scope measurement question

hi all,

Can someone clarify if using a scope to measure the voltage across a resistor (e.g shunt resistor) is perfectly fine with a DC supplied circuit? If memory serves me correct it is AC supplied circuit where you have to be careful not to creat a SC due to common grounds.

If someone can clarify this for me, its been some time since i dabbled with a scope.

Thanks

The concern is measuring AC mains voltage which is not isolated from ground. If you hook the ground clip of a grounded scope to one of the AC lines you can create a short-circuit with catastrophic results.

Measuring other types of AC circuit voltages (such as from a normal transformer) that are isolated from the main's ground is ok. Also the measurement of any DC voltages is normally no problem since the DC usually comes from a supply isolated from the AC mains.

This is one of the reasons to use the A-B mode of the scope.