Allen-Bradley LOGIX 5000 User Manual

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Chapter 2
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018 279
Execution
Function Block
Condition Action Taken
Prescan EnableIn and EnableOut are cleared to false.
Tag.EnableIn is false EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is true EnableIn and EnableOut bit is set to true.
The instruction executes.
Instruction first run Out n-1 = 0
The algorithm used to calculate Out will not be
executed.
Instruction first scan Out n-1 = 0
The algorithm used to calculate Out will not be
executed.
Postscan EnableIn and EnableOut bits are cleared to false.
Structured Text
Condition/State Action Taken
Prescan See Prescan in the Function Block table.
Normal Execution See Tag.EnableIn is true in the Function Block table.
Postscan See Postscan in the Function Block table.
Example
The PI instruction is a regulating instruction with proportional and integral gain
components. The integral gain component is set by the user in radians/sec; this
sets the basic frequency response of the PI regulator. The proportional gain sets
the overall gain of the block, including the proportional AND integral gain of the
block.
Excluding initialization and holding/clamping functionality, the following
diagram shows the PI block’s basic regulating loop while in the linear mode.

Allen-Bradley LOGIX 5000 Specifications

General

Brand	Allen-Bradley
Model	LOGIX 5000
Category	Controller
Language	English