Setting up an industrial networked system involves many factors. Here are some important points to consider before you purchase any equipment or software.
Adding a wireless interface to wired controllers and I/O offers new options for segmenting networks. Critical I/O and controller traffic could use the wired network interface while less critical tasks could be done wirelessly.
There are convincing arguments about whether or not to go wireless in today’s automated manufacturing environments. On the pro side, wireless can be an important upgrade to operations because it can be more cost effective – reducing labor and materials associated with wired systems. Wireless offers connectivity for remote areas or those that might ordinarily be too difficult to service. In addition, wireless controllers and I/O can manage devices and processes in inaccessible areas or where network wiring is hard to install. And, the wireless route can provide return on investment (ROI) for a new project before spending time and labor to set up a wired system. For these and other reasons, automation engineers and administrators are increasingly considering wireless networks including wireless LAN (WLAN), wireless Ethernet, or Wi-Fi.
However, there are nay-sayers who claim that wireless network security can be easily compromised even though they are more secure than personal wireless networks. The flawed wired equivalent privacy (WEP) security algorithm was replaced by Wi-Fi protected access (WPA) including the temporal key integrity protocol (TKIP). WPA2 uses the more secure advanced encryption standard (AES) 802.11i algorithm. It is compliant with the National Institute of Standards and Technology (NIST) FIPS 140-2. These standards can offer increased security for a wireless environment. WPA2-compliant products should be used for industrial wireless implementations.
Wireless system reliability is another bugaboo because it depends on network size, physical environment, number of network users and how much they use it, and interference from other devices. For small, all-wireless operations, devices may perform well in ad hoc (peer-to-peer) scenarios where each device can detect and communicate with other similarly configured devices within range. This example requires a relatively small investment for hardware. For a larger network, infrastructure mode is recommended because it routes communication through one or more wireless access points (APs).
Since wireless communications are based on radio signals, the physical environment determines how well the network performs. Obstacles on a warehouse floor, for instance, can interrupt or deter signals. Therefore, you should place APs, wireless routers, and wireless repeaters to cover the entire area that needs wireless transmission. Radio frequency (RF) interference and electromagnetic compatibility (EMC) problems reduce network reliability when other devices such as cordless phones, Bluetooth devices, and microwave ovens, interfere with signal reception.
Reducing interference from other devices may involve changing channel frequency within a range or moving into a less crowded frequency. Wireless networks compatible with 802.11b and g standards use 2.4 GHz. Changing to an 802.11a-compatible system that uses 5GHz might offer less interference. Wireless standards also differ in the number of non-overlapping channels they allow. 802.11b and g allow three so frequencies must be reused when more than three APs are required in the same system. 802.11a offers more channels.
Network reliability also depends on the number of users and their use of the system. Simple data transfer typically needs little bandwidth. Heavier use, such as transferring large files or interacting with multimedia can slow network traffic. Networks using 802.11a or g standard are faster than those using 802b.
Another major issue to consider when weighing wireless versus wired is the availability and cost of I/O components. Many automation manufacturers supply wireless products that differ from their regular lines. A wireless component may have been purchased or developed by a separate manufacturing division. Or a subset of the regular product line may be adaptable for wireless use by module carriers or similar devices. These scenarios can cause problems.
Wireless I/O may not include features the application requires or features that make design easier such as simpler methods of wiring to field devices. For example, if an application needs specific signal inputs or channel-to-channel isolation, the wireless I/O product line may not include them. Limited availability could mean expensive workarounds or the decision to scrap the idea of going wireless altogether.
The wireless network set up process usually involves buying special wireless components such as module carriers, I/O modules, racks, and terminations. For the most part, customers who install a wireless network for automation must carry a separate inventory of spare parts, further increasing the cost of going wireless. To bypass these issues, look for a manufacturer whose wireless line includes a large array of reliable I/O, requires very few extra components, and whose I/O is independent of network type.
Making early decisions
If the wireless version from your vendor’s product line is different, you will have to choose at the beginning of a project whether to use wired or wireless communications. So, you must specify components and commit to a networking methodology early in the process. This situation affects the project from overall approach to details of field connections. If your method is unsatisfactory, changing it means more time and expense to buy, install, reconfigure new components, and redesign the system. These additional costs often include I/O and network hardware parts, as well as software costs for licensing, training, and programming wireless I/O.
Wireless I/O should perform more like a typical laptop computer which includes both wired and wireless capability, can adapt to a wired or wireless network while offering the same functions, and uses the same software with either method.
