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Why to consider PoE in industrial applications

12 questions to ask before selecting an Ethernet network
The reliability and cost effectiveness of providing both data and power over a single cable are improved with PoE (Power over Ethernet). PoE is an elegant technical solution that allows cables to carry electrical power and administrators to have control over power distribution to industrial equipment. Since acceptance of the IEEE 802.3af PoE standard in 2003, equipment vendors have been designing standards-based products that leverage the numerous advantagesTraff and benefits of PoE.

Complex devices such as Human-Machine Interfaces (HMI), optical sensors and level measurement devices are the most likely current applications for PoE. High-bandwidth security applications, such as network video surveillance applications, are also seeing wider integration with PoE due to reduced power demand from devices and greater availability of PoE+ equipment.

The following are several advantages that motivate the move to PoE in industrial application settings:
 

Safety


The basic principle is that PoE is a safe power solution, protecting both legacy equipment from damage and users from hazards of electrical power. Maximum voltage is under the limit for “high voltage” applications. To avoid damaging devices or accidental contact with even this relatively safe level, the power sourcing equipment (PSE) sends a 10-volt test current to verify there’s a 25 ohm resistor at the powered device (PD) before full power is applied. If the PD stops using power, power from the PSE stops and testing resumes.

Over-current, under-current and fault protection are also part of the PoE standard. The delivery is specially designed to protect network equipment from overload, under-powering or mistakes during installation. System integrators can set the power limitation for each port on the PoE switch. This can help protect the switches from providing too much power.

Administrators can also incorporate Classification to aid in power management, reliability and safety. When in the start-up process setting up a PoE connection, the PD can indicate its power class to the user. There are five power classes, and only three different bands of power level that devices can fall into. 
 

Cost Savings


One cable for both data and power for the network connection is most cost effective, for both installation and maintenance. With PoE, you are reducing the time and expense of having electrical power cabling installed, in addition to the installation costs of conduits and outlets. Plus, network cables do not require an electrician to fit them.
 

Flexibility 


PoE is standards based, so interoperability across vendors is guaranteed. All variations of network topologies can be configured with PoE, including ring, mesh and other networks. Plus, industrial network management tools such as RSTP/STP, IGMP and VLANs are available on high-quality industrial PoE switches. Single-cable power and data delivery, typical in fieldbus networks, is available with PoE. Plus, configuration changes on the factory floor are made simple by PoE. It makes sense to do it with a single cable instead of two, where possible. PoE technology is designed to operator over standard network cable, such as Cat 5, using conventional RJ45 connectors.

The flexibility of location should also be considered. Without having to be bound to an electrical outlet, devices like IP cameras and wireless access points can be located where they need to be—not where an outlet is available. Using industrial PoE switches, system integrators can get network access almost anywhere.
 

IEEE 802.3at Standard for PoE+


Other implementations of PoE exist, such as the enhanced standard IEEE 802.3at, also known as PoE+. PoE+ increases the power available at the powered device up to 25.5W on ports, allowing devices that require more than 15.4W to power on when connected.

PoE+ provides added power so that high-bandwidth devices, such as Pan-Tilt-Zoom security cameras, thin clients, video phones and WiMAX transmitters, can be connected to the network. The extra power will also expand PoE to more of the factory floor, making it possible to power a larger number of edge devices from a single PoE port.

 

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