Connecting the industrial edge

In the same way that wireless connectivity has changed the way people communicate in their business and personal lives, it is also revolutionizing how plant automation networks work. While adoption has been slow, more networks are using wireless Ethernet protocols to add new devices, extend the networks into hazardous locations and establish connectivity with devices and systems that may be in ...

By Ed Nabrotzky, Molex Inc. September 1, 2009

In the same way that wireless connectivity has changed the way people communicate in their business and personal lives, it is also revolutionizing how plant automation networks work. While adoption has been slow, more networks are using wireless Ethernet protocols to add new devices, extend the networks into hazardous locations and establish connectivity with devices and systems that may be in motion, such as robotic cells and material handling systems.

Part of this is driven by the cost imperative of connections in a plant. If you consider the connection pyramid diagram, it is clear that the biggest installed cost savings of wireless occurs when you get to the edge or end devices on a network (Fig. 1). Even though most typical installs are using wireless connections only for data gathering at the top of the pyramid (plant intranet or SCADA layer), the edge connections outnumber this data access point by five orders of magnitude.

Wireless networks also make operator interaction simpler and easier by enabling handheld devices to communicate with different devices or take measurements from various instruments. When you add in the flexibility of design, the avoidance of hazardous environments and the fact that cables have been proven to be prone to failure under rough use over time, it seems obvious that reliable wireless connections would have great benefit on the plant floor.

Since we use wireless connectivity extensively in our day-to-day lives, our generation is getting more comfortable with the technology. We expect the same functionality and advantages this has brought to our businesses and personal lives to be available on the plant floor. The good news is that while plant floor wireless has lagged significantly behind the development of consumer applications, a wide range of industrial wireless protocols and standards are already being evaluated and implemented in real applications today.

Industrial wireless protocols

By far, the most common implementation of wireless Ethernet is the 802.11x variants (where x = 0.1, b or g). These high data rate and familiar access points are pervasive in our office and public environments, with low costs and familiarity for our IT groups being a big plus for adoption. However, these features can also be the undoing of this solution for the plant floor — especially as we try to migrate the connectivity to the edge devices. Security can be difficult and is managed through corporate policies, many competing signals can cause setup problems and low cost access points provide a temptation for installers to put in equipment that was not designed for the rugged conditions or certifications needed in many industrial applications.

These access points are also ideal for transferring large buckets of information (not typical of plant floor data producers) and have high latency or delays built in because of overhead when shifting many small packets of data (very typical of plant floor data). Some popular adaptations have been made, however, in process automation — especially the WirelessHART protocol (based on IEEE802.15.4) from the HART Communication Foundation — for connecting to devices and systems. A standard adapter interface for WirelessHART has been agreed to by Profibus International in conjunction with other process fieldbus organizations.

Zigbee is another 2.4 GHz wireless network that is low-cost and very robust. It uses a self-healing mesh topology to ensure that setup is easy and interference can be worked around. It was built for small data payloads and has a greatly reduced overhead to ensure there is less delay or latency in forwarding information through the mesh. With its low power profile, it is also useful in remote locations or battery-enabled devices. As such, it is gaining some popularity in metering and instrumentation. But it is too early to tell if it will really gain the adoption that can take it past the tipping point of economies-of-scale and widespread support in consumer devices.

Wireless interface to sensors and actuators (WISA) is an industrial technology being promoted by ABB as the way to solve not only the wireless data problem but also the wireless power problem. It uses a small data payload and frequency hopping to target the desired characteristics of the factory. While it has been announced and implemented on some test cells, it has its share of skeptics because the large antenna loops required and the potential issues associated with transmitting the power required cause many to see it as impractical.

A very common (perhaps soon challenging 802.11x for the top spot) approach is Bluetooth — another open wireless protocol in the 2.4 GHz range for exchanging data over short distances from fixed and mobile devices. Bluetooth has some tremendous advantages, including the ability to uniquely identify and connect with various devices and reconnect easily whenever an authorized device comes within range — similar to ODVA quick-connect for tooling changes.

