Mitigation of Single Point of Failure Risk in Multifuel Boiler through Implementation of Double Channel Digital Input for RUN PAF Indication
Keywords:
distributed control system, critical equipment, digital input, primary air fanAbstract
The Primary Air Fan (PAF) is critical equipment in a multifuel boiler, and its RUN status is used for permissive and interlock functions in the Distributed Control System (DCS). The existing configuration used a single channel digital input, creating a potential single point of failure if the receiving channel failed. This study proposes a preventive improvement using double channel digital input with OR (1oo2) logic. The method consisted of field observation, evaluation of the existing configuration, wiring and Function Block Diagram (FBD) design, implementation, and functional verification. Verification covered 14 conditions: four loop tests, four simulation tests, two failover tests, and four permissive/interlock checks. All 14 conditions met the defined functional criteria, giving a 100% functional test success rate. In both failover tests, CAL RUN PAF remained active when one input channel was disabled while the other still indicated RUN. The result demonstrates that the preventive improvement maintained the RUN PAF indication under the individual channel-failure conditions tested. The implementation is limited to the DCS terminal and digital input side, while the field signal source and cable remain single-path. Thus, the result demonstrates functional mitigation of the tested failure condition, not a quantified reliability or availability improvement.
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