Intelligent Signal Processing Overcomes Challenge of Tank Obstructions Impacting Level Measurement Accuracy

One of the most challenging applications for non-contacting radar level transmitters has traditionally been providing accurate and reliable measurements in tanks with internal obstructions. These obstructions include agitators, heating coils, pipes, ladders, or baffles. That is because structures such as these can reflect microwave signals, creating what are known as false echoes. This then makes it difficult for a radar transmitter to identify which is the genuine echo from the material surface. Distinguishing between genuine echoes and false echoes from obstructions is crucial. However, in an Instrumentation Monthly article, ‘Ensuring Accurate and Reliable Level Measurements in Tanks with Obstructions’, I describe how Emerson’s patented Smart Echo Supervision™ intelligent signal processing technique is now overcoming this challenge.

Internal obstructions in tanks have traditionally made it challenging for non-contacting radar level transmitters to provide accurate and reliable measurements.

When a radar transmitter interprets a false echo as a genuine surface echo, it results in an inaccurate level reading. This can have serious consequences, such as an overfill and subsequent spill. Such incidents could endanger personnel and cause costly environmental harm. Furthermore, inaccurate readings can lead to tanks being underfilled. This can disrupt production schedules, cause product shortages, or lead to inefficiencies in downstream processes. Some other effects are compromised product quality and reduced process efficiency. The article explains that certain measures can be taken to mitigate these challenges. It states:

…The first thing to consider should be the position of tank openings. If there is an existing nozzle located with an entirely unobstructed view to the product surface, then it is obviously best practice to position the radar device there. However, it is rarely the case that a nozzle will be ideally situated, which means that other solutions are required.

Some technology vendors recommend using deflector plates. These are typically installed at angles, close to tank obstructions. They redirect and dissipate radar waves that would otherwise reflect from these objects back to the transmitter. By eliminating these echoes, a transmitter can more easily distinguish the true material level. However, as the article explains:

…installing deflector plates can be challenging, especially in tanks with limited access or high complexity. Plates positioned incorrectly can cause unwanted reflections or even block part of the radar beam, resulting in signal loss or creating ‘blind spots’ in the measurement. In addition, if the tank contains sticky, viscous, or dusty materials, build-up on the plates can alter the angle of reflection or create false echoes.

Another means of mitigating the effects of tank obstructions is false signal suppression, which involves the user ‘telling’ the radar transmitter which reflection is the genuine surface echo. The transmitter can then create a threshold that blocks false echoes from being considered as valid. This can be effective but as the article points out, it has its limitations:

…To ensure all false echoes are managed, the tank should be emptied so the device can see them. Having to empty the tank is an inconvenience that can needlessly prolong the commissioning process. Also, we know that the character of echoes from obstructions can change over time. This can happen, for example, with changes in the vapour space of the tank, changes in temperature and also from coating from the process. Because the device creates the threshold based on current echo characteristics, when those echoes change, the threshold setting the device originally created may no longer be sufficient to exclude a false echo from consideration. This could reintroduce an inaccurate level measurement with the associated risks described above and would require having to empty the tank to rerun false signal suppression.

In Rosemount non-contacting radar level transmitters from Emerson, Smart Echo Supervision intelligent signal processing technology automatically identifies and suppresses false echoes caused by internal tank obstructions, enabling the real product surface to be accurately and reliably measured.

The article goes on to describe how Emerson’s Rosemount™ non-contacting radar level transmitters utilise Smart Echo Supervision. This provides accurate and reliable level measurements in tanks with obstructions. It does so without the complexity of having to install deflector plates or run false echo suppression. I explain that this technique:

…dynamically evaluates the behaviour of all viable echoes in real time. It then ranks all the echoes according to which behave the most like a material surface echo over time. The echo that most behaves like a reflection from the material surface is then tracked as the genuine surface echo, and all other echoes are automatically suppressed. The technology continually adapts to changes in the echo profile, which can happen as the surface level changes or as tank conditions vary.

This enables Smart Echo Supervision to reduce or even eliminate the need for any type of intervention against false echoes. Should intervention be required, this can be performed quickly and easily from the control room simply by selecting and suppressing a false echo on a graphical user interface.

Rosemount non-contacting radar transmitters with Smart Echo Supervision make it easier to achieve reliable and accurate level measurements. This provides end users with confidence in data. It results in safer and more efficient operations. To learn more about Smart Echo Supervision, visit www.Emerson.com/RosemountNonContactingRadar.