1. Home
  2. Electronics Design
  3. Active Probe vs Differential Probe
  4. Page 2

Active Probe vs Differential Probe

[snip]

Hopefully I got this right. It's somewhat new ground for me. (Hey! A pun :) )

1) Battery powered scope: I say no problem with CM noise. The scope probe and scope form only 1 loop. Same with a USB scope +battery powered laptop. It all floats.

2) Scope without ground plug:

Electric Box -----L--------[ ] Scope---probe--->[PCB] +------------N--------[ ] |----------->[ ] |------------G----X X----+ ~ + capacitive | coupling | to +------------------------- earth

Note: Risky...

There are 2 loops. The probe coax is one.. The earth path is the other. Since G and N meet at the electric box, it's up to the scope's power supply to not couple noise. I'd expect more CM noise compared to a battery powered scope.

D from BC

Reply to
D from BC
Loading thread data ...

Sure, as long as you don't get zapped. A rig like that could work kilovolts off ground. "Optocouple" the waveforms back to ground by photographing the screen!

The last case, regular scope without a ground plug, will still have some capacitive coupling back to the AC line, so some hf ground-loop noise can still happen.

But, in all cases, only one floating common exists. The Tek TPS allows four separate folating signals to be scoped simultaneously.

John

Reply to
John Larkin

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.