High Pass Filter (HPF)

This information applies to the

CompactLogix

5370,

ControlLogix

5570,

Compact GuardLogix

5370,

GuardLogix

5570,

Compact GuardLogix

5380,

CompactLogix

5380,

CompactLogix

5480,

ControlLogix

5580, and

GuardLogix

5580 controllers.

The HPF instruction provides a filter to attenuate input frequencies that are below the cutoff frequency.

Available Languages

Ladder Diagram

This instruction is not available in ladder diagram logic.

Function Block

Structured Text

HPF(HPF_tag);

Operands

Function Block

Operand	Type	Format	Description
HPF tag	FILTER_HIGH_PASS	structure	HPF structure

Input Parameter	Data Type	Description
EnableIn	BOOL	Enable input. If false, the instruction does not execute and outputs are not updated. Default is true.
In	REAL	The analog signal input to the instruction. Valid = any float Default = 0.0
Initialize	BOOL	Request to initialize filter control algorithm. When true, the instruction sets Out = In. Default is false.
WLead	REAL	The lead frequency in radians/second. If WLead < minimum or WLead > maximum, the instruction sets the appropriate bit in Status and limits WLead. Valid = see Description section below for valid ranges. Default = 0.0
Order	REAL	Order of the filter. Order controls the sharpness of the cutoff. If Order is invalid, the instruction sets the appropriate bit in Status and uses Order = 1. Valid = 1 to 3 Default = 1
OversampleDT	REAL	Execution time for oversample mode. Valid = 0 to 4194.303 seconds Default = 0
RTSTime	DINT	Module update period for real time sampling mode Valid = 1 to 32,767ms Default = 1
RTSTimeStamp	DINT	Module time stamp value for real time sampling mode. Valid = 0 to 32,767ms Default = 0

Output Parameter	Data Type	Description
EnableOut	BOOL	Indicates if instruction is enabled. Cleared to false if Out overflows.
Out	REAL	The calculated output of the algorithm.
DeltaT	REAL	Elapsed time between updates. This is the elapsed time in seconds used by the control algorithm to calculate the process output.
Status	DINT	Status of the function block.
InstructFault (Status.0)	BOOL	The instruction detected one of the following execution errors. This is not a minor or major controller error. Check the remaining status bits to determine what occurred.
WLeadInv (Status.1)	BOOL	WLead < minimum value or WLead > maximum value.
OrderInv (Status.2)	BOOL	Invalid Order value.
TimingModeInv (Status.27)	BOOL	Invalid TimingMode value. For more information about timing modes, see Function Block Attributes.
RTSMissed (Status.28)	BOOL	Only used in real time sampling mode. Set to true when ABS (DeltaT - RTSTime) > 1 millisecond.
RTSTimeInv (Status.29)	BOOL	Invalid RTSTime value.
RTSTimeStampInv (Status.30)	BOOL	Invalid RTSTimeStamp value.
DeltaTInv (Status.31)	BOOL	Invalid DeltaT value.

Structured Text

Operand	Type	Format	Description
HPF tag	FILTER_HIGH_PASS	Structure	HPF structure

See Structured Text Syntax for more information on the syntax of expressions within structured text.

Description

The HPF instruction uses the Order parameter to control the sharpness of the cutoff. The HPF instruction is designed to execute in a task where the scan rate remains constant.

The HPF instruction uses these equations:

When:	The instruction uses this transfer function:
Order = 1
Order = 2
Order = 3

with these parameter limits (where DeltaT is in seconds):

Parameter	Limitations
WLead first order LowLimit
WLead second order LowLimit
WLead third order LowLimit
HighLimit

Whenever the value computed for the output is invalid, NAN, or Plus or Minus sign

INF, the instruction sets Out = the invalid value. When the value computed for the output becomes valid, the instruction initializes the internal parameters and sets Out = In.

Affects Math Status Flags

Major/Minor Faults

None specific to this instruction. See Common Attributes for operand-related faults.

Execution

Function Block

Condition/State	Action Taken
Prescan	EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is false	EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is true	EnableIn and EnableOut are set to true. The instruction executes.
Instruction first run	N/A
Instruction first scan	Recalculate coefficients.
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 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.

This example is the minimal legal programming of the HPF function block and is only used to show the neutral text and generated code for this instruction. This is for internal purposes only and is not a testable case.

Filter	Graph
1st order filter
2nd order filter
3rd order filter

Function Block

Structured Text

HPF_01.In := Velocity_Feedback;

HPF_01.WLead := Cutoff_frequency;

HPF_01.Order := 2;

HPF(HPF_01);

filtered_velocity_output := HPF_01.Out

Structured Text Syntax

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