PC-based control is used across every segment of industry—except real-time control of large-scale process plants. There are historical reasons, primarily initial problems with PC reliability in general and PC operating systems in particular. A secondary concern was the lack of programming software for PCs geared towards process applications.
But now PCs are being used to perform critical real-time control in applications closely related to process plants. "Our 758 Series I/O-IPC was used to fully automate the pipe-handling/gripping tool for a Norwegian onshore/offshore oil and gas rig," notes Charlie Norz, product manager of I/O systems at Wago. Like large-scale process plants, drilling rigs have very critical uptime requirements.
"Our I/O-IPCs are equipped with Linux 2.6 for real-time deterministic scanning and highly consistent cycle times for PID loops. Our PCs provide C-code programming for developing custom function blocks, and also feature our IEC 61131-3 PLC programming tool," explains Norz. Standard and intrinsically safe remote I/O were used in this application, as the operating environment was a mix of Zone 1 and Zone 2, similar to many process plants.
An operating system specifically designed for automation applications is INtime from TenAsys. "INtime enables performance-critical application elements to run on dedicated cores of a multicore processor, along with additional complementary application software on other cores," explains Kim Hartman, VP of sales and marketing at TenAsys.
"Unlike general-purpose operating systems that do dynamic loading of application tasks onto processors as the system runs, the INtime approach is to fix tasks to processors as the application is loaded, and assign the resources that a particular task needs to the processor core that will run the task. This guarantees that an interrupt from an I/O device will be serviced in a particular amount of time, as is required with real-time applications," explains Hartman.
PCs are used to program and run almost every third-party, advanced process control (APC) application. "Modern APC technologies leverage the relatively low cost and advanced computing power of server- and workstation-based platforms—and combine with universal connectivity via standard Ethernet to provide a cost-effective, high-performance solution," says Don Morrison, process performance solutions manager at Honeywell Process Solutions.
"Honeywell's Profit Suite is an example of a comprehensive suite of PC-based APC technologies, and it interacts with any vendor's distributed control system. At the IRPC refinery in Rayong, Thailand, our APC software enabled an increase in production of 7%, an increase in overall operational efficiency, and nearly 100% uptime of the application," says Morrison. Although this isn't a real-time control application, it does show a deep understanding of sophisticated process control and integration embedded in a PC platform.
PC-based control can be trusted on large-scale process control applications, such as the vacuum coating machine at a major Taiwanese LCD manufacturer. "The machine and its associated equipment required six racks of I/O and over 60 DeviceNet-enabled mass flow controllers, all controlled by a single SoftPLC. Displaying and controlling the many features of the machine required a three-bay control console with three 21-inch, rack-mount monitors and two industrial PCs," notes Cindy Hollenbeck, VP at SoftPLC.
According to the SoftPLC's machine-builder customer, this application wasn't suited to a PLC. "We appreciated the ease of tying together that many I/O, the flexibility of the remote racks, the capability to integrate DeviceNet, and the ability to communicate with a remote PLC used to run an external conveying system. This could have been done with a PLC, but at about six times the cost and two times the man-hours."