A measurement method of holding output voltage for air discharges of ESD generator

Abstract

An air discharge immunity test method causes unstable testing reproducibility every testing due to many factors such as the approach speed of an electrostatic discharge (ESD) generator and climate conditions, whereas its method is being used as a mandatory test specified in the International Electrotechnical Commission (IEC) standard, since an actual charged human accompanies air discharges. Furthermore, the IEC standard also prescribes the holding time of over 5 s where the decrease of the discharge electrode voltage due to current leakage, prior to the air discharge, should not be greater than 10 %, despite the fact that the measurement method has not been specified. In this study, we propose a novel method for simply measuring the holding output voltage of an ESD generator with a commercially available high voltage probe connected through a wire to a small metal sphere for contact discharges and air discharges, the principle of which is validated experimentally. To show the effectiveness of the proposed method, measurements of the holding output voltages for two types of defective ESD generators collected from the market are conducted along with a normal ESD generator in a shielding room, in which a temperature and a relative humidity are changed from 24.8 to 29.3 degrees centigrade and from 36.1 to 72.3 %, respectively. The result shows that at an absolute humidity of below 13 g/m3 all the ESD generators provide less than 10 % decrease rates in 5 s just after the trigger of the air discharge mode, however, at an absolute humidity of over 14 g/m3 the defective ESD generators cause more than 10 % decrease rates, while the normal ESD generator gives less than 10 % decrease rates even at an absolute humidity of 21 g/m3.