Acoustic measurement of the arc voltage applicable to arc welding and arc furnaces

A new technique is proposed for determining the time evolution of the voltage in the column of an electric arc. It is based on measurement of the sound wave produced by the arc, which is shown to depend on the rate of change of the electrical power fed to the arc column. There is no electrical connection to the arc circuit so that the errors usually caused by the voltages induced by the arc DI/dt's and ohmic drops in the arc electrodes are avoided. The technique is of interest for controlling the voltage or length of the arc and offers applications in arc welding and the operation of arc furnaces.