Scope question/problem - Page 2 - Electronic Circuits Projects Diagrams Free

Sceadwian · 3rd July 2008, 03:47 AM

Lead based paint usually isn't electrically conductive, it is however electro-magnetically conductive. Even electrically isolated the sheer amount of conductive molecular elements spread across space are equivalent to an RF short circuit. As frequency increases the dielectric becomes less and less an issue.

kchriste · 3rd July 2008, 04:41 AM

This might be the time to build a Faraday workshop! Just kidding as it is overkill for hobby use.
But it is what I use at work when repairing sensitive instruments. I'd go crazy chasing ghosts otherwise. See if your scope probes came with some little spring like pieces which fit over the ground ring on the tip. You'll have to pull off the hook clip to see the ground ring near the probe tip. These are used to provide a shorter ground path when working with RF circuits.

speakerguy79 · 3rd July 2008, 04:54 AM

Yeah, I've used those before, we called them 'pigtails' at the last place I worked (doing PWM amplifier stuff and having to look at edges). I'll see if the probes came with any.

Interesting fact, I looped the wire around itself several times and by varying the orientation was able to make the noise go from >60mv pk-pk to 18mv pk-pk.

I still want to try it in other locations to make sure there's not some issue with the scope and noise, it being a rather expensive purchase for me. But I am feeling a little bit relieved. Still, 12mv pk-pk at Dad's office building seemed like a little more than I expected.

If anyone can tell, I'm real concerned about noise in the work that I do

Mikebits · 3rd July 2008, 05:08 AM

I imagine that the noise level has such a low current, that when the probe is actually on a circuit under test, the signal will vanish.

speakerguy79 · 3rd July 2008, 04:20 PM

I had the ground clip on the probe tip though...

speakerguy79 · 4th July 2008, 02:41 PM

Any other comments?

Mikebits · 4th July 2008, 08:16 PM

The ground clip has x length which acts like an inductor at 200 MHz. Also you may notice this more now because your scope input has such a wide BW. I am really quite envious.
Check think link, it discusses the issue.
http://www.cs.umbc.edu/~plusquel/650...surements1.pdf

Take note of page 9

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3rd July 2008, 03:47 AM	(permalink)
Sceadwian	Lead based paint usually isn't electrically conductive, it is however electro-magnetically conductive. Even electrically isolated the sheer amount of conductive molecular elements spread across space are equivalent to an RF short circuit. As frequency increases the dielectric becomes less and less an issue. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har." Last edited by Sceadwian; 3rd July 2008 at 03:48 AM.

3rd July 2008, 04:41 AM	(permalink)
kchriste	This might be the time to build a Faraday workshop! Just kidding as it is overkill for hobby use. But it is what I use at work when repairing sensitive instruments. I'd go crazy chasing ghosts otherwise. See if your scope probes came with some little spring like pieces which fit over the ground ring on the tip. You'll have to pull off the hook clip to see the ground ring near the probe tip. These are used to provide a shorter ground path when working with RF circuits. __________________ --- The days of the digital watch are numbered. --- Last edited by kchriste; 3rd July 2008 at 04:42 AM.

3rd July 2008, 04:54 AM	(permalink)
speakerguy79	Yeah, I've used those before, we called them 'pigtails' at the last place I worked (doing PWM amplifier stuff and having to look at edges). I'll see if the probes came with any. Interesting fact, I looped the wire around itself several times and by varying the orientation was able to make the noise go from >60mv pk-pk to 18mv pk-pk. I still want to try it in other locations to make sure there's not some issue with the scope and noise, it being a rather expensive purchase for me. But I am feeling a little bit relieved. Still, 12mv pk-pk at Dad's office building seemed like a little more than I expected. If anyone can tell, I'm real concerned about noise in the work that I do

3rd July 2008, 05:08 AM	(permalink)
Mikebits	I imagine that the noise level has such a low current, that when the probe is actually on a circuit under test, the signal will vanish.

3rd July 2008, 04:20 PM	(permalink)
speakerguy79	I had the ground clip on the probe tip though...

4th July 2008, 02:41 PM	(permalink)
speakerguy79	Any other comments?

4th July 2008, 08:16 PM	(permalink)
Mikebits	The ground clip has x length which acts like an inductor at 200 MHz. Also you may notice this more now because your scope input has such a wide BW. I am really quite envious. Check think link, it discusses the issue. http://www.cs.umbc.edu/~plusquel/650...surements1.pdf Take note of page 9 Last edited by Mikebits; 4th July 2008 at 08:19 PM.