Signal Conditioning

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Crosstalk between NI SCC AI04 modules

Setup: We have a SC-2345 carrier with two AI04 analog input modules. The grounds (pin 1) of the two modules are tied together externally (and I understand both pin 3s are also connected internally). The grounds are also conencted to AI Sense of the carrier through a 100K resistor. The inputs are both connected to ground through 10M pulldowns.

 

Problem: When one input goes floating, the other has an offset. I calculated the ground would have to change -0.7V to cause the offset. Does anyone have more details on the internal circuitry? Is there a clamping diode or something else from the floating module that could affect our ground?   

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Akeeg,

 

 Thanks for the setup information. How are you measuring this device to see that you have an offset? Additionally, what kind of connecters are you utilizing (it shouldn't make a difference but it would be good to know)

 

If you would like National Instruments to research this further for the internal circuitry of the device, it would be best to create a service request at http://www.ni.com/support because we would need to go through a process to see if hardware information can be released. You are always open to keep this discussion post open in case anybody else in the community has any other input.  

Regards,

Ali S.
Applications Engineering
National Instruments
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