The difference between DCS and SIS

DCS -Distribution Control System Disclosed control system, factory control -level system, conventional data collection, and equipment control are completed.
SIS-SAFTY Instruments System System System Security Instrument System, a type of locking system, generally the safety protection and control of factory process equipment, and sometimes includes unit safety protection control.
DCS for control, SIS for protection.

DCS is a distribution control system, mainly operation, SIS instrument safety system, is a safety protection system.

SIS is a security chain

DCS is the control system, SIS is to protect the system of DCS