Distributed intelligence

ometime in the next year or so, companies are going to release control products that will change the landscape of automation and process control. These changes may be the most dramatic to hit our industry since 1975, when the introduction of distributed control systems (DCSs) completely upset the analog control apple cart, threw the established control industry into turmoil, and caused dozens of old, slow-moving control vendors to fail. By the time the DCS trend had swept the industry it had helped create a whole new set of control equipment suppliers.

The biggest difference now is that in 1975 Honeywell caught the rest of the industry with its pants down when it introduced the TDC 2000. This time, several–if not all–of the control vendors have their R&D “skunk works” busy creating new distributed intelligence products, so it’s likely most will come to the market at about the same time.

Essentially, a new type of control system is coming down the pike, and it promises to save you millions of dollars in hardware costs, provide access to the most advanced control and monitoring software at a fraction of today’s price, eliminate security problems, and allow unattended process plant operations. What’s more, it will be better suited to solving your problems than today’s overly complex systems.

“The great thing about the control business today is the equipment and software is finally evolving to the point where we can make the solution fit the problem,” says Edward Bullerdiek, control group leader at Marathon Ashland Petroleum in Detroit. “In the past we've always had to make the problem fit a usually imperfect solution. The user community knows how this ended up—usually not well.”

Two technologies are involved: one at the bottom of the control pyramid and one at the top. One begets the other.

			FIGURE 1: TINY PROCESSOR
			The first-generation Mote is a tiny (3x3 cm), battery-operated computer that communicates via wireless. It has a small operating system (TinyOS), and enough memory and hardware capability to perform control and monitoring tasks. The next generation Mote will be half this size.

The Dream Begins Here
Let’s start at the very bottom of the control system architecture, with “motes.” A mote is a tiny $50 processor, about the size of your fingernail (See Figure 1). It is battery operated, communicates via wireless Ethernet, has a small operating system (TinyOS), and has enough memory and hardware capability to perform control and monitoring tasks. It’s eerily reminiscent of the “smart dust” in Michael Chrichton’s recent novel, Prey.

The technology can put a web-enabled processor at every sensor and every actuator. As long as another mote is within 100 ft. or so, it requires no hardwired network. Hundreds of motes in a process plant can form a spiderweb-like mesh or sensor network that provides unlimited numbers of pathways to pass information back and forth. Such a network has multiple levels of redundancy because, if any single mote fails, dozens of others stand ready to move network traffic. (See “Developing Your Potential,” Sept. ’04, p57 and “Technically Speaking,” Sept. ’04,  for a discussion of mesh networks and the Zigbee protocol.)

Similar devices are available. Mote is the term used for sensor nodes created by University of California Berkeley and their partners, including Crossbow and Intel. TinyNode is another example, which is a sensor/actuator node produced by Embedded Research Solutions, Annapolis, Md. A more generic term is a “sensor node.” 

The National Institute of Standards and Technology (NIST) calls all this technology “pervasive computing.” 

To keep it simple, we’ll call them all motes and sensor networks for the time being. Whatever you call them, motes are the ultimate in distributed monitoring and control. 

Consider the ramifications of a sensor network in your plant. What does it cost you to transport the output of a traditional 4-20 mA pressure transmitter to your DCS and then on to your enterprise resource planning (ERP) system? The 4-20 mA signal first has to run via a twisted-pair wire through a hazardous environment and intrinsic safety barrier to an A/D converter on an I/O board mounted on a rack in a NEMA 12 enclosure out in the plant.