All about encoders

Encoders

  • Incremental encoders
  • Absolute encoders – single turn
  • Absolute encoders – multi turn
  • Linear measuring technology
  • Inclinometers
  • Connection technology
  • Technical basics
  • Encoders
  • Introduction
  • Functional principle encoders
  • Incremental encoders
  • Absolute encoders
  • Installing encoders
  • Functional Safety
  • Encoder Technology
  • Encoder Glossary
  • Linear measuring technology
  • Technology magnetic measuring system Limes (incremental / absolute)
  • Technology draw wire systems / Length measuring kits
  • Inclinometers
  • Encoder Technology
  • Encoder Connection technology
  • Encoders Introduction / Cables and connectors
  • Optical fiber signal transmission
  • General information
Encoders can be used in applications, where length, positions, speed, or an angular position are measured. They transform mechanical movements into electrical signals and can be divided into incremental and absolute measuring systems. Incremental encoders generate pulses, where the number of pulses can be a measure of speed, length, or position. In absolute encoders, every position corresponds to a unique code pattern. No reference runs after starting-up are necessary as with incremental systems. Safety is increased and the time taken for reference runs is saved.
Encoders – Introduction
Application examples
In principle, we can supply all encoders, whether with a solid shaft or in a hollow shaft version. Using a hollow shaft encoder saves up 30 % of costs and up to 50 % of the required space compared to a shaft encoder. This is achieved by avoiding additional couplings, brackets, and other assembly aids. To mount a hollow shaft encoder it just needs to be pushed onto the shaft, clamped, and in the simplest case prevented from rotating by using a cylinder pin. Moreover, in principle, hollow shaft encoders require less installation depth.
Encoders Assembly and Function
Optical scanning (incremental)
A disc fitted with a grating, having a code pattern of slits and bars, is mounted so that it can rotate between an LED and a receiver. The light emitted by the LED is modulated by the mask and grating and then strikes the receiver, which produces a signal proportional to the luminosity. When the disc rotates this signal has a shape that approximates a sine wave. Optical scanning (absolute) The light that is emitted by an LED is modulated by a code pattern, which is applied to a rotating disc. A unique bit pattern is assigned to each position and this is generally available as Gray Code. The advantage, compared with incremental encoders, lies in the fact that any movement of the shaft whilst voltage is not applied is immediately detected when power is re-applied, ensuring the correct position is always available.
Magnetic scanning
The magnetic field created by a rotating permanent magnet is scanned by a sensor ASIC. Each angular position has underlying field vectors, which are converted by the ASIC into incremental signals. Depending on the version, this signal will be emitted as an incremental signal or in absolute form as a SSI, 0 … 10 V, 4 … 20 mA signal, or as a Fieldbus signal.
Limes rotary / Limes ring
The Limes rotary magnetic measuring systems are suitable for machines and plants where installation space is tight. The bearing-less and non-contact measuring principle allows error-free operation in environmental conditions that require a high IP protection level (up to IP69k) or high rotary speeds.
Processing of the signals: (optical, incremental encoders)
The sine wave signals are then processed in a specially designed electronic circuitry. Most controllers require square-wave signals on their input. The signals are therefore pre-processed accordingly in the encoder and made available using various output circuits depending on the application.
Encoders: Number of channels
Encoders with one output channel:
Encoders with one output channel are used where no direction sensing is needed, e.g. speed control or length measuring.
Encoders with three output channels:
In addition to the two channels A and B a zero, the pulse is available, which occurs once per revolution and is usually used for the reference run (zero point calibration) of a machine.
Encoders with two output channels:
Applications, where the direction of rotation should be sensed, e.g. positioning, require encoders with two channels A and B being shifted 90° out of phase. By detecting the phase shift, the direction can be determined.

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