Incremental and Aboslute encoder
Encoder is a rotary transducer capable of proportionally converting the displacement made to its rotation shaft into an electrical signal. The electrical signal, incremental or absolute, is used by the acquisition system to quantify and control the movement of the moving parts. The encoder therefore acts as a measuring system for moving parts. Let’s find out what is the difference between incremental and absolute encoders?
Incremental information consists of a two-bit Gray code (phases A and B) in quadrature (50% duty cycle). The phase shift between the two bits is 90 ° electrical and it is necessary to check the direction of rotation. Hohner Automazione srl assumes by convention that the increase is positive when phase B anticipates phase A with rotation of the shaft clockwise, with a view from the same. A reference (Zero or Marker) is also available, which indicates the completion of the tour completed. The size of this pulse can be supplied on request from 90 ° electric up to some periods (with reference to the duration of the pulses)
The following paragraph illustrates the functionality of the absolute encoder from which we understand the difference between incremental and absolute encoders.
The absolute mode provides unique signal encodings, clearly indicating the sense of increase and the value achieved avoiding costly calculations. This technique is useful for angolar applications. Consider the association that can be obtained between a 360 position encoder and the angle of rotation: 1 ° = 1 position. In environments where the problem on power supply would make encoder rephasing difficult and expensive, absolute detection is extremely advantageous. The reading of the absolute position is taken directly from the coded optical disk. The disc being integral with the shaft allows not to “forget” the position even in the absence of the encoder power supply.
Gray, Binary, BCD, ASCII are codes generally used to express univocally the position assumed by the encoder
GRAY: The main characteristic of Gray code is the change of only one bit at a time: this one technique allows to univocally interpret the value assumed in that position and is an extremely convenient code to use in very noised environments.
BINARY: is used by all computing equipment: the encoders that provide this encoding are useful when it is necessary to save time otherwise spent in the conversion of the code itself.
BCD: is useful in all those systems that directly request the display of the position taken by the encoder in a certain position (display, counters): this coding is structured in decades where each digit indicates a decimal weight.
ASCII: (mostly used in serial systems) allows the encoder to talk directly with Personal Computer through interface cards and standard or dedicated protocols.
The difference between incremental and absolute encoders is therefore clear. It is possible to conclude by recommending the incremental encoder where positioning is required and the absolute encoder where a cyclical angle control and / or in the absence of encoder power supply is required.
Hohner Automazione srl presents on its website a complete range of incremental and absolute encoders