PES technology used in SIS

The PES can be a programmable controller, a distributed control system controller, or an application-specific, stand-alone, micro-programmable logic controller (micro-PLC). The complexity of the PES results in numerous paths to failure, including dangerous and safe failures. Many failures are unsafe. Some techniques that can be used to minimize these failures of PES are 

Diagnostics are tests, which are performed periodically to detect some of the dangerous faults that prevent the SIS from responding to a demand. Various types of faults that can occur are included in Table N.1  

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Faults that immediately disable the capability of the SIS to respond to a demand (critical faults) Stuck on or stuck off of a critical output point 

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