Capacitive proximity sensor with an integrated drift compensation electrode

Capacitive proximity sensors suffer from output drift caused by atmospheric changes and circuit temperature rise, which particularly affects long-range measurements. Existing compensation methods often increase system complexity or fail to address circuit-specific drift. This paper proposes a novel drift compensation method integrating a calibration electrode (CE) into the sensor structure, enabling switching between proximity sensing and drift measurement modes using a single detection circuit. In the sensing mode, the CE is open, and object proximity is detected. In the calibration mode, the CE is grounded, shielding the sensor from objects and isolating drift. Drift is compensated by subtracting the calibrated value. Evaluations showed that narrower gaps between the sensing and calibration electrodes improve the detection and compensation performance, although excessively narrow gaps prevented compensation. Long-term experiments demonstrated a reduction in drift variation over 6 h, achieving stable detection of a proximity object beyond 30 cm. This method significantly enhances the measurement range of capacitive proximity sensors. • A dedicated calibration electrode is installed above the sensing electrode for drift compensation. • Capacitance is measured using an astable multivibrator circuit. • Long-range proximity detection is achieved by compensating for sensor drift.