Wireless on the Factory Floor
For those grounded in wired networks, untangling wireless-related issues for plant-floor applications can be as intimidating as reworking networked I/O connections without documentation. If you haven’t jumped into wireless communications yet on the plant floor, or even if you have, here are some questions and answers to help clear the air about wireless. For more, also see the Control Engineering Wireless Implementation Guide, online.
Providing answers are:
Bob Gardner, Banner Engineering, SureCross wireless product manager;
Jim Toepper, Moxa Americas product manager, connectivity group, industrial wireless group;
Robert Jackson, National Instruments senior product marketing manager, wireless; and
Paul Brooks, business development manager, networks portfolio, and Cliff Whitehead, manager, strategic applications, Rockwell Automation.
|Automated guided vehicles are among many plant floor wireless applications, Banner Engineering says.|
Q: Is wireless networking ready for prime-time factory applications?
Gardner : Yes! My garage door has been wireless for more than 20 years, not to mention the WiFi connection built into my laptop. To implement wireless in plant environments, factories require reliable deterministic signals with a known output condition if an error were to occur. Wireless communication of I/O and serial data is the next step for plants that want to optimize resources and ensure all assets are performing at peak capabilities.
Jackson: Wireless is ready for a more central role as an add-on system to the existing wired infrastructure. This ability to combine wired and wireless measurements will allow end users to preserve investments and use wireless technology in applications where it makes sense.
Q. What are some common uses for wireless networks in a factory?
Brooks and Whitehead : Today’s wireless deployments generally occur in applications where wired networks present challenges, making wireless increasingly simple and cost-effective. With its periodic signal monitoring and data collection capabilities, wireless also becomes increasingly valuable to mobile workers. While wireless can improve cost and operational efficiencies, it does not necessarily make deployment easier.
|Signal strength depends heavily on environmental factors. Site survey graph shows interference; yellow bars should remain solid, left to right, without gaps, Moxa says.|
Q. In a wireless implementation, what should a user, original equipment manufacturers (OEM), or system integrator consider?
Jackson : The correct wireless protocol depends on the application. Software working at the application layer helps a system support multiple protocols. This allows users to combine the advantages of different protocols, and better isolates them from technology evolutions.
A tiered strategy to wireless network support may provide the best service to a broad set of applications. Offer a tightly integrated hardware/software solution for industry standards, such as Wi-Fi, for the best end user experience. At the same time, provide support for proprietary and emerging standards through software abstraction, so end users can preserve software investments while maintaining flexibility as protocols change.
For instance, wireless data acquisition can use Wi-Fi for easy connectivity and high bandwidth measurements. Software drivers [or other tools, such as OPC servers] can connect applications to a range of proprietary wireless sensor network (WSN) nodes from third-party suppliers.
Q. What are the three tiers for wireless?
Jackson : Existing and developing wireless protocols can be grouped in three areas. Each category has unique benefits:
Wi-Fi: high bandwidth PC connectivity;
Protocols based on IEEE 802.15.4: low power; and
Cellular standards: distance.
Offering solutions that address all three areas with a standard software model and interoperable gateways will provide the flexibility customers need to deploy scalable and robust applications.
Q. What’s needed for a wireless implementation?
Brooks and Whitehead : To help enhance the success of an industrial wireless installation, it should include the following features:
A plan for the wireless deployment’s scope throughout the installation’s life cycle.
A baseline survey of the radio frequency (RF) environment in and near the deployment areas, including during lift truck transportation, material movement, and other environmental conditions. Users should leverage professional expertise as well as tools like access points to detect rogue devices, and advanced modeling software to map expected radio strength and eliminate coverage gaps.
A plan to perform periodic baseline survey updates that help adjust to changing RF conditions.
|Regulatory controls mandate an increase in the level of process monitoring, tracking and supervision, Rockwell Automation says.|
Q: That seems like a lot. Shouldn’t wireless be easier than wired?
Gardner : If you consider the labor involved with running a wire, wireless is inherently easier. However, because wireless is a new technology with new tips, tricks, and terminology (such as node and gateway), the product specification step can be slightly more complicated than other, more familiar, networking methods. After the first project, many of the semantics and experience-based issues are resolved.
Brooks and Whitehead : Manufacturers should understand that wireless complements, rather than replaces, wired infrastructure.
Jackson : Wireless offers several advantages including, reduction in installation costs, ease and scalability of deployments, and the ability to address new applications where wiring is prohibitive.
Q. Can wireless be plug and play?
Gardner : With the correct wireless technology, users can simply plug it in and go. A number of factory-configured kits enable this kind of simple installation.
