i am using pci6221 daq card i am getting too much distortions in input signal

[ASRA]

Hi,

     I need to control the electric rods of a steam boiler and iam using NI PCI-6221 daq card.I have used K type thermocouple and giving its output to the channel AI at pin 68 and pin 34 of terminal block CP -68LP, after signal conditioning from instrumentation amplifier using IC tl084.But the channel is giving constant signal of 10 volts even i have not connected any input to the analog channel.Why is that so?....

• One more thing is that i have got too much distortions when i applied my conditioned thermocouple's output as input to the analog channel AI.

• Tell me should i use input in RSE mode or differential mode?
• Should i use a voltage follower before applying any input to daq card?
• How can i make my signal smooth so that i can do programming on my signal showing temperature?
• My input is voltage and i need to show the corresponding value of temperature (in degree celcius) on my front panel of VI.  

[CWolf]

Rather than setting this up as a voltage task, I would recommend doing a Temperature task.  This will take care of a lot of these things for you.  You should be able to directly connect your K type thermocouple to the pins on the CB-68LP and read the temperature.  Also, how are you handling cold junction compensation?  In the thermocouple task, you will have to select some type of CJC. 

I hope you are able to get better results by setting it up this way.  

Cheers,

Christina