Abstract

Linear dipole type DC electric field sensor was newly developed, and continuous observations by means of 3-D sensor system composed of three sensors installed orthogonally with each other have been conducting since 2017. However, their measured intensities have been remained uncertain, because they could not be calibrated from a reason that, at present, there dose not exist any facility for making uniform electric field in a wide area. So, in order to establish a method for obtaining reliable electric field intensity from output voltage of the sensor system, fundamental function of the sensor system has been examined. Since resistor R which is to be connected to input terminals of differential pre-amplifier is a key parameter in the sensor system, it was needed to examine a characteristic curve of the output voltage as a function of R. For this purpose, simultaneous observations of natural electric fields were conducted by means of plural sensor systems installed in parallel. From obtained characteristic curve, an optimum value of R could be decided, and a formula showing a relation between reliable electric field intensity and output voltage of the sensor system was found. Validity of the formula has been verified by results of simultaneous observations of a lightning pulse by means of two vertical sensor systems whose element lengths were different. Their results have shown same electric field intensity. As the result, the linear dipole type DC electric field sensor system with the formula has been perfectly established as a practically useful sensor system.