Natural Log (LN)

This table lists the controllers and applications that support this instruction.
Architecture
Standard applications
Safety applications
CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, and GuardLogix 5570 controllers
Yes
No
CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers
Yes
Yes
The Natural Log (LN) instruction takes the natural log of the Source and stores the result in the Destination. The Source must be greater than zero or a minor fault will occur.
Available Languages
Ladder Diagram
LN_LD_avail_v31
Function Block Diagram
Function Block Diagram supports these elements:
FBD Block
LN_FBD_avail_v31
FBD Function
TIP:
FBD Function is applicable to CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers only.
LN_avail_FBDFunction
Structured Text
This instruction is not available in structured text.
TIP:
Use LN as an operator in an expression to compute the same result. Refer to Structured Text Syntax for more information on the syntax of expressions and assignments within structured text.
Operands
IMPORTANT:
Unexpected operation may occur if:
  • Output tag operands are overwritten.
  • Members of a structure operand are overwritten.
  • Except when specified, structure operands are shared by multiple instructions.
There are data conversion rules for mixing numeric data types within an instruction. See Data conversions.
Ladder Diagram
Operand
Data Type
CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, and GuardLogix 5570 controllers
Data Type
CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers
Format
Description
Source
SINT
INT
DINT
REAL
SINT
INT
DINT
LINT
USINT
UINT
UDINT
ULINT
REAL
LREAL
Immediate
tag
Find the natural log of this value.
Destination
SINT
INT
DINT
REAL
SINT
INT
DINT
LINT
USINT
UINT
UDINT
ULINT
REAL
LREAL
tag
Tag to store the result of the instruction.
Function Block Diagram
FBD Block
Operand
Data Type
Format
Description
LN
FBD_MATH_ADVANCED
tag
LN structure
FBD_MATH_ADVANCED Structure
Input Members
Data Type
Description
EnableIn
BOOL
Enable input. If false, the instruction does not execute and outputs are not updated.
Default is true.
Source
REAL
Value for which the instruction finds the natural log.
Output Members
Data Type
Description
EnableOut
BOOL
Indicates if the instruction executed without fault when it was enabled.
Dest
REAL
Result of the instruction.
FBD Function
TIP:
FBD Function is applicable to CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers only.
Input Operands (Left Pin)
Data Type
CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers
Description
Source
SINT
USINT
INT
UINT
DINT
UDINT
LINT
ULINT
REAL
LREAL
Value of which to find the natural log of this value.
Output Operand (Right Pin)
Data Type
CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers
Description
Dest
REAL
LREAL
Result of the function.
Affects Math Status Flags
Controllers
Affects Math Status Flags
CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers
Conditional
CompactLogix 5370, ControlLogix 5570, Compact GuardLogix 5370, and GuardLogix 5570 controllers
Yes
Major/Minor Faults
None specific to this instruction. See Index through arrays for array-indexing faults.
Execution
Ladder Diagram
Condition/State
Action Taken
Prescan
N/A
Rung-condition-in is false
Set Rung-condition-out to Rung-condition-in.
Rung-condition-in is true
Set Rung-condition-out to Rung-condition-in.
Dest = value of natural log of the Source.
Postscan
N/A
Function Block Diagram
FBD Block
Condition/State
Action Taken
Prescan
N/A
EnableIn is false
Set EnableOut to EnableIn.
EnableIn is true
Dest = value of natural log of the Source.
If overflow occurs
Clear EnableOut to false.
else
Set EnableOut to true.
Instruction first scan
N/A
Instruction first run
N/A
Postscan
N/A
FBD Function
TIP:
FBD Function is applicable to CompactLogix 5380, CompactLogix 5480, ControlLogix 5580, Compact GuardLogix 5380, and GuardLogix 5580 controllers only.
Condition/State
Action Taken
Prescan
N/A
Normal Scan
Dest = value of natural log of the Source
Instruction first run
N/A
Instruction first scan
N/A
Postscan
N/A
Examples
Ladder Diagram
LN_LD_ex_v31
Function Block
LN_FBD_ex_v31
FBD Function
LN_example_FBDFunction
Structured Text
result := LN(value);
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