Rigol DS2072 recording - max frames vs sample rate - Page 1
Forum section: electronics / testgear

author: Circlotron
author_rank: Super Contributor
timestamp: October 03, 2013, 04:11:34 am
content: On my new  scope if I crank the horizontal speed up a bit and start recording it only gets to 7 frames and stops. 14MB = full. I don't need super zoomable horizontal resolution so is there a way, while staying at the same horizontal speed, to dial down the sample rate so I still get say several thousand samples per frame but LOTS more than 7 frames before I run out of memory? That is to say, can I set the sample rate independently of horizontal speed?

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: October 03, 2013, 05:30:14 am
content: Push the acquire button and lower the "MemDepth".

author: Circlotron
author_rank: Super Contributor
timestamp: October 03, 2013, 05:59:04 am
content: Okay, so the lowest setting is 14kPoints.Does that mean 14,000 samples per frame, 1000 per horizontal division?If so, 56MB / 14,000 = 4000 frames, 14MB = only 1000 frames.How does one get up to 65535 frames?

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: October 03, 2013, 06:16:08 am
content: The 56M sample buffer is not the same thing as the record buffer (or "segment memory".) There's 128M of that. But that still doesn't allow for 65000 frames... The other piece of info you're missing is that "Auto" MemDepth can choose values you can't, including values less than 14k. The only way to get 65000 frames is to go to the fastest timebase and choose auto as the memory depth.You might want to grab the manual pdf (the 266 page one from your CD or from rigol. Not the crappy 40 page thing on tequipment.) It has a nice chart of memory depth vs maximum number of recorded frames that probably would have gotten you a bit further in your inquiries. It generally covers things pretty well. For example, the thing that frustrated me the most when I first got my scope was the behavior when zooming in. It kept moving my signal off the screen! If I'd bothered to read the manual...Quote

author: Circlotron
author_rank: Super Contributor
timestamp: October 03, 2013, 06:50:22 am
content: Aha...From page 10-2 of the user guide:------------1. End FramePress End Frame and use [rotation symbol] to set the desired number of frames to be recorded. The number of frames available is related to the memory depth currently select------------Presumably if Auto depth is selected the sampling rate is changed according to the desired number of frames selected. Will find out in about 2 hours when I get home.

author: Circlotron
author_rank: Super Contributor
timestamp: October 03, 2013, 12:03:53 pm
content: Quote from: Circlotron on October 03, 2013, 06:50:22 amNuh. Sampling rate seems to stay high-ish on auto.Quote from: Galaxyrise on October 03, 2013, 05:30:14 amThe MemDepth option was grayed out. Fiddled around for ages then finally it wasn't grayed out.What did I do? When would it / would it not be grayed out.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: October 03, 2013, 03:02:42 pm
content: Like I said, you have to choose a very fast timebase for Auto to select the smallest memory depth. Try 50ns/div or faster.As for MemDepth being grayed out, my guess would be you had the record menu up since you were playing with the End Frame option. If the scope is either stopped or is in record/playback mode then the memory depth is locked.

author: Electro Fan
author_rank: Super Contributor
timestamp: October 03, 2013, 03:58:14 pm
content: Quote from: Galaxyrise on October 03, 2013, 06:16:08 amAny chance you could post the chart and relevant page(s)? Thanks

author: marmad
author_rank: Super Contributor
timestamp: October 03, 2013, 10:38:44 pm
content: Maximum number of segments (frames) which can be recorded with each sample length:

author: Circlotron
author_rank: Super Contributor
timestamp: October 03, 2013, 10:43:05 pm
content: Thought of a reasonable solution to what I want to do now. Just set the horizontal timebase so that a single scan takes say 60 seconds or whatever the test period is. The sample rate will go as high as it can commensurate with this duration. Then feed it signals. Then zoom the trace as necessary to see the details. Doesn't have the advantages or convenience of separate numbered frames but the trace is continuous / contiguous so there is nothing missing.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: October 03, 2013, 10:51:54 pm
content: Without knowing what you're doing, I don't know if this is a useful suggestion... but something I've done is put the scope in "normal" trigger mode and set the trigger level so that the trigger never fires. Then start recording, and press the force button each time I have the DUT stabilized in the next test configuration. Then once I'm done, I can compare the different tests really easily in the playback mode.

author: marmad
author_rank: Super Contributor
timestamp: October 03, 2013, 10:56:29 pm
content: Quote from: Circlotron on October 03, 2013, 10:43:05 pmYou do know that the 'frames' (actually a bad name to call it) are not time-based, but trigger-based, right? As long as you set your trigger to start the timebase of the portion of the signal trace you want to examine, then it's possible to use the segments efficiently.

