DSO sample rate in window zoom mode? - Page 1
Forum section: electronics / general

author: Smokey
author_rank: Super Contributor
timestamp: December 31, 2012, 12:47:34 am
content: Something I've wondered about but haven't actually checked yet is what happens to the sample rate when you do a windowed zoom some time after the actual trigger event.For example, say you are monitoring a line with a pulse that happens every 50ms and you want to check the rough pulse to pulse jitter by looking at the leading edge of the second pulse. You set the timebase to like 10ms so you can see two events on the screen at the same time with the event that actually triggered way to the left. Then you do a windowed zoom around the second pulse 50ms after the trigger and zoom way in on the leading edge so the window timebase is like 50ns or something. What happens to the sample rate? Are you getting the sample rate from the 10ms/division of the global timebase, or the much faster 50ns window timebase?I guess this is where segmented memory shines, but even without it does window mode automatically delay the acquisitions to get the best sample rate? Anyone ever tested that on the cheaper Rigols vs Tek vs Agilents without segmented memory?

author: CarlG
author_rank: Regular Contributor
timestamp: December 31, 2012, 01:49:49 am
content: EDIT:I don't know how I got this wrong...think I must've read 4.00 MSa/s as 4.00GSa/s...jahonen has shownherethat the Agilent 6000/7000-series sample rate in the zoom window is what you would get with the main time base set to the zoomed time base. At least in that case, but it's reasonable to think that it's the same for other settings.I'll be disappointed if the Agilent 2000X/3000X/4000X-series doesn't behave the same way.I wouldn't say that this application is where segmented memory shines most, even if you could use it for this particular case. But you'd lose the "feeling" that a live view would show of how much the jitter there is. You would also not be able to make a good statistical analysis of the jitter (using the automatic measurements) due to the limited number of events you'd get.//C

author: CarlG
author_rank: Regular Contributor
timestamp: January 20, 2013, 09:12:26 am
content: Had a look at some Hameg scope manual, and they seem to have done their job well50x zoom, 50x sample rate (at least in this example).(picture from HAMEG_MAN_EN_HMO72x-202x.pdf)

author: TMM
author_rank: Frequent Contributor
timestamp: January 20, 2013, 03:49:26 pm
content: Not sure about DS2000/2000X etc but on my Rigol DS1052E the sample rate remains constant, so a windowed zoom is no different to doing a single shot and then altering the timebase, so the following applies:in 'short memory' mode (16K Samples) at 1ms/div it samples approximately ~200-250 times per division (every ~5us). The resolution of the display is 25pixels per division, so the maximum zoom without loss of resolution will be:5us*25px = 125us/divand the capture length will be:16KSa*5us = 80msNow, if i set it to long memory (1M Samples) then it samples ~20,000 times per division (every ~50ns). Therefore the maximum zoom without loss of resolution will be:50ns*25px = 1.25us/divand the capture length will be:1MSa*50ns = 50msObviously there are drawbacks to enabling the longer memory (such as display update rate), and every scope will be different in how it determines what samplerate to use.As a general rule of thumb you can expect to be able to zoom in and out by around an order of magnitude without problems, although it should be pretty obvious when you are zooming in too far if you disable Sin(x)/x interpolation.With a scope like the DS1052 you are best off centering the second pulse on screen, adjusting the timebase as low as you can without the trigger being affected, then zoom. Edit: actually you don't even need to use the zoom feature because the Rigol can delay the capture, awesome. Therefore the only reason you would need to use the windowed zoom is if you needed to monitor both timebases at once.edit2: actually it limits the delay when you set it to a low timebase, sometimes 300ms sometimes 600ms? seems the change depending on which timebase you set it up on, not quite sure what is going on there.

author: tinhead
author_rank: Super Contributor
timestamp: January 20, 2013, 09:57:33 pm
content: Quote from: CarlG on January 20, 2013, 09:12:26 ami would not trust every pictureThe zoom window is having 100us/DIV now, the full period of the waveform is 1ms, so 1kHz signal.The Main TB is set to 2ms, sure, but check the sample rate, it is 100kSa. So all what we can see is that theDSO is still 100x faster sampling in MTB window than the waveform frequncy in zoom window.Therefore no prove for faster sampling in zoom window. The 5MSa label in Zoom window means simply nothing.A signal with let say 100kHz would make difference, but i assume Hameg exact such picture for reason.

author: CarlG
author_rank: Regular Contributor
timestamp: January 21, 2013, 07:57:48 am
content: Quote from: tinhead on January 20, 2013, 09:57:33 pmWell, it's OK being sceptical, and one can never be too sure about anything.Anyway, I had another look in the manual and found their explanation of the screen shot, where it specifically states that the  figure is the actual sample rate (though I don't see why they don't add "/s" i.e. using a correct unit). And yeah, you could argue against this explanation too, but if it's wrong then I'd say they're upright lying. However, to be 100% sure, you have to check yourself.

author: tinhead
author_rank: Super Contributor
timestamp: January 21, 2013, 10:27:17 am
content: i would say they means the line on top, there are all the settings they described. But yeah, this can be really answered by an Hameg owner.