Here is the situation: a grain handling company in Minnesota needed level measurement for a cluster of eight grain silos. This seemed like a usual, run-of-the-mill request. However, the cluster consisted of six 120 foot tall concrete silos that were arranged in such a way that they formed additional storage, which resulted in two interstice or star-bin silos. Narrow tall silos present problems of their own, but the more complex geometry of interstice or star-bin silos is truly a challenge for most radar transmitters operating around 25 GHz.
Because the silos are narrow, the fill stream also can take plenty of the free space available in the silo and doesn’t leave a clear path for the propagating signal to make a consistent level measurement. Another common challenge these days is that technical personnel can’t spend hours optimizing level instruments. Thus, easy to install and configure instruments are a must.
In this particular case, the instrument supervisor on-site needed a level solution for the silo cluster, and coincidently, one of the instrument technicians was familiar with the SITRANS LR560 radar transmitter from a different location and simply suggested to the supervisor to use them “because they work.”
When the salesman later checked with the grain handling facility to see how things were going with their new radars transmitters, the instrument supervisor said that all were working fine except one. The level on one of the silos seemed to be stuck at 70% high. The salesman offered to come to see what was preventing the radar transmitter from reading the correct level. The plan was to show them how to use the built-in wizards of their radar instruments to help them analyze the echo profile or signal response inside the silo. When there is limited access to physically see what is going on in the silo, you can rely on the software built into the radar instruments to be your eyes. However, when salesman visited the site, the instrument supervisor reported that all the eight units were now working great.
So, what changed?
The instrument supervisor, in the meantime, had checked inside he silo and discovered that there was a support steel beam blocking the signal path of the radar transmitter. All he had to do was to aim the LR560 a couple of degrees away from the obstruction to avoid seeing the support beam. This is what you get when a level transmitter that has a narrow transmission signal having just 4 degrees of signal spread. Not only can it easily ignore obstructions but the signal is narrow enough that the fill stream and the radar signal do not cross paths, even in narrow silos.
Mainstream radar level transmitters, which operate around a 25 GHz, have a broad signal and require extra setup and tuning – even in common cylindrical silos. Narrow, star-shape silos can truly be a challenge if not impossible for these transmitters. The great thing is that the 4 degree narrow signal of the LR560, due to its 78 GHz operating frequency, allows you to install it in difficult level applications and it becomes a simple task…just like a walk in the park.
This is a great benefit, especially when personnel are scarce or busy dealing with every day site operations. Actually, there is nothing simple about the application considering the tight and irregular geometry and obstructions found in cluster silos, but with the right radar instruments, simplicity becomes the norm.