AD2 Issue - Noise in Scope Display of Generated Wave Form

[CharlesB]

Hello...

I recently purchased the Digilent Analog Discovery 2 device, along with the BNC adapter for the AD-2, directly from Digilent for an online  EET class (EET-150) that I am taking at Southern Illinois University at Carbondale this semester.  I am a newbie to the electronics world, and have very little experience with oscilloscopes and/or Signal Generators.  This is my first device of this kind.

When I use this AD-2 device in my many required labs for this class, my Professor is reviewing the output of both the oscilloscope wave forms that are displayed on the screen and capured/exported, and how the wave form generator is set up (Sine wave, Frequency, Period, etc)........he is telling me that he sees two problems with my particular AD-2 and BNC adapter devices.

1.  When performing probe compensation, I can never get a completely square wave using my Digilent 460-004 probes.  I have purchased 3 different sets of these 460-004 probes from 3 different sources (in addition to the set I purchased directly from Digilent), and neither of the 3 different sets of new probes can generate a completely square wave as required for a fully compensated probe.  The upper let corner of the square wave for each different probe is curved downward slightly and cannot not be corrected by tuning the Compensation Adjustment Screw on the various probes.  It can only be corrected  to having this upper left corner NOT being perfectly square.  The Professor and I have tried many various configuration changes to Frequency, Period, Amplitude dropdowns on the waveform generator........and Position, Offset, Base, Range dropdowns on the oscilloscope with no change to the ability to get a completely square wave while tuning the probe.  Because I have tried this now with 3 different sets of new 460-004 probes, and various generator and scope configurations with no success, my Professor feels this is a result of a possibility faulty AD-2 device or BNC adapter device.
2. When using the Waveforms software, and when doing very simple, basic  waveform measurements (Sine, Square, Triangle, etc) using the oscilloscope function, the wave displayed on the scope is showing an extraordinary amount of noise for a simple, basic waveform. (both the waveform generator and the oscilloscope are running of course).  Again, the Professor and I have tried many various configuration changes to Frequency, Period, Amplitude dropdowns on the waveform generator........and Position, Offset, Base, Range dropdowns on the oscilloscope with no change to the noise being displayed. Again, because if this additional issue, my Professor feels this is a result of the AD-2, or the BNC adapter devices that I purchased possibly being faulty, and in need of a replacement.

What do you guys think the issue is here??? 

Could my AD-2 and/or the BNC adapter be faulty??  Could there be an issue with the Waveforms SW that I am using?? (Waveforms Version: 3.18.1 64-bit Qt5.12.9 Windows 10 (10.0) Qt5.12.9).  I am really stumped here, and need some help.

Any guidance and advise will be greatly appreciated.

Thank You

Chuck Burk

 

[attila]

Hi @CharlesB

1. I'll leave this for @JColvin

2. See the following post. Please attach some screenshots to have more information, to see what you saw.

 

 

[CharlesB]

Thanks guys......

So here is the export of my Scope Compensation screen.......you can see that the upper left corner cannot be corrected no matter what I try.  I will send the screenshots of the noise issue in my next post

 

 

 

[CharlesB]

Here is a screenshot of both the waveform generator and the scope showing the excessive noise in a Triangle wave as seen from the scope.....the probe is connected directly to the alligator clips on the waveform generator cable.....black to black......red to probe.  there is no actual circuit in this being measured.

[attila]

Hi @CharlesB

If this is with 10x probe then it is excpected. With 10X it can have 50/500Vpk2pk range, 3/30mV resolution and due to higher impedance more susceptible to noise radiation. With 1X 5/50Vpk2pk 0.3/3mV
C1 10X average + noise 50Vpk2pk
R1 1X average 5Vpk2pk 

[CharlesB]

Interesting.........I am, indeed, using 10x probes that are set at the 10x setting......and the Waveforms Oscilloscope setting for CH1 is set to 10x as well.

That most likely answered the "noise" question..........thank you very much for that.

 

How about the Probe Compensation issue question........do you have any ideas why I cannot get clean corners on my generated square wave while tuning the Compensation Adjustment Screw on the 3 sets of new 460-004 probes from 3 different sources (in addition to the set I purchased directly from Digilent)???

Thanks for your continued support with these questions.

Chuck

 

[JColvin]

Hi @CharlesB,

Regarding the BNC probes not correctly compensating, Digilent is actively looking into this.

At some point, the quality of the probes that we were procuring changed so that newer sets of probes are no longer to able to fully compensate the analog input signals as compared to the older batch of probes from the same manufacturer that were able to easily overcompensate the same signals. For our part, we are working on sourcing some new probes that will work consistently (the first new options we sourced did not perform as advertised) as well as seeing if any hardware changes can be made to the BNC Adapter for more reliable operation.

Unfortunately, what this means is that Digilent does not have solution to offer at this point in time, though as soon as I hear that a solution has been found I will let you know.

Thanks,
JColvin

[CharlesB]

Thank You so much JColvin!!!

I really appreciate it.

This explains so much........I look forward to hearing from you again once you guys find a definitive solution 

Thanks again!!

Chuck Burk