Selection & LimitingBeginnerIEC 61131-3

MIN (Minimum Selection)

Returns the smaller of two or more input values.

The MIN function returns the smaller of two (or more) input values. It is used for low-select control strategies from redundant sensors, implementing output ceilings, finding minimum values in process data, and conservative safety-oriented value selection.

Parameters

Inputs

Name	Type	Description
IN1	ANY_NUM	First value
IN2	ANY_NUM	Second value

Outputs

Name	Type	Description
OUT	ANY_NUM	Minimum value (smaller of inputs)

Ladder Logic Example

// Ladder Logic - MIN (Low-Select)
//
// |----[MIN]----|
// | IN1: Sensor_1        |
// | IN2: Sensor_2        |
// | OUT: Lowest_Reading   |

Structured Text Example

// Low-select from redundant sensors
Lowest_Pressure := MIN(Sensor_1, Sensor_2);

// Cap output to maximum
Capped_Output := MIN(Calculated_Output, Max_Allowed);

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Platform-Specific Implementation

Siemens (TIA Portal)

Use MIN instruction in TIA Portal SCL. In LAD/FBD, use comparison with MOVE.

Allen-Bradley (Studio 5000)

No direct MIN; implement with LES comparison and MOV.

CODESYS

Use MIN() function in ST.

Common Applications

Low-select from redundant sensors
Output ceiling enforcement
Conservative value selection
Minimum inventory tracking
Safety-oriented value selection

Frequently Asked Questions

What is MIN (Minimum Selection) in PLC programming?

Returns the smaller of two or more input values. The MIN function returns the smaller of two (or more) input values. It is used for low-select control strategies from redundant sensors, implementing output ceilings, finding minimum values in process data, and conservative safety-oriented value selection.

What are common applications of MIN (Minimum Selection)?

MIN (Minimum Selection) is commonly used for: Low-select from redundant sensors, Output ceiling enforcement, Conservative value selection, Minimum inventory tracking, Safety-oriented value selection.

How do I use MIN (Minimum Selection) in different PLC platforms?

Siemens: Use MIN instruction in TIA Portal SCL. In LAD/FBD, use comparison with MOVE. Allen-Bradley: No direct MIN; implement with LES comparison and MOV. CODESYS: Use MIN() function in ST.