NI 9213 module connected to cDAQ9189 Chassis: Getting noise in thermocouple data

[SmitaSingh]

Hi all,

I am facing a pretty annoying problem that has been consuming most of my time over the past days. My configuration is a cDAQ 9189 with a 9013 TC module and using flexlogger to record the data

now when I am using the thermocouples to connect to the controller of my furnace there is no noise in the controller's panel. But when I am placing 20 more thermocouples inside the furnace and connecting it through the NI DAQ there is lot of noise in data. I have attached the graph.  Can anyone guide me how to reduce the noise?

[SmitaSingh]

I have not connected the com to the groud or negative terminal of the DC power supply. Could this be the reason for the noise in my data?? and also I am not shielding my thermocouples. 

 If this is the reason how to connect COM to to the ground or DC power supply? there are two port in COM. So do i have to short the teo port n connect the grounding cable to the negative terminal of COM Port ?