Dual Channel input and possible delay

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BSI
Newbie
Posts: 0
Joined: Wed May 12, 2010 3:15 pm
Location: Canada

Dual Channel input and possible delay

Post by BSI » Sun Jun 29, 2014 10:00 pm

Some possible issue with a scope acquiring simultaneousl with two channels

Set up:
Pico 4227
1 input signal, sine wave ~ +/- 2.5V , period ~ 8 microsec

Measurement on PicoScope 6:
Both Ch A and B on same +/- 5V input range, trigger is on channel A, level 0V. All good
The signal feeds into both channels, using a BNC splitter.
Capture1.JPG
Same setup but time windows reduced to 500ns: OK
Capture2.JPG
Now I lower ch B input range (the one with no trigger on it) to 500mV : The 0 crossing in theory identical starts being offset. The changing slope on signal B is to be expected since the vertical range (and scaling) has changed accordingly.
Capture3.JPG

Now I lower ch B input range to 50mV : The 0V crossing is now ~50ns offset
Capture4.JPG
Why is there an offset ? is this to be expected?

If I swap the cabling going into the input channels A and B no change, the delay does not follow the channel swap so it rules out a delay in the external cabling.

Also the delay always appears to be such B rises occurs before A rises, whichever channel is set as trigger.
Capture5.JPG
Capture6.JPG
Thx
L.

BSI
Newbie
Posts: 0
Joined: Wed May 12, 2010 3:15 pm
Location: Canada

Re: Dual Channel input and possible delay

Post by BSI » Mon Jun 30, 2014 12:41 am

ahem.... I forgot to place two 50 Ohm adapters at the front-end, which seems to solve the issue....
L. :oops:

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