The most recognized standard
detailing machine safety system design integrity
levels is ISO 13849-1 (EN 954-1) Safety Related Parts of Control Systems
, which establishes five levels of safety circuit integrity, the lowest being Category B and the highest, Category 4.
Because Category 3 and 4 applications
require the use of both redundancy
and self-checking, they are often equated with the US standard of control reliability
. However, in a Category 4 application, the requirement is to detect a fault
at or before the next demand on the safety system.
Integrity: (Machine Safety) The degree to which a circuit, system or device can be expected to perform an anticipated function unimpaired in the even of a fault. [ MORE »