This blog builds upon the recent Intro to PoE & How It Can Help Your Industrial Network post and looks at some choices in building an industrial Ethernet network that supports PoE.
PoE is having important repercussions for industrial applications. The simplicity of combining signal and power in one Ethernet cable connection contributes to the already-rapid transition to Ethernet-based industrial control systems. Wireless access devices, IP phones, surveillance cameras, and a growing number of specialty devices are available, demonstrating how PoE can help solve industrial information and control systems applications problems in innovative ways. PoE industrial sensor and controller devices are now available. While the available power in a PoE-connected device is generally limited to about 13 watts, the vast majority of modern industrial sensors take less than 10 watts. It may soon be possible to power a full SCADA system from ports on Ethernet switches, along with non-traditional devices such as phones and cameras and PCs. PoE offers the potential for an economical standards-based high-performance industrial network far beyond what is available today.
PoE technology brings power, as well as data transfer, to devices via standard twisted-pair Ethernet cabling in a network. In effect, PoE provides a new standards-based way for Power Sourcing Equipment (PSE) to provide power to a wide variety of Powered Devices (PDs) in areas where it is physically or financially prohibitive to offer AC power. The cost savings and reliability improvements involved in not having to install and maintain power wiring in addition to Ethernet cabling, especially in remote locations, provide the incentive for many industrial users to immediately evaluate this technology.
A device called a Midspan Power Source (MPS) has been developed for use in some office applications to "inject" PoE power into an existing Ethernet network where the Ethernet switch is not configured as a PSE. The MPS box sits between an existing Ethernet switch and the target PDs. While perhaps more cost-effective than replacing an existing Ethernet switch with a PoE switch, MPSs provide another point of failure in a system that may require high availability.
A typical device such as the GarrettCom Magnum PES42P and PS14P PoE (PSE) Switches bypass the need for an extra box by building the "injector" into the switch itself. Clearly, at only a few hundred dollars for 4-port outdoor-rated PS14P switch units, it makes sense to take advantage of the inherently increased reliability of a single unit to provide both data transmission and power. The PES42P offers the additional benefit of offering one or two fiber links in a small six port switch. Other managed switches from Hirschmann and GarrettCom extend PoE flexibility by allowing PoE and non-PoE ports to coexist in larger rack-mount units. There is no need to incorporate MPS boxes into the industrial environment as existing non-PoE switches can be re-deployed to other areas of the network.
Under the PoE standard, features such as remote power-down or remote reset can be implemented using a system management package, such as the Simple Network Management Protocol (SNMP). Such niceties provide additional flexibility in deploying PDs at the edge of the industrial network.
With the introduction of PoE, industrial Ethernet suppliers – and users – have a beneficial new technology for heavy-duty environments such as utility substations, mines and quarries, transportation systems, factory facilities, and warehouses. In large industrial campuses or factories where configurations change on a frequent basis, the ability to decouple expensive electrical rewiring from the placement of PDs is highly advantageous. In an environment where budgets are tight and demand for increased productivity is constant, the simplicity of PoE makes it a strong candidate for high acceptance in system upgrades. With both PoE-enabled industrial switches and PDs coming onto the market, Belden predicts rapid adaptation as both vendors and industrial users recognize the cost and reliability savings, as well as the inherent installation convenience.
Today, both PoE (supporting up to 15.4 watts/port per the 802.3af standard) and PoE+ (supporting up to 25.5 watts/port per the 802.3at standard) products are available. Network designers must insure that the networking switch (and any midspan devices) as well as the powered devices i.e. cameras all support either the 802.3af or 802.3at standard for the desired data rate. Additionally, the switches should be examined to insure that you are getting the number of ports supporting PoE that you need. Some switches offer both PoE and non PoE ports in the same units.
Industrial-rated components and cabling are also keys in deploying a PoE network. For industrial and outdoor environments, temperature and other hardening components should be examined. Both GarrettCom and Hirschmann offer ruggedized Power over Ethernet solutions from the DIN rail to the backbone to connect to your Belden industrial cables.