What is the difference between industrial Controller and prototype(Study)level controllers or Raspberry pi/Arduino Vs. Industrial Controllers(PLC, NON PLC) controllers
Industrial controllers are driven by really intense quality requirements. For example, a single controller may be responsible for a bioreactor growing a batch of culture worth $1,000,000USD to a manufacturer. Industrial controllers have to run for months and months without failure.
In contrast, prototype, hobby and study controllers such as the Raspberry Pi and Arduino are designed to support exploration and teaching. Although quality is important, it is not a primary concern. For Raspberry Pi controllers, ease of use is paramount. Raspberry Pi excels at ease of use and is a rich platform for experimentation.
These failures that I accept for the Raspberry Pi would be unacceptable for an industrial controller. For industrial controllers, I would choose a C++ web server such as Mongoose, which is small, simple and quite robust. Now I could certainly run Mongoose on the Raspberry Pi, but Raspbian itself might not be best for industrial control. Industrial controllers tend to have custom-built and tightly managed operating systems created by Yocto
Industrial controllers are often subject to strict regulations, especially in the biotech sector, where mistakes can impact human life and welfare. Even simple things like enclosures are regulated. For example, an industrial controller enclosure is often subject to "waterproofness ratings".
Taken together, the stringent constraints on industrial controllers cost manufacturers and consumers a lot, but that cost provides high value in terms of safety and yield. Thankfully, many hobbyists are able to create controllers with equivalent functionality (but with less stringent quality) using MCUs such as Arduino and Raspberry Pi. Indeed the latter provide a fertile frontier of new ideas and techniques for all controllers.