CAPACITIVE ROTATION SENSOR
Capacitive Rotation Sensor
In the arrangement one plate of the capacitor rotates with a rotating object (shaft) and the other plate is kept stationary. Since the common area A is proportional to the angle of rotation q, may be written as
where K is a sensor constant. This is a linear relationship between C and q. The capacitance may be measured by any convenient method. The sensor is linearly calibrated to give the angle of rotation. The sensitivity of this angular displacement sensor is
Capacitive Displacement Sensor
The arrangement) provides a sensor for measuring transverse displacements and
proximities. One of the capacitor plates is attached to the moving object and the other plate is kept stationary. The sensor relationship is
Again, the sensitivity is unity (negative) in the nondimensionalize form, which indicates direct sensitivity of the
sensor (in the reciprocal sense).
Since the gain of the operational amplifier is very high, the voltage at the negative lead (point A) is zero for most practical purposes (because the positive lead is grounded). Furthermore, since the input impedance of the op amp is also very high, the current through the input leads is negligible.
Linearizing amplifier circuit for a capacitive transverse displacement sensor.