Definition:
A Logic Solver is the hardware and software (usually has software) that processes input signals from sensors and issues outputs to final elements to achieve safety functions. This could be a safety PLC, relay logic, a smart logic module, or a fancier instrument with a built in relay for just this purpose.
A logic solver, a final element, and the 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, application program
Cited Source:
- IEC 61511-1:2016, Clause 3.2.36
- Inst Toole Online Magazine – What is a Logic Solver?