We've added open connectivity to our machines via an Ethernet port on our industrial PC. Now, some of our customers are inquiring about wireless connectivity to pull some operating data from places that would be cost-prohibitive with a wired solution. There are many "standards" on the wireless side. What's analogous to wired Ethernet in terms of widespread industrial acceptance?
—from March '10 Control Design
Answers
802.11 Options
Most wireless installations follow 802.11 standard guidelines, which are broken down into individual segments, including 802.11a, 802.11b, 802.11g and soon to be 802.11n. Speed, or bandwidth, is the major difference associated with each standard.
When implementing a wireless system, first identify any wireless devices installed in the area. Also, the number of machines from which you will need to access or retrieve information may dictate which 802.11 standard is right for you. You may want to consider analogs to be Ethernet-wired to create a separate wireless segment or network.
It also is imperative to establish a level of security that ensures only selected personnel have access to the machines over wireless. Data encryption should also be implemented to ensure secure communications.
Remember that distance from point to point also can be an issue. Also, since wireless is a shared medium, be sure to analyze how much data needs to extracted or sent to the machines.
Marty Jansons,
Network Consultant,
Siemens Industry
Cellular and Wi-Fi
Many companies are realizing that wireless solutions are more cost-effective than wired solutions and are easier to deploy, even in the most challenging locations.
Currently, most companies use two main types of wireless technologies: cellular and Wi-Fi. Cellular, being the most far-reaching and versatile of the two, is often deployed in extreme and harsh industrial environments.
Wi-Fi offers faster transfer speeds than cellular does, but it has a very limited range — usually only 150–300 ft, depending on the type of equipment, depending on the wireless-local-area-network (WLAN) protocol being used and depending on whether the solution is an indoor or outdoor deployment. Wi-Fi standards, as determined by the Institute of Electrical & Electronics Engineers (IEEE), include 802.11a, 802.11b, 802.11g and, the most powerful, 802.11n.
Cellular technologies are the more widely deployed solutions. They require less equipment, since data is transferred over existing infrastructure provide by wireless carriers such as AT&T, Verizon and Sprint, so only the cellular modem is required to enable the machines to communicate with each other and relay data. They can be placed almost anywhere that has cellular service.
Current cellular standards include 2G, 2.5G and the more widely deployed 3G, or third generation. Some carriers already are deploying 4G networks, but that availability is quite limited, as the technology is still in the maturation stage.
Previous initial forays into cellular data networks included analog and more switched data communication methods such as analog dial over advanced mobile phone system (AMPS), IS-95 circuit switched data (CSD) over cellular or even tethering to the more recent types of cellular phones over cellular digital package data (CDPD) systems, integrated digital enhanced network (iDEN) and code division multiple access (CDMA) systems. The current approach, from a cellular network perspective, is geared around packet-based transmission control protocol/Internet protocol (TCP/IP) networking.
This represents a challenge for many customers who have an analog async serial infrastructure but prefer to leverage TCP/IP for cellular connectivity. One of the ways to approach these needs is with a cellular router and cellular modem product. Some solutions have the physical interface to connect to these legacy infrastructures via RS-232c async serial connections or RJ11 for traditional dial environments.
One key ability to be aware of is that there are multiple options to convert this data format to TCP/IP, which then can be sent over the cellular data network, whether it is the latest 3G high performance networks or even the 2 and 2.5G networks that exist in the market.
Determining which type of wireless technology is right for you will involve looking at the locations and distances involved in your environment, the type and amount of data traffic that you need to transfer and the availability of cellular coverage in your area.
David Graybeal,
Vice President, North American Sales,
Sixnet
Invisible Extension
Wireless connectivity is typically an invisible extension to the connectivity already existing to either serial connections or Ethernet connections. There are many wireless technologies that can be added to an automation environment at relatively low cost.
The introduction of wireless does bring with it a number of side effects: reduced bandwidth, an increase in communication faults, the potential for unexpected disruptions and added complexity that will need maintenance.
In the case of reduced bandwidth, it is important to understand the needs of your application and craft your communications through poll frequencies and proper data blocking. In many scenarios, communications are predictable, as you are always polling the same data. In some cases, communications are unpredictable, as protocols might be unsolicited.
Know your particular application and plan for the worst case. Use the tools that come with your communications solution to monitor your bandwidth and test your communications in varying scenarios.
Proper planning is key. Communication faults are a fact of life, so that necessitates having processes in place to reduce their likelihood. Component failures are one thing. In addition, are your antennas high enough to deliver a strong signal? Are there disruptions, such as a crane, lift, truck or new shelving, that might provide a disruption and affect your communications? If there is a problem, plan ahead on troubleshooting techniques.
Know the tools you'll need to use and have them handy. Murphy's Law will strike, and it is always at the worst possible time. There are tools available to monitor your infrastructure. Industrial SNMP tools will enable you to monitor your infrastructure with your automation HMI/SCADA systems.
Lock down your wireless connectivity so that it is dedicated to the task at hand and is not open to new connections. Unexpected disruptions result from the wireless laptops you bring into the plant or the new system that is now interfering with the old one. Let's not get into the malicious attacks that are possible. Processes are the best way to mitigate these issues and manage who has access and how additional connections are made.
A wire is pretty simple, but the appeal of wireless — low installation costs, connectivity to hard-to-reach areas, ad hoc connectivity — is great.
Wireless also brings more devices to manage, firmware to update and configurations to manage when failures require a replacement.
Make sure everything is properly documented. The technology is very reliable and will likely be installed and forgotten. Then comes that day when something is broken. You have downtime, and you need to scramble for replacements. Again, know where your documentation is and make use of real-time tools to monitor your infrastructure and help troubleshoot failures as quickly as possible.
Roy Kok,
Vice President of Sales and Marketing,
Kepware Technologies
