PLC’s are very rugged dedicated computers that run real-time operating systems tailored to industrial control applications.
PC’s are generally less rugged computers that run non-real-time operating systems that are tailored to do general purpose computing.
We might start by listing some general features of the two platforms:
- Very rugged
- Real-time operating system
- Lower power processors than PC’s
- Highly deterministic
- Huge installed base, long history of reliability.
- Proprietary programming tools.
- Proprietary programming languages.
- Highly connective
- Very fast processors
- Less deterministic than PLC
- Relatively low cost
- Large knowledge base
- Huge data storage – virtually unlimited.
- Wide array of programming tools.
- Standardized programming languages.
Over a period of the last couple of decades there has been much debate over PC’s on the factory floor. The debate largely centers on hardware ruggedness issues, and determinism. Since it is possible to ruggedize PC hardware, the main debate may be over the perceived lack of determinism of PC’s as industrial controls. It might be worth note that the people who are the most vocal on determinism are PLC manufacturers.
The lack of determinism is potentially a real issue with PC’s as industrial controls. It must be quantified and considered when using PC’s as controls, and appropriate programming practices must be used to assure the level of determinism required by the application is achieved.