The invention relates to a method of measuring the voltage over the welding seam in a roller head welding machine or spot welding machine with wire electrodes. The invention furthermore relates to a device for carrying out the process.
It is known to monitor the quality of electrical welds, in which connection reference may be made to European Patent Application No. 373 422. Such a device in particular requires measurement of the voltage over the welding seam in order to control the energy input to the welding seam.
As is well known (DE-PS 38 22 908), voltage measurement takes place on the roller head mount or on the roller head. This necessitates a costly compensation of the parasitic resistances measured at the same time, which arise from contamination of the roller head, from the bearings and from the means for transmitting welding current to the roller heads.