Functional Safety and Control Reliability
Functional safety describes the ability of a control system to perform safety functions correctly over the lifetime of a machine. These principles apply to electrical, electronic, programmable and fluidic control systems. In the past, the term “control reliability” was used to mean the same thing but is no longer widely used.
Engineering controls are the second level in the Risk Reduction Hierarchy, immediately following Elimination or Substitution of the hazard. Some engineering controls, such as barrier guards, fixed, and movable guards do not, on their own, need to have a reliability analysis done – as long as the basic design requirements have been met.
Movable guards are required to have interlocks by all modern machinery standards. Safeguarding devices including light curtains, safety mats, area scanners, and similar presence-sensing equipment must also be connected to the control system of the machinery. Since these devices are all required to work automatically to protect workers when they may not be aware of potential danger, these systems must be reliable. The question is…how reliable?
Functional safety requirements are also applied to Emergency Stop systems.
Emergency stop and safeguarding systems are not the same and may have differing levels of reliability requirements, with safeguarding typically requiring higher levels of reliability.