Application manual for PSRclassic and PSRmultifunction, and the modular safety relay system
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102597_en_03
2.1
Functional safety
Safety-related parts of machine control systems are frequently assigned to provide safety
functions. The contribution to risk reduction of machinery by the safety-related parts of a
control system (SRP/CS) is determined in accordance with EN ISO 12100.
In order to achieve the necessary functional safety of a machine or system, it is essential for
the safety-related parts of the safety equipment and control devices to operate correctly
and, in the event of failure, for the system to remain in the safe state or enter a safe state.
The requirements for achieving functional safety are based on the following basic objec-
tives:
–
Avoiding systematic errors
–
Controlling systematic errors
–
Controlling random errors or failures
The requirements of the safety-related parts of a machine control system are specified in
EN ISO 13849 (and EN 62061). The standard specifies the various safety levels in the form
of the “performance level” (PL) (and “safety integrity level” (SIL)) for the safety-related parts
according to the degree of risk and describes the characteristics of the safety functions.
2.2
Practical procedure in accordance with
EN ISO 13849
In practice, the following steps have proven effective when designing safe control systems
in accordance with EN ISO 13849.
2.2.1
Definition of the safety function
The safety functions must be defined first. This information is derived from the risk assess-
ment.
Example:
Trigger event:
Opening the safety door.
Response:
The robot drive is set to a safe stop state. The power semicon-
ductor pulses are disabled.
Safe state:
Power circuit has no power.
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