Abstract: To meet the requirements of electric field detection in low-density, high-impedance plasma environments, a spherical electric field sensor and its associated signal-processing circuitry were investigated. The sensor features a potential reference that can float with the input signal. The V–I characteristics, ideal operating point, and impedance characteristics of the spherical probe were analyzed based on the orbital-motion-limited (OML) theory. A floating power supply was designed for the preamplifier, enabling the probe to measure potentials within ±100 V. Meanwhile, a stable bias current over a range of ±90 μA was achieved through a linear control scheme applied to the bias current. In ground-based simulation experiments, the V–I curves obtained from probe scanning agreed well with the theoretical model. The derived electron density ranged from 1.64×10¹⁰ to 1.92×10¹⁰ m^-3, while the electron temperature ranged from 0.468 to 0.508 eV, consistent with the preset plasma parameters. When the probes operated stably at the ideal operating point, the average potential difference between the two probes was 0.037 V, which was close to zero. Experimental results show that the dual-probe sensor can achieve potential measurements over a large dynamic range with good inter-probe consistency. The bandwidth reaches 88 kHz, and the equivalent electric field noise is 1.65 mV/m at a 50 m probe separation. These characteristics enable differential measurements of space electric fields.