Sensitive to dust and humidity. Linear Provide simple non-contact sensing of shafts and rotating objects. Rotational Small and rugged non-contact sensors. Insensitive to oil, dirt, humidity and dust. Require a salient object to trigger the sensor.
Gear teeth provide a natural stimulus for certain proximity sensors.
Linear Best accuracy. Non-contact sensor that uses reflected laser light to measure the distance to an object. Used to make accurate linear displacement measurements. Not nearly the accuracy of a laser interferometer. Because optical encoders can provide position information at high speeds, they are typically found in position and velocity feedback systems.