thermocouple NI daq setup problems

I am trying to get thermocouple reading on my National Instrument PCI-6034E DAQ card with a CB-68LP. I can't seem to get a stable temperature reading. So i tried using a AD595 to see if there is some sort of amplification needed to help. After setting it up, i still experience a fluctuation. Within a 0.8 degree celsius range. But when i connect this to a regular multimeter it gives a stable reading. What can i do to stabilize the temperature reading from the NI equipment?

I think you will find that you do need the thermocouple amplifier; this solves a lot of problems with interfacing that you would have difficulty overcoming otherwise. The darned things are expensive though!

OK, well, in order to ensure your thermocouple readings are stable you have to make sure that the thermocouple wires go all the way back to pins 1 and 14 on the amp. Any connections along the way have to be supported by type K (I'm assuming type K...) connectors - the pins on these are made from the same alloys as the thermocouple wires themselves, specifically nickel/chromium and nickel/aluminium (K type!). It can be quite hard to identify which of these is which but obvioulsy the polarity has to be observed all the way along the chain.

The data sheet for the 595 has some more in-depth information about how the cold junction is maintained at the local (amplifier) side and is also quite specific about how the PCB should be laid out to ensure stable performance.

Also, thermocouples are notable for their simplicity and robustness especially at high temperatures. Not so much though for their accuracy, although this can be quite good depending on how well made they are...

It's a bit of a tricky art really. I'm sure that there are many time served industrial engineers that would have far more useful input than I've given here, I'm simply relaying the experience I've had recently in building a reflow oven.