TWI Industrial Member Report Summary 210/1983
By J C Needham
The effects on the voltage waveform of the position of the potential takeoff points and of circuit inductance are described in relation to measurement of resistance in spot welding. Three methods for combating these deleterious effects and for deriving true resistive potentials are given. These can then be utilised in the monitoring and/or control of both resistance spot and seam welding, with potential contacts taken remote from the electrodes, as at the transformer secondary. The preferred method, which is independent of the inductance value, is based on integrating the voltage over the peak part of the current loop. These techniques can also be used for measuring cable resistance in situ, and for distinguishing, for example, between two and three sheet thicknesses in mixed batches.