had a couple questions enter my mind while pondering using my snap on low amp clamp, how does the ground connection affect your amp clamp readings? say you have the ground going straight into your scope, is the shielding on the wire and in the clamp working? would it change anything if the ground from the amp clamp goes to the scope, and also to a test lead to ground on the vehicle? would it help or hinder interference? make the shielding work better? that’s why the shielded test leads work, the shielding in the test lead is grounded to the vehicle you are testing. snap on scopes share the ground, so if you have the amp clamp on one channel, and measuring voltage on the other channel at the same time? does it affect the amp clamp reading since it’s sharing a ground with the voltage reading? hence my previous question? never understood how you can have common ground, and measure two different signals. you would think it would screw up your measurements. any thoughts?? probably over thinking it, but that’s how you learn. if you never ask why you never learn anything new.
First, there is an important difference between AC and DC. This goes for the way the amp clamp works as well as how the signals (may) affect each other. When measuring DC signals generally they refer to the low potential (Bat negative) as ground/earth/low reference etc. As long as all relevant signals refer to the same low potential there will be no problem to measure any number of signals at the same time.
AC signals are different, they do not refer to a steady common low potential but as they change direction and magnitude of current flow so will their reference. You may want to connect one of your SO scope channels to an inductive crank sensor - signal and ground wire - and another channel to a digital signal like cmp. Look what happens, don't be afraid you won´t hurt anything.
Regarding how amp clamps work: in DC mode they typically employ a hall sensor to measure the magnetic field strength through induced voltage which then is translated into current flow. This signal obviously does need a (low) reference in order to be meaningful.
Shielding is a technique used to keep interference away from the relevant signals, it is ment to take out the disturbing noise by grounding it. Ground, again, is the low potential and for the very same reason an amp clamp reading will not be affected by a simultaneous voltage reading with the same ground/low potential.
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