RFID readers and tags
RFID (radio-frequency identification) lets a machine know exactly which pallet, tool or product is in front of it. A tag on the item stores an ID and data; a reader reads it by radio without contact or line of sight.
How it works
The reader's antenna creates a radio field. When a passive tag enters the field, the field powers the tag's chip, which answers with its ID and data. No battery is needed in the tag, and it can be read through dirt, paint and plastic.
Frequencies
| Band | Typical range | Used for |
|---|---|---|
| LF 125 kHz | a few cm | access cards, tools, works near metal |
| HF 13.56 MHz | up to ~30 cm | work-piece carriers, production data (ISO 15693), NFC |
| UHF 860–960 MHz | several metres | logistics, pallets, many tags at once |
Read and write
Industrial tags are not only read: the reader can write data too. A pallet carrier tag can store the product type, the next process step and the results (OK/NG, torque values), so every station knows what to do and the history travels with the part.
Connecting to a PLC
The reader (or an RFID interface module) connects to the PLC over PROFINET, EtherNet/IP, IO-Link or a serial link. The PLC program:
- waits for "tag present" (or a photo-eye at the station),
- starts a read command and waits for "done",
- copies the ID and data into data registers,
- decides what to do: process, skip or reject.
Always handle the "no tag" or "read error" case: stop the pallet and raise an alarm rather than guessing.
RFID vs barcode
| RFID | Barcode / DataMatrix | |
|---|---|---|
| Line of sight | not needed | needed |
| Writable | yes | no |
| Dirt tolerance | high | low |
| Cost per item | higher | almost zero |
Try it yourself. Wire sensors, contactors and a PLC, write ladder logic and press RUN in the free PLC Sim Lab Playground. Nothing to install.
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