Special rules, about variables computed from multi-sensor measurements, enable detection of defects that sensors may not detect otherwise.
Not all hazards can be identified directly. Special rules involving calculation of physical invariants may be defined, to enable detection of such hazards.
Typically, minor leakage from a valve or a container cannot be detected by direct measurements. If in a specific scenario (such as in maintenance testing) a container should be ultimately closed, then the ration Pressure / Volume should be fixed in a fixed temperature. This can be formalized in a rule. Violation of this rule may indicate leakage from the container.
Updated on 30 Oct 2016.