can resist condensation and dusty environments. Radar antennas are available to withstand very high pressures and temperatures, and corrosive environments.

Ultrasonic is appropriate in applications where the vapor space is consistent in composition, and can be temperature compensated to minimize the impact of changing vapor space temperature on the speed of sound.

Sonic (acoustic) is similar to ultrasonic, but operates at lower frequencies. This is useful in the typical dusty solids application, because low frequency sound waves are absorbed less as they travel through dust than high frequency sound waves…

In solids applications, where the objective is to map as much as of the surface as possible, a wide beam angle is preferred. Wider beam angles allow the user to map more of the surface with fewer antennas. Even with wide beam angles, multiple antennas are required to obtain a complete ‘wall-to-wall’ surface map in wide or irregularly-shaped vessels, bins and silos…

Rosemount Multi-Scanner Controller: Continuous System

Rosemount Multi-Scanner Controller: Continuous System

By having a surface visualize with the peaks and valleys and total volume, inventory can be more tightly controlled reducing excess carrying costs. Mark concludes:

The chosen technology – radar, ultrasonic, acoustic, other – would measure levels at multiple points on the surface, and create a map of the surface. The best surface map, with wall-to-wall vessel coverage and the finest detail, yields the most accurate volume calculation and the best visibility to peaks and valleys – but also the highest capital investment. The return on that investment is the ability to better manage solids inventory, reduce safety stocks and minimize inventory costs and risks.

The Rosemount 5708S Volume and Visualization 3D Solids Scanner provides 3D visualization of the measured surface and the ability to connect several scanners into systems to measure larger vessels. The signals are merged together to provide a single view of the entire contents.

Here’s a form to help you evaluate your solids measurement application and connect with a specialist in your world area. You can also connect and interact with other level measurement experts in the Level group in the Emerson Exchange 365 community.