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's networks based on Common Industrial Protocol (CIP). The 24 V dc auxiliary power specification is expected this month, according to reports made at the 2009 CIP Networks Conference & 13th Annual Meeting, Feb. 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 Ethernetwww.cechina.cn, PoE, specification, which goes through the same wires), says Bob Lounsbury, chair for the ODVA EtherNet/IP Physical Layer Special Interest Group (SIG).

　　Total current in the system, as seen by power supply PS1CONTROL ENGINEERING China版权所有, is the sum of the currents at each device (load): ltotal = IL1 + IL2 + IL3.  The "Auxiliary Power..." paper mentioned above explains voltage drop and other calculations.

　　The power (actually 18–24 V dc depending on distance from the source) would operate e-stops, I/O sources and devicesCONTROL ENGINEERING China版权所有, actuatorsCONTROL ENGINEERING China版权所有, and controllers—all of which may need more power than PoE or PoE-Plus wire can deliver, explains Lounsbury, who is also a principal engineer at Rockwell Automation. Work on the specification has involved several ODVA CIP groups, including the DeviceNet Physical Layer SIG. That group began considering 24 V dc power for CIP devices five years ago, covering topology, cable, and connectors. (The system is designed to provide no less than 18 V dc.)
　　Among details expected in the specification are support for:
　　Star, linearwww.cechina.cn, and daisy chain topologies;
　　4-pin mini and micro connectors; and
　　5-pin IP67 connectors (compatible with Profibus).
　　Safety also is being considered, Lounsbury says, by ensuring male pins wouldn't be exposed, and trying to make sure damage wouldn't occur if cables were accidently plugged in where they shouldn't be.