grounding unused pins of DAQ

[Monireh]

Hello,

I am using ni USB DAQ 6008 for my project; Shall I connect the pins that I don't use to ground?

Looking forward to hearing from You

                                                           M

[RavensFan · Accepted solution]

It shouldn't be necessary.

Although if you actually include a channel in your data acquisition that is not connected to anything, you might read a ghost image of the previously read channel when you go to read the unused channel.  In which case grounding the unused channel would prevent that.

But then why would you set up a DAQ task that reads a channel that isn't connected?

[Clint1000]

I'm using a PXI6229 to measure (DAQ Assistant,AI9 ,RSE,100 samples, 1 kHz) the wiper on a 500 ohm pot.  the voltage goes from 1-9 vdc based the wiper position.  The pot is in a UUT fed to my test set thru a mil connector.    I have a 22 g wire. going form a mil connector to the scb68 pin 66.  The ground from the supply voltage that feeds the outer legs of the pot go from the mil connector to the scb 68 gnd.  If I look at the graph in DAQ Assit I have a 400 mv ppk, 60 hz signal.  This  causes the average value (DC) to jump all over. An earlier post asked if unused channels should be grounded...should they??  I'm picking up 60 hz noise from somewhere.  I know I haven't explained everything in the test set but if I pull the connector off the daq card that goes to the scb68 the noise is still there.  Could the PXI chassis couple noise onto the DAQ??

Thanks..

[even-And]

For future reference, I recommend creating a new thread rather than commenting on an old one. New threads receive more visibility and in turn more comments. 

Unused channels do not need to be grounded. If you're picking up a 60 Hz noise from somewhere I'd check the power supply. Noise from a power supply is around the 60 Hz range

[Clint1000]

Thanks Steve...most times I get responses from old threads..I will create a new one in the future.

The power supplies are clean.  The problem we are having is the noise is intermittent.  So its going to be fun to troubleshoot.  One time we did see the noise I grounded one of the channels we brought out to banana jacks and it went away.  Now the noise is gone so I can see if that ..grounding ..will always work.  Any additional info would be great.  I also have been in contact w a National App Engr.

Clint