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Industrial Ethernet Book Issue 65 / 35
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Tracking assets: RFID meets industrial Wi-Fi

Globalisation and mobility trends have profoundly affected industrial plant operations and entire business models, with assets that make up the supply chain being constantly in motion. Efficiently managing people, products, equipment and raw materials is essential to keep global manufacturers competitive. One fast growing technique that enables this is a combination of wireless networks with RFID technology.

IN THE PAST, a lack of visibility into the location of valuable assets has hindered efficiency and resulted in operational problems such as misplaced mobile tools, jigs, machinery, parts, or work-in-process (WIP) inventory. This results in high equipment leasing and/or replacement costs to offset losses.

Worker safety and security is another issue. Accidents and security incidents can make it life-critical to quickly locate employees and building exit routes. Context-aware conditions help minimise injury and losses. As manufacturers seek to continuously improve business agility, quality, reliability and safety, they are taking advantage of increasing intelligence in devices and networks.

Increasingly 'smart' devices, which include radio frequency identification (RFID) tags and sensors that have advanced diagnostics, are contributing to the billions of devices now connected to IP networks. This proliferation of smart devices is referred to by some as the 'Internet of Things', and it is projected to grow to trillions of devices that will be connected using the emerging IPv6 protocol1. For manufacturers, a growing number of connected smart devices promises to revolutionise portability, mobility, context-aware condition and use of critical assets.

However, devices must be continuously connected - including in tough manufacturing environments - and be integrated to deliver context-rich information, alongside with data. The combination of smart devices with wireless networks is now able to deliver powerful smart services, such as context-aware, real-time asset management and location services.

RFID + wireless

Technology analyst firm IDC included smart services using RFID as one of its ten Manufacturing Industry Predictions for 20112. Indeed, the past year has seen an explosion of RFID solutions used to track almost everything imaginable.

Research firm Gartner suggests that the explosion of mobile smart devices is leading to an equivalent explosion of mobile applications, which will create new wireless infrastructure requirements3. When RFID solutions are teamed with wireless networks, manufacturers can suddenly increase operational visibility almost anywhere. Today, RFID and wireless networks are able to deliver immediate, unprecedented visibility into assets, WIP and people's locations.

Manufacturers have been piloting and deploying RFID in their organisations for some time, and several trends are developing.

Passive or active?

There are both 'passive' and 'active' RFID tag types. Passive RFID uses low cost tags that are generally disposable as consumables (as used in shops to prevent theft etc), while active RFID uses more sophisticated tags that cost a little more at typically Euro 17 - 68 ($25- $100). There is also a third type - semi-passive tags. These are similar to active tags in that they use a battery to run the microchip's circuitry, but they cannot communicate with RFID readers. To conserve battery life, some semi-passive tags remain in a 'sleep' mode until contacted by a reader.

Active RFID tags possess greater functionality and tend to be associated with supply chain or manufacturing process workflows. They are reusable and have batteries that last five or more years. Active RFID tags can also function as low-cost remote sensors that broadcast telemetry back to a base station. Active-RFID deployment is a sector that is seeing good payback and return on investment for manufacturers.

Looking at wireless transmission, work with RFID and the Real Time Location System (RTLS) has led to the development and support of multiple RFID technologies. The first is Received Signal Strength Indicator (RSSI). This is a measurement of the power present in a received radio signal. RSSI is generic radio receiver technology metric, which is usually invisible to the user of the device containing the receiver, but is directly known to users of wireless networking of IEEE 802.11 protocol family.

RFID technology

Active RFID tags have an onboard battery to power the microchip's circuitry and transmit signals to readers. Typically, active tags can be read from distances of around 30m. They also allow more applications by offering two-way communications, sensor integration, independent system intelligence, and constant viability. Active RFID tags work using Received Signal Strength Indication (RSSI) or Time Difference of Arrival (TDOA) technologies.

RSSI: Some tags associate with APs to provide a regular beacon or 'chirp' (a 416-bit 802.11 frame). This reduces tag/AP interaction to a simple unidirectional packet - there is no state for the AP to maintain and no IP address required. Also, less radio time means a longer battery life. This is common amongst IEEE 802.11 wireless protocol families, whether a, b, g or the newer n flavour. Other tags send out a more constant signal, become associated with the AP, providing a more constant awareness with stronger integration. However, battery life is shorter.

In an 802.11 Wi-Fi network, the APs are arranged so that they receive signals from the RFID tag and triangulate its position based on the received signal strength at each AP. The stronger the signal, the closer the tag is to the AP. Each AP sends it's strength metric to the wireless control system, which interprets the signal strength via an appliance and middleware. This provides coordinates via APIs to user interface software, which - in turn - specifies location. The results can be sent as coordinates or shown on a visual map.

For Lightweight Access Point Protocol (LWAPP) environments, location information is sent to the Location Appliance andWireless Control System (WCS) rather than an alternative separate non-LWAPP engine, which can also calculate tag positions. Accuracy can be 2 - 3m, depending on environment, location and AP density.

TDOA: This is similar to RSSI in that the network APs triangulate tag locations based upon the signal, but here it is the time it takes for the signal packet(s) to arrive at the AP that is important. The shorter the time taken for the signals to be detected, the closer the tag is to the AP, and a position is estimated using one or more locating algorithms in the location appliance andWCS. This method is more resilient for high ceilings and outdoor applications, and is less disturbed by building structures.

