The following video explains the functioning of an incremental encoder. Distance measuring systems using this type of encoder can also be named as a relative or incremental measuring system.
The absolute encoder has a coded disc. Each track of this disc represents a binary number of the code. As an example, you see here the binary code .
The construction of an absolute encoder is more complex compared to an incremental encoder, since it requires a decoder. But the big advantage is that any angle position of the shaft can be read at any time - even after a power failure. Therefore it can not lose a count value.
If you want to count the number of revolutions, you need a multiturn encoder. This example shows a two-stage multiturn encoder with its main components.
In order to count the number of revolutions, an internal reduction gear is connected to the drive shaft. So the measured value is composed of the angular position and the number of revolutions. Depending on the number of revolutions which have be counted, more gears with encoder discs can be added.
This animation describes the great advantage of the direct measurement to the indirect measurement using the example of a milling machine
The resolver is a sensor used in a servo drive system to give information about rotor position and rotational speed. As a feedback device, it closes the gap to a closed-loop motor control system.