Imagine if you no longer had the additional cost and complexity of connecting configurable and analog sensors, actuators and even RFID separately from the rest of your standard discrete I/O (inputs/outputs). Instead, you just plugged them in using standard low-cost 3 conductor cables with all your other discrete I/O into an I/O block. This is what the new industrial connectivity standard called IO-Link provides. This standard was started in Europe and is supported by most European controls and automation companies. Now it is gaining momentum here in North America, including products that now support IO-Link for Ethernet/IP networks. Many times when IO-Link is suggested for the first time, let alone IO-Link based RFID, thereaction is “I don’t want another bus system”. That’s where the misunderstanding can start. IO-Link is not a feildbus like DeviceNet or Profibus, nor an Ethernet based bus like Ethernet/IP. It is an open discrete connection standard (point to point) that allows the ability to communicate sensor, actuator or even RFID parameter and diagnostic data with standard UART protocol using 24V pulse modulation. In simpler terms, for the sake of this discussion you connect the RFID reader to a discrete I/O point on an IO-Link Master I/O block. That IO-Link block places the RFID reader’s data onto the bus. An example for Profibus is shown in the diagram to the left.
The benefit is that it allows the RFID reader to be treated like any other discrete device wiring wise. A conventional low-cost 3 wire discrete connection and cable is all that’s required to connect the reader for lengths up to 20 meters. The serial data is output on the standard signal line of the connection using 24V pulse modulation as shown in the illustration below.
This also means that you can mix other devices, including analog devices, using the same method. This has several other benefits to it, including a major simplification of the topology, the ability to run multiple RFID readers off a single I/O block and it can translate into a significant cost savings in price per reader and wiring.
Another great quality is that the RFID reader’s data is handled in the same manner as though the reader were directly connected to the PLC on a bus, but without any special dedicated wiring. Because the reader is located like an I/O point on an I/O block, the data read from the tag is still sent to an input and output data memory defined in the PLC. The tag data is sent in frames based on the size of the memory block defined for the reader as a device. In an example, using Profibus and a Siemens S7 program, a GSD file is used to configure the IO-Link Master I/O block and the RFID reader is assigned a data module size of 8 bytes input and 8 bytes output. RFID tag data is then transferred using these 8 defined bytes to and from the reader not unlike a bus connected version.
So with the use of IO-Link, RFID readers can now be integrated into a discrete remote I/O scheme as though they were just another I/O device. Where’s the application benefit you might ask? Well for example, think about where bar code for industrial applications like pallet assembly is used. In many of these applications, wiring schemes using I/O blocks exist already making integration easier and lower cost then running new communication cables and drops. This also allows a more reliable, flexible and competitive cost solution to pallet based bar code because there is no need to run or maintain serial channels along the line at individual stations or at the PLC while gaining the greater reliability and longevity of RFID. If you’re interested in learning more about IO-Link and the vendors that support it, go to: http://www.io-link.com/en/index.php. For information about Balluff’s RFID products for IO-Link, see our web page at: www.balluff.com/io-link.