Digital Scope Sampling Rate - Page 1
Forum section: electronics / testgear

author: dan3460
author_rank: Frequent Contributor
timestamp: October 09, 2015, 01:54:02 pm
content: I have a basic, cheap, Owon 5032 (I think)oscilloscope. It has a manually set sampling rate (1k,10k,100k,1M and 10M). In most DSOs that I have seen the sampling rate is adjusted automatically as you change the timebase, longer time lower sampling rate, shorter time higher timebase.Because is a pain to change the sampling rate every time it has been set forever at 1k, when sampling higher frequency waves I always found then unstable, I thought that they were like that and live with them. I actually forgot that it was a sampling setting.Last night I was watching a youtube clip on capturing two very different frequency wave form together in a scope and up-ing the sampling rate when looking at the lower frequency wave you can zoom and look at the other higher frequency wave. Very simple and trivial, but sometimes you don't think about this. Anyway, this got me thinking if my scope has this feature, remember that I have forgotten that it existed, as it did I played with it and here is my questions:- why do other scopes change the sampling rate based on the timebase?- Would it be a problem if I left the highest sampling rate even if I'm sampling low frequency waves?Sorry for thee lengthy post.Thanks

author: SteveLy
author_rank: Regular Contributor
timestamp: October 09, 2015, 02:06:01 pm
content: Quote from: dan3460 on October 09, 2015, 01:54:02 pmI'm fairly inexperienced with DSOs but I believe it's a trade off between getting enough samples per second to yield a good representation of the waveform at a given time-resolution (time/div) and waveform update rate (as well as general usability and responsiveness of the scope). If you leave it at the highest sampling rate at low frequencies, the scope will be unnecessarily hampered in performance. This is more so for low-end scopes.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: October 09, 2015, 05:23:19 pm
content: Quote from: dan3460 on October 09, 2015, 01:54:02 pmHmm, that doesn't sound like the sample rate (which has a unit in MSa/s or GSa/s), that sounds much more like a setting for the sample memory size.QuoteIt's not "adjusted" automatically, the sample rate simply changes in accordance with the minimum time that needs to be captured (one screen width i.e. 10 or 12 divisions, and the time base setting decides how long that is) and the available memory. And it's a simple necessity that with a given memory size if you need to capture a longer period then the sample rate needs to be lower.Have a read through this:http://blog.teledynelecroy.com/2013/06/back-to-basics-sampling-rate.htmlQuoteAgain, when the timebase changes the sample rate has to change, too.QuoteAgain, this is very likely a memory setting, and no, you can leave it at max if you want to, which would give you the max sample rate possible at each timebase setting. However, at a given sample rate larger memory needs longer to fill, so your scope will take longer to update the screen (i.e. it becomes slower).Better scopes manage sample memory automatically so that the selected size is enough to give the best sample rate while keeping it small enough to maintain high update rates.

author: dan3460
author_rank: Frequent Contributor
timestamp: October 09, 2015, 05:48:03 pm
content: Quote from: Wuerstchenhund on October 09, 2015, 05:23:19 pmThanks for the answer, I will check but I think the label said "sampling". In any case, I tested this using 2 waves, 1kHz and 3MHz. With the scope triggering on the slower wave and the "sampling/memory" button set to 1k, nice slower wave but just a bouncing line on channel 2 for the fastest wave. Stopped the scope, zoomed in and I can only see a line for the faster wave. Only change that was made was the "sampling/memory" to 10M, now instead of a line for the faster wave I get a ribbon. stopping the scope I can zoom in and actually see the faster wave.Regardless of that, the only problem that I can see, after reading your posts, is that storing that many samples may reduce the amount of wave data that I can store.Thanks again.