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The Fluid Systems Engineering and Management Blog

by Swagelok Northern California

Nine Common Questions About Process Analyzers

by Jeff Hopkins, on 9/19/18 9:00 AM

The man who wrote the book on sampling systems has the answers

"Connecting a process analyzer to an industrial plant may seem to be a simple task; but really, it’s quite complex. It demands a melding of instrumentation, analytical chemistry, and chemical engineering knowhow, and few people are skilled in all of those technical arts. "

Tony Waters - From the Preface of Industrial Sampling Systems

Tony Waters has heard it all when it comes to problems with process analyzers. His book, "Industrial Sampling Systems," captures the knowledge acquired during a career of more than 50 years of practical experience with industrial process analyzers. Here are his answers to nine of the most common questions he’s encountered:

Q: Why can’t I remove (or re-vaporize) the liquid condensate in my gas sample?

A: It’s because the sample has already fractionated and the gas analysis has changed.


Q: My filter blocks often, so should I be using a bigger filter?

A: Yes, a bigger filter will last longer, but it may cause an unacceptable time delay.


Q: Why is excessive time delay such a common problem with sampling systems?

A: It’s a common problem as time delay is invisible. An analyzer that is "99 percent reliable" may be reliably measuring what happened yesterday!

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Q: Should I use a probe?

A: Most of the time, yes. A probe can exclude some of the solids or liquids in the process fluid, and provide a faster response to process change.


Q: What is the best size of tube or pipe for the sample transport lines?

A: The best size is the one that provides the desired speed, turbulent flow and reasonable pressure drop, without having an excessive flow rate.


Q: Is there software to design sampling systems?

A: Software is useless if you don’t know what you’re doing.

Sampling Systems Book Cover_SM

Industrial Sampling Systems, the definitive reference guide by expert Tony Waters (book excerpt)

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Q: What pore size of sintered stainless steel filter is best to protect an analyzer?

A: Any one you like. They all stop the same size particles!


Q: What’s a key difference between the system design for a filter and for a coalescer?

A: The key difference is you can have a fast bypass flow from a filter, but the coalescer bypass flow must be slow.


Q: What is the most common mistake that people make with analyser sampling systems?

A: The most common mistake is choosing the lowest bidder without having a clear specification of what is to be provided

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