The objection of this study is to develop a lightning warning system based on the measurement of electric field intensity on the ground level.
In this thesis, changes of the electric field intensity formed by thunderclouds are theoretically described. Also two types of calibration system, such as a cylindrical guard electrodes and a parallel-plate electrodes, are proposed to determine the sensitivity and frequency bandwidth of the lightning warning system.
In order to accomplish the high sensitive lightning warning system, the principles and design rules of a rotation-type field mill are studied. The lightning warning system consists of the rotation-type field mill as an electric field sensor, an impedance changer, and a two-stage amplifier.
The field mill is composed of two isolated electrode vanes, a grounded stator and a rotor. The impedance changer necessary to maximize the time-constant of the lightning warning system is designed by using an operational amplifier(CA3130) with extremely high input impedance of 1.5 [TΩ].
From the calibration experiment, the frequency bandwidth and the sensitivity of the field mill are DC ∼ 200 [Hz] and 0.267 [mV/V/m], respectively. Maximum resolution of the developed lightning warning system is about 73 [V/m], and can be measured the electric field strength up to about 18.7 [kV/m]. For the purpose of measuring a higher level of the electric field strength, the sensitivity can be conveniently adjusted with a voltage divider in parallel connected to the output of the impedance changer.
To ensure the sensing ability of the developed lightning warning system in the actual situation, computer simulation using thundercloud models was carried out, and the result showed that the system can monitor the movement of thunderclouds within 6 [km] from the observation site.