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Electronics => Beginners => Topic started by: swgertsch on January 14, 2016, 06:42:17 pm

Title: DS1054Z 3v+3v=4v?
Post by: swgertsch on January 14, 2016, 06:42:17 pm

New to oscilloscopes. Just bought a DS1054Z and I have been playing around with it to familiarize myself with its capabilities. Did a Math (A+B) operation against two signals feed from the probe calibration source. The individual source (CH1 and CH2) signals are identical (no surprise) but when I add them together the (A+B) resultant voltage appears to be 4Vpp. See attached picture.

Note: The two input signals are superimposed on each other.

No sure what is going on here. Can anyone explain this phenomenon? 

Also, there appears to be excessive noise at the 0V level (A+B) signal plot.

Title: Re: DS1054Z 3v+3v=4v?
Post by: rrinker on January 14, 2016, 06:49:09 pm

 You didn't have one probe on 10X, did you?

Title: Re: DS1054Z 3v+3v=4v?
Post by: Monkeh on January 14, 2016, 06:52:57 pm

You have the math trace set to 1V per division. It's clipped.

Title: Re: DS1054Z 3v+3v=4v?
Post by: swgertsch on January 15, 2016, 06:55:58 am

Your absolutely right, the math A+B trace is clipped with the vertical scale set at 1v/div. I did not suspect the clip because the top of the A+B trace appears to be visible (it should not be there is the signal is "off" the screen).

Anyway, I changed the vertical scale of A+B to 2v/div and "magically" the resultant is what I expected to see.

I would have thought there would be some flag/message for the user (me) that the displayed section of a trace was being vertically clipped.

So what did I learn? If the signal touches the top/bottom of the display assume the signal trace is being clipped from the display.

Title: Re: DS1054Z 3v+3v=4v?
Post by: bitshift on January 15, 2016, 07:23:12 am

Quote from: swgertsch on January 15, 2016, 06:55:58 am

So what did I learn? If the signal touches the top/bottom of the display assume the signal trace is being clipped from the display.

Yes, I usually have a rough idea of the level of the signal and then start with a larger V/div and then trim it down to fit the signal.

Just for interest, you could guess that the signal was being clipped. No real world signal would be so perfectly clean and noise free on the edge of the scope display (look at the existing waves, the sum has to be as noisy as both combined).

Title: Re: DS1054Z 3v+3v=4v?
Post by: Mechatrommer on January 15, 2016, 10:22:08 am

Quote from: swgertsch on January 15, 2016, 06:55:58 am

I did not suspect the clip because the top of the A+B trace appears to be visible (it should not be there is the signal is "off" the screen).

i agree clipped signal should not be visible. this is software bug that we have to live with $399 china made scope.. dont expect too much perfection :P

Title: Re: DS1054Z 3v+3v=4v?
Post by: Jeroen3 on January 15, 2016, 10:36:38 am

Clipping is expected behavior, even for analog scopes. That it exactly matched the top of your screen is your bad luck.