Power over Ethernet (PoE) technology was pioneered by Cisco engineers during the IT boom of the 1990s, but it wasn't scaled to a wide range of industrial applications until the mid-2000s. "PoE" describes any power-transmission system that uses a standard Ethernet cable to transmit data and power within a single housing. The IEEE has standardized two such systems: Alternative A, which extracts a common-mode voltage from the center tap of standard Ethernet pulse transformers, and Alternative B, which transmits power over unused pairs in 10BASE-T or 100BASE-TX cables. Several additional PoE frameworks have found use in specialized industrial applications.
General Industrial Capabilities
Modern PoE frameworks have several attributes that make them ideal for general industrial use. Whereas ancestral PoE devices were originally designed for use in relatively stable data-center environments, many next-generation systems are hardened for industrial use. Most have features that can withstand electrical interference, including:
- Reverse polarity protection
- Surge protection to 3,000 volts or higher
- EMI/RFI insulation
Hardened metal casings, "ruggedized" enclosures and insulation that can withstand temperatures between minus 40 and 170 degrees are crucial as well. Since the industrial business cycle is usually much longer than the standard IT cycle, industrial PoE equipment should be designed to last at least seven years without significant degradation.
Typical Machine Vision PoE Configuration
Not all machine vision devices that use PoE technology operate in such harsh environments, but many do. Their configurations follow a predictable pattern. Each camera in a given network is connected to a PoE switch or splitter with standard CAT5e cables. The switch is connected to a wall-based power source with a standard power cable and a PC-based data processing system via a 10/100 Ethernet cable.
Benefits for Machine Vision Users
Since PoE cables transmit power and data along CAT5e cables that can reach lengths of 100 meters, they allow machine vision cameras to function in previously inaccessible areas like high ceilings, exterior roofs, freestanding poles and outbuildings without dedicated power sources. It follows that PoE machine vision networks are far more flexible and easy to set up. These networks' power and data transmission needs can also be managed from a central location, and just one uninterruptible power supply (UPS) device is sufficient to ensure that no component cameras lose power during an outage. Finally, PoE devices receive commands and transmit data far faster than devices that don't utilize this technology.
Machine vision networks that use hardened PoE systems enjoy a number of obvious advantages, and ongoing advances in PoE technology promise to provide additional benefits as time goes on. It doesn't take much technical knowledge to harness the power of this technology, so there's little downside to trying it out.