Robust Analog Multisensory Array System for Lossy Capacitive Sensors Over Long Distances

A robust capacitive multisensory readout system is presented in this article. The system consists of a few thousand lossy capacitive-based sensors that can be modeled as a parallel connection of sensor capacitor and undesirable leakage resistance. The real system in our application will consist of a high number of capacitive sensors used for the monitoring of relative humidity in a high-energy detector at the European Organization for Nuclear Research (CERN). However, our findings apply to any set of capacitive devices aimed at any other sensing application. Furthermore, the proposed system is intended for harsh environments (e.g., with high radiation levels and magnetic field presence) where the readout system is separated from the sensor and placed far away, connecting to them via cables. In such cases, the presence of cables brings another issue to the readout system-parasitic capacitance. Using long cables, we introduce high values of parasitic capacitance that make the sensor capacitance practically invisible to the readout unit. This article presents an effective, robust, and analog method, based on a quadrature-phase shifter and an auto-balancing bridge, used to overcome the sensor leakage resistance and parasitic capacitance caused by the cables. The experiments for various values of capacitance and leakage resistance at different frequencies and the influence of different cable lengths and types are analyzed and discussed.