Electromagnetic flowmeters

[panou]

Hello
I have to install flowmeters in PPE pipes for measuring the flow of HCl(hydrochloric acid) 35%. Should i install the grounding rings as the manufacturer suggest? And also what is the straight unimpeded run at the inlet of the flow sensor? The manufacturer suggest 5xD (sensor diameter). Thanks in advance for your time.

 

[m777182]

I assume that the manufacturers suggest you what to do to save time and money by saving problems that may occur if you do not follow their suggestions. At least they have more experience with flowmeter installations then an individual with maybe one or two instruments in the entire plant.
m777182

 

[panou]

Thanks for your answer m777182.
I suppose that the rings are for achieving the same potential between inlet and outlet of the plastic pipes but i was waiting for a justification.

 

[JimCasey]

The magnetic flowmeter is inducing a microvolt signal proportional to the velocity of the flow in the line (Faraday's principle). If you do not ground plastic pipe properly, it can accumulate static charge that measures hundreds of volts. That's a bad signal/noise ratio. Ground the meter per the manufacturer's recommendations.

 

[Skogsgurra]

Oh? That much?

No. It is not possible when there is a (conductive) liquid in the pipe. The plastic will stay close to the liquid's potential. It is more about keeping the liquid itself on a quiet (ground) potential. A potential of a few 100 millivolts would be just as bad, considering the low signal level.

The rings couls be called "guard rings" and they are there to keep any electric field or field gradients away from the neasuring system.

Gunnar Englund

http://www.gke.org

 

[JimCasey]

Thanks, Gunnar. You are of course correct. Magmeters will only work on conductive liquids, and the threshold value I have seen published is 2 micromhos. The rings protect against static electricity, also against ground potential. ALSO, the rings can serve to help protect the liner from abrasive chunks when the magmeter is being used on a slurry. Almost all magmeters use TFE liners, which are not very abrasion-resistant.