Potential gradient is measured using an EFM-100 Electric Field Mill from Boltek. It is mounted in inverse position about 0.9 m above ground using Boltek 3 feet tripod inverting mounting kit.
Calibration was done using a reference EFM-100 located on the ground surface at several places around the installed EFM-100 to find a correction factor, which is applied on raw data.
Analog output of EFM-100 is sampled at 25 Hz by dedicated datalogger with GPS time stamping. Data are stored in specific binary format before being converted to BADC-CSV.
The instrument is located at Studenec, station of West Bohemian seismic network of the Institute of Geophysics CAS, Czech Republic 50.258°N, 12.518°E at 666 m a.s.l.
Measurement frequency is 25 Hz (0.1 s response time)
This is used in the Glocaem potential gradient network