Reading AI and thermocouple reading using virtual channels

[sambarvadai]

Hi All
This is the configuration of my apparatus
SCXI 1102- thermocouple readings
PCI-MIO-16E-4 card

i want to read both analog inputs (from a front feedthrough panel) and a thermocouple reading simulataneously. I tried defining the channels as DAQmx global channels and tried to use the specific DAQmx polmorphic VI to read both the AI and the thermocouple reading simultaneously. But it looks like the AI affects the thermocouple reading. When i change the AI, the thermocouple reading also gets erratic(changes to lower values, sometimes even negative). Can anyone help me on this. Im absolutely new to this. Excuse me if the question was pretty trivial. Thanks a million

sambar

[The Crow]

What kind of AI are you reading?

[The Crow]

I think that the problem is in the connection of AI, the method Dadmx will be correct. Probably the PGIA (Programable Gain Analog Input) is saturated by the AI. You can make and adquisition with only the analog input. Send me the result please. Bye

[sambarvadai]

I was using a standard voltage input in the range of 0.2-0.4 Volts. I have connected my analog input to the feed through panel and the ground to the analog ground terminal on the feedthrough panel. For the thermocouples, i have connected them to the CH+ and CH- terminals respectively. Do you think it is some ground problem?

When i use the example given in the Example finder to read thermocouple data (SCXI 1102 thermocouple.vi) things work fine.

Thanks again
sambar

[The Crow]

I am sure that the problem is the ground, perhaps in the AI have a voltage with a virtual o floating ground, and then you have to put two bias resistors connected in parallel with the signal leads of a floating signal source. you can view this in the 6034E/6035E user manual: Multifunction I/O for pci, pxi and compactspci bus computers, probably you have a similary manual to SCXI. Good Luck. Bye

[Spencer S.]

Sambar,

To which pins on the feedthrough panel are you connecting your signal? Make sure you are not connecting it to channel 0. All of your SCXI channels are multiplexed to channel 0 on your PCI-MIO-16E-4. If you are unsure of the pinout of your feedthrough panel, the KnowledgeBase linked below provides this information:

Pinout for the SCXI-1302 50-Pin Terminal Block

Good luck with your application.

Spencer S.