Recently we've had a few level measurement-related posts--one on a refinery desalter vessel application and another on guided wave radar setup, calibration, and diagnostics. To continue on this theme, I've discovered an article, Determining the level best in radar measurement, on the U.K.-based ConnectingIndustry.com website. Emerson's Sarah Parkerhighlights contacting and non-contacting radar level measurement application considerations. She opens by contrasting contacting and non-contacting application fits [hyperlinks added]:
Contacting is generally a good fit for small spaces, and can replace older technology such as displacers and capacitance probes. Non-contacting is usually better for dirty, viscous and/or corrosive applications and when agitators are present. Currently, contacting devices, called guided-wave radar (GWR), are more prevalent because they can provide both interface level measurement (e.g. oil and water), and standard direct level measurements.
I'll highlight just a sample of the guidance she shares. In steam applications over 30 bar (435 PSI):
…end-users should look for GWR systems that have a dynamic vapour compensation method to ensure the accuracy of the device in such an environment.
Where reflected radar signals are weak [hyperlinks added]:
…it is important to select a radar with features such as dual port or direct switch technology, which minimises the losses in the returned signal.
Sarah describes things to consider when choosing a GWR probe type:
Unless a coax-style probe is used, probes should not be in direct contact with a metallic object, as this will impact the signal. Twin and coaxial probes are susceptible to clogging and build up. If the application involves dirty, sticky liquids or those that can coat, then only single lead probes should be used.
Non-contacting radar level measurement is better for more viscous applications like asphalt. GWR:
…is not suitable for extremely viscous products where fluid flow is minimal. If GWR is used with viscous fluids and is installed in a bypass chamber, then the chamber should be heat traced and insulated to ensure fluidity.
You'll want to read the article for Sarah's thoughts on measuring various liquid surface and layer interface conditions, fluid dielectric properties, extreme temperature and pressure environments, safety critical applications, advanced diagnostics, and installation best practices.
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