Combined Effects of Test Voltages and Climatic Conditions on Air Discharge Currents from ESD Generator with Two Different Approach Speeds

Air discharge immunity testing for electronic equipment is specified in the standard 61000-4-2 of the International Eelectrotechnical Commission (IEC) under the climatic conditions of temperature (T) from 15 to 35 degrees Celsius and relative humidity (RH) from 30 to 60%. This implies that the air discharge testing is likely to provide significantly different test results due to the wide climatic range. To clarify effects of the above climatic conditions on air discharge testing, we previously measured air discharge currents from an electrostatic discharge (ESD) generator with test voltages from 2 kV to 15 kV at an approach speed of 80 mm/s under 6 combinations of T and RH in the IEC specified range and non-specified climatic range. The result showed that the same absolute humidity (AH), which is determined by T and RH, provides almost the identical waveforms of the discharge currents despite different T and RH, and also that the current peaks at higher test voltages decrease as the AH increases. In this study, we further examine the combined effects of air discharges on test voltages, T, RH and AH with respect to two different approach speeds of 20 mm/s and 80 mm/s. As a result, the approach speed of 80 mm/s is confirmed to provide the same results as the previous ones under the identical climatic conditions, whereas at a test voltage of 15 kV under the IEC specified climatic conditions over 30% RH, the 20 mm/s approach speed yields current waveforms entirely different from those at 80 mm/s despite the same AH, and the peaks are basically unaffected by the AH. Under the IEC non-specified climatic conditions with RH less than 20%, however, the peaks decrease at higher test voltages as the AH increases. These findings obtained imply that under the same AH condition, at 80 mm/s the air discharge peak is not almost affected by the RH, while at 20 mm/s the lower the RH is, the higher is the peak on air discharge current.