1756-RM001B-EN-P, Using ControlLogix in SIL2 ... - Tuv-fs.com

10-2 Use and Application of Human to Machine InterfacesChanging Parameters in Safety-Related SystemsA parameter change in a safety-related loop via an external (that is,outside the safety loop) device (for example, an HMI) is only allowedwith the following restrictions:• Only authorized, specially-trained personnel can change theparameters in safety-related systems via HMIs.• The user who makes changes in a safety-related system via anHMI is responsible for the effect of those changes on thesafety loop.• Users must clearly identify the variable that are to be changed asunder the control of the ControlLogix controller inside thesafety loop.• Users must use a clear, comprehensive and explicit operatorprocedure to make safety-related changes via an HMI.• Changes can only be accepted in a safety-related system if thefollowing sequence of events occurs:a. Changes are sent from the HMI to the ControlLogix controllerin the safety loop.b. The ControlLogix controller in the safety loop sends thechanges back to the HMI–before accepting the changes oracting on them.c. The user verifies that the changes are correct.In every case, the operator must confirm the validity of thechange before they are accepted and applied in the safety loop.• The software used in the HMI and the ControlLogix controller(in this case, RSLogix 5000) should be designed to verify thatchanges to the safety system are within acceptable limits and donot otherwise compromise the safety system.• The user should test all changes as part of the safety validationprocedure.Publication 1756-RM001B-EN-P - October 2003