The manufacturing operations in many industrial fields (i.e. nuclear, chemical automotive and Oil&Gas) are subjected to several intrinsic hazards, which could lead to high risk for operator, property and environment. A Safety Instrumented System (SIS) tries to mitigate and prevent dangerous failures, therefore it is projected to not introduce other errors and failures in the system under analysis. Condition monitoring and limit alarm trip are mandatory in order to detect the health state of the SIS and limit the number of faults due to the additional safety systems. This paper focuses on the use of diagnostics for a temperature sensor widely used in Oil&Gas safety application.