Bonkers vortex meter spells double trouble

By Greg McMillan and Stan Weiner

Greg: Our April puzzler on why a vortex meter measuring toothpaste went bonkers wasn’t so puzzling for our more experienced engineers, Ronald Bruton and Hunter Vegas.

Ronald: The viscosity of toothpaste is probably too high to get a nice, fully developed turbulent flow, without which you don't get predictable vortices. Even if the Reynolds number indicates fully turbulent flow, it is probably based on a constant viscosity, which would not exist with toothpaste anyway. At best, toothpaste is a Bingham plastic; at worst, some bizarre thixotrope.

Hunter: Now this one was too easy. You need to be well into the turbulent flow regime to generate consistent vortices for the meter to work. With toothpaste's viscosity, it's going to take quite a flow rate to get there! Some interesting things that have created vortex meter headaches: 

1. A drop in process temperature raised the viscosity and density high enough to cause low flow cutout issues where we had none before.
2. Some brands are susceptible to polymer build up problems. The polymer doesn't form on the bar but tends to form in small crevices. On some meters, this can restrict motion or plug sensor ports and after a few days the meter just stops working for no apparent reason.
3. Some meters use piezo crystals that age and after a while start missing pulses and read low.
4. I had one batch of meters develop a weak ground path in the electronics. When a motor (or other AC device) would short in the plant, suddenly all of the meters would begin merrily counting 60-Hz sine waves from the noise floor. Luckily we caught this one in water batching and NOT in production!
5. Vortex meters are a wonderful way to discover unsupported pipe as they are great at counting pipe vibration pulses. (Thankfully a few pipe supports and a noise band rejection adjustment usually eliminated that problem.)
6. Vortex meters make great strainers. I have found Coke cans, oyster shells, and rocks in front of them. (Remember to shine a light into the upstream piping when you clean them out to make certain nothing else is waiting for you when you close it back up!)

Stan: We had a mess of problems--particularly for about the first 10 years after they were introduced. I remember when the president of engineering showed up in my office wanting to know why the meters didn’t work on the big new project. When I later told my boss that the big guy came to me and not vice versa, he still said, “I don’t know why you talk to him. Every time you do, I get in trouble.” I was good at stirring things up. It may be the reason an agitator from a washing machine turned up my office one day for the “agitator of the month” award.

Greg: There were significant improvements in the technology over the next couple of decades but, as per Stevie Ray Vaughan, there were the sources of great blues from the double trouble of an erratic vortex separation and velocity profile by pushing the limit. Sometimes we forgot that a vortex meter has requirements for straight runs upstream that get more stringent at low velocities.

Stan: The rangeability of a vortex meter is based on a meter size that often corresponds to pipe size that is smaller than what is economical in terms of a system pressure drop.

Greg: I am sure there are a lot of great stories, which we didn’t get before the editor in chief’s deadline. It now takes us up to four months to get a reply into Control Talk, so hang in there. The following is an excerpt from an interesting reply to the March puzzler from Dietrich Schilberg.

Dietrich: Just because the temperature starts ramping does not mean the process is integrating. It may in fact be ultimately self-regulating, but with a long time constant (lag). It turns out this doesn't matter much, because you tune a loop the way it first starts to respond.

Stan: Here is also a recent reply from Calvin Burnett to our January puzzler on the shift at high noon.

Calvin: If it's not too late, I had the exact same issue with a mass meter. A contractor decided that the mass meter was a comfortable spot for him to eat his lunch. The tubes don't vibrate at the same frequency with a 200-lb. pipe fitter perched on top.

Greg: Now for a Top 10 List from Jonathan Mertz (son of Glenn Mertz) that every parent can relate to these days:

Top 20 Signs Your Son Knows More about Computers than You

1. You are wired and your son is wireless.
2. Your son is working and living in Silicon Valley with two computer jocks whose girl friends work for software companies. You call to ask why your computer won't do anything. After a long conference, the five of them tell you to shut it off.
3. After one week with the new computer, your 12-year-old is rewriting the game programs because they are too easy.
4. Your 15-year-old is rewriting the control valve sizing programs because the local vendor doesn't understand the manufacturer's version.
5. Your son gets a higher starting salary than you make after 30 years on the job.
6. Your son refuses to work on your system because it is too primitive.
7. Y0ur k1d 5p34k5 1n 1337 4nd y0u c4n7 und3r574nd 17.
8. You use your computer for playing games and he uses it for writing games.
9. You use your computer for watching videos and he uses it for making videos.
10. You find a web site that's really cool and later learn that your son created it.
11. You still use Windows 95 (or 98, or 3.1, or NT) and he is telling you about the expected advancements in Longhorn.
12. Your kid is using operating systems that you haven't even heard of.
13. Your kid has more computers than the rest of the family combined.
14. You use a soldering iron to repair old stereos and he uses it to repair old motherboards.
15. You don't know how many megs are in your son’s terrabyte RAID array.
16. Your son tells you he wants to major in EE and you think he means Elementary Education.
17. You think that when your son is doing peer-to-peer he's talking with friends.
18. Your son asks for Ethernet and when you show him a bundle of 10-base2 coax, you're promptly informed that it's about 15 years out of date.
19. Your kid is studying networking and you wonder why he needs a course on meeting people.
20. Your son can turn off the parental controls faster than you can set them up.

This Month’s Puzzler

Why Did the Electrode Change When It was Inserted?
Why did an electrode in a recirculation line show a change in vessel pH before an electrode inserted into the vessel? Send an e-mail with your answer to The Puzzler, CONTROL questions, or comments to controltalk@putman.net.