Power over Ethernet Plus: Ideal for factory automation
|CIP networks: 24 V dc Power with Ethernet specification expected in April ; and|
With the latest IEEE802.3at High-Power Power-over-Ethernet (PoE) standards due for ratification this year, PoE now supports a broader range of enterprise IP terminals as well as industrial applications including access control systems, RFID access points, and a wide range of e-stops, inverters, linear encoders, actuators, gateways, controllers, sensors, simple motion devices, and industrial interfacing I/O sources, and devices.
Even the earlier 12.95 W-per-port IEEE802.3at PoE was sufficient for most modern industrial sensors, which require less than 10 W. At 25.5 W per port, PoE Plus may soon enable a full supervisory control and data acquisition (SCADA) system to be powered from ports on Ethernet switches, while simultaneously powering non-traditional IP factory terminals including IP wireless access points, phones, cameras, notebook computers and thin clients. PoE also will help fuel the integrated industrial network, including applications like logistics process control and associated inventory tracking, work-in-process control and production planning capabilities. In all of these applications it can be difficult (if not impossible) to locate power outlets everywhere IP terminals are required.
PoE advantages include robustness, reliability, standards-based interoperability and compliance, and operational cost savings from intelligent energy management, increased network availability, remote diagnostics and power management, and the elimination of expensive wiring and power outlets. PoE also delivers important safety advantages, by enabling a centralized uninterruptible power supply to cost-effectively distribute back-up power to individual Ethernet terminals. This increases network service reliability, and allows administrators to monitor critical functional parameters, set alarms, and safely manage power restoration when required.
PoE Plus already meets key Industrial Ethernet cabling and connector standards . It uses Cat5-or-higher cables that have a 100 m loop resistance of 25 Ohm compared to the 40 Ohm for standard Cat3 cables, which reduces the voltage drop and power dissipation in the cable. Also, both the original and PoE Plus standards specify two-pair connectors for power distribution, which is consistent with Industrial Ethernet’s two-pair M12 connector specification. PoE Plus-compatible technology can be used to drive up to 51 W to powered devices by using all 4-pairs available in a Cat5-or above cable, increasing even more PoE Plus’ applicability.
PoE can be deployed either via a new PoE switch or PoE Midspans to the existing Cat5-or-above cabling between the existing switch and terminals. Midspans provide the most flexible, scalable and economical solution, are generally compatible with any type of Ethernet switch and terminal, and are available in many configurations and port densities.
As IP convergence spreads through the enterprise and factory floor, PoE is a key force for driving network integration. It removes the power restrictions facing industrial Ethernet controllers and network topologies, and enables a growing array of terminals and devices to be economically, efficiently and very conveniently powered over the same standard cabling as data.
Daniel Feldman is director of marketing, telecom, analog mixed signal group of Microsemi Corp. www.microsemi.com and chairs the PoE/PoE+ technical committee at the Ethernet Alliance at www.ethernetalliance.org.
– Edited by Mark T. Hoske , editor in chief
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