Instrument Loop diagram represents detailed drawing showing a connection from one point to control system.
It could be connection between: Field instrument to control system (or vice versa), Signal from Control Panel to control system (or vice versa),Signal from MCC to control system (or vice versa),Signal from one control system to another system.
Loop diagram shows instrument (in a symbol) and its terminal numbers which are to be connected, instrument cable number, junction box number, terminal number assigned for the specified instrument, multi-pair cable and pair number , marshaling cabinet number, terminal number in marshaling cabinet, control system details (rack, slot, I/O channel). It also clearly indicates location of each equipment by means of border line.
A limit Loop Diagram usually shows a single control loop which means it could only contain just one input (sensor to control system), just one output (control system to final element) or combination of both.