| Electronics > Beginners |
| oscilloscope display explanation wanted |
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| David Hess:
If the oscilloscope has an index graded display, then usually multiple acquisitions are combined into a histogram for every LCD frame. This is what gives DSO displays that fuzzy look which resembles an analog display. I would be nice if the oscilloscope indicated how many acquisitions are made per LCD frame but none do. |
| vk6zgo:
--- Quote from: james_s on December 12, 2018, 02:42:14 am ---If you want true realtime, get an analog scope, but what do you hope to achieve? Do you think your eyes will be faster than the scope? If you think a delay between the signal being captured and appearing on the screen is a problem then you aren't using the scope correctly. --- End quote --- Even then, when the beam lights the phosphor, what you are seeing is the result of a smaller, but still real delay. |
| james_s:
Ok yes, but that's getting really nitpicky. There is always going to be some delay too as light from anything travels from the source to your eyes, but that delay is going to be many orders of magnitude less than any other delays involved. An analog scope is as close to real-time as it gets. I struggle to think of an application where that is really necessary though. |
| David Hess:
There is no comparison between an LCD operating at 60 frames per second typical or 16.7 milliseconds per frame and an analog oscilloscope with a latency on the order of 200 nanoseconds. The LCD is actually significantly worse than its frame rate would suggest because of processing delay unless the DSO is capturing directly into the frame buffer like some of the early Tektronix DPO models did. As a practical matter however, the difference is irrelevant. I would be quite willing to live with the latency imposed by limited LCD refresh rates if the processing software itself operated in real time which is the exception. Most modern DSOs have horrible latency well beyond what the LCD is capable of. Incidentally, with a fast analog oscilloscope like a Tektronix 7104, it is feasible to view the screen at a distance where the speed of light delay is greater than the delay through the oscilloscope. The 7104's vertical delay line is only 45 nanoseconds. The 7104 is actually fast enough to sweep the CRT beam with an apparent speed faster than light. |
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