Sanderscj,
    The input signal to the plc needs to be converted (obvious statement i know) the 0-9.9v sounds a bit unusual to me. I suggest if you have 24v dc available at the application, contact your local instrument and process control company ( look for one flogging thermocouples in thier ads. They can sell you a "2 wire hockey puck " unit which will give you 4- 20 ma . Run this through your plc input ( IF IT IS ISOLATED ) with a precision 500ohm resistor (ie < 1%) hooked in parellel across the input terminals.
    If the unit is not an isolated input talk to the instrument company they will have a suitable signal converter. The PLC manufacturer may have an input card to suit.
   What brand is the plc. You will not get a reading from the A/I terminals for a thermocouple. What temps are you measuring NEC have a chip thats good to about 50C.
Let us know how you go.
regards Don

Suggestion: Generically, a voltage amplifier is meant to amplify the voltage. Check manufacturer products over
http://www.thomasregister.com
for a possible thermocouple - plc finetuned set.