Eletric field detectors (EFD) on the EXOS-D satellite measure the vector electric field by both the standard double probe technique (EFD-P) and the newly developed ion beam technique (EFD-B). The EFD-P system has proved to provide high quality data due to the direction of the antennas which is always perpendicular to the sun-earth direction regardless the spin phase of the satellite. The EFD-B ststem has not yet been fully operated and we are waiting for an orbital phase suitable for the beam experiment. This paper describes the instrumentation of both systems, and preliminary observational results obtained by the EFD-P such as the Langumuir characteristics of the probe in the plasmasphere and the convection electric field in the auroral ionosphere.