08.04.2016

A Single-cable solution: Absolute rotary encoders with Power over EtherCAT

Industrial Ethernet is now a widely accepted standard for automation technology. The networking of devices familiar from the traditional field buses have also been established for new, Ethernet-based interfaces; the bus cable is connected from one device to another. Together with the voltage supply, each node has 3 connector cables. Occasionally this "Daisy-Chain" cabling is not practical. When that occurs, the Power over Ethernet system, offered as an option by TR-Electronic for the Cxx58 family with EtherCAT-P, is an exceptional choice. . The rotary encoder is then supplied with voltage by suitable distributors, e.g. from Beckhoff, directly via the data cable. A star distribution topology is used for this purpose, i.e. each remotely supplied node has its own cable to the distributor node. This is comparable to Power over Ethernet in an office environment, where for example, VoIP phones, access terminals, network cameras and WLAN access points are directly supplied by a switch. If star wiring is advantageous for a specific system configuration, the wiring requirement can also be reduced to one line per rotary encoder through Power over EtherCAT-P. On each line, a maximum of 3A is available for sensor supply, so a single-cable (daisy-chain) structure becomes possible.

The rotary encoder has a specially coded M8 connector which can easily withstand the typical rigors of everyday industrial use. Incorrect connections are avoided by these exclusively coded connectors. Specific cables with molded plugs are a perfect solution for applications with compact-machines. The M8 plugs fit into very narrow grommets allowing for a small overall cable profile.

The signal and power transmission uses the same wires in accordance with the IEEE standard 802.3af. Four-core Industrial-Ethernet cables are therefore sufficient. The rotary encoder has an M12 connection which can easily withstand the usual rigors of everyday industrial use. Depending on the control configuration, disconnection and connection is even possible during operation ie. ("Hot Plug"). This opens up the possibility of flexible system and machine concepts, for which the necessary functional modules are assembled and networked according to requirements, without touching the control software. The rotary encoders from TR can also take advantage of the genuine absolute architecture without counters and batteries: even without a connection to the controller, the rotary encoder "notices" every position change. If the machine module is re-connected, the real position value of the monitored machine part is immediately seen in the controller, without any reference of travel needed.

Rotary encoders with Power over EtherCAT for control technology are absolutely compatible with rotary encoders for series cabling. With an industry-standard resolution of 8192 steps per revolution and 4096 resolved revolutions, the rotary encoders in series CEx58 acquire all rotary and linear travel information of a machine with reliable and repeatable accuracy. Signal processing is fast enough so that together with the EtherCAT network designed for dynamic drive systems, position control with a CE_58 ETC encoder is easily achieved.

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