Does anyone know if there are available passive trip amplifiers?
I have a thermocouple in field and a digital input to my PLC. The module must convert and set a threshold (basically it's a mV signal). I'll break some specs if I bring power there so I need it to draw necessary power from the DI card.

 

Not sure what you mean with a "passive" trip amp but here are a few of people who make trip amps for thermocouples:

Acromag (http://www.acromag.com/)
Action Instruments (http://www.actionio.com/)
Moore Industries (http://www.miinet.com/products/)
M-Systems (http://www.m-system.co.jp/english/index.html)
Omega (http://www.omega.com/pptst/DRG-AR.html)

William (Bill) L. Mostia, Jr. PE
Sr. Consultant
SIS-TECH Solutions, LP