In the previous article, we explained the working principle of an encoder and provided a detailed introduction to incremental encoders. Today, we will discuss another type of encoder: the absolute encoder.
As the name suggests, an absolute encoder is an encoder that outputs an absolute value. We know that an encoder consists of a connecting shaft, a code disk, a light source, and an output circuit. The code disk of an absolute encoder differs significantly from that of a relative encoder, as shown in the following diagram:
The left side shows the code disk of an absolute encoder , and the right side shows the code disk of an incremental encoder. It can be seen that the gratings on the incremental encoder code disk are evenly distributed, while the absolute encoder code disk is divided into many bands of varying sizes. The following image may make this clearer:
An absolute encoder outputs a set of binary numbers. Its code disk is divided into many concentric channels, each called a "track". Each track has a separate output circuit to represent a single binary bit. For example, in the diagram above: the outermost track represents bit 0, followed by bit 1, bit 2, and bit 3. The more tracks there are, the wider the measurable range. The diagram below shows the waveform of the track output circuit when the code disk rotates:
Absolute encoders can be divided into single-transformer and multi-transformer encoders. Single-transformer encoders can measure the absolute position within one revolution and are suitable for measuring angular displacement; the number of revolutions that multi-transformer encoders can measure depends on the encoder design and is generally used to measure length and determine the accurate position within a certain length.
The main differences between absolute encoders and incremental encoders are as follows:
1) Incremental encoders output pulse signals, while absolute encoders output a set of binary values;
2) Incremental encoders do not have a power-off retention function, while absolute encoders can retain data after power failure;
3) Incremental encoders have no limit on the number of revolutions, while absolute encoders cannot exceed the range of revolutions;
4) Incremental encoders are relatively cheaper;
Remember this: the biggest difference between absolute encoders and incremental encoders is the difference in their code disks. Additionally, many encoders used in industry today support bus-based output (such as Profinet). These encoders, which integrate bus interfaces, can be accessed directly via the bus, which is very convenient.
