Rockwell Automation Publication 842E-UM001C-EN-P - September 2016 11
Chapter 2
Encoder Overview
The 842E family of encoders uses EtherNet/IP technology to provide its data 
to a programmable controller. These encoders include an embedded 
EtherNet/IP switch to connect additional EtherNet/IP capable products in 
series and/or support a Device Level Ring (DLR) topology for Ethernet media 
redundancy.
The 842E is an ultra-high resolution encoder in single-turn and multi-turn 
versions. These encoders have 18-bit single-turn resolution. The multi-turn has 
an additional 12 bits for counting the number of revolutions.
Overview of the Encoder
What Is an Encoder?
Encoders can electronically monitor the position of a rotating shaft to measure 
information such as speed, distance, RPM, and position. Rockwell 
Automation® offers various light- and heavy-duty incremental and absolute 
encoders. Our accessories help you easily install and efficiently use our 
encoders.
What Are the Different Kinds of Encoders?
Incremental
A simple and cost-effective solution for a wide variety of applications, 
incremental encoders electronically monitor the position or speed of a rotating 
shaft. Encoder feedback is compatible with programmable controllers, 
numerical controllers, motion controllers, and other position systems. 
Rockwell Automation® offers light-duty and heavy-duty incremental encoders 
for different shaft loads. Ruggedized incremental encoders are available with an 
enclosure rating of NEMA Type 4 and IP66. Incremental encoders are also 
available in solid and hollow shaft models for various mounting options. 
Applications include: machine tools, packaging machinery, motion controls, 
robotics, and DC drives.
Absolute
An absolute encoder has a unique digital output for each shaft position. The 
use of absolute encoders assures that true position is always available, regardless 
of power interruptions to the system. Absolute encoders can be single-turn or 
multi-turn.