Issue Displaying Waveform at > 500 sec/div Settings

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Issue Displaying Waveform at > 500 sec/div Settings

Post by Engineer_1572 »

Hello. I need to run a long test (8 hour duration) and I don't necessarily need to sample the measurements at a high rate. I would like to set the time base of my picoscope such that the entire 8 hour test waveform can be seen on one screen (i.e. one frame). This translates to a time base setting of 5000 sec/div. (Fyi, I have a Picoscope 5444D MSO with Picoscope and I've set the "slow sampling transition" parameter to 200ms/div. I am running Windows 10 on a laptop connected to the 5444D.) I set the time base to 5000 sec/div and started running the test and what i saw on my picoscope screen did not make sense. Please see the attachment. (Note that the attachment shows 500 sec/div which is the same issue as 5000 sec/div.) What I found is that for any time base setting between 200 msec/div and 200 sec/div the scope works as expected in that each waveform datapoint is populated on my picoscope screen as soon as that particular datapoint is acquired by the hardware (5444D). In other words, i don't have to wait 2000 seconds (10 x 200 sec/div) for the scope to acquire the entire waveform (one frame of data) and then update the entire waveform (one entire frame) on the picoscope screen. However, for any time base setting of 500 sec/div or greater the scope would not update the waveform on the picoscope screen at the same time that the waveform data was being acquired. Instead, picoscope would only update the waveform on the screen at the end of the frame (time/div x 10) or whenever i would select the "stop capture" button. That means that if i'm using a 5000 sec/div setting I would have no idea what the waveform looks like until the end of the frame meaning that I would have to wait for 50000 seconds (13 hours 53 minutes) to see the waveform. Why is there inconsistent behavior in that the scope works as expected up to 200 sec/div but then for 500 sec/div or greater it does not work as expected in terms of "live" updating the waveform ? Is this a bug or am I missing something in my picoscope settings ? Thanks in advance for any help.

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Joined: Mon Aug 11, 2014 11:14 am

Re: Issue Displaying Waveform at > 500 sec/div Settings

Post by Gerry »

Hi Engineer_1572,

I apologise for the delay in answering (this post got overlooked in the run up to Christmas).

First of all, the scope does work, in terms of 'live' updating of the waveform, you just need to clear the display first.

What you are probably observing is a delay in redrawing the screen. This happens when you have restarted a capture, with a slower Timebase, where the previous capture was not completed, because the previous data is not replaced until there is enough data to replace it. The overall time that it takes to recollect the same amount of data, especially due to the longer time taken to actually collect the much slower arriving samples, can result in no activity for quite a long time. This then gives the appearance of not updating the display until all of the samples have been captured, unless you stay and watch it for long enough. The data file below shows that the 500s/div Timebase setting does indeed result in the display being updated as the samples are collected (when you zoom out you will see that the Timescale extends to 1h23m20s for a 500s/div Timebase).
Slow streaming.psdata
(32.94 KiB) Downloaded 29 times

The problem is that the screen will only update once more data has been collected than the data that is currently being displayed. So, the solution is use a method to clear the screen, so that as soon as you start your capture there is no need to wait for the trace to advance beyond the already displayed trace, therefore the samples will be displayed immediately as they are captured. You can clear the display by doing the following:
(a) set the Timebase to 1s/div
(b) select Trigger Mode of Single
(c) change the Threshold of the Trigger to a value beyond the peak of the signal
(d) set the Pre-Trigger to 0%
(e) start a capture
(f) stop the capture once the display is clear (note if it doesn't clear on the first attempt just start the capture again)
Clearing the display.png
Clearing the display.psdata
(6.96 KiB) Downloaded 25 times

Once you have used cleared the display as above, you can just set the Timebase back to the slow value you want, and turn of the trigger (by selecting a Trigger Mode of None). If you then need to clear the display, at some point, again you can just select a 1s/div Timebase, and Select a Trigger Mode of Single to do it (all of the other trigger settings will still apply, unless you have made additional changes to them). You can even use the data file example as a settings file for clearing the display.


Technical Specialist

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