SPE: Single Pair Ethernet
Several qualities possessed by SPE make it ideal for use in process industry environments. First, its maximum length is 1,000 meters—10 times that of previous industrial Ethernet forms. That said, this extension isn’t accomplished without some trade-offs. SPE’s communication speed is 10 Mbit/second, while four- and eight-wire Ethernet can reach speeds ranging from 100 Mbit/second to as high as 10 Gbit/second. Still, this represents a marked improvement over both fieldbus, which has a maximum communication speed of 31.25 Kbit/second, and HART, which has a maximum communication speed of 1,200 bits/second.
In this way, SPE represents a kind of middle-ground between legacy fieldbus and other forms of industrial Ethernet. While fieldbus might not currently offer data transmission speeds that can fully tap the larger quantities of data being produced by Internet of Things (IoT)-equipped devices, four- and eight-wire Ethernet may provide more than is necessary, says Guadalupe Chalas, senior marketing specialist at Phoenix Contact.
“For these field devices, you might need longer cable distances but less bandwidth. So, what happens is if you’re talking about bandwidth specifically, you don’t want to put a standard Ethernet connection of 100 Mbit/second on something that only needs eight or 10 Mbit/second. That would be overdesigned,” Chalas says. “In that case, you’re using an expensive connection on an application that doesn’t need it.”
In addition, SPE has swapped the RJ45 connectors native to most Ethernet cables. Not only are SPE’s connectors more rugged, and thus better suited to harsh industrial conditions, but they are significantly smaller and match ports commonly available on existing sensors and other field instrumentation.
"The number one reason that standards organizations are heading in this direction is to ensure greater interoperability," says McKenzie Reed, technology manager for standards development at Harting. "The RJ45 is a commercial product that migrated into the industrial market, and that is what standard organizations working on SPE are putting a ton of time and attention into making sure doesn't happen again because of the quality, compatibility, and performance issues that surround the RJ45 connector when used in industrial environments.”
Finally, SPE enables power over data line (PoDL), which is capable of transmitting up to 50 watts of power over the same twisted pair of wires that transmits data. According to Reed, this can be used to deliver power to small sensors and other forms of simple instrumentation in the field, allowing end-users to further cut costs by eliminating secondary power supplies.
APL: Advanced Physical Layer
APL refers to an installation architecture that can be used to render SPE intrinsically safe for applications in hazardous environments. This is achieved in conformity with IEC technical specification 2-WISE, which defines port profiles for multiple power levels to limit the flow of current in areas where explosions may occur.
According to Al Beydoun, president and executive director of ODVA, while other forms of industrial Ethernet can be used in hazardous environments, they require additional precautions be taken, such as installing mechanical cable protections, using shorter cable runs that must be determined using appropriate calculations, and sheltering connections in additional cabinets and enclosures. By eliminating these needs, APL cuts costs, reduces complexity, and allows for longer cable runs without compromising safety.
Moreover, APL is designed to be compatible with pre-existing Fieldbus Type A cabling, which may significantly ease the process of adoption. This is possible because, while APL is a change to an Ethernet cable’s physical layer, its increased data transmission capacities are enabled by a compatible device’s network interface controller (NIC) and physical transceiver (PHY), rather than the cabling itself. As a result, industries such as oil and gas or wastewater management in which existing cabling may be buried, encased in concrete, or otherwise difficult-to-reach locations can easily make the transition by updating devices and connectors without needing to rip and replace their entire cabling infrastructure.
