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Cannot capture signal using trigger

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Cannot capture signal using trigger

Postby WimvWijn » Fri Nov 10, 2017 3:22 pm

I'm a new user, and no expert in electronics, scopes etc. In order to familiarize myself with Picoscope6 I tried to replicate a very simple experiment as explained on your website: 'Home / Library / Educational experiments / Experiments with a capacitor'. The only difference is that I use a 9V DC power supply, and my resistor is 3k3.
Somehow, the signal is not captured and I have no idea why. Does anyone have any ideas what I might be missing?
Thx. in advance.
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Re: Cannot capture signal using trigger

Postby alan » Sat Nov 11, 2017 9:49 am

Hi,

A couple of suggestions - first check with no trigger that when you measure across the 9V battery the line on the scope trace jumps from 0V to 9V (just in case there is a duff lead or odd setting on the scope).

I suggest you set the timebase to say 500ms/div and you should be able to see the line jump up / down as you connect / disconnect the 9V from the battery.

Next still at 500ms/div measure the RC curve from your circuit. Feel free to save it and post it here but once you have it on screen it will be easier to set suitable settings for the trigger in terms of voltage, rising or falling slope and where the trigger occurs - 50% pre trigger is a good start.

Regards
Alan
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Re: Cannot capture signal using trigger

Postby WimvWijn » Sun Nov 12, 2017 2:19 pm

Hi Alan,
Thx. for taking the time to respond. I did as you asked, see attached data file. The charging event of interest takes place at 0.3 s. (The slow discharging at 2.7 s occurs when I disconnect the power again - not relevant here).
As I further reduce the Collection Time value (from 500 ms/div down to 2 ms/div it becomes more difficult to manually capture the charging event, but I can visually see the rising curve-shape widening, so the capacitor seems to charge properly. I also noticed this by applying a large Horizontal Zoom (e.g. 100x) in the captured screen.
Strange enough I managed once to capture a charging event using the trigger (Single, 200 mVm 50% pre-trigger) using a time-base of 20 ms/div, but never again after that, let alone at even shorter time-base values.
I'm puzzled....

Wim.
Attachments
Problem_query.psdata
(35.61 KiB) Downloaded 16 times
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Re: Cannot capture signal using trigger

Postby Martyn » Mon Nov 13, 2017 6:42 am

Try using a Repeat or Single Trigger on a Rising Edge at 4.5V and with a pre trigger of 50% , these are set in the bottom toolbar.

This should put the middle of the RC curve in the centre of the screen, you can then change the timebase and still see the curve.
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Re: Cannot capture signal using trigger

Postby WimvWijn » Mon Nov 13, 2017 6:12 pm

Hi Martyn,

That works. Thanks! I understand now that my previous trigger setting must have been too low for the Pico to react, right?

BR, WimvWijn
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