Definition:
A Logic Solver is the hardware and software (maybe!) that processes input signals from sensors and issues outputs to final elements to achieve safety functions. This could be relay logic, a safety PLC, a smart logic module, or a fancier instrument with a built in relay for just this purpose.
A logic solver, a final element, and instrument together are the key elements in a SIF.
Key Points:
- Safety PLCs are the most common logic solvers.
- Must meet required SIL depending on the application.
- Some SIL instruments have relays that can provide a digital contact to trip the Final Element. Thus the logic solver is embedded in the Instrument.
Example:
A Triconex PLC is configured to perform ESD shutdowns is a logic solver.
See also: Safety PLC, Smart Logic Module, Instrument
Cited Source:
- IEC 61511-1:2016, Clause 3.2.47.