Measuring power with analog oscilloscope

[ALVARO_CS]

An of the topic question
I recently bought a Mini DS202 oscilloscope (portable)

Where do I connect the ground clip in the case of an alternating current source ? (eg. the 2 output leads of a coil and a rotor with magnets )

(slowly learning)
thanks
Alvaro

[ayeaye]

> Any chance you post (in spare time) video explaining this process in details?

I may do that, but unfortunately i think i would not have enough time for that in any foreseeable future. So don't wait for a video, please try to understand it by what was written.

> How do you snapshot analog scope screen?

I used to do it with my webcam, and guvcview. Just hold it in hand, but it has to be held at the center of the screen, and straight, which is somewhat difficult to do.

> Is the resolution important?

No. Because with an image manipulation program such as gimp, it can be easily scaled, rotated and otherwise transformed.

> Where do I connect the ground clip in the case of an alternating current source?

It depends on your AC source. Like for the example above, i used a wall adapter, that outputs AC voltage. The '-' on the AC source, is the terminal that may be actually connected to the ground. The ground clips of the oscilloscope probes (both are connected to the oscilloscope ground) should be connected to that terminal. Because both the AC source and the oscilloscope may be connected to the ground, and in that case connecting the scope ground to the other terminal causes a short circuit, which may do a lot of damage, to the AC source and to the oscilloscope.

Whether the AC source and the oscilloscope are grounded, and what terminal of the AC source is grounded, can be found by measuring the resistance between the oscilloscope ground and a terminal of the AC source, with a multimeter. If both are grounded, then the resistance is zero. If they are not grounded, like it actually was in my case, though by how i connected the oscilloscope they could as well be grounded, then the oscilloscope ground can be connected anywhere in the circuit. This is called a "hanging scope", but the resistance between the oscilloscope ground and the AC source terminal has to be carefully measured then, and one must be sure that there is never a connection, otherwise it may cause a great damage.

> (slowly learning)

I'm a beginner too, i have not done any electronics as work or anything, though in the university i somewhat learned electronics. It is about finding out what is necessary, all that is about knowledge, more so than experimenting.

To get gschem, install gEDA, this is the general download page for Windows, Linux and macOS  http://wiki.geda-project.org/geda:download . These are the Linux debian packages  https://packages.debian.org/search?keywords=geda , the package should be geda-gschem , you would likely find it with your package manager. There are downloads for Windows  http://www.delorie.com/pcb/geda-windows , you should download the zip file and geda-runtime.exe . There is a bit to download for Windows, but you may not regret, you will also get a great circuit simulator ngspice for Windows.

[ALVARO_CS]

thank you ayeaye
My question refers to isolated systems, that is: neither the source nor the scope are grounded, or at last, the scope ground is its own chassis without an (earth) ground reference, and the setup of the coil-rotor is also "floating" so when the coil is producing AC (via induction) there is no -lead and no "hot" line as both alternate.

Or did I got it all wrong ??
thanks
Alvaro

[ayeaye]

No, you got it right, if your scope is not grounded, then you can connect the scope ground to anywhere in the circuit (floating scope). Make sure though that your scope is not grounded, like when you give it power by a power adapter, then the power adapter may be grounded and then also the scope is grounded.

[ALVARO_CS]

Thank you