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issue with 3424 and block mode vi

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issue with 3424 and block mode vi

Postby aiyoung » Tue Aug 09, 2011 2:49 am


I've been trying to get the block mode example VI to run correctly with a trigger on a 3424 pico scope.

I noticed that when i press run, the graph will trigger even though the instrument that is supposed to trigger the scope isn't running.

I then disconnected the BNC cables from all channels of the scope, ran the vi again, and it would still start taking data with out waiting for the trigger event.

After pressing stop on the labview VI, the graph shows a really large square wave right a the start of the graph. Around 40 V!

I connected the picoscope to a waveform generator to aid in trouble shooting this issue.

I noticed the same issue as before where you can see the huge square wave at the start of the graph and then some data from the function generator.

See the image linked below.


When i use the picoscope software, i get the following image which is linked below.


Hopefully someone has run into this issue before and it's an easy fix.

Thanks for reading my post.

Re: issue with 3424 and block mode vi

Postby Martyn » Tue Aug 09, 2011 9:20 am

Please contact the technical team directly at support@picotech.com and attach a zipped copy of your Labview files and the sample images and they will be able to assist you.

Kind regards,
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Re: issue with 3424 and block mode vi

Postby aiyoung » Tue Aug 09, 2011 3:51 pm

Okay will do.

Re: issue with 3424 and block mode vi

Postby aiyoung » Tue Aug 09, 2011 5:36 pm

I think i'm making some headway into the issue.

The reason it would start on it's own was because i inadvertently changed the field that corresponds to "Auto_trigger_ms" in the node that calls "ps3000_set_trigger2" to 1 ms instead of 0.

One thing that i could use some clairification on is the threshold field.

in the programming guide, it's unclear of how the user should use this field.

The guide says "This is scaled in 16-bit ADC counts at the currently selected range. If an external trigger is enabled the range is fixed at +/- 20V"

Does this mean the number i enter into that field is a percentage of the range?

I found that the trigger output on the equipment i want to use to trigger the picoscope is a falling edge that has an amplitude of 3 mV.

Re: issue with 3424 and block mode vi

Postby gruntman » Tue Aug 16, 2011 8:44 pm


The trigger threshold will be the ADC count of the trigger channel voltage range. For example, say you are triggering off of channel A, channel A is on the 2V voltage range, and you want to trigger at 3mV, you would input in 49. You figure this by desired trigger level * 32764 / voltage range or in this situation .003 X 32767 / 2 = 49


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