author: Circlotron
author_rank: Super Contributor
timestamp: October 03, 2013, 11:47:12 pm
content: Yep, it is trigger based. So does that mean you are stuck with showing only one pulse at a time? Maybe not if I dial back the timebase to get overlapping images. I want to see a trend of the last several pulses leading up to an anomaly, and how it attempts to recover.

author: marmad
author_rank: Super Contributor
timestamp: October 04, 2013, 12:57:24 am
content: Quote from: Circlotron on October 03, 2013, 11:47:12 pmIt all depends on how you set up the trigger; there are many intricate ways it can be set up based on delays, etc.

author: Circlotron
author_rank: Super Contributor
timestamp: October 04, 2013, 01:28:57 am
content: I just tried it and it appears to be a series of abutting images.What I'd rather have is a pulse in the centre and say two each side, and the next frame shows things moved along by one pulse, not one screen width.

author: marmad
author_rank: Super Contributor
timestamp: October 04, 2013, 01:43:22 am
content: Quote from: Circlotron on October 04, 2013, 01:28:57 amVarying the horizontal position allows you to capture what a signal did before a trigger event (pre-trigger viewing), determining the length of viewable signal both preceding and following a trigger point. But the DSO can not be re-triggered (i.e. start another 'frame' capture) until it has captured the entire length of the current timebase setting - then filled the pre-trigger buffer again.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: October 04, 2013, 03:12:28 am
content: Quote from: Circlotron on October 04, 2013, 01:28:57 amSo can you trigger on the anomaly? Then you can set the timebase and trigger position so that you see the pulses before and after it, and you don't need recording at all.

author: Circlotron
author_rank: Super Contributor
timestamp: October 04, 2013, 03:20:29 am
content: Quote from: Galaxyrise on October 04, 2013, 03:12:28 amHaven't got that particular board here right now. Just practicing on an entirely different board. But I see what you are saying.Just trying the recording thing again. It only updates every 1 second and there is "D 1.00000000 sec" at the top RHS corner of the screen. How can I decrease that delay?I am =such= a noob with DSOs

author: marmad
author_rank: Super Contributor
timestamp: October 04, 2013, 03:42:54 am
content: Quote from: Circlotron on October 04, 2013, 03:20:29 amIf by 'update', you mean record another segment - again, it's not time-based but based on the trigger frequency. If the trigger frequency is greater than the current sample length, then the 'update' rate will be approximately equal to the sample length. If the trigger frequency is less than the sample length, then the 'update' rate will be approximately equal to the trigger frequency.The "D 1.00000000 sec" indicates the Trigger Position (relative to screen/sample center).

author: Circlotron
author_rank: Super Contributor
timestamp: October 04, 2013, 03:50:47 am
content: The trigger frequency is about 3.9kHz and the update rate is about once per second...

author: Circlotron
author_rank: Super Contributor
timestamp: October 04, 2013, 03:58:45 am
content: Quote from: marmad on October 04, 2013, 03:42:54 amOkay... I was using 50uS/div but the trigger position was 1 second to the left of centre so it was taking 1 second for the scan to reach centre hence the delay & slow update. Now isMUCHbetter.

author: Circlotron
author_rank: Super Contributor
timestamp: October 04, 2013, 04:21:11 am
content: Can't post image attachments! Not even to external photo site. Work must have a firewall. I'll zip and attach them to the following post.

author: Circlotron
author_rank: Super Contributor
timestamp: October 04, 2013, 04:45:22 am
content: Now this might illustrate my problem I was talking about before.In frame 1548 everything is okay.In frame 1549 things have gone bad for a moment.There must be a bit of a delay between 1548 and 1549 to miss it, especially seeing the timebase is only 50uS.Screenshots are in zip file.

author: Circlotron
author_rank: Super Contributor
timestamp: October 04, 2013, 04:53:37 am
content: Uh yeah.. probably didn't trigger on the bad pulse because I had the level set right near the top.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: October 04, 2013, 05:47:21 am
content: Some ways to catch that:A Runt trigger. It's named after what you're looking for, after all!I've recently gotten good mileage out of the pulse trigger for this as well. Set the trigger level up near the top of the normal pulse like you have it in the screenshots. Then use the|>|mode and set the threshold duration to 400us (1.5x the period of your pulses) That should cause it to trigger on the normal pulse after the runt pulse. (Note that you can use the jog/shuttle to set the threshold duration.)Once you have the trigger set up, crank up the time base & memory depth, put your trigger point where in the sample you want the event to occur so you get enough data before and after the trigger point. Set the scope in single mode and wait.