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Upgraded from PCI 6533 to a PXIe 6536

Hello,

 

I have 2 test stations that use the PCI 6533 DIO, I had a a requirement to build another test station and had to go with the PXIe 6536. I am in the process of updating all my VI's that use Traditional DAQ drivers to DAQmx. I have come across a problem that has beaten me up. The code works on the PCI6533 cards. I have taken a Logic analyzer and captured a plot of the good DIO. When I am using the PXIe 6536 would appear to be loaded down or nonexistent when testing a UUT. When no UUT present and I test just the DIO it seems to be there. My question is what has changed between the 2 types of DIO's that would load down a signal like this. There has got to be some line or something that is loading it all down.

 

Any help would be appreciated!!!

 

Scott

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What is the input impendance of your UUT?  Digging through the PXIe-6536, I found a 50 Ohm output impedance spec.  I couldn't find anything similar for the PCI-6533.  So the impedance mismatch is likely your problem.


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Hey Scott,

 

Is this helpful? http://digital.ni.com/public.nsf/allkb/7BE799A204AC77CF86256C3E007593BC

"The output impedance of the NI-6533 will be approximately 15 to 40 Ohms (<20 ohms typical) and the input impedance is 100 kOhms."

 

Here's the data sheet for the 6535-7 family, for your reference: http://sine.ni.com/ds/app/doc/p/id/ds-114/lang/en

Note that the output impedence spec is 50Ω, but input impedence is "High-impedance" (50 kΩ to ground). It's hard to give you much more information without knowing your application though.

Brian Morgan | NI Software Engineer, R&D
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