Abstract
Taking part in the triggered lightning experiments at Okushishiku mountain top, Ishikawa, Japan since 1986, the authors have developed portable digital systems for measurment of fullsize lightning current on site with attainable highest accuracy. The principal difficulties under the strong effects of electromagnetic disturbances by close range lightning discharge, such as shielding of electronic circuits and noise clearing, have been successfully overcome from the viewpoints of both hard- and softwares. A coaxial shunt resistance of 1 mΩ, for which, later on, replaced 0.4 mΩ of minimum residual inductance and an A/D converter with sampling rate of 10MS/s are coupled with a host computer through the optical fiber connection. A series of experimentally obtained waveforms of positive lightning currents are considered to reveal obviously the characteristics of original discharge mechanism. To cover up the inherent weakness of digital measurement for unknown quantities, the extended application of those systems has been realized by introducing an optical LAN system of two range current measurement of different sensitivities or three range with an additional voltage element.
