In the field of industrial automation, the Programmable Logic Controller (PLC) serves as the core brain of production lines, controlling machinery, conveyors, robotic arms, and other equipment. Radio Frequency Identification (RFID) technology, on the other hand, gives industrial systems the ability to "see" and "identify" objects. When RFID is integrated with a PLC, factories can achieve automated tracking and intelligent decision-making for products, workpieces, raw materials, and even Tools.
This article provides a systematic overview of how RFID can be used with PLC controllers, including hardware connection methods, common communication protocols, application scenarios, and key selection considerations.
Before RFID integration, PLCs typically relied on the following methods to identify objects:
| Method | Limitation |
|---|---|
| Photoelectric sensor | Can only detect presence, not identity |
| Barcode scanner | Requires line of sight, sensitive to dirt, slow read speed |
| Manual scanning | Inefficient, error‑prone |
RFID provides PLCs with the following core capabilities:
Unique identification – Each RFID tag has a unique ID that can be linked to product serial numbers, process parameters, and more
No line of sight required – Tags can be embedded inside products or covered with oil/dirt and still be read
Simultaneous reading (UHF) – Identify multiple tags in one operation
Read/write capability – The PLC can not only read tags but also write production records (e.g., completion time, test results) back to them
In simple terms: RFID gives the PLC a pair of "eyes that can read and write".
An industrial RFID system consists of four main parts:
RFID Tag – Attached to the object to be identified; Stores data
RFID Reader/Head – Reads or writes to the tag
RFID Processor / Interface – Connects the reader to the PLC and translates protocols
PLC Controller – Executes logic control, receives RFID data, and makes decisions
In modern industrial RFID products (e.g., from Siemens, Balluff, Turck, Cognex, etc.), the reader and communication module are often integrated into one unit, directly outputting a protocol or signal recognizable by the PLC.
There is no single "standard connection" between industrial RFID and PLCs. Instead, the following common options are chosen based on site requirements and PLC brand:
Principle: RFID reader outputs digital signals (e.g., 24V DC) to the PLC‘s input points
Signal examples: Tag Present, Read Complete, Error
Use case: Simple detection where no tag data (ID or user memory) needs to be transmitted
Advantages: Low cost, simple configuration
Disadvantages: Cannot retrieve tag ID or user data
Principle: RFID reader communicates via a serial port to the PLC’s serial module, using ASCII or binary protocols
Common protocols: Custom strings, modbus RTU
Use case: Projects requiring reading of tag ID or small amounts of user data
Modern PLCs often connect serial RFID readers via serial‑to‑Ethernet converters, but this approach is gradually being replaced by industrial Ethernet.
This is the most scalable and standardized solution today. Major PLC brands favor specific protocols:
| Protocol | Main PLC Brands | Features |
|---|---|---|
| Profinet | Siemens | Real‑time, deeply integrated into Siemens ecosystem |
| EtherNet/IP | Allen‑Bradley (Rockwell) | Preferred in North American factories, based on CIP |
| Modbus TCP | Almost all brands | Open, simple, low cost |
| EtherCAT | Beckhoff, Omron, etc. | High‑speed motion control applications |
Most industrial RFID manufacturers (e.g., SICK, Pepperl+Fuchs, Balluff, Ifm) offer products supporting these protocols, along with function blocks (FB) or sample programs that can be directly used in PLC programming environments (e.g., TIA Portal, Studio 5000).
Principle: IO-Link is a point‑to‑point serial communication standard that connects RFID readers via standard M12 cables
Features: Uses ordinary I/O cables to transmit both process data and service data while retaining digital I/O functionality
PLC requirement: Requires an IO-Link master module; supported by almost all major PLC brands
IO-Link is an excellent choice for adding RFID capability to existing digital I/O architectures at low cost.
Requirement: On an engine assembly line, ensure each bolt‑tightening station operates only on the correct engine model.
Solution:
Fit each engine pallet with an RFID tag
Write the engine model into the tag
The PLC at the tightening station reads the tag via an RFID reader
The PLC automatically selects the corresponding tightening program (torque, angle)
Result: Eliminates assembly errors caused by model mixing, achieving zero‑defect production.
Requirement: Quickly switch between different recipes and packaging materials on the same production line, reducing manual verification time.
Solution:
Each product carrier carries an RFID tag
The PLC reads the tag to identify the product type
It automatically changes dosing parameters, date‑printing format, and packaging film type
Result: Changeover time reduced from 15 minutes to 30 seconds.
Requirement: A CNC machine needs to verify whether an authorized tool is installed and record its usage count.
Solution:
Embed a high‑temperature‑resistant RFID tag into each tool holder
Install a small RFID read head inside the machine
The PLC reads the tool ID and checks it against an allowed list
After each use, the PLC writes the remaining life count back to the tag
Result: Prevents machine crashes due to incorrect tool mounting and enables predictive maintenance of tool life.
Requirement: When an Automated Guided Vehicle (AGV) arrives at a station, it needs to identify the station and confirm the material to be picked up.
Solution:
Install low‑frequency RFID tags at floor stations (immune to dust)
Integrate an RFID reader and PLC on the AGV
Upon arrival, the PLC reads the station ID and executes the corresponding task command
Result: Low‑cost, reliable AGV station identification and task dispatching.
When choosing an RFID system for PLC control, consider the following dimensions:
| Factor | Recommendation |
|---|---|
| Read distance | <10 cm → LF (125 kHz / 134 kHz) 10‑50 cm → HF (13.56 MHz) >50 cm → UHF (860‑960 MHz) |
| Environmental interference | Metal / liquid environments → prefer LF or HF |
| Tag data capacity | Small (4‑32 bytes) → HF/LF Large (>128 bytes) → UHF or high‑capacity HF |
| PLC brand | Siemens → Profinet Rockwell → EtherNet/IP Others / mixed → Modbus TCP or IO‑Link |
| Write required? | Frequent writes → choose FRAM tags (longer write endurance) |
| Temperature | High temperature (>120°C) → specialty high‑temp tags |
Although programming varies by brand, the logical structure is generally similar. Below is a basic outline using Siemens PLC + Profinet RFID reader:
Hardware configuration: Add the RFID reader’s GSD File in TIA Portal, assign IP address and device name
Call function blocks: Insert manufacturer‑supplied standard function blocks such as RFID_Read and RFID_Write
Trigger operation: Trigger the read command on a sensor rising edge
Parse data: Receive tag ID and data; store in a DB block
Logic control: Activate motors, cylinders, alarms, etc. based on the tag content
Many RFID vendors (e.g., Balluff, Ifm) provide free sample libraries for TIA Portal, Studio 5000, and other environments that can be reused directly.
Adam