PLCs Pack it in

Programmable automation controllers enhance PLC's process-control capabilities. Programmable automation controllers, like these from National Instruments Corp., complement and enhance PLC operations by performing special tasks above and beyond an average PLC's capabilities, such as machine vision and highspeed process data acquisition and analysis. This cFP-2120 Compact Fieldpoint processor from NI is an example of the new PACs developed for embedded control or distributed I/O applications. Typical uses for these controllers include measurement taking with data logging, pid loop monitoring and control, realtime situation analysis, and simple I/O operations such as valve actuation and motor control. Ethernet connectivity with a built-in Web server transmits information gathered by the system to any OPC client or HMI/Scada display. Programmable logic controllers, or PLCs, are ideal for discrete logic control. However, as PLC process control and automation complexity expands, shoehorning new requirements into these ubiquitous devices can prove difficult. There is a significant and still-growing need for devices with expanded processing power, advanced I/O interfaces, and more control capabilities. Craig Resnick of the ARC Advisory Group coined an appropriate name for these devices. He calls them programmable automation controllers, or PACs. PACs represent the next evolution in automation controllers made possible by exponential advances in computer technology. Thus, companies like General Electric, Rockwell Automation, Siemens, can pack more processing capability into small and highly rugged devices that require less power. Differences between traditional PLCs and the newer PACs become apparent when comparing software-execution models. PLCs generally follow a linear execution of their programming code. The PLC reads values from input modules and updates its internal input registers. These input values are then used to create or modify other register values according to specific rules of logic dictated by the PLC program. Then the PLC updates its output modules with the newly calculated values and the