PLC analog comparators

[sanderscj]

I need to incorporate voltage signals from thermocouples into a plc program, but the plc only accepts signals from 0.0V to 9.9V whereas the thermocouple voltages are in mV. Any ideas on how to convert these small voltages into valid signals?

 

[don01]

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 &quot;2 wire hockey puck &quot; 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

 

[jbartos]

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.