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Maximizing sample depth

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Maximizing sample depth

Postby vpconway » Thu Jun 25, 2015 3:50 pm

I understand at least part of this has been discussed elsewhere in the forum but I'm hoping for more specific answers.

I have a 3206D MSO that has 512MS memory and am using PicoScope 6.11.4.929 beta. I am trying to capture as much as possible at a 500ns sample period. I need a trigger channel and a data channel. Both are digital outputs. I also need to use the post-trigger delay. I do not need to record the trigger channel. I am using a single shot trigger.

First there seems to be a limit of 100MS. If only channel A is enabled I can select 5s/div and the samples control to 100MS or greater and get 99,206,347 samples at 504ns/sample. if I select 10s/div the sample interval increases to 1us. Increasing the samples control does not help. I return to 5s/div then enable channel B. My sample depth drops to 50MS. I have 512MS and am only using 2 channels, and the trigger is set to single. Please explain.

I was recording 100MS using the digital channels but also needed to use the post-trigger delay which was greyed-out when using digital. It's also greyed-out now with only analog channels enabled. What am I missing? Should this feature be available with digital channels enabled? I also thought the 100MS limit was a digital issue and I would have increased depth with only 2 analog channels.

Thank you,
Vance
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Re: Maximizing sample depth

Postby Hitesh » Mon Jun 29, 2015 11:49 am

Hi Vance,

At 5s/div, the PicoScope will be collecting data in streaming (Slow Sampling) mode. The PicoScope 6 software will limit the record length in streaming mode to 100MS (shared between all channels).

You can change the timebase at which PicoScope 6 switches to streaming mode via the Tools -> Preferences option. Change the Collection Time in the Sampling tab to a value above 5s/div e.g.:

Preferences_sampling.PNG
Sampling tab in Preferences dialog

Try adjusting the number of samples once you have changed the mode and set the trigger to Single.

Please note that you will not see the data displayed on the screen until it has been collected.

Regarding the trigger delay, the driver API functions do allow the setting of a trigger delay so I will report this to the Development Team.

Regards,
Hitesh

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Re: Maximizing sample depth

Postby vpconway » Mon Jun 29, 2015 5:06 pm

Thank you very much. I was able to capture the data in 100s segments. I'm also looking into the SDK. It may be worth my while to develop something more specific but as-is I can capture much more with this unit than any other I have access to.

FYI, The post-trigger delay being greyed out when using analog channels appears to be coupled with the slow sample transition. Changing this setting allowed me to capture with a sample period around 400ns for a 100s sweep and delay 500 seconds.

Something that would be nice would be and external trigger. I imagine there was a need to compromise and external trigger was lost. In this particular use I essentially wasted memory to trigger the scope with a rising edge. Even if a separate port is not available, configuring one of the channels as "trigger only" could free memory for data collection.

I'm quite please with the functionality.

Thanks again.

Vance
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Re: Maximizing sample depth

Postby Hitesh » Tue Jun 30, 2015 2:53 pm

Hi Vance,

It appears that the Trigger Delay feature is not possible in streaming mode captures at the present moment. Changing the slow sampling transition point as you have done will allow this.

I will put forward a feature request for future consideration for an external trigger. If you have already enabled a digital channel on a port e.g. in the range D0 to D7, then you can use of these channels as an external trigger without loss of memory depth as each bank of 8 channels (D0 to D7 and D8 to D15) is considered to be one channel (the Programmer's Guide provides more information about this).

Good to hear that you are pleased with the functionality :D

Best wishes,
Hitesh

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