Need help with two textbook questions: Course: Programmable logic controllers Questions: For what control problems do we need to use analog modules

Need help with two textbook questions:Course: Programmable logic controllersQuestions:For what control problems do we need to use analog modules or HMI devices? What are some of the safety considerations when installing or maintaining PLCs? What is a proper grounding? Would like an answer today, but if not today then tomorrow will be fine.