Siemens SIRIUS 3SK1

3SK1 safety relays
Manual, 04/2013, A5E02526190021A/RS-AA/01
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Safety systems - General information
4
4.1 What is safety?
Safety defines a state in which the risk of damage is reduced to a tolerable level, or which
can be regarded as risk-free. Following on from this definition, functional safety concerns
persons, machines and the environment.
The objective of safety systems is to reduce the risk for humans and machines that is posed
by a use case to an acceptable level. The first step is, therefore, to identify the risk of a use
case. In order to make a reliable assessment regarding the application, each individual
function of a machine or plant must be analyzed for potential hazards.
For further information, refer to the brochure "Safety of machines and plants" which is
available here as a download: Functional safety (http://wwwsiemens.com/safety
).
4.2 Safety function
A safety function describes the reaction of a machine/plant to the occurrence of a specific
event (e.g. opening of a protective door). Execution of the safety function(s) is carried out by
a safety-related control system. This usually comprises three subsystems, detecting,
evaluating and reacting.
Detecting (sensors):
● Detection of a safety requirement,
e.g.: EMERGENCY STOP or a sensor for monitoring a hazardous area (light array, laser
scanner, etc.) is operated.
Evaluating (safety relay):
● Detection of a safety requirement and the safe initiation of the reaction (e.g. switching off
the enabling circuits).
● Monitoring the correct operation of sensors and actuators
● Initiating a reaction upon detection of faults
For the 3SK1 products described in this manual, this concerns evaluation units for safety
functions.