Machine Design

Reconfigurable I/O takes industrial control in new direction

Think of it as a way to handle situations where the millisecond scan times of an ordinary PLC just won't work. That was how one engineer from Austin-based National Instruments Inc. described that company's just-released CompactRIO controller, which draws its name from Reconfigurable I/O technology. It has a form factor that resembles a miniprogrammable logic controller (PLC) but packs much more power. At the same time, NI personnel say CompactRIO makes more sense for industrial applications than processors built on PC104-format boards.

NI claims the CompactRIO computing engine can implement multiloop analog PID control systems at loop rates exceeding 100 ksamples/sec, perform digital control loops at rates to 1 Msamples/sec, and evaluate multiple rungs of Boolean logic in less than 25 nsec.

One feature getting top billing, however, is the controller's use of FPGA (field-programmable gate array) technology. FPGAs that form the backbone of the CompactRIO chassis get programmed via the firm's LabView graphical development tools. The drag-and-droporiented LabView is much easier to use, claims NI, than traditional logic programming tools such as VHDL or C++. Expectations are that Lab-View will help put CompactRIO systems into high-speed control systems, sensor-level signal processing, and into areas where FPGAs can offload low-level processing from the computer.

A four-slot CompactRIO embedded system measures 7.07 3 3.47 3 3.47 in. and weighs 3.47 lb. The dc-powered system typically consumes 7 to 10 W and can withstand temperatures ranging from 40 to 158F and up to 50 g of shock. I/O modules in the CompactRIO format are hot-swappable, have up to 2,300 Vrms withstand, and 250-Vrms continuous isolation.

There is also an expansion chassis that connects directly to a digital port on a PXI/PCI R Series device. The FPGA sits on the PXI/PCI device and Compact RIO provides expansion I/O and signal conditioning.

NI officials credit advances in FPGA technology with making systems such as CompactRIO practical. It is only recently, they say, that FPGA pricing has made these parts candidates for high-volume systems. In the reconfigurable chassis, FPGAs take over tasks that would otherwise need special-purpose hardware. They handle the connections between the controller and various I/O modules for such tasks as sensing and control of actuators.

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