Instruction Manual PROTECT-PSC
V 2.6R01 / 04.19
1
–7
1.6
Safety function
The safety functions realised by the PROTECT-PSC are defined as follows.
1. A two channel safety input is read. The PS program running in the CPU module
controls the state of the outputs depending on the input information. On request,
this leads to a two channel shut-down. In the case of several input and output
pairs, each path is viewed as a separate safety function. The safety function of the
output is defined as the switching off of the power in the case of semiconductor
outputs or opening contacts in the case of relay outputs.
2. The second safety function is identical to that named under 1. with the one
difference that two two-channel safety inputs of a slave station are used here.
The further calculations of the PL/SIL apply to a two-channel safety fuction.
In the case of a one-channel input the requirements of PL b/c, Category 2 as per
ISO 13849-1 are only fulfilled if the safety function is marked by the change of the
input from ON to OFF. The minimum demand interval for a safety function of
PL b/c, Category 2 amounts to 55 hours. In the event of a safety function of PL b/c,
Category 2 being realised, a testing of the entire safety function including sensor
and actuator in accordance with ISO 13849-1 has to be ensured.
1.7
Performance Level
The Performance Level (in brief PL) to ISO 13849-1 describes the ability of safety-
orientated assemblies to perform a safety function under foreseeable conditions
(which must be included in the assessment) in order to achieve the expected risk
reduction. The PL is divided into 5 categories. This categorisation is made not with
numbers but with the letters a to e.
The simplest way to determine the PL required for an application is to assess the
risk based on a risk graph.
Summary of Contents for PROTECT-PSC
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