IEEE 802.3af Power to Doom Fieldbus and HART? Draft standard will define how to provide power for Ethernet data terminal equipment March 28, 2002 The latest IEEE 802.3 draft standard (P802.3af) will define how to provide power for Ethernet data terminal equipment (DTE) having IEEE 802.3 interfaces, low power requirements, and LAN connectivity. With the entire world moving toward Ethernet networks, this new standard could have deleterious implications for fieldbus, HART and 4-20 mA networks and loops. Especially since one of the targeted areas for the new standard is industrial automation. A quick review of documents on the IEEE web site (http://www.ieee.org) indicates the new standard will preserve the four-pair Cat 3 and Cat 5 cabling, but it will allow equipment to draw electrical power from the same conductors used for data transmission. No information is yet available on the power levels to be supplied, but this raises the possibility of an entirely new generation of intrinsically safe field instrumentation communicating via and powered by Ethernet. This new instrumentation could supplant 4-20 mA field devices and interface directly to control systems and higher level software, such as plant historians and ERP systems. With Ethernet, instrumentation can communicate via the web and Microsoft"s .net architecture (see related news story on CE .net). If that is the case, why would the industry need HART and fieldbus networks? Wally Pratt, chief engineer for the HART Communication Foundation (http://www.hartcomm.org), says there will be no immediate impact on HART. "HART field devices are mostly 8-bit micros running on small amounts of memory," he says. "Ethernet needs much more memory and computing power. Generally, it requires fast 32-bit processors to keep the pipe full." Presumably, it is difficult to make an intrinsically safe 32-bit processor. "The application layer is a big problem, because Ethernet does not have one," he explains. "As a result, any product offerings will be fragmented until a unifying force is found, such as Profibus, Ethernet/IP, etc." Dave Glanzer, director of technology development at Fieldbus Foundation (http://www.fieldbus.org), says the standard is not a threat to the two Ethernet-based Foundation fieldbuses, H1 and HSE. "I am not an authority on 802.3af, but I think HSE is compatible with 802.3af because HSE uses the TCP/IP layer and a socket interface," he says. "Also, 802.3af will not replace H1 because of intrinsic safety, power, and cost considerations. H1 is optimized for integration at the field device level." Although Foundation fieldbus and HART seem safe at the moment, the jury is still out on all the other fieldbuses and industrial networks that do not have Ethernet versions.