Ignoramus29580 wrote:
Let's say that I have a cable and I want to measure the AC current
going through it. Up to, say, 100 amps.

I could use a current transformer, right?

If I have a say 200:1 current transformer, then on a 100 amp AC
current it would want to produce a 0.5 amp current. Then if I stick,
say, a 1 ohm resistor across it, it would produce 0.5*1 = 0.5 volts
AC across the resistor.

Is that right?

Yes, assuming that you haven't exceeded the primary
or secondary current ratings for the transformer.

Furthermore, since you're probably looking to
use it on your tig welder inverter, the transformer
probably should be rated to be accurate for
pulse work rather than just 60hz sine waves.

Here's more than you want to know about CT's:

http://www.kappaelectricals.com/technical.html#current

Oh, and don't ever leave the secondary open with
a load in the primary....