While PLCs (programmable logic controllers) have been around for more than 40 years, recent advances have greatly increased their capabilities, blurring the line between a PLC and PAC (programmable automation controller). What differences remain between these two categories? Is there a performance gap between PLCs and PACs that users should keep in mind when choosing the best solution for a particular application?
Typically PLCs have been best suited for machine control, both simple and high speed. Common characteristics of these PLCs are simple program execution scans, limited memory, and a focus on discrete I/O with on/off control.
On the other hand, a PAC is geared more toward complex automation system architectures composed of a number of PC-based software applications, including HMI (human machine interface) functions, asset management, historian, advanced process control (APC), and others. A PAC is also generally a better fit for applications with extensive process control requirements, as PACs are better able to handle analog I/O and related control functions. A PAC tends to provide greater flexibility in programming, larger memory capacity, better interoperability, and more features and functions in general.
If the application includes monitoring and control of a large number of analog I/O points, then a PAC is generally the better solution. This is also the case when the application encompasses an entire plant or factory floor, a situation that typically calls for distributed I/O in large numbers, along with extensive loop control—functions better suited to a PAC than to a PLC.
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