Ridding those Pesky Ground Loops and EMI Problems

From my RSS feed, an Automation World article, Wireless Eliminates Ground Loop Noise, caught my attention. It brought back memories of being a systems engineer on offshore oil and gas production platforms. These platforms are huge steel structures and as such, have a nice solid ground.

These structures also act as antennas for electromagnetic interference (EMI) from the starting and stopping of large motors and generators. I became very familiar with the filtering features on the inputs to the automation systems we had at the time.

Unfortunately, I didn’t then know ModelingAndControl.com‘s Greg McMillan who pointed out some downsides with signal filtering:

…signal filtering can be used to smooth out the noise but this adds a lag that reduces the ability of the flow loop to deal with pressure disturbances and valve issues.

The article identifies what will warm the hearts of Electrical Engineers but may be overlooked by other engineers:

What’s more, the tests turned up an added bonus. “Because the wireless transmitters are battery powered, this totally isolates them from spurious ground-loop potentials that get introduced into any reaction vessel from a number of different sources, and which drive pH sensors crazy,” Broadley observes. During the test, when a ground-noise-induced spike appeared on the wired pH signal, it was not present in the wireless transmitter output.

I know how much time I spent chasing spurious, phantom issues caused by EMI or ground loops on onshore facilities. I imagine a few of the plant engineers who come upon this post, may have similar stories to tell. For some plants, this may turn out a bigger advantage than the wiring savings or trapped diagnostic information in HART field devices.

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