Industrial Ethernet: Environmental conditions determine hardware selection

Selection of commercial or industrial hardware like Ethernet switches should be based on the environment, says Carl Henning, deputy director, PTO, Profibus and Profinet North America.
By Control Engineering Staff April 17, 2009

PTO training classes help sort out industrial Ethernet questions .

Selection of commercial or industrial hardware like Ethernet switches should be based on the environment, says Carl Henning, deputy director, PTO, Profibus and Profinet North America . In a controlled environment akin to office conditions, commercial switches are acceptable; in hot, humid, vibration-prone, electrically noisy environments, industrially hardened switches are required. Managed or unmanaged switches can be used, but managed switches provide the capability to speed troubleshooting and repair, Henning says.
Profinet is standard, unmodified Ethernet protocol, Henning says, so commercial or industrial devices can be used. (Additional considerations apply in motion control applications.) In addition, some switches have Profinet I/O capability built in so they can communicate typical IT data to Profinet PLCs and HMIs. Typical IT protocols like SNMP can also be used to communicate that data to any computer.
“One very important but often neglected consideration is the cable. Unshielded twisted pair (UTP) cable is typically used in the office. Its jacket material is likely not suitable for the atmospheric conditions of the plant floor where temperature extremes and oily vapor or other contaminants may be present,” Henning says. Lack of shielding can be a problem in electrically noisy areas. While TCP/IP protocol has provision for resending noise-corrupted frames, timing is unacceptable for industrial applications, he says. Shielded cable is highly recommended for the plant floor. “This is a lesson learned from long-established serial fieldbuses like Foundation Fieldbus, DeviceNet, and Profibus. All these recommend or require shielded cable. This is not a factor of the protocol, but of the environment. In exceptionally noisy areas, fiber is a good choice for Ethernet runs,” Henning says.
Wireless is also an option for connecting Profinet devices. Since Profinet is standard IEEE 802.3 wired Ethernet, it also inherently supports standard IEEE 802.11 wireless Ethernet. Environmental conditions are again the deciding factor in selecting commercial or industrially hardened devices like wireless access points.
Other points, Henning offers:

  • Safety: the way safety fieldbuses work makes the hardware selection and media selection irrelevant to the safety aspect. Any choice is acceptable for the safety network.

  • Redundancy: not commonly seen in the commercial world, but often needed in the industrial world. The redundancy techniques that are used in the office world do not respond fast enough to satisfy industrial speed needs. Profinet has some unique solutions to speed up response to a fault.

  • Switches: Just because you can use an unmanaged switch does not mean you should use an unmanaged switch: learn more.

Also see “

Plug into Industrial Ethernet Protocols

: Industrial Ethernet protocols can be standard and unmodified, or modified to be industrially hardened. Perspectives from some protocol proponents clarify needs for various implementations.”
www.us.profinet.com
– Edited by Mark T. Hoske , editor in chief
Control Engineering News Desk
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