One thing I am sure of is that the INSTRUMENT LOOP DIAGRAM and the INSTRUMENT LOOP SHEET are the same thing. They are used to visualize the connection of the control pannel to the field instruments measuring something outdoors(these connections form "loops"). See:

INSTRUMENT LOOP DIAGRAM. A drawing showing the connections from the field device all the way through to the system terminations.
www.prosolinst.com/newpage13.htm

Safety control:
Control interlocks that automatically activate to prevent the operation of equipment, or cause other equipment to activate, or deactivate, when a process variable is outside of a specified range, in order to bring the process into a safe condition. This information is typically documented with the P&IDs, logic diagrams, INSTRUMENT LOOP SHEETS, equipment specification sheets, and vendor information;
www.google.com/search?q=cache:hazmat.wv.net/PDF%20Files/Typ...

loop = bucle (cerrado), lazo (cerrado) )Eurodicautom, web)

I would suggest:

Diagramas de lazos/bucles de instrumento(s)

or simply:

Diagramas/esquemas de cableado de instrumentos.

hope it helps.

Davorka