The pursue for PoE started decades ago. At first, Voice over IP needed power from a separate source. The simple DC power of Plain Old Telephone Service was missed. PoE answered the question of how to provide power and data over a single cable, simple and dependable. The reliability and cost effectiveness of providing both data and power over a single cable is improved with PoE and it has become a clear choice in multiple applications.
PoE was a missing feature that has now found a home in industry. It is an elegant technical solution. As Ethernet-TCP/IP has become common in control rooms and network backbones and access links, PoE has expanded the use of Ethernet on the factory floor.
By employing PoE technology in an industrial setting, users have the ability to supply redundant power to many sensors without having to provide a local outlet. Without PoE, the sensors are passive and data needs to travel long distances (up to 100 meters) to the point of control or a local power source must be installed to drive the sensors. With PoE a redundant power source can be used to power all the sensors through the single existing Ethernet cable without the trouble of installing multiple power sources all around the factory floor.
Now there is no technical reason that Ethernet cannot reach and power most industrial devices. Here are some of the options available for powering PoE and benefits that are motivating the adoption of PoE in industrial applications.
PoE costs less than fibre and is delivering higher and higher data speeds. Data delivery rates are now at 1 Gbps (10/100/1000 Mbps) over Cat5e and Cat6. The new IEEE 802.3bz standard has the capacity to deliver speeds of 2.5 to 5 Gbps over 100m with an immediate view toward 10 Gbps. PoE has more than enough data speed to support devices in a small LAN.
PoE does not require an additional power supply, as data and power are supplied altogether over one cable. The previously developed standard—IEEE 802.3at—provides 30.8W of power. The most recently developed standard—IEEE 802.3bt—provides 60W of power.
PoE is a safe power solution. Maximum voltage is under the limit for “high voltage” applications. To avoid damaging devices or accidental contact with even this relatively safe level, the PSE (Power Sourcing Equipment) sends a 10-volt test current to verify there is a 25ohm resistor at the PD (Powered Device) 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.
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 the 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 just makes sense to do it with a single cable instead of two, where possible.
PoE is one means of providing power source redundancy. When added to the ability to configure Ethernet for redundant data configurations, it’s a powerful combination. The complexity of combining various networks often requires more equipment, programming, and maintenance. A single network is simpler and has real advantages.
PoE devices adapt to changing environments, as they can be easily moved and reconnected at the switch level and easily integrate into changing network configurations. PoE is plug and play, an entire network doesn’t need to be brought down to add or subtract devices.