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What is PoE? Using Power over Ethernet for IoT

By ·Categories: Tech Explained·Published On: October 13th, 2021·4.8 min read·

What is PoE? 

Power over Ethernet (PoE) transmits electric power with data simultaneously over data pairs on ethernet cables. PoE provides both data connection and operating power to industrial, IoT and even consumer electronics devices.

The thinking required to decide how to power your home computer is probably limited to choosing which outlet you’ll plug it into. But powering industrial and IoT devices is frequently much more complicated. The reduced power draw of industrial computers is an appealing feature. That said, the way you provide power can make all the difference to system longevity, costs and ultimately project success. 

Enter Power over Ethernet, a popular alternative to dedicated power supplies used to provide devices with the power they need over the ethernet cable that’s already attached. PoE has become a popular choice for industrial hardware users looking to reduce the number of wires they need in their infrastructure to ensure reliable power delivery. 

How PoE Works

PoE systems are comprised of Power Sourcing Equipment (PSE) and Powered Devices (PD). PSEs provide a direct current to a standard ethernet cable, which transfers it to a PD at distances up to 100 meters. 

The Institute of Electrical and Electronics Engineers (IEEE) defines multiple Power over Ethernet standards for a variety of power levels. The most common of these standards are IEEE 802.3af and IEEE 802.3at. These standards provision up to 15.4W and 25.5W (respectively) to downstream PDs over two of the data pairs. Newer standards allow for higher power by providing power over all four data pairs. These include 60W with IEEE802.3bt (Type 2), or 100W with IEEE802.3bt (Type 3).   

All PSE devices are capable of powering downstream devices with a power level equal to or lower than the sourcing capability. This means that an IEEE 802.3at compliant PSE can power both IEEE 802.3at and IEEE 802.3af devices. The capabilities of the PSE must be selected based on the requirements of the downstream PD devices.  

Safety Considerations

The IEEE standards define a working voltage of 55V DC. This allows for sufficient power to downstream devices over long distances without suffering from power losses in the transmission medium. There are multiple levels of classification and detection that occur between the PSE and the PD before the full voltage and power levels are allowed. This is done in order to ensure that non-PoE devices and non-compliant PoE PDs are not damaged by high voltage on the Ethernet cable.

During this detection and classification procedure, a specialized chip on the PSE communicates with another integrated circuit on the PD. The PSE advertises its capability to the PD, and the PD responds with its requested power level. If the PSE is not capable of supporting the full power required by the PD, the connection will not be established. This prevents brown-outs on the PD. Only after a valid detection and classification signature is provided, will the PSE provide the full requested power to the network port.  

When a PoE PSE is connected to a non-PoE device, the initial detection phase will not be acknowledged by the downstream device, and power will not be applied. This makes PoE capable ethernet ports safe for use with non-PoE devices.  

Once a link between a valid PSE and PD is established, multiple levels of protection at both ends exist to ensure that both devices are operating within the established limits of the IEEE standard. The PSE or PD devices monitor the voltage and current through the Ethernet link. The connection will be severed if overcurrent or overvoltage conditions are detected. Automatic detection is done to re-establish the link between the PSE and PD once the cause of the fault is removed. 

Why Use PoE?

First and foremost PoE is extremely easy to install because the wiring required is likely already in place. PoE also allows users to cut costs by eliminating the need to run both data and power cables for new or existing devices. 

To allow PoE installations to be used with legacy non-PoE devices, there are Power over Ethernet splitter devices. A PoE splitter  acts as a PoE PD and separates the power and data connections from an upstream PSE into individual connections for data and power (typically with a regulated 12V or 24V DC output).

In addition to savings on wiring, there’s no need to find or create outlets to power each of your devices. The long-term cost savings for utilizing a Power over Ethernet infrastructure can be significant. This is especially true if your organization requires hundreds, or even thousands of devices.

Examples of PoE In Action 

As the Industrial Internet of Things (IIoT) expands, the number of PoE applications continue to increase as well. PoE is heavily used in IP camera and wireless projects. It’s ubiquitous in surveillance applications, where it enables fast setup and deployment. Combining PoE with Wi-Fi and/or Bluetooth technologies allows for entire projects to be freed up from wall outlets.

Hawaii-based technology company ‘IKE Solutions uses Power over Ethernet as part of their machine vision solution to monitor catch and safety protocols onboard fishing vessels. Their system uses multiple cameras and complex processing of machine vision algorithms. Installing the system onboard fishing vessels presents both space and power constraints. 

IKE Solutions founder, Matthew Carnes, appreciates the PoE capabilities of OnLogic’s Karbon 700. With them, ‘IKE Solutions is able to greatly reduce its space and power requirements. Read our full customer profile on ‘IKE Solutions.

How OnLogic Can Help

For our part, OnLogic has helped clients create a wide range of innovative solutions utilizing Power over Ethernet. Many of OnLogic’s Rugged PCs offer PoE to make users’ experiences more efficient.  If you are looking for a PoE solution, check out OnLogic’s variety of systems with PoE

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About the Author: Victoria Scala

Victoria Scala is the Marketing Intern at OnLogic. Along with her business studies at The University of Vermont, she enjoys writing and exploring the Green Mountain State.