Allen-Bradley LOGIX 5000 Reference Manual page 328

Chapter 3 Filter
328
Execution
Function Block
Condition/State
Prescan
Tag.EnableIn is false
Tag.EnableIn is true
Instruction first run
Instruction first scan
Postscan
Structured Text
Condition/State
Prescan
Normal Execution
Postscan
Example
The HPF instruction attenuates signals that occur below the configured cutoff
frequency. This instruction is typically used to filter low frequency "noise" or
disturbances that originate from either electrical or mechanical sources. You can
select a specific order of the filter to achieve various degrees of attenuation. Note
that higher orders increase the execution time for the filter instruction.
The following graphs illustrate the effect of the various orders of the filter for a
given cutoff frequency. For each graph, ideal asymptotic approximations are given
with gain and frequency in logarithmic scales. The actual response of the filter
approaches these curves but does not exactly match these curves.
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018
Action Taken
EnableIn and EnableOut bits are cleared to false.
EnableIn and EnableOut bits are cleared to false.
EnableIn and EnableOut are set to true.
The instruction executes.
N/A
Recalculate coefficients.
EnableIn and EnableOut bits are cleared to false.
Action Taken
See Prescan in the Function Block table.
See Tag.EnableIn is true in the Function Block table.
See Postscan in the Function Block table.