This part of ISO 17657 specifies current sensing coils of the toroidal-coil type as a current sensor for welding current meters or a welding current measuring system used to monitor the welding current in resistance welding, and is applicable for both current types, i.e. alternating current of 50 Hz or 60 Hz and direct current.
GSO ISO 17657-3:2013 history
2013GSO ISO 17657-3:2013 Resistance welding -- Welding current measurement for resistance welding -- Part 3: Current sensing coil