For self-teach studies, try the following....
Flash an output 1 second on, 1 second off, repeat 4 times, then wait 10 seconds, then repeat the whole cycle. How long will the output be off between repeat cycles ? How long will the complete cycle take ?
A process control valve has "open" and "closed" feedback inputs. Describe at least 3 ways the PLC can monitor for the valve operating correctly.
Those valve feedback signals are connected to an input module, how can you be sure the input data you read is valid ?
.. to be continued (possibly)