in an electric discharge machine including an electrode and a workpiece installed opposite each other with an insulating working liquid filling the gap therebetween and which is used to machine the workpiece by causing an electric discharge across the gap , two components of the frequency spectrum of the voltage waveform of the electric discharge across the electrode and the workpiece are analyzed to distinguish between normal and abnormal discharge conditions . the device includes elements for determining the conditions in the gap and which generate a signal according to the conditions of the interpole gap , based on the results of this analysis . when an abnormal condition exists , the size of the interpole gap may be changed , and the quiescent time between application of pulse voltages may be altered . also , depending on the degree of abnormality , different quantities of dielectric fluid may be pumped through the interpole gap to remove accumulated impurities .