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MSO-X 3054A Waveform display Invalid

Question asked by seen on Apr 16, 2013
Latest reply on Apr 17, 2013 by ksmith
When are scope waveforms valid and what causes them to be invalid?  How are invalid waveforms flagged when an automatic measurement is not begin made?  These questions will make more sense after reading the problem I encountered capturing waveforms covered below.

Measurements were made using all four analog channels.  The scope math ability was used to subtract two of the channels.  The math result matches one of the channels captured.  The matching waveform is a square wave.  The scope measurement ability was used to capture the TOP and BASE values of the two waveforms that should match.   The TOP measurement result for *the physical channel (CH4)* showed >15.1V.  The > sign indicates the measurement is suspect and may be invalid.  The voltage/div for the physical channel supported a TOP value of at least 50V. The 15.1V TOP measurement matched the waveform displayed.  The math channel showed a TOP value 45.8V.  *Therefore, the physical channel was incorrectly captured and displayed.*  Subsequent captures resulted in several bad captures (ones with >) before a valid waveform and measurement (one without >) were made.   All waveforms were captured without averaging.

Thanks for your help.
------------------- update April 30
A scope error has not reoccurred for the same setup.  I contact Agilent, and the general feeling was that the channel ADC was overdriven which resulted in unpredictable behavior.  To tests this idea, I over drove the channels by one or four divisions using the same setup.  The one division overdrive did not cause errors.  The four division overdrive affected the overdriven channel but not the interleaved channel.  

I verified the scope does not flag waves that are overdriven when a measurement is not made.

Revisiting the original scope error, I cannot explain the failure seen by ADC saturation.  Channel 4 is not excessively overdriven and the interleaved channel 3 is a DC level within the scope bounds.

I will update this again if I learn something new.  Right now the scope is working and I have an interesting design to work on.

Edited by: seen on May 1, 2013 12:14 AM  

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