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Noisy downward voltage spikes from NI 9215 - Analog input

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Hi, I'm using an NI 9215 module to measure the differential voltage from a 9V battery.  Three of the four channels show random downward spikes, only the last ch3 signal is within spec. 

 

Different slots and two different 9174 chassis were used, same results as shown were produced. 

 

The module was just calibrated by NI. 

 

Any help? 

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Accepted by topic author kevin_lu

My immediate guess is a grounding issue.  Did you put in a bias resistor to COM on your negative channels?  The BNC version has this built in.


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Should've read the user manual Smiley Sad


@crossrulz wrote:

My immediate guess is a grounding issue.  Did you put in a bias resistor to COM on your negative channels?  The BNC version has this built in.


 

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