A Node-RED node that provides common IEC 61131-3 Ladder Logic instructions for building PLC-style logic flows directly inside Node-RED.

Features

Contacts

| Instruction | Description | | ----------- | --------------------------------------------------------------------------- | | NO | Normally Open contact. Passes execution when the source value is true. | | NC | Normally Closed contact. Passes execution when the source value is false. |

Comparison Instructions

| Instruction | Description | | ----------- | ---------------------------- | | EQ | Equal (==) | | NEQ | Not Equal (!=) | | GT | Greater Than (>) | | GE | Greater Than or Equal (>=) | | LT | Less Than (<) | | LE | Less Than or Equal (<=) |

Math Instructions

| Instruction | Description | | ----------- | -------------- | | ADD | Addition | | SUB | Subtraction | | MUL | Multiplication | | DIV | Division | | MOD | Modulus | | ABS | Absolute value | | SQR | Square root | | MOV | Move value |

counter Instructions

| Instruction | Description | | ----------- | -------------- | | CTU | counter up |

Output Instructions

| Instruction | Description | | ----------- | ---------------------------------------- | | SET | Sets the destination variable to true | | RESET | Sets the destination variable to false | | CTU | OBJ {"Q":true,"CV":15} |

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Supported Data Sources

Input values can be read from:

• msg
• flow
• global
• Numeric constants
• Boolean constants
• String constants

Output values can be written to:

• msg
• flow
• global

Status Display

The node provides a compact real-time status display similar to PLC ladder diagnostics.

Examples:

NO motor_run(true)→TRUE

GT temp(85)>limit(80)→TRUE

ADD a(10)+b(5)→result=15

DIV x(9)/y(0)→÷0ERR

SET →motor=TRUE

RST →alarm=FALSE

The status indicator also changes color:

• Green = instruction result is TRUE
• Gray = instruction result is FALSE
• Red = execution error

Example

Greater Than Comparison

Source A: msg.temperature
Source B: msg.limit

Instruction: GT

Input:

{
  "temperature": 85,
  "limit": 80
}

Result:

{
  "ladder": {
    "func": "GT",
    "result": true
  }
}

Addition

Source A: msg.value1
Source B: msg.value2

Instruction: ADD
Destination: msg.result

Input:

{
  "value1": 10,
  "value2": 5
}

Output:

{
  "value1": 10,
  "value2": 5,
  "result": 15
}

IEC 61131-3 Inspired

This node is inspired by the instruction set commonly found in PLC programming environments implementing the IEC 61131-3 standard.

It allows Node-RED users to create ladder-style logic using familiar industrial automation instructions without requiring a PLC.

Installation

npm install @vitormnm/node-red-instructions-ladder-iec-61131-3

Restart Node-RED after installation.

License

MIT