Patent ID: 8258421

Claim:
A shielding gas flow controller ( 100 ) for an electric arc welding apparatus for insertion into a shielding gas supply line between a shielding gas source ( 200 ) and a shielding gas valve ( 800 ) of the electric arc welding apparatus, the flow controller having a shielding gas ( 200 ) input and a shielding gas output ( 600 ), a controllable gas valve ( 110 ) connected between the shielding gas in- and outputs and having a control input ( 170 ), and a controller means having a first input ( 400 ) for receiving a welding signal representing an electrical welding arc current ( 900 ) of the welding apparatus during a welding operation and a gas flow setting control ( 300 ) means adapted to generate a flow setting output being function of the welding signal and representing a desired shielding gas flow, wherein the shielding gas flow controller further comprises an input pressure sensor ( 120 ) connected to the shielding gas input and arranged to provide a shielding gas input pressure measurement ( 150 ) to a second controller means input, and an output pressure sensor ( 140 ) connected to the shielding gas output and arranged to provide a shielding gas output pressure measurement to a third controller means input ( 160 ), and a flow setting output modifying means adapted to modify the flow setting output of the gas flow setting control means based on the shielding gas input and output pressure measurements, the welding signal, and a charateristic of the controllable valve into a control signal ( 170 ) for input to the control input of the controllable gas valve so as to maintain during the welding operation a substantially constant shielding gas flow in the shielding gas supply line to the welding apparatus corresponding to the flow setting output substantially independent of actual shielding gas input and output pressures at the shielding gas in- and outputs, respectively.