In the industrial control world, its all about performance. With every year that passes control system performance improves. This is heavily influenced by the computer industry’s ever increasing cost effectiveness which has driven the convergence of so many industrial control products to PC based solutions.
As control technology has progressed over the last few decades, the performance requirements haven’t really changed much in a certain sense. In the case of Computer Numerical Controls, the basic performance hasn’t really changed. The big difference has been the cost. The early CNC at $500,000 has been replaced by today’s production CNC at $50,000.
Certainly, there have been significant advances in capability, larger machine structures for aerospace applications, high precision applications and even the advent of the “maker bot” low end machines. But the basic relationships required to shape parts in 3 dimensions are the same.
Yes, there are example of industries and applications that simply didn’t exist 50 years ago, like semiconductors, flat panel displays, etc. Most of the improvements in electronic motor controls and motion control actually derive from the work done to improve the disk drive spindle motor.
But generally speaking, industrial control has migrated from specialized control hardware, to the PLC, a general purpose, high reliability form of controller, to personal computer based solutions. Primarily due to the low cost and high performance computing power of the PC.
Some of the performance attributes have to do with how a given control is architected. In the push for high reliability, the PLC goes to great lengths to insure that memory cannot be compromised, input-output hardware is extremely resistant to external electrical interference, and state changes are captured in a rigidly deterministic manner to insure that control code executes consistently. In the PC there are PLC emulators that have been approved by various agencies that qualify their performance as equal to PLC’s.
Some attributes of performance are not obvious. The operating system and its performance become part of the control system equation. If the OS faults, the control system is down. Hence the advent of Real Time Operating Systems, Linux and a host of other solutions aimed at reliability.
It can go deeper than that. Exactly how the OS deals with interrupts can mean the difference between reliable operation and catastrophic failure. Windows CE has different performance attributes over Windows for industrial control application.
In the PC architecture, how does data move from the disk drive to the operating program? In the PLC how does the backplane impact the update rate of field I/O?
In the software realm, newer operating systems have made possible multi-threading programs that allow several task to execute simultaneously in the same hardware and software environment with complete coordination between tasks. Robotic and CNC applications with multiple system operating in a single controller are able to execute separate programs with sophisticated anti-collision detection.
So exactly where the control system performance originates from is not exactly a function of a specific piece of hardware, but rather the result of hardware, OS and software combined to achieve a desired outcome. Not a simple matter.