Safety Instrumented Systems (SIS) perform a different function to Programmable Electronic System (PLC / PES / PCS / FGS / DCS). The function of the SIS is to bring process equipment or plant to a safe condition when a process variable exceeds the limit of acceptable value. When combined with the Fire and Gas System (FGS), we usually refer to the combined package as the Integrated Control and Safeguarding System (ICSS).
Logitech Engineering regularly join forces with HIMA, SICK, Yokogawa and Allen Bradley (+many others) to create fully integrated ICSS systems.
The SIS must always be independent from the process control system. The field sensors (instrumentation) and control actions (valves, pumps) are independent of the process control system and usually perform a controlled emergency shutdown of the process. Therefore, its primary role is safety.
Fail-safe and fault tolerant hardware is selected to ensure the integrity of the SIS. Each component must have a proven failure mode,
with a calculated PFD (Probability of Failure on Demand). This is calculated using historical failure rate data,
and the sum of each components PFD determines the integrity of the system.
Undetected failures could permit the process to continue operating while in an unsafe condition. Periodic and systematic testing of the equipment ensures that unsafe states are avoided, and improves the safety integrity level (SIL).
Stem Cutter RPEQ
In May 2017, Logitech Engineering assisted
MHO Infrastructure to certify a new
Stem Cutter machine for Pacific Aluminium at the
Boyne Island Smelter (BSL) to satisfy AS:4024 Category 3 Machine Safety Compliance. By combining guarding with proximity sensors and redundancy,
the machine is now much safer to operate. A comprehensive risk assessment and compliance test was conducted for every conceivable operating condition and failure mode.