Instrumentation Engineering Question:

Answer #1
A closed control loop in a very basic manner consists of
sensor, transmitter, controller,signal converters and final
control elements.Actually in a practical loop there will be
many other instruments apart from this to support the
working of above mentioned instruments.

Answer #2
The control loop main key components is sensor,controller & final control element
sensor mean level transmitter,RTD,flow meter,pressure transmitter,pressure switches
final control element mean control valves, pumps vent valves