Source: realpars

Absolute Vs. Incremental Encoders: Major Distinctions

Encoders are vital to motion systems. Data suggests the encoder market will experience a significant spike in growth by 2022. The market is currently dominated by two types of encoders: Absolute encoders and incremental devices. For more information about absolute encoders, you can visit rozum.

So, what sets them apart?

Absolute Rotary Encoders

Source: amazon

Rotary devices link to a shaft, as the shaft oscillates, the device sends out pulses. These pulses indicate the velocity of the object. By calculating the sum of pulses per one complete rotation of the shaft, the resolution can be determined.

These devices provide a square-wave signal in two conduits that are counterbalanced to each other by 90 degrees. As the rotation augments, an output signal is stimulated.

Absolute Encoders

Source: rls

The benefits of an absolute rotary device have is that it offers a unique position value immediately. It comes on by examining the position of a coded element.

Absolute encoders are made up of device disc- which is made up of slots on a power-transmission shaft and a stationary pickup. The drive saves a dedicated code for each shaft position. Each position is synched to a unique system. It also records movements that happen when there is a power outage into accurate position values immediately; the encoder is switched on again.

We have two types of absolute devices, namely:

Single-turn and multi-turn devices.

The Single-turn device is responsible for calculating displacement in a single turn from a starting position. The process is repeated for every revolution.

Multi-turn devices function just like single-turn; however, they differ in the way they track the sum of revolutions of the shaft using a unique word for each position and number of revolutions.

Absolute rotary devices are a better option as the safety system is superior. Single-turn is a preferable choice as it is suited for short travel situations. Multiple-turn are ideal for complex positioning. The latter logs position data electronically using binary format. Its resistance to electrical noise is a significant advantage over incremental devices.

Note, absolute rotary devices are more expensive than incremental devices.

Absolute Rotary Encoder Advantages

Source: motioncontroltips
  • Recalls its position after an electrical failure provides nonstop position monitoring
  • It has scaling, and Fieldbus functions, speed, preset.
  • It allows you to ascertain the precise position of a machine and regulate the storage of electronic data.
  • Flexible interface options ranging from analog, Parallel, Ethernet, Serial and Fieldbus
  • Single-turn and Multi-turn revolution options are obtainable.
  • It operates on a magnetic measuring principle.
  • Absolute devices come with a resolution of up to 16 bits, or 65,536 pulses per revolution (PPR).

Incremental Encoders

Source: wikipedia

The output signal of incremental devices is created every time the shaft oscillates for a specified period. The sum of signals per turn determines the resolution of the device.

Each time the devices comes on, it starts counting from zero, notwithstanding the previous position of the shaft.

Incremental encoders have two essential requirements:

  •  A starting point must be marked in all positional tasks, especially during the startup of the control system and when power to the device has been interrupted.
  •   Incremental devices must re-home using the appropriate reference point when shut down.

Rotary incremental devices come with an external buffer for data storage. It comes with battery backups that jettison the need for re-homing after scheduled or unscheduled shutdowns. Incremental encoders’ ease of use and cheapness make them a better alternative to absolute devices.

Incremental Rotary Encoder Advantages

Source: techtonics
  • Perfect for pulse counting or frequency observation usages such as speed, direction, and position monitoring
  • Cheaper than an absolute device and less complexity.
  • A, B, Z, and inverted signals as HTL (Push-Pull) or TTL (RS422)
  • It has a pulse count of up to 16384 PPR
  • The scaling functionality is adaptable.
  • It uses a magnetic measuring principle
  • Incremental devices come with a 50,000 PPR resolution.

Significant differences between absolute and incremental devices

As you have already come around the general understanding of both types of devices, their respective uses, benefits as well as other properties, now is the time to state differences tied to these different sets of devices.

  • The absolute devices come along with a unique device or series of numbers for each shaft position to determine the status of the encoder itself. But in the case of the incremental devices, it is the other way around. The incremental devices are to generate a specific, one time, digital signal every time the shaft rotates to a certain angle.
  • The absolute encoders are cost-effective devices and don’t consume power at all times. The only costs that you would have to bear regarding the absolute devices are when a reading is taken. Only then would it use a fraction of electricity to carry out its duties, and once the text is received and stored, the consumption would again reach zero. On the other hand, the incremental device needs to be powered throughout the operation of taking the reading and then interpreting and storing it. Even after that, it would consume power and hence is less cost-effective.
  • To bring about a design that requires less power input is not easy at all, the orchestration of design, its physical infrastructure as well as the mode of operation each and everything is quite costly to manage and come about. So, in comparison, the absolute devices cost more than the incremental devices. The very reason regarding which the incremental encoders are less expensive is that these are less complicated than the absolute devices.
  • One of the most leaping and convenient benefits brought about by the absolute device is that it would retain all of the information which it was recoding even if the power is lost. But on the other hand, each time the power is unplugged, or a surge occurs, the system would display an error in terms of the incremental devices. Thus, the reading would have to be retaken, and all efforts would go futile.

As you have assembled a brief integration regarding both absolute and incremental devices, it is now up to you to place a verdict depending on the type of business you run and regarding your various requirements. Both of these can be an ideal fit for specific companies, and in comparison to customized solutions, having the characteristics of both are also available. However, it still would depend on your business needs and other features as well.

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