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Different readings on ChA&ChaB - 4227

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Different readings on ChA&ChaB - 4227

Postby BSI » Thu Mar 06, 2014 4:57 am

Hi,
I am working on an application where I need to acquire a given signal simultaneously on both channels A and B. I use a BNC splitter and BNC cables to connect to the digitizer. To test out the signal I apply a 5 V square wave on the split inputs.

I have noticed a discrepancy between the reading on both channels. Swapping the BNC inputs does not change the signals I am getting. I tried three 4227s, acquiring data using the SDK via LabVIEW, and also directly with Picoscope 6. Below is what I get:

Pico2Channels.jpg
Graph 1 shows difference between ChA and ChB, while Graph 2 shows the same signal with another 4227.
The third digitizer gave again another discrepancy more or less like the one on graph 1.


I would expect the two channels to give me something very much identical unlike what I am seeing. Any idea?
Thx

Laurent
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Re: Different readings on ChA&ChaB - 4227

Postby Martyn » Fri Mar 07, 2014 11:57 am

Would it be possible to post a psdata file for a single waveform for each of the examples. This will help us see the full settings for the scope.

Trace 1 does look as if it may be within specification so possibly no a problem. Trace 2 is more interesting and would require closer investigation, there may be an issue with this particular device.

Are you using terminators or direct cable connections ?
Martyn
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Re: Different readings on ChA&ChaB - 4227

Postby BSI » Fri Mar 07, 2014 4:34 pm

HI Martyn,

Direct connection, no terminators. Swapping cable has no effect. Acquiring A alone, then B alone produces the same results as seen as when acquiring both channels: Channel B shows the same artifact.
Thx.

PS: away from my desk until March 15.
Attachments
20140307-0001_BSI Dual Channel.psdata
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Re: Different readings on ChA&ChaB - 4227

Postby Martyn » Mon Mar 17, 2014 1:06 pm

Can you contact support@picotech.com we need to see device that gave Graph 2 back here as there may be an issue with it.
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