Modbus TCP/IP Device Data-logging to CSV File using Python

Modbus TCP/IP to CSV Datalogger

This project logs Modbus TCP/IP device data into daily CSV files for historical storage and analysis. It uses pymodbus for Modbus communication and is designed for reliability and ease of use.

Library Version Details

Features

• Reads Modbus holding registers (default configuration)
• Per-address reading for flexibility (supports non-consecutive addresses)
• Logs only when values change (no duplicate entries)
• Each register/address is logged with timestamp, type, address, and value
• Timestamp format: DD-MM-YYYY HH:MM:SS for easy sorting and readability
• Configurable update interval; logs data exactly at the interval defined, compensating for processing time
• Robust reconnect logic: automatically reconnects to Modbus device if communication fails
• Handles CSV file lock (e.g., if open in Excel): retries writing instead of crashing
• Supports reading from a specific Modbus slave ID (see MODBUS_SLAVE_ID in config)
• Easy configuration via src/config.py
• Data is stored in daily CSV files in a folder structure: logs/<Year>/<Month>/<DD-MM-YYYY>.csv

Project Structure

modbus-csv-datalogger-03092025
├── src
│   ├── main.py               # Main application logic
│   ├── modbus_client.py      # Modbus TCP client wrapper
│   └── config.py             # User configuration for Modbus/interval
├── requirements.txt          # Python dependencies
├── README.md                 # Project documentation

Installation

1. Clone the repository:

   git clone <repository-url>
   cd modbus-csv-datalogger-03092025
   

2. Install dependencies:

   pip install -r requirements.txt
   

Configuration

Edit src/config.py to set:

• Modbus server IP and port
• Modbus slave ID (MODBUS_SLAVE_ID) to target a specific device
• Register types and addresses to read (currently only holding registers enabled)
• Update interval (in seconds)
• CSV base path (CSV_BASE_PATH) for log storage

Example (src/config.py):

MODBUS_SERVER = '127.0.0.1'
MODBUS_PORT = 502
MODBUS_SLAVE_ID = 1  # Modbus slave ID to read from
MODBUS_READ_CONFIG = {
    "holding_registers": {
        "addresses": [0, 1, 2, 5, 6, 7]
    }
}
UPDATE_INTERVAL = 5  # seconds
CSV_BASE_PATH = "logs"

To enable other data types (coils, discrete inputs, input registers), uncomment and configure them in MODBUS_READ_CONFIG.

Usage

Start the datalogger:

python src/main.py

• The app reads configured Modbus addresses at the set interval from the specified slave ID.
• Only changed values are logged to the CSV file.
• Each value is stored with timestamp, type, address, and value in a daily CSV file.

Testing

• Ensure your Modbus server is running and accessible.
• Change Modbus register values to see new rows logged in the CSV file for the current day.

Advanced

• Supports all Modbus data types (add to MODBUS_READ_CONFIG as needed).
• Easily extend for batch reads, custom logging, or data export.
• See code comments in main.py for details on logging, reconnect logic, and interval handling.