The connection of identification devices was not initially mapped by the OPC Foundation in the OPC UA protocol. The Association for Automatic Identification, Data Acquisition and Mobile Data Communication (AIM) therefore decided in 2014 to close this gap and develop an OPC UA classification for identification systems. The protocol should standardize the transmission of data and standard commands between RFID read/write heads (OPC UA servers) and controllers or PCs (OPC UA clients). Using this classification, RFID systems or other identification systems such as barcode readers can be connected to controllers or other OPC UA clients in the future. The user benefit: If they have connected an RFID interface to their controller that transmits its data in accordance with this OPC UA classification, they can simply replace the RFID interface with another manufacturer's interface without having to make any changes to their controller or industrial PC.

While a prototype of the classification was presented at Hannover Messe 2015, the final version 1.00 was released this year. The classification maps the most important and general commands for communicating with RFID read/write heads, including commands such as identifying a device and reading or writing to a data carrier. In addition to the evaluation of process data, the classification also includes standard parameters of the identification devices. A data area has been reserved in the protocol for specific commands, which does not affect the function of the generally valid standard commands.

OPC UA for RFID readers from Turck

Proprietary interfaces between the PLC and RFID reader, which were previously common (gray dashed line), are no longer necessary with OPC UA.

© Turck

In order to be able to offer users RFID products with the standardized OPC UA classification as quickly as possible, Turck has developed a defined interface with the Fraunhofer Industrial Automation Application Center (IOSB-INA) that translates the Turck RFID language for the OPC UA classification. As the Fraunhofer IOSB-INA already had experience with OPC UA from an earlier project in which an OPC UA nano server was integrated on a sensor, the hardware requirements that an OPC UA RFID interface must fulfill could be quickly derived. Turck has defined the hardware of future RFID interfaces accordingly: The core of the devices will be a Texas Instruments ARM Cortex-A8 processor with a clock rate of up to 700 MHz. The main memory of the system requires 256 Mbytes, and Linux OS is envisaged as the operating system.

The interface is not integrated directly on the read/write heads, but is integrated in the RFID interfaces in line with the modular concept of the 'BL ident' RFID system - i.e. on the I/O components to which the RFID read/write heads are connected. Users will therefore continue to connect sensors and actuators in parallel to RFID read/write heads in the future; trigger signals can still be connected to the same interface or I/O module next to the readers.

A proprietary language will continue to be spoken over the last meter from the RFID interface to the reader. Nevertheless, communication is completely transparent for the user. The RFID devices of the manufacturers that integrate the OPC UA classification are parameterized uniformly from OPC clients. The RFID readers are initialized automatically after connection to an OPC UA client. Users can then configure the readers via a PLC or a PC. It is also possible to browse an OPC UA server (RFID interface) via the OPC UA client. As OPC UA also has an interface to SAP, connection to ERP and MES systems is also possible without complex programming.

Author:
Bernd Wieseler is Head of Product Management RFID Systems at Turck in Mülheim.