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OPC UA Server Configuration Guide

Overview

The OPC UA server is configured via a JSON file (tags_config.json) that defines all tags, their data types, and simulation behavior.

Configuration File Structure

{
  "TagName": {
    "type": "float|int|string|bool",
    "initial_value": <value>,
    "simulate": true|false,
    "simulation_type": "random|increment|sine|static",
    "description": "Tag description",
    ... additional parameters... 
  }
}

Tag Parameters

Required Parameters

Parameter Type Description
type string Data type: float, int, string, or bool
initial_value varies Starting value for the tag

Optional Parameters

Parameter Type Default Description
simulate boolean false Enable value simulation
simulation_type string "random" Simulation mode
description string "" Tag description

Simulation Types

1. Random Simulation

Generates random values within a specified range.

Parameters:

  • min (number): Minimum value
  • max (number): Maximum value

Example:

{
  "Temperature": {
    "type": "float",
    "initial_value": 20.0,
    "simulate": true,
    "simulation_type": "random",
    "min": 15.0,
    "max": 25.0
  }
}

2. Increment Simulation

Increments value by a fixed amount each update.

Parameters:

  • increment (number): Amount to add each update
  • max (number, optional): Maximum value before rollover
  • reset_on_max (boolean, optional): Reset to min when max reached

Example:

{
  "Counter": {
    "type": "int",
    "initial_value": 0,
    "simulate": true,
    "simulation_type": "increment",
    "increment": 1,
    "max": 1000,
    "reset_on_max": true
  }
}

3. Sine Wave Simulation

Generates values following a sine wave pattern.

Parameters:

  • amplitude (number): Wave amplitude
  • offset (number): Center point of wave
  • period (number): Period in seconds

Example:

{
  "Level": {
    "type": "float",
    "initial_value": 50.0,
    "simulate":  true,
    "simulation_type": "sine",
    "amplitude": 30.0,
    "offset": 50.0,
    "period":  60
  }
}

4. Static (No Simulation)

Tag value remains constant unless written to.

Example:

{
  "Status": {
    "type": "string",
    "initial_value": "Running",
    "simulate": false
  }
}

Data Types

Float

Floating-point numbers with decimal precision.

{
  "Pressure": {
    "type":  "float",
    "initial_value": 101.325
  }
}

Integer

Whole numbers only.

{
  "Count": {
    "type": "int",
    "initial_value": 0
  }
}

String

Text values.

{
  "Message": {
    "type": "string",
    "initial_value": "System OK"
  }
}

Boolean

True/False values.

{
  "AlarmActive": {
    "type": "bool",
    "initial_value": false
  }
}

Environment Variables

The server can be configured via environment variables:

Variable Default Description
UPDATE_INTERVAL 2 Tag update interval in seconds
OPC_ENDPOINT opc.tcp://0.0.0.0:4840/freeopcua/server/ OPC UA endpoint
OPC_SERVER_NAME Python OPC UA Server Server name
OPC_DEVICE_NAME EdgeDevice Device/folder name
OPC_NAMESPACE http://opcua.edge.server OPC UA namespace

Setting Environment Variables

In systemd service:

[Service]
Environment="UPDATE_INTERVAL=5"
Environment="OPC_DEVICE_NAME=Tank1"

In command line:

UPDATE_INTERVAL=5 python3 opcua_server.py

In LXC container:

lxc exec opcua-server -- systemctl edit opcua-server
# Add Environment variables

Command Line Options

python3 opcua_server.py --help

Options:
  -c, --config CONFIG     Path to config file (default: tags_config. json)
  -l, --log-level LEVEL   Logging level:  DEBUG, INFO, WARNING, ERROR
  -i, --interval SECONDS  Update interval in seconds

Examples:

# Use custom config file
python3 opcua_server.py -c my_tags.json

# Enable debug logging
python3 opcua_server.py -l DEBUG

# Set 5 second update interval
python3 opcua_server.py -i 5

# Combine options
python3 opcua_server.py -c custom. json -l INFO -i 1

Complete Examples

Manufacturing Line

See config/example_tags_manufacturing.json

Process Control

See config/example_tags_process_control.json

Simple Test Setup

See config/example_tags_simple.json

Best Practices

  1. Use descriptive tag names: Makes debugging easier
  2. Add descriptions: Document what each tag represents
  3. Set realistic ranges: Match real-world sensor ranges
  4. Use appropriate data types: Don't use float for counters
  5. Test configuration: Use --log-level DEBUG to verify tags load correctly

Troubleshooting

Tags not updating

  • Check "simulate": true is set
  • Verify simulation_type is valid
  • Check logs: journalctl -u opcua-server -f

Invalid JSON

  • Validate JSON syntax (use jsonlint. com)
  • Check for trailing commas
  • Ensure all brackets/braces are closed

Type conversion errors

  • Ensure initial_value matches type
  • Check min/max values are correct type
  • Review logs for specific error messages