06 March 2009
Like a round peg in a square hole, end-users can face incompatibility when designing and deploying 24 V auxiliary power on the factory floor. In response, ODVA is creating a ‘Power with Ethernet’ specification for ODVA Common Industrial Protocol (CIP) networks. The 24 V dc auxiliary power specification is expected in April, according to those involved, at the 2009 CIP Networks Conference and 13th Annual Meeting, February 24-26.The 24 V dc output power from an EtherNet/IP compatible device would run in a separate cable from the cable used for Ethernet data (as opposed to the IEEE Power over Ethernet, PoE, specification, which goes through the same wires), says Bob Lounsbury, chair for the ODVA EtherNet/IP Physical Layer Special Interest Group (SIG). The power (actually 18-24 V dc depending distance from the source) would operate e-stops, I/O sources and devices, actuators, and controllers, all of which may need more power than PoE or PoE-Plus wire can deliver, explains Lounsbury, principal engineer, Rockwell Automation. Work on the specification has involved several ODVA CIP groups, including the DeviceNet Physical Layer SIG, which began considering 24 V dc power for CIP devices five years ago, covering topology, cable, and connectors. (With DeviceNet, power can drop to 11 V dc.)Among details expected in the specification are support for:- Star, linear, and daisy chain topologies;- 4-pin mini and micro connectors; and - 5-pin IP67 connectors (compatible with Profibus). Safety is also being considered, Lounsbury adds, by ensuring male pins wouldn't be exposed and trying to make sure damage wouldn’t occur if cables were accidentally plugged where they shouldn’t be.– Mark T. Hoske, editor in chief
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