full thottle switch - how ammeters work

[amalventano at sc.rr.com (Allyn)]

> By the way, how can a meter NOT receive voltage if it's reading
amps??????????????  i.e. one > MUST have voltage in order to have amperes.
Right, Toby?  Allyn?

> Larry

ok, larry, heres how it works. its not that the meter must _receive_
voltage, its that its only capable of _reading_ voltage. when reading
amperes the input is ran through a *very* low internal resistance (a shunt).
the meter then internally reads the voltage across the shunt, and displays
it with a current scale instead. the lower the shunt resistance, the more
accurate the reading (you want the meter to look like the rest of the
circuit - i.e. straight piece of wire), so the shunt resistance is usually
very low (0.001 ohms). so, basically, a meter set to read current is similar
to running around with a set of jumper cables (well, they cant handle that
much current, but you get the point).

hth
Al