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Bad analog input using laptop, but normal on desktop


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3 replies to this topic

#1 brian6091

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Posted 06 September 2012 - 11:30 AM

I'm using a U6 to record analog input from an battery-powered differential amp (http://www.wpiinc.co.../SYS-DAM80.html). The signal is about 1 V peak-to-peak, and I'm recording on single-ended with one lead connected to AN0 and the other to SGND. When I have the labjack plugged into a desktop computer I see what I expect, but when I plug the labjack into a laptop, I don't see the signal I expect, and I see additional line noise and many harmonics of that (50Hz in my case). This doesn't improve when I plug the power charger for the laptop in. I assume this is a ground issue, but I don't know how to resolve it, and I would like to use the laptop since it is mobile. Any ideas?

#2 LabJack Support

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Posted 06 September 2012 - 12:03 PM

Sounds strange. I assume you mean that you have the output of the amp connected to an input on the U6? What if you use GND rather than SGND?

#3 brian6091

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Posted 06 September 2012 - 12:12 PM

Sounds strange. I assume you mean that you have the output of the amp connected to an input on the U6? What if you use GND rather than SGND?


Yes, that's how I connected it. Connecting to GND rather than SGND didn't seem to change anything.

#4 LabJack Support

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Posted 06 September 2012 - 12:15 PM

What are you using for software? Make sure all applicable settings are the same. Do a basic test with the channel just jumpered to GND to confirm that the U6 input is working up to spec. If you look at the signal voltage with a DMM and Scope, does it look different in the 2 cases?


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