Further Effects of Test Voltages, Relative Humidity and Temperature on Air Discharge Currents from Electrostatic Discharge Generator

Air discharge immunity testing for electronic equipment is specified in the standard 61000-4-2 of the International Electrotechnical Commission (IEC) under the climatic conditions of relative humidity from 30 to 60 % and temperature from 15 to 35 degrees Celsius. This implies that the air discharge testing is likely to provide significantly different test results due to a wide climate range. To clarify effects of the above climate conditions on air discharge testing, we previously measured air discharge currents from an electrostatic discharge (ESD) generator with test voltages from 2 kV to 15kV at an approach speed of 80 mm/s under 6 combinations of relative humidity and temperature in the IEC specified and non-specified climate range. The result showed that the same absolute humidity provides almost the identical waveforms of the discharge currents despite different relative humidity and temperature, and also that the current peaks at higher test voltages decrease as the absolute humidity increases. In this study, we further examine the effects of air discharges on test voltages, relative humidity and temperature with respect to two different approach speeds of 80 mm/s and 20 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 climate conditions, while at a test voltage of 15 kV in the IEC specified climate range 20 mm/s approach speed causes the current waveforms entirely different from those at 80 mm/s despite the same absolute humidity, and the peaks are not affected by the absolute humidity, however, under the IEC non-specified climate conditions, likewise the case at 80 mm/s, the peaks decrease at higher test voltages as the absolute humidity increases.