Wireless controller and I/O can help manage devices and processes in accessible areas or where network wiring is hard to install.
In a perfect world
Automation manufacturers can help. They should provide broad support for wireless standards beyond 802.11b to give engineers more options to improve individual system reliability. They should include support for the best available security standards. For example, they should offer a full range of wireless I/O and reduce the number of extra components or adapters needed for a wireless installation. It would also help if wireless automation suppliers would design controllers and I/O that can communicate with both wired and wireless Ethernet networks as needed.
If support was included for all three of the most commonly used wireless standards in the world today, you could use wireless access points, routers, and repeaters from nearly any vendor to build their wireless networks. Depending on system needs, you could choose the higher 5 GHz band to avoid interference from other devices. Or, you could choose a faster standard for higher throughput. You could also opt between the ad hoc and infrastructure modes to suit the size and design of the network. For system security, you should be able to include WPA2 encryption algorithms with 802.11i AES to design a robust industrial wireless network.
Wireless system reliability depends on network size, physical environment, number of users and how they use it, and interference from other devices.
The ability to use identical I/O components in both wired and wireless networks could save time and money during design, implementation and use. During the design phase, you might specify I/O with the assurance that you could use the product line in either network. During the implementation phase, you would use the same methods and costs for installing I/O and wiring to field devices would apply to both networks. Hence, there would be no need to retrain technicians. If communication is changed from wireless to wired during a project, no additional costs would be incurred for I/O or field wiring. During system use, one set of spare parts would need to be in stock for maintenance. In fact, wireless networks might be more attractive if manufacturers required fewer wireless components. In the end, initial system costs and costs associated with maintaining an inventory of spares would be less.
Flexibility is key
Wireless controllers and I/O should support wired and wireless communication. In this scenario, if you design a project using wireless technology and then discover a wired network would be better, you would be able to use the same hardware. Further, adding a wireless interface to wired controller and I/O also offers new options for segmenting networks. For example, critical I/O and controller traffic could use the wired network interface while less critical maintenance, troubleshooting, or local HMI tasks could be done wirelessly with a similarly configured laptop computer.
The controller functions and I/O should remain the same regardless of which network is used. Only the physical medium would be different so all I/O features and supported protocols would be the same.
Finally, software should not change. Because control and HMI programs would run on wired and wireless networks with no modification, there would be no additional costs for licensing, training, programming, and maintenance.
One manufacturer comes to the rescue
Opto 22 incorporated many of these upgrades into its wireless products including its Snap PAC system, a distributed system for industrial automation, remote monitoring, and data acquisition, and to its Snap I/O which can be used as remote I/O with Allen-Bradley Logic PLCs and PC-based control systems.
The Snap PAC controller has two independent Ethernet interfaces (two IP addresses; two network interface cards, or NICs). These interfaces can be used for redundant links or for segmenting networks. Adding wireless support means that the PAC now has three Ethernet interfaces (three IP addresses; three NICs). One is wireless and two are wired. The wireless controller can segment a wired from a wireless network and provide a redundant link as well.
The Snap PAC brain has two switched Ethernet interfaces (one IP address; one NIC). The switched interfaces allow the intelligent I/O processors to be daisy chained, if needed. Adding wireless support to the brain means adding a second IP address. So the brain can communicate through either a wired or wireless network. These controllers and brains retain the same function whether they are used wired or wirelessly.
All standard industrial protocols supported by the wired Ethernet interface are fully supported over wireless. These protocols include ODVA’s EtherNet /IP, Modbus/TCP, OptoMMP, SNMP, SMTP, and FTP. The same control and HMI development software is used regardless of physical network. Controls programs running on the PAC require no modification for wireless communication.
In addition, communications for wired and wireless networks are set up in the same configuration software and can be done at the same time or one network type can be added later. Opto 22 offers the same I/O modules, racks, and other components for wired and wireless applications. Analog, digital, and serial SNAP I/O modules are available to be used with either network.
Opto 22’s controllers and brains support 802.11a, b, and g in both ad hoc and infrastructure modes. You can use the higher frequency 802.11a standard at 5 GHz to avoid interference. You can also use the faster 802.11g standard and the WPA2/AES algorithms for secure transmissions. Or, if needed, you can use WEP or WPA for backwards compatibility. All three are supported by Opto 22’s controllers and brains.
Editor’s note: The materials for this article was supplied by Opto 22.
Filed Under: Wireless, I/O modules, Networks • connectivity • fieldbuses