Math OperationsBeginnerIEC 61131-3

SUB (Subtraction)

Subtracts second input from first input, outputs the difference.

The SUB function block subtracts the second input from the first input and outputs the difference. It is used for calculating deviations, error signals (setpoint minus process value), position differences, and remaining quantities in PLC programs.

Parameters

Inputs

Name	Type	Description
IN1	ANY_NUM	Minuend (value to subtract from)
IN2	ANY_NUM	Subtrahend (value to subtract)

Outputs

Name	Type	Description
OUT	ANY_NUM	Difference (IN1 - IN2)

Ladder Logic Example

// Ladder Logic - SUB (Error Calculation)
//
// |----[SUB]----|
// | IN1: Setpoint        |
// | IN2: Process_Value   |
// | OUT: Error_Signal    |

Structured Text Example

Error_Signal := Setpoint - Process_Value;
Remaining := Total_Qty - Consumed_Qty;

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Platform-Specific Implementation

Siemens (TIA Portal)

Use SUB instruction in TIA Portal.

Allen-Bradley (Studio 5000)

Use SUB instruction in Studio 5000.

CODESYS

Use - operator in ST or SUB function block.

Common Applications

PID error calculation
Position deviation
Remaining quantity
Differential pressure
Time difference

Frequently Asked Questions

What is SUB (Subtraction) in PLC programming?

Subtracts second input from first input, outputs the difference. The SUB function block subtracts the second input from the first input and outputs the difference. It is used for calculating deviations, error signals (setpoint minus process value), position differences, and remaining quantities in PLC programs.

What are common applications of SUB (Subtraction)?

SUB (Subtraction) is commonly used for: PID error calculation, Position deviation, Remaining quantity, Differential pressure, Time difference.

How do I use SUB (Subtraction) in different PLC platforms?

Siemens: Use SUB instruction in TIA Portal. Allen-Bradley: Use SUB instruction in Studio 5000. CODESYS: Use - operator in ST or SUB function block.