As terminal operators, oil refineries and other facilities with tank farms strive for greater accuracy and control of product movement and inventories, they are increasingly moving toward more sophisticated tank gauging methods, replacing traditional technologies such as float-and-tape. One area showing a lot of promise, while creating a good bit of confusion, is non-contact radar.
Emerson's Andreas Hessel recently published an insightful piece in Flow Control Magazine titled, Selecting the Right Frequency for Radar Level Measurement, In the article, he discusses one of the most confusing parts of the selection process: choosing the right frequency.
Andreas jumps right in by explaining the three main categories. Here's a snippet from the article:
Non-contacting radar instruments using high-frequency (75 to 85 gigahertz [GHz]) technology have been introduced, complementing the low- (6 to 11 GHz) and mid-frequency (24 to 29 GHz) devices already extensively deployed to provide accurate and reliable level measurements.
So this is not a one-frequency-fits-all kind of processes, as he warns:
The different frequency bands are not equally suited to every application, so the strengths and weaknesses of each must be carefully considered in light of how various process conditions can affect performance.
That’s all good to know, but how does a prospective user begin to sort through how this works in practice? He suggests some practical considerations:
…high-frequency microwave signals are absorbed to a greater degree when propagating through a medium, so the signal return is weaker. In level measurement applications, high-frequency radars are more adversely affected by challenging process conditions such as those with condensation, vapor, foam and dust, which again affect the signal return and subsequent accuracy.
This sounds like a strong point in favor of lower frequencies. Rosemount’s two main non-contacting radar product families are the 5400 and 5600. The former is available with 6 or 26 GHz frequencies, and the latter uses 10 GHz.
Rosemount seems to be firmly behind the idea of lower frequencies are better. So what is the appeal of high frequency units? Hessel explains:
High-frequency signals can enable small beam angles using small antennas. A small beam angle is beneficial because it helps avoid obstructions in tanks and vessels. Low-frequency radars can also achieve small beam angles, but they need larger antennas, so a user needs to consider what fitting sizes are available on the relevant vessels.
So it comes down to a basic point: size matters. Low- and mid-frequency units perform better in most situations, but they have larger, bulkier antennas. If the mount is constricted, a high-frequency unit may be a better fit.
When working with a small tank opening, the ultimate question for users may be, are we better off modifying the tank to accept a bigger antenna the better performance delivered by low- and mid-frequency units, or should we get used to the problems we’re likely to encounter with a high-frequency device?
See how others have solved the conundrum. Connect and interact with other level measurement experts in this Level group and in the Tank Gauging group in the Emerson Exchange365 community.
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