page_title: Incremental encoder
section_title: Mechanical
hierarchical_section_title: Incremental encoder / Signal types / Mechanical
caption_attribution_description: English: rotary encoder with pushbutton Deutsch: Inkrementalgeber mit Taster
context_page_description: An incremental encoder is a linear or rotary electromechanical device that has two output signals, A and B, which issue pulses when the device is moved. Together, the A and B signals indicate both the occurrence of and direction of movement. Many incremental encoders have an additional output signal, typically designated index or Z, which indicates the encoder is located at a particular reference position. Also, some encoders provide a status output that indicates internal fault conditions such as a bearing failure or sensor malfunction.
  Unlike an absolute encoder, an incremental encoder does not indicate absolute position; it only reports changes in position and, for each reported position change, the direction of movement. Consequently, to determine absolute position at any particular moment, it is necessary to send the encoder signals to an incremental encoder interface, which in turn will "track" and report the encoder's absolute position.
  Incremental encoders report position changes nearly instantaneously, which allows them to monitor the movements of high speed mechanisms in near real-time.
context_section_description: Mechanical (or contact) incremental encoders use sliding electrical contacts to directly generate the A and B output signals. Typically, the contacts are electrically connected to signal ground so that the outputs will be "driven" low when the contacts are closed, effectively making them mechanical equivalents of open collector drivers and therefore subject to the same signal conditioning requirements (i.e. external pull-up resistor).
  The maximum output frequency is limited by the same factors that affect open-collector outputs, and further limited by contact bounce – which must be filtered by the encoder interface – and by the operating speed of the mechanical contacts, thus making these devices impractical for high frequency operation. Furthermore, the contacts experience mechanical wear under normal operation, which limits the life of these devices. On the other hand, mechanical encoders are relatively inexpensive because they have no internal, active electronics. Taken together, these attributes make mechanical encoders a good fit for low duty, low frequency applications. For example, PCB- and panel-mounted rotary mechanical incremental encoders are commonly used as hand-operated controls in electronic equipment.
caption: A PCB-mounted, rotary mechanical incremental encoder
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