A capacitive encoder uses the change in capacitance value of a capacitor as a means to measure displacement. Typically, the capacitive sensor’s principle elements are arranged so that the capacitance changes as a moving elements displace relative to the stationary plates of the capacitor.
The capacitance effect is used in lots of sensors:
Capacitive encoders can offer high-resolution and accurate position measurement in benign environments. Capacitive encoders are, however, uncommon in safety related applications because they can be sensitive to foreign matter or changes in temperature or humidity. The effect of condensation or buildup of electrostatic charge on a capacitive encoder can lead to mis-reporting of position.
Inductive encoders, such as IncOders from Zettlex are increasingly viewed as a suitable alternative to capacitive encoders – particularly for harsh environment applications, such as aerospace, defence, medical and oil & gas.