Convergence of these devices is interesting, but what can you do with it? Opto22's Edwards says, "We've also seen convergence in terms of the types of applications in which PACs, PLCs and embedded control are used. From their beginnings, PACs were designed to perform a variety of functions, whereas the PLC's ancestry is closely rooted in discrete control."
So it isn't just ladder logic anymore. But the convergence has pulled the PLC along too. Edwards notes, "Among other features, the faster, smarter processors found in modern PLCs make them suitable for the added domains in which PACs and embedded computers operate. These include process control, motion control and data acquisition. So, although PACs' more organic origins for use in multiple domains make them an extremely efficient, well-designed, multi-disciplinary controller, the much broader range of inputs now accepted by modern PLCs help make them just as well-suited for process and other applications as they are for discrete control."
Edwards continues, "In addition to expanded communications capabilities and a wider cross section of potential applications, the latest generation of PLCs and PACs now boast several other features previously associated more with PC-based or embedded control. These include the use of Intel-based processors, onboard flash memory, removable memory in the form of microSD cards and an easier-to-understand file system."
Most PLCs, PACs and embedded controllers are equipped with native USB communications capability as well, making it possible to use USB memory sticks to program or take data from the device. (Of course, this has a dark side, as we saw in 2010 with the Stuxnet virus, which used a "candy drop" USB stick to get inside the security perimeter of an Iranian nuclear facility.)
As a significant indicator of what this convergence means, ISA recently established a Building Automation Division. Similar devices are being used in both process and building controls as energy management becomes an integral part of process control. For several years now, ABB, Siemens and Schneider Electric have been discussing the convergence of power control and process control in manufacturing plants, which can only occur because the devices used in each application area are, or can be, the same.
Resnick says that this will have a significant effect on the way control solutions are specified and rated. "Solution performance competitive differentiation will be based on the functional software capabilities and IP, as well as the wired/wireless network's speed, security, accessibility and adherence to open standards, rather than the hardware that is processing the software and networking technology.
How soon will we be using the same controllers to run our plants and turn our lights on and off? The capability exists now and is becoming greater all the time.
But Rezabek points out, "fitness for purpose still wins the day. Maybe my iPhone-based PLC is great for flushing the toilets in the truckstop, or even Christmas light animations on my front lawn (It can play iTunes at the same time!), but the large process industries put extraordinary demands on process controls."
Rezabek goes on, "Even in our preferred suppliers' DCS systems, unforeseen 'features' crop up, especially in the portion that's running under common PC operating systems. It can literally take years to run all the bugs into a corner and squash them. The stakes are high—my operations manager says he can justify a $10,000 ultrasonic flowmeter just to improve his odds of choosing the optimum pump to shut down for maintenance.
"It's not just the computing power to invert matrices or solve complex logic and display it all in gorgeous graphics," Rezabek concluded, "It's knowing that it won't do what we don't want it to do, ever, over the course of months and years of 24/7/365 production."
So while convergence of devices, networks and protocols is clearly the way the future shapes up, it will, as usual, take longer to penetrate the process industries.