What is a fail-safe PLC?
Designed to move into a safe state in the case of a failure such power outage, system error, or hardware malfunction, a fail-safe PLC (Programmable Logic Controller) The fundamental idea underlying fail-safe design is that no extra energy or action should be needed to halt the operation and guarantee safety a major principle in industrial automation safety.
Usually, important devices like emergency stop pushbuttons are normally closed (NC) in a fail-safe system. This means they pass a signal during normal operation; any power loss or wire breakage causes an open circuit that automatically removes power from actuators and stops processes. This natural quality guarantees that a failure causes a safe stop situation without depending on outside assistance.
Siemens SIMATIC S7 F-series, for example, modern fail-safe PLCs include built-in safety mechanisms including redundant CPUs, self-diagnostics, and monitoring tools. Plug-in I/O, connectivity, and function modules allow these systems to be easily scaled, hence enabling their use in a variety of applications.
Fail-safe PLCs follow international safety standards such EN 954-1, ISO 13849, and IEC 61508, which categorize systems into categories (Cat. B to 4) depending on their risk assessment and dependability. Category 4 systems, for instance, offer the greatest degree of risk reduction and are usually employed in important uses including nuclear plants or chemical factories.
Unlike general-purpose PLCs, safety PLCs stress redundancy and internal diagnostics to identify flaws before they develop into dangers. Companies such as Pilz, Siemens, and Schmersal offer certified safety PLCs able to satisfy these exacting criteria.
A fail-safe PLC controls industrial operations but also guarantees that, in any failure situation, the system switches to the safest possible condition.