Combined effects of relative humidity and temperature on air discharges of electrostatic discharge generator

An air discharge immunity test for electronic equipment prescribed in the International Eelectrotechnical Commission (IEC) standard causes unstable testing reproducibility due to many factors such as the approach speed of an electrostatic discharge (ESD) generator, relative humidity, ambient temperature and the like. Nevertheless, the air discharge method is a mandatory test in the present IEC standard which also specifies as climate conditions relative humidity from 30 % to 60 % and temperature from 15 to 35 degrees centigrade. This implies that the air discharge testing is likely to provide significantly different test results due to a wide range of climatic conditions. To elucidate the above climatic effects on air discharge testing, we measure air discharge currents from an ESD generator under several combinations of relative humidity and temperature. The result reveals that absolute humidity, which is derived from the relative humidity and the saturated water-amount determined by the temperature, is the same the discharge current waveforms become almost identical despite different relative humidity and temperature.