Surge protection on thermocouple inputs

[oldfieldguy]

Didn't find anything definitive in a search here, and I Googled the web, too.

One of my minor stations took a pretty good lightning hit during a recent storm and blew a bunch of I/O cards, all RTD and thermocouple inputs.

Not really in my purview as a power guy, but is there a particular surge suppressor made to be inserted between the thermocouple wire going to the field and the I/O card for our control system.

I found several different surge suppressors for RTD's but I seem to be missing something that will work for the thermocouple circuits. If you have specific models in mind, I'd prefer DIN rail mounting.

old field guy

 

[waross]

Possibly remote transmitters and a 4:20 ma system.
Easy to change I/O cards.
You may be able to ground one lead of the thermo couples.
A close hit by lightning is hard to protect against.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[oldfieldguy]

Bill--

You've mirrored my thoughts so far. Management (and the instrumentation guys) doesn't want to go with remote transmitters because of the complexity of the changeover.

I just had a conversation with the boss bout protection against really close/vigorous hits. I was hoping somebody knew of a DIN-mount device I could put in the control cabinet between the incoming TC lines and the I/O card. Such things are common as mud for other I/O


old field guy

 

[DRWeig]

OFG --

I've had good luck with Ditek, they're mostly into commercial-grade stuff. See what you can see at

http://www.ditekcorp.com,

or get in touch with their tech support guys.

With just a thermocouple (low impedance, small signal), you might be able to get some relief with just a bunch or 15V MOVs across the TC terminals and to ground?

Just my thoughts...

Let us know what you decide on!

Good on ya,

Goober Dave

 

[waross]

Thermo couples are such low impedance that it must be common mode voltages blowing the I/Os.
Put whatever suppressors you can find on the system. The next time you get a close in hit, say:
"Wow. It's impossible to protect against a hit that close!"
And then replace the I/Os and the surge suppressors. grin
Seriously, Goober Dave may have the best answer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[danw2]

What about an intrinsic safety barrier. Although this applies a barrier 'backwards', protecting the receiver from a fault in the field (as opposed to protecting the field device from arcing/sparking due to a fault in the safe/receiver area). Why wouldn't it work?

Of course, an I/S barrier costs almost as much as a low end temp transmitter.

 

[itsmoked]

A barrier would work very well. Nice idea. It doesn't require power either.

Keith Cress
kcress -

http://www.flaminsystems.com