An encoder is a device that senses mechanical motion and as a result produces digital signals. It is an electro-mechanical device that helps the users by providing them with vital information regarding position, direction and velocity while operating the motion control systems. There exist a couple of types of encoders, namely “linear” and “rotary”. The difference between these two is the kind of motion they detect. The linear encoder works with motion that is along a linear path while the rotary encoder is concerned with rotational motion. The generic classification of encoders is done in view of the generated output.

The overall linear and rotary encoders are furthers-divided into two classes. They are “incremental encoders” and “absolute encoders”. Both encoders have a similar structure in terms of construction but they are quite different physical properties and understanding of motion.

An encoder classified as an incremental encoder produces a continuous streams of pulses. These pulses are then used for the determination of both position and speed. An encoder of the absolute encoder category can be used to mark positions directly as it produces special bit configurations.

Another name for the incremental rotary encoder is the term “quadrature encoder”. These are the type of encoders that make angular measurements. They do this through utilizing special sensors that use mechanical, ocular and magnetic index for counting.

The absolute encoders have parts that are quite similar to those present in the incremental encoders. These encoders make use of light source (LED) and a photo-detector. The difference in their construction is that they use disks which have concentric circle markings instead of the disks that have uniformly spaced lines as patterns.

The linear encoders are basically sensors, transducers or simply a reading head that is attached to a scale. Its primary function is the encoding of position. The sensor detects the scale and then the position is converted into either an analog signal or a digital signal. The signal is then converted into a digital readout. The movement is measured by the shifts in positions over the progression of time.

This same type of technique is utilized by both types of encoders that is optical and magnetic linear encoders. The main differentiating factors between these two lies in the physical properties.

The two components in a magnetic encoder are a rotor and a sensor. There exist various techniques for the detection of changes in magnetic fields. However, the two main types are the “Hall effect” and “Magneto resistive”. Hall Effect uses the principle of magnetic deflection of electrons that cause variations in the voltage. These changes are then detected by the sensors. Magneto resistive functions on the principle of magnetic fields causing variations in resistance. These changes are then detected by the sensors.