Analogue input cards being damaged 1

[simisteven]

I have a problem with a siemens analogue input card sustaining damage. Thermocouple from an injection mould is connected to the AI card. The TCs are in close proximity to the 230v heater wires in same wireway in mould. Faults on heaters sometimes transfer to TC and TC cables carry a surge or spike into the AI card which blows it. Question. Is there any recommended interface that can be put between thermocouple and analogue input card?
I can also be contacted at crowther.steven@gmail.com

 

[ScottyUK]

Run the instrument cables in a separate wireway. Are the thermocouples screened? Screening and separation are both good practice - depending on where you are, separation might well be a code requirement too.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[roydm]

How about using a passive intrinsic safe barrier as you would for hazardous location.
If the thermocouple input is referenced to ground you could use a back to back diode on each wire to ground, The thermocouple voltage is too low to bias the diodes but the accidental AC from the heater would. A potted bridge would accomplish this if you connect each or the thermocouple module terminals to one of the AC terminals and ground the + & - terminals
Hope this helps
Roy

 

[simisteven]

Thanks Scotty and Roy. Unfortunately the common wireway is internal to the mould and cannot be altered. Tight space is a major problem. I would like to use an IS barrier if it can be specced to accept the signal from a thermocouple, so if you can recommend one pse do.
Thanks again for your assistance.

 

[itsmoked]

Here - Let the studying begin:

http://www.mtl-inst.com/products/barriers/index.htm

Note the surge protection devices.


Or:

http://www.am.pepperl-fuchs.com/products/productsubfamily.jsp?division=PA &productsubfamily_id=1542

Keith Cress
kcress -

http://www.flaminsystems.com

 

[simisteven]

Thank you Itsmoked I will follow up on these sites
regards
Steven