Help with Oscilloscope - Missing lines?

- D
- Dave Nubury
  
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posted
19 years ago

Mon, Apr 18, 2005 10:42 PM

Just picked up a used scope. 20MHz.. - Supposed to be in great working condition. Came with no leads. I just attached a couple of aligator clips to the input (Ch1) for now.

It seems to show AC fine. (Nice sine wave)..

However if I try to watch 5volt logic pulses from different sources, the vertical line in the state changes seems to be missing. For example. i would expect to see something like: ______ _____ _____ | | | | | | __| |____| |____| |__

but what I'm seeing is:

_____ _____ _____

_____ _____

Is this normal? Does it have something to do with not having a probe maybe? Crapy scope?

I would appreciate any info. Thanks Dave

- C
- CJT
  
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posted
19 years ago

Tue, Apr 19, 2005 1:43 AM

Think about how fast the beam is moving across the screen in the vertical portion compared with the horizontal portion, and what that means for its brightness.

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- J
- Jim Yanik
  
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posted
19 years ago

Tue, Apr 19, 2005 1:46 PM

"Dave Nubury" wrote in news:2JW8e.39108$vt1.25150@edtnps90:

The rise time of the input signal is too fast for the CRT phosphor to visibly display at the chosen sweep speed.The E-beam is moving much faster in the vertical axis than the horizontal axis,thus less time for the phosphor to absorb the beam energy,thus the phosphor absorbs much less energy,with resultant lower light output.If you looked while in a darkened room,or with an image-intensifier,you might see the rising edges. Some phosphors are better than others for certain conditions. Phosphor choice is always a compromise.

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