It seems an unlikely thing that after decades of control technology advancements we are still confused about the nature of PLCs, PACs and IPCs. In one of the preeminent control magazines this month’s issue is consumed with the subject and presents multiple perspectives on the selection process and merits of the respective vendors.
There are several reasons for this ongoing confusion. One is that the current market is saturated with control options that are undifferentiated. The microprocessor technology has advanced thousands of times in compute capability over what was available 10 years ago and it has blurred the lines of distinction between the various types of control. So things that were limitations of the PLC technology gave rise to the PAC. The gaps were all over the place, data storage, communications, motion control capability. So many different PACs suppliers sprang up to create solutions with various features to provide better control solutions that existed before.
That’s how all technology migrates. Unfortunately each supplier has their own idea about what’s important in a control system and each customer has the same issues. Sometimes they meet.
A more subtle aspect is the field of use. Control system experts define the market in the most broad terms possible such as discrete part manufacturing or process control. The real world is a lot more complex than that and we can get into very confused discussions when the lines of demarcation are themselves blurry. The underlying issue is the descriptive language that defines the problem, the mathematical tools use to describe the solution and the software system that is user configured to implement a solution. When a ladder diagram can truly capture the scope a control system functionality there is no reason took beyond that capability.
Early forms of electronics for the controls industry did not have the capability to handle analog data very well, and the domain of “process control” was predominantly analog with math intensive PID loops required to control process applications. Early process control systems were crafted specifically to manage large distributed installations with hardware architectures and software that were suited to the specific needs of these applications.
It all comes down to what works most effectively and how much it will cost. What we call it is less of an issue.