User manual

Publication 1756-RM093F-EN-P - January 2010 55
Safety Application Development Chapter 6
Specification of the Control Function
You must create a specification for your control function. Use this
specification to verify that program logic correctly and fully addresses
your application’s functional and safety control requirements. The
specification may be presented in a variety of formats, depending on
your application. However, the specification must be a detailed
description that includes (if applicable):
• sequence of operations.
• flow and timing diagrams.
• sequence charts.
• program description.
• program print out.
• written descriptions of the steps with step conditions and
actuators to be controlled. This includes:
– input definitions.
– output definitions.
– I/O wiring diagrams and references.
– theory of operation.
• matrix or table of stepped conditions and the actuators to be
controlled, including the sequence and timing diagrams.
• definition of marginal conditions, for example, operating modes
and EMERGENCY STOP.
The I/O portion of the specification must contain the analysis of field
circuits, that is, the type of sensors and actuators.
• Sensors (Digital or Analog)
– Signal in standard operation (dormant current principle for
digital sensors, sensors OFF means no signal)
– Determination of redundancies required for SIL levels
– Discrepancy monitoring and visualization, including your
diagnostic logic
• Actuators
– Position and activation in standard operation (normally OFF)
– Safe reaction/positioning when switching OFF or power
failure
– Discrepancy monitoring and visualization, including your
diagnostic logic