Rockwell Automation AADvance Controller Safety Manual - Manual (Page 91)

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Document: 553630
ICSTT-RM446K-EN-P Issue: 10
_C
4-35
Maintenance Overrides
Maintenance Overrides set inputs or outputs to a defined state that can be
different from the real state during safety operation. It is used during
maintenance, usually to override input or output conditions in order to
perform a periodic test, calibration or repair of a module, sensor or actuator.
To correctly implement a maintenance override scheme within the AADvance
system, the override or 'bypass' logic shall be programmed within the
Application Program, with a separate set of safety-related input points or
variables enabling the bypass logic.
In order to accommodate maintenance overrides safely, TÜV has
documented a set of principles that shall be followed. These principles are
published in the document "Maintenance Override" by TÜV Süddeutschland /
TÜV Product Service GmbH and TÜV Rheinland.
There are two basic methods to check safety-related peripherals connected to
the AADvance system:
 External hard-wired switches are connected to conventional system inputs.
These inputs are used to deactivate sensors and actuators during
maintenance. The maintenance condition is handled as part of the system's
application program.
 Sensors and actuators are electrically switched off during maintenance and
are checked manually.
In some installations, the maintenance console may be integrated with the
operator display, or maintenance may be covered by other strategies. In such
installations, the guidance given in section is to be followed. A checklist for the
application of overrides is given in the Checklists chapter.
Application Program Development
The application program development shall follow a structured approach as
defined in the AADvance AADvance Workbench documentation.
Development of application software consisting of programs (POUs),
User Defined Functions and user Defined Function Blocks must follow the
requirements defined in IEC 61511 (ANSI ISA-84.00.01) for LVL languages and
the requirements defined in IEC 61508 for FVL languages.
However, these requirements can be waived if the programs (POUs) used
have previously been tested and validated according to IEC61511 (ANSI ISA-
84.00.01)/IEC61508 and validation evidence is provided as part of the Project
Test Documentation.
The stages defined in the following sub-sections shall additionally be applied for
safety related applications.