Author Topic: How to use a scope ?  (Read 807 times)

mrichaud

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How to use a scope ?
« on: January 17, 2020, 03:14:36 PM »
Hi
I am a beginner and mostly software engineer ... so sorry for my stupid question.
I am using the Current Ranger with its OLED screen. Measurement with my arduino board are perfectly fine. Now I would like to use a scope to perform accurate time measurement of my low power device when it is sending data (wireless communication).
Each time I connect a probe to the current ranger, I can see that the data on the screen are getting completely erratic. Stanby mode I have 2.4mA (one led powered), when I connect the ground of my probe it is displaying something like 1000 mA ...
I have tried with 2 different probes and scope and get the same results.
Could you guide me trough the good process to use a scope ? I have read all the data available on the site.
Thanks.

Felix

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Re: How to use a scope ?
« Reply #1 on: January 17, 2020, 03:58:44 PM »
The essentials are explained in the guide safety and proper use page.
The GOLDEN rule for CR is to have at most 1 earth connected device (PSU that powers your DUT at input, USB connected PC for logging, scope at output).
You can easily add a USB isolator to eliminate this problem for the USB connection. Note that a USB connection even through isolation can introduce switching noise if you also have a scope at output.
For a scope you could use an isolation transformer but that can get expensive.
So it is very easy to just power the DUT with a battery. So you then eliminate the input having any connection to earth mains.

If your DUT is battery powered, then you can have an earth connected scope at output for nice and crisp readouts of the DUT activity.
Depending on your scope you will have to adjust it to capture the correct scale.

I like to put the scope in roll mode with 20mV/div and fastest roll speed. That way I can clearly see when the DUT wakes up and I have plenty of screen space to capture spikes and zoom in for detail. You can see such a screen capture from a radio transmission on the product page as well as throughout the guide.

Hope this helps.

mrichaud

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Re: How to use a scope ?
« Reply #2 on: January 17, 2020, 04:10:39 PM »
Thanks a lot. Clear for me.