Siemens SINAMICS S120 Function Manual page 395

10.2.5 EN 62061
EN 62061 (this is identical to IEC 62061) is a sector-specific standard below IEC/EN 61508.
It describes the implementation of safety-related electrical control systems of machines and
takes into account the complete lifecycle - from the conceptual phase to de-commissioning.
The standard is based on the quantitative and qualitative analyses of safety functions,
whereby it systematically applies a top-down approach to implementing complex control
systems (known as "functional decomposition"). The safety functions derived from the risk
analysis are sub-divided into sub-safety functions, which are then assigned to real devices,
sub-systems, and sub-system elements. Both the hardware and software are covered. EN
62061 also describes the requirements placed on implementing application programs.
A safety-related control systems comprises different sub-systems. From a safety
perspective, the sub-systems are described in terms of the SIL claim limit and PFH
characteristic quantities.
Programmable electronic devices (e.g. PLCs or variable-speed drives) must fulfill IEC 61508.
They can then be integrated in the controller as sub-systems. The following safety-related
characteristic quantities must be specified by the manufacturers of these devices.
Safety-related characteristic quantities for subsystems:
● SIL CL: SIL claim limit
● PFH
Probability of dangerous failures per hour
● T1:
Lifetime
Simple sub-systems (e.g. sensors and actuators) in electromechanical components can, in
turn, comprise sub-system elements (devices) interconnected in different ways with the
characteristic quantities required for determining the relevant PFH
Safety-related characteristic quantities for subsystem elements (devices):
● λ:
● B10 value: For elements that are subject to wear
● T1:
Lifetime
For electromechanical devices, a manufacturer specifies a failure rate λ with reference to the
number of operating cycles. The failure rate per unit time and the lifetime must be
determined using the switching frequency for the particular application.
Parameters for the sub-system, which comprises sub-system elements, that must be defined
during the design phase:
● T2:
● β:
● DC:
Safety Integrated
Function Manual, 12/2018, 6SL3097-5AR00-0BP1
:
D
Failure rate
Diagnostic test interval
Susceptibility to common cause failure
Diagnostic coverage
Standards and regulations
10.2 Safety of machinery in Europe
value of the sub-system.
D
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