Q. Can a wireless site survey help? A plant floor can change quickly.
Toepper : Before deploying a wireless solution, know your environment. Site survey software tools available on the Internet may require a laptop or computer to measure the wireless signal. Most of the time in the industrial environment, it isn’t your laptop’s radio that needs the wireless connection. Be sure to measure signal strength using the radio and antennae of the wireless clients in the location throughout the time it will be used. (See implementation example above). Because radios differ in power, and antennas have different gains, it is more accurate to do a site survey this way. Hardware with a signal meter on it provides an advantage, making it easy to glance at signal strength bars.
Gardner : Some manufacturers have equipped wireless devices with an onboard site survey capability. Of course, plant environments and conditions change, and it is important that any wireless network you purchase has a strategy for identifying areas and times when the link is weakest. Some site survey tools use a separate communication layer than the I/O signals being collected. This enables the wireless network to perform its required task while monitoring its own radio frequency (RF) communication link.
Q. What are some wireless communication methods?
Jackson : Wireless de facto standards like Wi-Fi and cellular are widely adopted. Proprietary technologies in the 900 MHz and 2.4 GHz frequency bands also exist. In the past several years new protocols based on IEEE-802.15.4 have emerged that offer advantages for low power applications. Standard protocols exist, like ZigBee that address low power applications with lower data rates than Wi-Fi. These protocols have not seen the same adoption as Wi-Fi, but do offer interesting advantages in many applications.
[ More hel p: Use the Wireless Implementation Guide to match various wireless protocols to specific applications . Also, see below for additional links and information from Emerson Process Management, HART Communications Foundation, ISA, and others.]
ONLINE EXTRA More questions and answers, plus scroll down for links to additional resources.
Q. Any particular areas for concern?
Jackson: An obstacle to making wireless easier is end users ability to integrate wireless measurements into existing wired systems. Graphical system design tools allow end users to preserve wired measurement systems while integrating new wireless technologies.
Q. Are there new wireless options emerging?
Brooks and Whitehead: With IEEE 802.11n (Wireless-N) emerging as an attractive wireless network for high-speed control and monitoring applications, Rockwell Automation is testing this technology to determine its ability to meet the broad range of needs in industrial automation using standard, unmodified wireless Ethernet.
Q. What’s different about IEEE 802.11n that can help?
Brooks and Whitehead: Several technical features of Wireless-N will help simplify wireless deployment, including multiple-input multiple-output (MIMO), beamforming, and rogue radio detection. These features will be especially beneficial in environments that experience dramatic short-term change, like a smelter with multiple moving cranes. We anticipate this technology to complement and easily integrate with long-haul communications using Internet protocol (IP) over commercial radio technologies, and with wireless mesh networks based on the WirelessHART and ISA100.11a protocols.
Q. What is like to be in our wireless future?
Jackson: As the wireless market for smart devices matures, we will explore opportunities to deliver additional products and software drivers for interoperability so customers can combine the advantages of bandwidth, low power, and distance to solve their applications.
Brooks and Whitehead : As wireless technology such as Wireless-N evolves, wireless will become more acceptable for control; first for slower control loops, and eventually for high-speed, discrete control.
ONLINE resources (also search using Zibb atop www.controleng.com.)
– Control Engineering Wireless Implementation Guide ;
– Tutorials on RF and communications fundamentals : A set of tutorials on radio frequency (RF), microwave, and wireless devices and signals will advance knowledge of related applications, including test and measurement applications, National Instruments (NI) says. “Next-Generation Test System Developers Guide” teaches how to incorporate measurements into an automated test system.
– Wireless band designation and frequency allocation tables from NI; and
– AIMing for Automated Vehicles blog from Control Engineering .
|Mark T. Hoske is Control Engineering editor in chief. Reach him at MHoske@cfemedia.com .|
|Do site surveys (see graphic above) with the antenna, wireless transmitter, and receiver on location during the time they will be used, Moxa Americas recommends|
Implementation example: Wireless signal strength, commercial vs. industrial
A tool to measure real-time wireless signal strength shows an application where signal strength drops out quite often using a commercially available wireless product in an industrial application, says Jim Toepper, product manager, connectivity group, industrial wireless group for Moxa Americas. A consistently solid line all the way across the graph (see above) would show a better implementation. The exact reason for the dropped signal, Toepper says, was twofold:
The break room was next to the access point and a microwave oven was on the other side of the wall. Microwave ovens interfere with 802.11b/g 2.4 GHz signals.
Weak transmit power of the radio made for an unreliable signal. An industrial wireless product corrected the problem, using 5 GHz (IEEE 802.11a) instead, he explains.