This also means security is built in at the chip level, avoiding the need for IT to get involved with firewalls and corporate procedures to prevent unauthorized access to the network. It also has a built-in interference avoidance scheme using 64 different frequencies to automatically screen out interference from other sources — a critical advantage on complex plant floors crowded with other devices. With really inexpensive integration costs and built in support in many consumer devices such as cell phones and PDAs, it can be a handy method for operator interface, and has the potential to be the winner in the race to connect the industrial edge.

For these reasons, a number of organizations are looking at Bluetooth as an ideal method for linking devices wirelessly to extend Ethernet industrial networks. An initiative to standardize a solution for factory automation is now underway, primarily in the Profibus International organization based on IEEE 802.15 (Bluetooth) as the wireless link and IO-LINK for the field connections.

Also, a new extension to the protocol — low-energy Bluetooth — is being developed to allow small, inexpensive, very low-power devices to link to a network using Bluetooth technology. These devices, with tiny batteries (or even energy harvesting as per WISA), will be able to talk to network hubs more proficiently than under traditional Bluetooth protocols. Low-energy Bluetooth will add a new chapter to the Bluetooth saga and enable the potential to extend wireless further onto the plant floor.

Key transceiver chip makers are increasingly combining 802.11x and Bluetooth due to the popularity in many consumer devices. Almost all cell phones and laptops computers now have a dual interface and common antenna array. This is driving costs through the floor and making reference designs and engineering development very easy for adoption on plant floor devices.

New technology investment drives wireless

Bluetooth, of course, has a strong background as the premier protocol for consumer and business wireless devices such as cell phones. Technology advances in those applications will likely transfer to plant floor applications. For example, Molex has invested significantly in RF research, including the recent acquisition of a Motorola research and development center in Aalborg, Denmark. Molex manufactures more than 100 million antennas every year with a customer list boasting several major cell phone manufacturers. One of the key advances in this area is Laser Direct Structuring (LDS) antenna manufacturing technology.

LDS is accomplished by applying a combination of resins susceptible to a laser on a part, then etching them with a laser to produce a conductive trace. This has several major benefits. It is inexpensive, especially in large volumes. It requires almost no space on the device since the antenna can be etched on the housing or another part of the device. It is also 3-D in nature, so more antennas can be packed into tighter spaces, improving efficiency.

Traditional methods of creating an antenna involve either a PIFA array (a trace laid out on the circuit board) or a component antenna (usually ceramic). The first takes up more space, requires a circuit board and is inherently less efficient due to its 2-D nature. The latter is an excellent choice for devices produced in lower volumes, but must be purchased as a component, then soldered to the board, taking up more space and making it more expensive.

Since LDS antenna arrays are inexpensive to produce and can achieve excellent density, they may be ideal for high-volume plant floor applications involving small, low-power devices and sensors. The 3-D nature of the array may enhance other possibilities as well, such as opportunities for energy harvesting.

Perpetual energy harvest

A fascinating technology that will enable more extensive plant floor wireless applications is energy harvesting. Energy harvesting involves taking the magnetic field generated from the antenna and harvesting that energy through a storage circuit.

Nokia has announced that within as soon as two years it may be able to introduce a cell phone that powers or recharges itself from ambient wireless signals in the area surrounding it. The Palm Pre just launched a new wireless charging pad called Touchstone that employs a similar approach. It is likely that in the future as this technology develops, many of our consumer devices will never have to be plugged in for charging.

This technology will have important implications for industrial automation. While technology such as WISA exists today for using energy self-sufficient sensors, more complex, high-power devices may be able to use additional advances to self-power and reside on the 2.4 GHz Bluetooth network, opening up an entirely new range of applications on the plant floor. Since devices will not have to be replaced or repowered, the cost of implementing and maintaining sensor networks may drop dramatically.

The Bluetooth standard is the most practical, efficient and cost-effective way of providing Ethernet connectivity to small and even micro devices and sensors. By thinking small, industrial network developers can power major changes in automation strategies.

Author Information
Ed Nabrotzky is a global product manager at Molex Inc.