Pepperl+Fuchs VAA-2E-G4-SN Instruction Manual page 25

Summary of
requirements
3 The requirements of B and the use of tried
and tested safety-related principles must be
fulfilled.
The control units must be designed so that:
- a single error does not result in the loss of
safety functions and
- whenever it is feasible in an appropriate
manner, the individual error is detected.
4 The requirements of B and the use of tried
and tested safety-related principles must be
fulfilled.
The control units must be designed so that:
- a single error does not result in the loss of
safety functions and
- The individual error during or before the
next requirement for the safety function is
detected. In case this is not possible, an
accumulation of errors must not result in loss
of the safety function.If errors occur, the
safety function still remains intact.
1)
The risk evaluation indicates whether complete or partial loss of safety function(s) due to errors
occurring is acceptable.
Subject to reasonable modifications due to technical advances.
Pepperl+Fuchs Group • Tel.: Germany +49 621 776-0 • USA +1 330 4253555 • Singapore +65 67799091 • Internet http://www.pepperl-fuchs.com
Summary of the requirements for categories
System behaviour
If an individual error occurs,
the safety function remains
intact.
- Some, but not all errors are
detected.
An accumulation of
undetected errors can result
in loss of the safety function
If errors occur, the safety
function still remains intact.
Errors are detected early
enough to prevent loss of the
safety functions.
VAA-2E-G4-SN
1) Fundamental
principle for
achieving safety
by the structure
Copyright Pepperl+Fuchs, Printed in Germany
25