What is the Difference between Absolute and Incremental Encoders?

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There are many types of encoders but they basically fall into two main sensing techniques. Those being: Linear and Rotary.

Within those categories, there differing encoder measurement types such as absolute and incremental.

There are also various electromechanical technologies such as magnetic, optical, inductive, capacitive, and laser, to name a few.

The Linear Encoder uses a transducer to measure the distance between two points. These encoders can use a rod or a cable that is run between the encoder transducer and the object that will be measured for movement.

As the object moves, the transducer’s data collected from the rod or cable creates an output signal that is linear to the object's movement.

As the distance is measured, the Linear Encoder uses this information to determine the position of the object.

An example of where a Linear Encoder may be used is for a CNC milling machine where precise movement measurements are required for accuracy in manufacturing.

Linear Encoders can be “Absolute” or “Incremental” measurements.

A Rotary Encoder collects data and provides feedback based on the rotation of an object or in other words, a rotating device. Rotary Encoders are sometimes called Shaft Encoders.

This encoder type can convert an object’s angular position or motion based on the rotation of the shaft, depending on the measurement type used.

“Absolute Rotary Encoders” can measure “angular” positions while Incremental can measure things such as distance, speed, and position.

Rotary Encoders are employed in a wide variety of application areas such as computer input devices like mice and trackballs as well as robotics.

The next encoder, which is a “Position” Encoder, is used to determine the mechanical position of an object. This mechanical position is an “absolute” position.

They may also be used to determine a change in position between the encoder and object as well. The change in position in relation to the object and encoder would be an incremental change.

Position Encoders are widely used in the industrial arena for sensing the position of tooling and multi-axis positioning. The Position Encoder can also be Absolute or Incremental.

“Optical” Encoders interpret data in pulses of light which can then be used to determine such things as position, direction, and velocity.

The shaft rotates a disc with opaque segments that represent a particular pattern.

These encoders can determine the movement of an object for “rotary” or “shaft” applications while determining the exact position in “linear” functions.

Optical encoders are used in various applications such as printers, CNC milling machines, and robotics. Again, these encoders may be Absolute or Incremental.

In a Rotary “Absolute” measurement type encoder, a slotted disc on a shaft is used in conjunction with a stationary pickup device.
When the shaft rotates, a unique code pattern is produced.

This means that each position of the shaft has a pattern and this pattern is used to determine the exact position.

If the power to the encoder was lost and the shaft was rotated, when power is resumed, the encoder will record the absolute position as demonstrated by the unique pattern transmitted by the disc and received by the pickup.

For incremental measure encoders, the output signal is created each time that the shaft rotates a measured amount. That output signal is then interpreted based on the number of signals per revolution.

The incremental encoder begins its count at zero when powered on. Unlike the absolute encoder, there are no safeguards regarding the position.

Because the incremental encoder begins its count at zero in startup or power disruption, it is necessary to determine a reference point for all tasks requiring positioning.

Hopefully, we have given you a basic understanding of what’s out there and when you may want to choose one particular type over the other.

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