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Technical Paper: Wireless Ethernet
Applying Wireless to Ethernet/IP
Industrial Networks
Ethernet has matured into a standa...
Ethernet/IP also supports direct I/O communication                  monitoring purposes, then true determinism may not be
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Applying Wireless to Ethernet/IP Industrial Networks


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Applying Wireless to Ethernet/IP Industrial Networks

  1. 1. Technical Paper: Wireless Ethernet Applying Wireless to Ethernet/IP Industrial Networks Ethernet has matured into a standard communication Wireless Ethernet does have some limitations. protocol for industrial networks. Rockwell Automation’s Operating latency and the need for message implementation - Ethernet IP - has become widely repeats in noisy environments sometimes exclude popular, in part, because economical infrastructure wireless Ethernet modems from consideration in components are now readily available to users. Ease deterministic applications. It is important to under- of configuration and operation, high data throughput, stand the responsibilities of the Ethernet/IP network straightforward connectivity and ability to merge the or segment to determine if wireless is a viable factory floor with the corporate database have driven option. the Ethernet IP revolution in industry. In fact, it’s very success created a strong need to extend Ethernet IP Generally, wireless is quite appropriate in applica- networks beyond the ability to hardwire. Wireless tions where the network is used for data collection, Ethernet IP became an urgent requirement. equipment maintenance or noncritical (SCADA) control. The network is responsible for data ex- In addition to the elimination of costly wiring, wireless change, but not for relaying time critical commands Ethernet has become standard in many work places that, if delayed, could result in safety concerns or because it provides a high degree of convenience and serious process disruption. Wireless is commonly mobility. Wireless PCMCIA cards, access points, integrated where PLCs directly control the local switches and hubs are now commonplace in homes process, and need to be economically connected to and offices and are relatively inexpensive. The indus- the plant network. The network is used to transmit trial environment requires more, however, and special- explicit messaging , data transfers that are acknowl- ized Ethernet radio modems have been developed to edged between the controllers. Explicit messaging meet the industrial need. These modems are physically ensures that data packets are reliably transmitted hardened, have extended operating temperatures, and resent if necessary. allow the use of a wide variety of antennas and cables and have much greater range than commercial wire- less products. Diagram 1: Example of a wireless Ethernet/IP network using explicit messaging. The network supports PLC programming, data collection and SCADA function s. • 3535 Factoria Blvd.SE, Suite 100 • Bellevue, WA 98006 • Phone (425) 882-2206 • FAX (425) 867-0865 •
  2. 2. Ethernet/IP also supports direct I/O communication monitoring purposes, then true determinism may not be serving the role of a fieldbus over Ethernet cabling. In needed and wireless quite appropriate. Similarly if I/O is this mode, implicit messaging is used to directly used for noncritical control, wireless may be acceptable. communicate from the PLC program to the I/O device However if I/O timing is critical or safety mechanisms are via the Ethernet network. The Ethernet network dependent, then wireless is inappropriate. effectively serves as the communication infrastructure for distributed I/O. A fundamental trade-off in any wireless modem is range and data rate. Data-Linc Group has modems that offer Because Ethernet was not intended to be deterministic very long range (25+ miles with standard antennas) at (having guaranteed response times), Rockwell Automa- modest data rates (100 Kbps) or shorter range (2-5 tion has established network design recommendations miles, depending on antenna) at high data rates (1 to 6 to achieve a high degree of deterministic performance. Mbps). The SRM family of long range frequency Following these guidelines essentially ensure that the hopping modems provide an exceptionally high level of Ethernet segment is as fast as possible (e.g. Full noise/interference immunity in all operating conditions. Duplex 100BaseT and that unnecessary network traffic The FastLinc 810E (Access point) and 800C (PCMCIA is kept to a minimum. card) have maximum 802.11b data throughputs with typically twice the range of other products of its type. Wireless presents two concerns for use in deterministic The FastLinc 810E can also be configured as a I/O systems: data transmission rate and latency. wireless bridge. All Data-Linc modems are packaged in First, wireless Ethernet systems can not achieve the heavy gauge steel, have extended operating throughput of a Full Duplex 100BaseT segment. temperatures and can be connected to a wide variety of Diagram 2: Example of a wireless Ethernet/IP network using implicit messaging for noncritical data aquisition and control. Emerging wireless technologies may eventually address antennas and cable lengths for use in challenging this, but they are unproven at this time especially in factory floor or severe outdoor operating conditions. industrial environments. Secondly, industrial wireless systems must contend with interference and retransmit Data-Linc has extensive expertise in Rockwell Automa- packets when necessary. Error correction ensures that tion PLCs, HMIs, Drives and with Ethernet IP. We pro- data packets are successfully received, but causes vide both extensive pre- and post-sale technical sup- variability in message timing which negates high degree port and commonly pre-configure modems for our determinism. Direct sequence RF (e.g. IEEE 802.11b) customers. Data-Linc started as a Rockwell Pyramid has the best chance of predictable message timing, but Partner and was invited by Rockwell to become an direct sequence is not always ideal for factory floor Encompass Partner. communications due to interference susceptibility. Frequency hopping RF offers the highest level of interference immunity, but can have substantial latency and packet delay times. Call 425-882-2206 Wireless Ethernet may be an ideal communication to learn more about method for I/O if the system function and performance industrial wireless expectations are carefully considered. For example, if applications and the I/O system is for data acquisition for machine product capabilities. • 3535 Factoria Blvd.SE, Suite 100 • Bellevue, WA 98006 • Phone (425) 882-2206 • FAX (425) 867-0865 • PN 152-09905ra-001A