In another application there are chokepoints ('exciters'). This works using strategically placed readers or triggering devices - the exciters.When a tag passes within range of a 125 kHz exciter, the tag emits a short burst ofWi-Fi data that includes that exciter's unique identification.With an exciter, immediate tag recognition occurs as the tag is 'excited' and emits a response. Conventionally, it can take several minutes before tags chirp and the location is updated. Exciters, therefore, provide a more real-time experience for tracking moving items. Additionally, tags can be set to turn themselves on or off as they go through chokepoints.

In summary, RSSI is good for most indoor tracking applications and uses existing standards-basedWi- Fi networks. TDOA uses a more proprietary approach, but can be backhauled via Wi-Fi networks and is good for outdoor and difficult environments. Choke-points are good for tracking movement of assets through doorways and designated areas, so helping to prevent asset loss or tracking mislaid items.

Organisations that define standards and regulate the use of RFID include ISO, IEC, ASTM International, DASH7 Alliance and EPCglobal.

Open standards platforms

With different protocols and standards abounding, a key technology development has been the introduction of open standards based platforms.

The pace of adoption is starting to pick up. The customer stories below tell the business benefits side, but there are also IT and process benefits. With an open-standards WCS4, the application can integrate with warehouse, ERP and other business systems. Tracking WIP can become part of the overall methods of manufacture, not only for the supply chain, but also plant-floor activities, such as MES and WIP.

Challenges remain. Firstly, manufacturers want reliable and available systems. A system is now available that uses a wireless interference monitoring technology. This comprises special hardware built into certain APs, plus advanced interference identification algorithms that automatically detect radio interference and can map its source, rather like an integral spectrum analyser. Microwave and blue-tooth devices, for example, can cause interference. The system identifies the interference and detects where it's coming from and can mitigate it, providing a more reliable network.

Secondly, 802.11n adoption continues to grow. These are higher performance than the older networks, but manufacturers' IT departments may still have legacy deployments, so technologies are still needed to cope with both old and new. There are ways of improving the network performance of legacy 802.11a and g devices (older Wi-Fi networks), whilst still enjoying the benefits of a higher performance 802.11n Wi-Fi network.

Thirdly, videos of faulty machines, pictures of prototypes and digital signage are becoming increasingly common and add up to more, potentially disruptive, load on the network. So technologies will need to help manage loads, prioritise network activities and give a better quality of service. Moreover, as wireless network and fixed LAN convergence increases, manufacturers and their IT departments can use one system for wired and wireless management.

Case studies

Boeing improves operational efficiency - RFID and wireless solutions can help manufacturers overcome space and time barriers in keeping track of parts and tools. In Boeing's vast jetliner production environment, essential components and tools can easily be misplaced - and must be replaced to avoid production delays. Additional purchases and lost productivity quickly become very costly.

Boeing used its wireless network, RFID tags and location tracking software to help reduce losses. RFID tags were fitted to 1700 critical parts, tools and factory machines. Any part can be located instantly. Because each part has a tag, it can be quickly identified to resolve service issues, saving troubleshooting time and misdiagnosis. This improved productivity by enabling employees to quickly locate parts and tools, which also helped reduce production delays and the potential for government fines.

Viracon gains transparency - Leading architectural glass fabricator Viracon uses an RFID and wireless asset tracking solution with which RFID tags are attached to all of its 5800 workin- process glass carriers at three manufacturing campuses. Paired with a wireless network, this eliminated the need for a dedicated network of RFID tag readers. When operators need to find a particular glass carrier, they search for it using shop floor computers. The real-time location of the required carrier is presented on a site map, allowing carrier location within seconds and providing complete visibility. This system increased success rates in precisely locating carriers to 99%, reduced reproduction and scrap of lost carriers by 65%, and ensured that the correct glass is transported on time to the right destinations.

Continental tyre boosts production - Continental Tyre of the Americas' Illinois plant produces over 1000 different tyre stock keeping units (SKUs). Demand was increasing beyond capacity, so the company set out to remove bottlenecks and delays in its production process to increase throughput. Inefficient management of its thousands of carriers was causing unnecessary idle time and setups.

The company implemented a wireless network with RFID tags as part of a solution that tracks and manages tyre assembly and material carriers. This system tracks Work-In-Process (WIP) functions without needing a proprietary reader/sensor network. The system tells operators where the freshest rubber and tyre components are, how to get to them using their fork-lift-truck computer's visual map, where they're needed, and even the status and location of empty component and rubber carriers. The latter is important, since components can 'go off' during the curing process; lost WIP can cause wastage. As a result, there are reduced delays and production stoppages, minimised machine idle times, and significantly increased daily throughput. Scrap has been eliminated. Payback is around six months, and component tyre losses decreased by around 20%.

Tracking the Future

It is clear that RFID technology and wireless networks create a winning solution for a range of asset management, cost reduction, location tracking, and safety initiatives. The beauty of these solutions are their flexibility. Now a manufacturer can identify and manage almost anything to gain better operational visibility and intelligence.

RFID systems can also communicate directly with PLCs via ProfiNet, ModBus and Ethernet/IP etc., so are ideal for industrial applications that require the exchange of RFID data with ERP systems, as well as with devices such as PLCs.


1. Internet Protocol version 6 (IPv6) is a version of the Internet Protocol (IP) designed to succeed IPv4 as it allows for vastly more addresses.

2. IDC Insights: 10 Manufacturing Industry Predictions for 2011, January 13, 2011.

3. Top Technology Trends You Can't Afford To Ignore, Oct. 5, 2010.

4. Web Map Service (WMS) is a standard protocol for serving georeferenced map images over the Internet generated by a map server using data from a geographic information system (GIS) database.


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Source: Industrial Ethernet Book Issue 65 / 35
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