Control Systems

Prepare for Tomorrow's Digital Plant

Ubiquitous and cheap data will transform how an enterprise operates.

By Ian Verhappen, Industrial Automation Networks

Chemical manufacturers depend upon control systems to maximize plant performance and economics. These control systems increasingly use open technologies and digital communications such as fieldbus to supply vast amounts of data. However, all these data provide nothing more than a "data storm" or overload if infrastructure and standards aren't in place to manage and convert them into information.

The International Society of Automation (ISA) through its ISA-95 committee and other organizations such as MESA and MIMOSA are working together to define the tools and methods for transferring data between the various layers of today's integrated enterprise. Figure 1 depicts the ISA-95/Purdue model of these layers except for the business local area network (LAN) proper, which would be Level 5 and above. Fortunately, standards are coming into play that facilitate transfer of data between and through all these layers.

The OPC Foundation continues to develop the common interface for the field levels (1–3) of the model. These layers, because they involve process and real-time control requirements, must respond more quickly than others. OPC, which has been designed for easy connectivity between memory registers of devices, well suits the timelines required for data acquisition. The latest version, UA (Unified Architecture), is platform independent and thus applies to a wider range of products. OPC is rapidly becoming the de facto standard for transferring data in Levels 1–3.

Meanwhile, some variant of SQL likely will emerge as the de facto standard for Level 3 and above. At these levels the time constant often is in the range of minutes, hours or days -- so the definition of "real time" is relative. What's important, however, is seamless bidirectional integration of data. Production orders and business data must flow down to the control system for optimizing manufacturing operations for maximum profit; actual output rates, inventory data and equipment health/status information must go up into the business logistics systems for scheduling work, process orders and minimizing operational expenses in the real time of business transactions.

Ethernet Everywhere
Now that data have become more open and portable across multiple platforms and systems, the hardware problem -- sensing and gathering these data -- must be addressed. The probable solution will be "Ethernet everywhere" using the Internet Protocol (IP), which now is on version 6 (IPv6). A number of Ethernet appliances and most operating systems already support IPv6.

What makes IPv6 important? Its most consequential feature is a much larger address space (the sets of three numbers between 0 and 225 you enter for LAN addresses) than that of IPv4. Addresses in IPv6 are 128 bits long compared to 32-bit addresses in IPv4. This means you will use a five number address mask such as 255:255:255:192:068. IPv6 supports a total of 2128 (about 3.4×1038) addresses -- or approximately 295 addresses for each of the roughly 6.5 billion people alive in 2006 or 252 addresses for every observable star in the known universe. Simply put, we shouldn't have a problem putting as many sensors as we need anywhere we need them, especially considering we can use the same tricks employed today to extend the capability of IPv4.

One technology getting a lot of attention is wireless as a means to communicate to anything anywhere (see: "Whither Wireless"). A key benefit is that adding a new data point requires little more than the sensor, radio and power supply. Undoubtedly sensors will continue to get smaller and use less power, yet provide ever-greater processing capabilities (see sidebar).

Figure 2 provides details on the wireless Ethernet protocols being developed and supported by IEEE. Range and data transmission capability vary considerably from personal area networks (PAN) for short distance communications through to the new regional area networks (RAN) standard under development. A significant number of protocols (the combination of hardware and software) rely on the IEEE 802.15 standard as the basis for the radio in the local sensor network backbone. The most widely used application of 802.15 radios is ZigBee — but Bluetooth and several other technologies shown (as well as cellular phone networks) employ the same unlicensed 2.4-GHz frequency bands. So, one of the challenges facing everyone will be how to use this limited bandwidth for all applications targeting this region of the spectrum as their base. The figure doesn't show all the physical connection solutions such as copper- (IEEE 802.3) or fiber-based transmission media that require gateways to convert between the various physical layers and protocols.

Having the means of carrying a signal from one place to another is only part of the solution. You also must have a common language or protocol so sensors can communicate with each other and controllers. The protocol likely to impact the process automation environment most is the forthcoming ISA100 standard. It will incorporate security features expected and required in today's communications while also having gateways to allow transmission and coexistence with other protocols using the same radio frequency bands. The low bandwidth carrier coupled with energy conservation measures will limit how much data can be transmitted.
However, moving up to a higher bandwidth such as IEEE 802.11 (the same wireless we use at home) or higher, we can transmit not only data but also sound and video. Many of us already have IP-based phones on our desks. It soon will be possible for all communications in a plant to be IP-based including video imagery. Video already plays a role in factory automation where vision sensors check for proper placement of labels on products and correct location and orientation of chips on circuit boards. At a process plant, video can serve, for instance, to monitor flares, level in a vessel or status of a pump seal.

Radio frequency identification (RFID) is another technology that will become increasingly popular. Most applications today use passive tags for tasks such as asset tracking (e.g., a pallet in a warehouse or a checked suitcase at Hong Kong's airport). However, development of active tags -- ones that can change depending upon the conditions in which they find themselves -- will accelerate acceptance. Several manufacturers already offer tools that combine the low energy features of RFID with an 802.11 interface to allow you to use the web to effectively keep track of anything or anyone. Active tags will enable you to follow an object over its full lifecycle. In addition, it's not too much of a stretch to expand the capability of active RFID technology to create simple sensors able to measure one or two parameters such as temperature and pressure or humidity in real time and update information on the RFID network whenever there's a change.

The Impact
Plants soon will have access to ubiquitous and cheap data. This will make data mining increasingly important. Mining will move lower and lower in the enterprise -- down to the sensor level. Eventually sensor networks or at least their controllers will contain algorithms to correlate collections of data to create measurements that offer insights unavailable from individual data. Better interpretation of these data will differentiate successful world-class operations from the pack.

IAN VERHAPPEN, P.E., is director and principal consultant at Industrial Automation Networks, Inc., Wainwright, AB, Canada. E-mail at