Communications between BPCS and SIS

Communications between the BPCS and SIS can enhance the overall safety of the application. Comparing the SIS and BPCS process variables can provide enhanced diagnostics for the sensors, improving the integrity of the SIS and BPCS sensors. However, communications, particuiarly writes to the SIS, can compromise the safety integrity of the SIS. Provision shouid be made to ensure ail writes are valid and do not negatively impact the system safety or operation. 

There are five basic ways to approach external communication between BPCS and SIS  

2) Hardwired communication between BPCS and SIS for each device (e.g., contact status in SIS is transmitted to BPCS with a pair of wires). 

If the SIS requires hardwired communication for the successful execution of the safety function, the input point, wiring, output point, BPCS, and all components required for the BPCS to perform its required task should be taken into consideration for the SIS to meet the required SIL rating. 

This may be acceptable for all SILs, if review and analysis is done to assure that the safety function is not compromised. Measures to achieve write protection of the SIS include, but are not limited to, hardwired switch (or jumper) to limit write access and implementation of the SIS in SIS 

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