Category B and Category 1

Il Mean Time To Failure (MTTF)

Last edit: 11/08/2023

Subsystems of Category B must use Basic Safety Principles, detailed in ISO 13849-2 [14], and shall be designed according to relevant standards. This should guarantee that they can withstand expected operating stresses and influences of the processed material, like detergents (thanks for example, to the use of stainless steel) or other relevant external influences, like mechanical vibrations.
The Reliability block diagram of a Category B is shown in Figure 6.3. It is shown as having an Input a Logic and an Output however, each category is applicable to a subsystem: either an Input subsystem or an output subsystem, for example. Therefore, do not be confused by the figure: it shows a subsystem and not necessarily a Safety-related control system.