How Do You Connect RFID Readers to PLCs?

Published: September 15, 2009

How can I connect radio frequency identification readers to programmable logic controllers?

—Name withheld


Programmable logic controllers (PLCs) run the automation systems that operate many assembly lines and conveyors in distribution centers. With the introduction of RFID, it’s critical to link tag data to the PLCs, because the tags can trigger a variety of actions. For instance, they can determine which shipping line a pallet or case should be routed to, or segregate defective parts or products.

Companies looking to introduce RFID into an automated industrial environment should consider the enterprise’s broader technology architecture. Some questions to ask include: Does the PLC system connect to business intelligence or manufacturing systems? Does the RFID interrogator support a communications protocol compatible with that of the PLCs? And how will the RFID network be designed?

The right approach will depend on the answers to these questions. The ladder logic programs running the PLCs may need to be altered to create interfaces with RFID readers, or with corporate databases or other software systems. The code controlling the PLCs may be owned, or written by the hardware manufacturer, a systems integrator or another third party that did the original programming of the PLCs, so you will probably need to bring in the party that wrote the original PLC software to help write an interface.

The actual application program interface should not be difficult to create, but keep in mind the read-write speed of the RFID system and the speed of the assembly line or conveyor. Sometimes, there is insufficient time to write to a tag, confirm the serial number is unique and then kick the item off the line with a PLC device if the tag is defective or the serial number is not unique.

Our How-To section has a more detailed article for Premium Members (see How to Link PLCs and RFID).

—Mark Roberti, Editor,