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.