Improvements of the charge amplifier used in a capacitive angular-position sensor

The key to robust and yet accurate capacitive angular-position sensors is, besides a smart measurement principle, the design of the charge amplifier. In a given context robust means insensitivity to dirt, moisture and dew on the receiving electrodes. Other environmental influences play a secondary role and can be tackled routinely. This paper presents a charge amplifier model, and compares simulation results with measurements obtained by operating the amplifier under harsh environmental conditions. To verify these simulation results and to distinguish between measurement errors originating from the sensor topology and from the charge amplifier, a measurement system is demonstrated to observe charge amplifier influences on the measurement accuracy in isolation. With the aid of this system and the corresponding model, an improved charge amplifier circuit has been found. The achieved accuracy is fairly high even under the influence of large leakage currents. The superiority of the present model is compared to conventional designs.