An open loop traffic signal just cycles on a schedule and has no "knowledge" of traffic patterns or current traffic. A closed loop system would have sensors letting it know when traffic was present and a controller that would make decisions based on the traffic conditions.

what does a graph look like of for a closed loop & one for an open loop of the controller's output over time for a step change in the desired value of 10% assume the controller is set at P.B. =100% and Ti=30 seconds

loop checking is perform before cable termination..the difference between a close loop and open loop is,tha close loop has a feedback while the open loop has not.

it is when a control loop is open and processing

The sensitivity of an open loop control system is always 1, it is due to no feedback involved in open loop.