Less Than (LT)
When enabled, the LT instruction and the operator 
tests Source A is less than Source B.
tests Source A is less than Source B.Available Languages
Ladder Diagram
Structured Text
This instruction is not available in structured text.
TIP:
Use the operator
<
with an
expression to achieve the same result. Refer to Structured Text syntax for more information on the syntax of
expressions and assignments within structured text. Operands
There are data conversion rules for mixing numeric data types within an instruction. See Data conversions.
Ladder Diagram
Numeric Comparison
Operand | Data Type | Format | Description |
|---|---|---|---|
Source A | SINT INT DINT LINT USINT UINT UDINT ULINT REAL LREAL | immediate tag | Value to test against Source B |
Source B | SINT INT DINT LINT USINT UINT UDINT ULINT REAL LREAL | immediate tag | Value to test against Source A |
String Comparison
Operand | Data Type | Format | Description |
|---|---|---|---|
Source A | String type | immediate literal value tag | String to test against Source B |
Source B | String type | immediate literal value tag | String to test against Source A |
Affects Math Status Flags
No
Major/Minor Faults
See
LT String Compare Flow Chart
for faults.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 | Numeric compare: If Source A and Source B are not NANs and Source A is less than Source B. Set Rung-condition-out to true else Clear Rung-condition-out to false. |
Rung-condition-in is true | String compare: See LT String Compare Flow Chart. If output is false Clear Rung-condition-out to false else Set Rung-condition-out to true |
Postscan | N/A |
Example
Ladder Diagram
Structured Text
if value_1 < value_2 then light_3 := 1; else light_3 := 0; end_if; if value_3 < ’I am EQUAL’ then light_4 := 1; else light_4 := 0; end_if;
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