monitoring the secondary current ... 100,000Amp
1) is that 100 thousand amps?
2) as far as I remember welding require DC.
3) you are measuring the primary AC where a current transformer works.
4) just visualize if you were to measure the DC current and get 100mV you would need a resistor of one millionth of an Ohm and capable of handling 10.000 watts.

If, indeed the welding is done with 100 thousand amps (I doubt it) there is no way I know of.

Erik