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sbRIO 9606 communication dropout

Hello,

 

I have been having issues with my sbRIO-9606 and NI9683 GPIC set up when operating a switching power converter. When the voltage is high, the sbRIO loses communication with the computer I am using to program. That is, the ethernet communication drops out. The converter is floating and all the analog signals are isolated. I have follows the guidelines of differential signal connection to the GPIC AI to minimize common mode noise. The sbRIO chassis is solidly grounded to the earth ground. The power input is floating. The switching frequency is 2.5kHz. The analog and digital PWM signals are not isolated due to the power module/gate driver I am using.

 

I have noticed that if I ground the power ground of the sbRIO/GPIC, the issue is a bit better, that is I can go to a higher voltage without losing comms but problem still persists.

 

Has anybody experience this issue before? Any ideas on what other measurements I can make or solutions I can try?

 

Thanks you reading.

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Hey,

 

What voltages are you sending to the sbRIO? Also, what happens if you tie the negative terminal of everything that is currently floating to a common ground with the sbRIO? 

Britton C.
Senior Software Engineer
National Instruments
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The voltages coming to the GPIC 9683 are in +/-10V range.

 

I have not tried tying the AI- points to earth ground yet. I would like to avoid doing this to maintain the differential nature of the signals.

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Hey,

 

It sounds like it might be an issue with the way the system is wired. Try connecting both AI+ and AI- to ground through aroudn 50k resistors as is described in this article.

 

Field Wiring and Noise Considerations for Analog Signals

http://www.ni.com/white-paper/3344/en/#toc3

 

 

Britton C.
Senior Software Engineer
National Instruments
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The NI 9683 already implements pull down to ground. See page 8 here>>    http://www.ni.com/pdf/manuals/375960b.pdf

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Hey,

 

You're right, that wouldn't be a good idea. If you just hook a 10V p-p sine wave up to the sbRIO, do you see the same behavior?

Britton C.
Senior Software Engineer
National Instruments
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Negative, communication drops when converter is switching

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Hey, 

 

Since we don't see the behavior with normal 10V signals, it's possible that your converter is creating some transients that could be going outside of the acceptable voltage or current range for the 9606 and causing issues. I would scope your signal to see if that's the case. 

 

I would also check to see if just ethernet communication is going out, or if the entire sbRIO is going offline by having it regularly log something to a file on the sbRIO. By checking the log, you should be able to see if only communication was lost, or if the entire device stops.

Britton C.
Senior Software Engineer
National Instruments
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FYI, additional communication regarding this issue is occuring here.

Spex
National Instruments

To the pessimist, the glass is half empty; to the optimist, the glass is half full; to the engineer, the glass is twice as big as it needs to be has a 2x safety factor...
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