Basics - Altivar Process ATV630 Function Manual

Basics

Functional Safety
Automation and safety engineering are two areas that were completely separate in the past but have
recently become more and more integrated.
The engineering and installation of complex automation solutions are greatly simplified by integrated safety
functions.
Usually, the safety engineering requirements depend on the application.
The level of requirements results from the risk and the hazard potential arising from the specific application.
IEC 61508 Standard
The standard IEC 61508 Functional safety of electrical/electronic/programmable electronic safety-related
systems covers the safety-related function.
Instead of a single component, an entire function chain (for example, from a sensor through the logical
processing units to the actuator) is considered as a unit.
This function chain must meet the requirements of the specific safety integrity level as a whole.
Systems and components that can be used in various applications for safety tasks with comparable risk
levels can be developed on this basis.
EN ISO 13849 Standard
This European Standard specifies the validation process, including both analysis and testing, for the safety
functions and categories for the safety-related parts of control systems. Descriptions of the safety functions
and the requirements for the categories are given in ISO 13849-1 which deals the general principles for
design. Some requirements for validation are general and some are specific to the technology used. EN
ISO 13849-2 also specifies the conditions under which the validation by testing of the safety-related parts
of control systems should be carried out.
SIL - Safety Integrity Level
The standard IEC 61508 defines 4 safety integrity levels (SIL) for safety functions.
SIL1 is the lowest level and SIL4 is the highest level.
A hazard and risk analysis serves as a basis for determining the required safety integrity level.
This is used to decide whether the relevant function chain is to be considered as a safety function and
which hazard potential it must cover.
PFH - Probability of a Dangerous Hardware Failure Per Hour
To maintain the safety function, the IEC 61508 standard requires various levels of measures for avoiding
and controlling detected errors, depending on the required SIL.
All components of a safety function must be subjected to a probability assessment to evaluate the
effectiveness of the measures implemented for controlling detected faults.
This assessment determined the PFH (Probability of a dangerous Failure per Hour) for a safety system.
This is the probability per hour that a safety system fails in a hazardous manner and the safety function
cannot be correctly executed.
Depending on the SIL, the PFH must not exceed certain values for the entire safety system.
The individual PFH values of a function chain are added. The result must not exceed the maximum value
specified in the standard.
Safety
Integrity Level
4
3
2
1
EAV64334 06/2017
Probability of a dangerous Failure per Hour (PFH) at high demand or
continuous demand
-9 -8
10 ≤...< 10
-8 -7
10 ≤...< 10
-7 -6
10 ≤...< 10
-6 -5
10 ≤...< 10
15