The correct answer is: D. performs on/off control functions in relation to time.
A sequence controller is a type of controller that performs on/off control functions in relation to time. It is used to control a variety of industrial processes, such as batch processing, continuous processing, and packaging. Sequence controllers are typically programmed using ladder logic, which is a graphical programming language that is easy to learn and use.
Option A is incorrect because sequence controllers are not difficult to program. Ladder logic is a very intuitive programming language that is easy to learn and use.
Option B is incorrect because sequence controllers are not mechanical only controllers. They can be either mechanical or electronic.
Option C is incorrect because sequence controllers are still in widespread use. They are used in a variety of industrial processes.
Option E is incorrect because option D is the correct answer.