Allen-Bradley GuardPLC 1753, Safety Reference Manual

Page: 87 / 120

Publication 1753-RM002C-EN-P - September 2008 87
Technical Safety for the Application Program Chapter 8
Sequential Controls (Step Controls)
•
Verbal descriptions of the steps with step conditions and
actuators to be controlled
•
Flow charts
•
Matrix or table form of stepped conditions and the actuators to
be controlled
•
Definition of marginal conditions, for example, operating
modes, and EMERGENCY STOP
The I/O concept of the system must contain the analysis of field
circuits, that is, the type of sensors and actuators.
Sensors (Digital or Analog)
•
Signal in normal operation (closed-circuit principle for digital
sensors, life-zero for analog sensors)
•
Signals for error
•
Determination of redundancies required for technical safety
reasons (1oo2, 2oo3)
See the Safety of Sensors, Encoders, and Transmitters section,
page 29 .
•
Discrepancy monitoring and reaction
Actuators
•
Position and activation in normal operation
•
Safety reaction/positioning when switching OFF or power
failure.
Variable Declaration and
I/O Naming
The variable names and their data types are defined with the help of
the variable declaration editors. Symbolic names, consisting of a
maximum of 256 characters, are assigned to all variables of the
application program.
Symbolic I/O names, consisting of a maximum of 256 characters, are
also used for physical inputs and outputs.
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