March/April 2010

Special Secion: Wireless & Ethernet

Industrial Ethernet all the rage

Industrial Ethernet is designed to deal with harsh environments, data collisions, factory noise, factory process needs

FAST FORWARD

  • An industrial Ethernet network needs to incorporate collision detection.
  • When designing an industrial Ethernet network, consider options that make your network reliable.
  • Industrial Ethernet topology options include: star, tree, line, and ring topologies.
 
By John Rinaldi
 w8

 

Ethernet is a well known and recognized technology in the home and office environment. Recently, it has become the hottest trend in moving data in industrial applications on the factory floor. The factory floor, however, is a much different environment than home and office environments. This article highlights the differences between industrial and commercial Ethernet by comparing communication needs, process concerns, environmental challenges, and hardware.

 

Let's communicate

Industrial Ethernet has unique requirements based on two-way communications. To understand this, think about a possible application at a bottle-filling plant. Assume the plant is creating a new microbrew beer, Automation Ale. The filling operation will be run by an industrial Ethernet network.

The network works well because it uses "handshaking" to ensure message delivery. To illustrate this attribute, let's say our bottling device begins filling a bottle of Automation Ale at the command of the controlling PLC. The PLC is also responsible for sending the "stop filling" command when the bottle is full. If the message is lost on the network, the PLC is aware because it does not receive a delivery response, (part of the handshaking) so it knows to resend the command.

In the office setting, such a lost transmission is rarely important. If a web page gets lost in transmission, the user simply presses "refresh." In the production setting, though, we cannot wait for Automation Ale to spill on the floor before someone manually turns off the filler. The handshake saves ale, money, and time.

In an industrial Ethernet network, we also incorporate collision detection. If two messages collide in our network, the controlling PLC can resend the message to the device until it receives a delivery notice for the device. Ale continues its controlled pour, and no one is crying over wasted beer.

Automation Ale is quite popular in our scenario, so assume we need a few dozen bottlers, valves, sensors, and a PLC in our network. The operation must run at peak efficiency; an office Ethernet network would not accomplish this goal. That is because there is no collision detection.

Other factors to consider

Operations concerns: An area of concern regards the cost of downtime. When a network goes down in your office setting, it is an inconvenience, and some work may be impossible. Often though, an employee will simply need to move on to another task and tackle it without use of the Internet.

In a production setting, that downtime is costly. Assembly lines operating with continual processes can be rendered nonfunctional if one aspect fails. Critical processes could be ruined, leading to lost material and money.

Think for a minute of a factory producing tempered glass for windows. A continuous flow of glass moves from pour, to cut, over an assembly line a mile long.  The glass flow progresses through specific heat-ups, cool-downs, and rests to properly temper it to meet production specifications. If the line seized, the factory would be left with a mile of scrap glass. Much of it that would need to be removed manually due to the fact it had cooled hard on a portion of the line that was meant to deal with hot malleable glass.

When designing an industrial Ethernet network, you must consider options that make your network reliable. That often leads to increased costs.

Security: In an office setting, the information traveling through the network can be confidential and important, thus an office Ethernet network must guard against unauthorized use. The same is true in an industrial application. Another security threat in the industrial setting is the risk that an employee may break the system accidentally, creating a Garbage In/Garbage Out scenario or bringing the device or network to a complete halt.

Office and shop floor differences: You would not expect to see someone in the industrial setting wearing Italian suits or expensive leather shoes because it is much more suitable for them to be wearing blue jeans and steel-toed boots. These choices offer more protection from the environmental factors in the factory. The same attire considerations need to be taken for your Ethernet networks. Industrial Ethernet cables, switches, and connectors need to withstand the unique and harsh criteria in an industrial setting.

Environmental concerns

Temperature: Heat and cold are two factors that can have a major effect on a network. Cold is particularly damaging. At relatively cold levels, near freezing, a cable is susceptible to impact, which can cause a break in the cable, destruction of the protective jacket, or attenuation. At even colder temperatures, the cable may become brittle and break through no large force, but instead through simple bending.

Heat is also damaging. The protective jacket may melt, leading to shorts and vulnerability. Heat also causes attenuation over time.

Chemicals: Chemicals may cause a jacket to dissolve or change shape, leading to a shorter life and worse performance. Some solvents can also directly impact the internal cable should the protective jacket not be effective. Radiation, especially UV Radiation from sunlight, can cause discoloration and degradation of the jacket. Humidity can also degrade the cable.

The industrial Ethernet environment is harsh, and office Ethernet applications were not created for such environments. Taking measures to physically protect cables and connectors can minimize, or even negate, the effects of an industrial environment.

Factory noise: Electric and magnetic noise generated by large motors and high voltage devices can distort data transfers on the network.

Vibrations: Some processes may create vibration, which can cause degradation of the jacket and disconnection if poor connectors are used. You must consider what will happen when the machines switch is turned on.

Other notable differences

Topology: Commercial Ethernet is almost always configured in a star topology. Industrial Ethernet has many different topology options to fit diverse industrial applications. The topologies include star, tree, line, and ring topologies.

Heavy and light duty: Office Ethernet components are designed for a base level of use. Industrial Ethernet components can be considered for multiple levels of use. Thus, industrial Ethernet components can be divided into heavy and light-duty categories.

Cable: Cables can be classified as heavy or light duty. A light-duty industrial Ethernet cable may have slightly higher quality jacketing than office Ethernet cable. The cable may even be an office Ethernet cable if the conditions do not require extra protection. As you rise to heavy-duty cable, though, the jacket and metals improve. At some point, you begin to see complex and thick jackets around incredibly high-quality cable. Heavy-duty cable is more expensive than light-duty cable, so it is only used when necessary.

Connectors: Connectors can fall on a spectrum from office to light duty and up to heavy duty. Typically, industrial Ethernet connectors will not rely on basic snap-in lock mechanisms on the same level as office Ethernet. Instead, heavier lock mechanisms are used. In heavy-duty applications, sealed connectors are often used.

Industrial light and heavy-duty parts carry a premium price tag when compared to commercial components.

Ethernet is quickly becoming a well known and used technology on the factory floor. It offers cost, data volume, and transmission speed improvements over its fieldbus predecessors in industrial applications. Industrial Ethernet is able to effectively deal with harsh environments, data collisions, factory noise, and factory process needs. It is still Ethernet, just Ethernet designed to fulfill unique industrial needs.

ABOUT THE AUTHOR

John Rinaldi (jrinaldi@rtaautomation.com) has a great deal of experience in industrial control and is the coauthor of the book Industrial Ethernet. His company Real Time Automation, Inc. specializes in industrial networking software stacks, OEM modules, custom design, and off-the-shelf gateways to bridge protocols (www.rtaautomation.com).

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