Math OperationsBeginnerIEC 61131-3

ABS (Absolute Value)

Returns the absolute (non-negative) value of the input.

The ABS (Absolute Value) function returns the non-negative magnitude of the input value. Negative values become positive; positive values remain unchanged. ABS is essential for error magnitude calculations, deviation measurement regardless of direction, and ensuring positive values for distance and speed calculations in PLC programs.

Parameters

Inputs

Name	Type	Description
IN	ANY_NUM	Input value (may be negative)

Outputs

Name	Type	Description
OUT	ANY_NUM	Absolute value of input (always >= 0)

Ladder Logic Example

// Ladder Logic - ABS (Error Magnitude)
//
// |----[SUB]--------[ABS]---------|
// | IN1: Setpoint   IN: Error     |
// | IN2: PV         OUT: Abs_Err  |

Structured Text Example

Error := Setpoint - Process_Value;
Error_Magnitude := ABS(Error);

IF Error_Magnitude > Tolerance THEN
    Out_Of_Spec := TRUE;
END_IF;

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Platform-Specific Implementation

Siemens (TIA Portal)

Use ABS instruction in TIA Portal.

Allen-Bradley (Studio 5000)

Use ABS instruction in Studio 5000.

CODESYS

Use ABS() function in ST.

Common Applications

Error magnitude calculation
Deviation monitoring
Speed (magnitude of velocity)
Distance calculation
Tolerance band checking

Frequently Asked Questions

What is ABS (Absolute Value) in PLC programming?

Returns the absolute (non-negative) value of the input. The ABS (Absolute Value) function returns the non-negative magnitude of the input value. Negative values become positive; positive values remain unchanged.

What are common applications of ABS (Absolute Value)?

ABS (Absolute Value) is commonly used for: Error magnitude calculation, Deviation monitoring, Speed (magnitude of velocity), Distance calculation, Tolerance band checking.

How do I use ABS (Absolute Value) in different PLC platforms?

Siemens: Use ABS instruction in TIA Portal. Allen-Bradley: Use ABS instruction in Studio 5000. CODESYS: Use ABS() function in ST.