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How to select an encoder

Selecting the right encoder for your application can be a stressful task. With a variety of outputs, reading types and encoder body options to choose from, how can one get the best sensor for his application?

What is an encoder?
In general, an encoder is a device that converts data from one format to another. In position sensing, an encoder is a device which can detect and convert mechanical motion to an analogue or digital coded output signal.


Let us first explain the difference between incremental and absolute encoders.

Difference between incremental and absolute encoders

The difference between incremental and absolute encoders is analogous to the difference between a stop watch and a clock. A stop watch measures the incremental time that elapses between its start and stop, much as an incremental encoder will provide a known number of pulses relative to an amount of movement. If you knew the actual time when you started the watch, you can tell what time it is later by adding the elapsed time value from the stop watch. For position control, adding incremental pulses to a known starting position will measure the current position. When an absolute encoder is used, the actual position will constantly be transmitted, just as a clock will tell you the current time.

See incremental and absolute encoders.


Rotary and linear encoders

More specifically, an encoder measures position, while velocity, acceleration and direction can be derivated from position in either linear or rotary movement. Different functionality of encoders comes from different physical principles of operation, outputs, communication protocols etc.

 See rotary and linear encoders.

Minimum edge separation

Minimum Edge Separation means the smallest possible time between two adjacent edges of the quadrature signal. It is given as a unit of time (μs). Typical selections are 0.07 μs through 20 μs. When specifying a magnetic incremental linear or rotary encoder, you need to select a Minimum Edge Separation value which is lower than counting ability of counter and faster that the highest speed in your application, when taking resolution into account. Edge separation time is compromised by three parameters: counting frequency of subsequent electronics, maximum system speed and required resolution. Please refer to product data sheet for more information.

See rotary and linear encoders.