No longer is instrumentation required to just provide a variable or have the ability to be calibrated remotely, they are now being asked to provide diagnostic information. Radar level instruments have supported diagnostic functionality for over 10 years, but this has generally required someone to interface with a laptop. Moreover, the only time a problem was realized was when the instrument was in error mode. Process plants want instruments to be equipped with diagnostics that offer predictive capabilities. They want an instrument to let them know something is wrong in advance of a signal loss. Advanced diagnostics do just that.
This post will focus on the diagnostic capabilities of guided wave radar. While it is a contacting technology they are becoming more popular for just that reason. The energy is “guided” along an antenna and there is no longer the concern with loss of energy through the tank head space. Being a contact technology, however, they are susceptible to coating or bridging. This is true for any guided waver radar instrument.
Manufacturers have come up with ways to mitigate coating of the waveguide. It is common to use a Teflon coating for sticking applications. This tends to shed product better when compared to a metal surface. However, coating can still occur and you want to know this.
Signal Quality Metrics (SQM) is a technology that provides advanced diagnostic capabilities. It continuously compares the strength of the signal from the surface to the background noise. Over time, this ratio will change as more coating occurs. At a predetermined gain difference, the instrument will produce an alert, advising the user to interrogate the instrument. With asset management software, it will specifically tell technicians what the problem is. An echo curve can be produced which will show the instrument is loosing its signal.
No longer is coating only realized when the instrument has lost it signal (leaving you without a valid level measurement). You now have the ability to be alerted when a signal loss may occur. This allows for time to be scheduled to mitigate the problem and keep the process online. Advanced diagnostics are a great additional to an Reliability Centered Maintenance (RCM) program.
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