GE Intelligent Platforms created the concept of the Programmable Automation Controller with the introduction of PAC Systems automation controllers. Expanding on traditional PLCs, GE’s PAC controllers provide a highly reliable, high-performance advanced control platform for discrete logic control, motion control, and process control. PACs are standardized on PROFINET to provide an extremely high performance, reliable, simple to configure and install distributed IO network.
PAC is a relatively new term for small, local control systems. The name is derived largely from the popular PLC. One major difference between a PLC and a PAC is the programming interface. Most PLCs are programmed in a graphical representation of coils and contacts called Ladder Logic. Most PACs are programmed in a modern programming language such as C or C++. Because they are not restricted by the largely digital nature of Ladder Logic, PACs have become popular in systems with a high percentage of analog I/O, in systems with extensive network interface requirements or in systems with direct user interaction requirements.
The primary difference between a PAC and a simple PC-based control system is that in a PAC, the “box” containing the I/O, also includes the processor and software. In fact the CPU running the system is actually built into the I/O system itself. While a typical, slaved data acquisition system is hosted by some type of general purpose PC complete with mouse, monitor and other human interface devices (HID), a Programmable Automation Controller’s processor is usually dedicated to controlling the I/O system and often does not provide any direct human interface.
It is not uncommon for a PAC to run independent of any supervisory or otherwise outside controller, however there is usually some link to the outside world. This may be limited to providing a simple status such as “I have no error conditions to report at this time”, or it may such a tight connection that it allows an external computer take complete control while the interface between the two computers is alive. Typically, if will be in the middle where an external computer tracks system status, provides some control of key factors (e.g. temperature set point or target RPM), and/or offers the interface between the system and a human controller in charge of overall system operation.
PACs are often the heart of industrial control systems or process control applications. Programmable Automation Controllers may also be at the center of a portable data acquisition system or remote controller that allows an application to keep running even if its umbilical link to the outside world is cut.
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