Communications & Networks
A perfect match: Five benefits of using Ethernet with RFID solutions
March 29, 2011 by Helge Hornis
More than 10 years ago, an automotive customer asked us to develop an RFID system that not only controlled part of the manufacturing process, but also reported data to their production control system. While interfacing with the local machinery was done using serial communication, all data transactions with production control utilized the plant’s Ethernet system. The challenge was that there was not a suitable transaction protocol available, which meant that we had to define our own language to transmit the necessary information via TCP/IP, the Ethernet-based transport mechanism available at that time.
A lot has changed in the past decade, and PLC manufacturers, by virtue of their associated user organizations, have published strict specifications and methodologies for numerous industrially suitable Ethernet protocols. Ethernet/IP, PROFINET and a number of other industrial Ethernet-based protocols are available and supported by a large number of device manufacturers producing everything from HMI screens to drives to RFID systems. Because of this, Ethernet is now a great networking option for RFID systems. Below are the top five benefits of using Ethernet with RFID.
1. Speed and real-time performance. Ethernet has always had raw speed; that was never the problem. The issue was data collisions impacting the ability to receive data in a timely manner. But with the development and implementation of switches, everything has changed. Switches intelligently direct traffic so that collisions will not occur. Depending on the particulars of the Ethernet protocol, additional methods are used to enhance the real-time performance of the network. For example, bypassing certain TCP/IP layers of the stack reduces the time necessary to send data from the wire to the application layer. With switches, the potentially large data sets sent to or received from an RFID system are no longer a problem.
2. Network configuration and diagnostics. While speed and real-time performance are a requirement, they are not the main reason Ethernet is the network of choice for RFID applications. Fast system implementation and uptime of greater than 99.5 percent are common requirements, making superior configuration and diagnostics a must. Today’s Ethernet devices use a plethora of technologies designed to aid both programmers and users alike in this requirement.
During the commissioning phase, a web browser is the tool of choice to test all aspects of RFID systems, including correct cabling between the RFID controller and the read/write (R/W) heads. It is an unfortunate reality that the PLC code controlling a system is never ready until the very last moment. In the past, this meant that simple installation aspects were not tested (i.e. Are all cable connections correct? Are the R/W heads in a location where they can read the tags?). The most straightforward way to verify the operation of the RFID system and to determine if all R/W heads are functioning and adjusted correctly is to access tags. With an Ethernet-based system, no special software needs to be installed since the web browser can provide all essential functions. And because all RFID controllers are part of the network, it is not necessary to be at the location that is being tested. Consequently, tests are faster and can be performed earlier as part of the mechanical setup. The moment the PLC code is ready for testing, the programmer can focus on evaluating the operation of the logic.
Once operational, uptime is the main concern. Wouldn’t it be nice if the RFID system could inform maintenance when something goes wrong? Ethernet-based RFID makes this possible. Using the web page, the user can define conditions when the interface will send an e-mail. For example, in an engine plant, it is not uncommon to process one engine every couple of minutes. This means that the PLC must communicate with the RFID system every 120 seconds. If the R/W head fails, the PLC would know this when the next engine arrives at the work cell. Wouldn’t it be better if maintenance received this information the second the fault occurred? Sending an e-mail containing the exact location and the name of the part that needs replacing not only gives maintenance a head start of up to two minutes, it also tells them exactly where to go and what spare parts to bring.
3. Hardware setup. In the past, network topology was a real problem with Ethernet systems. For most machines, Ethernet’s star topology came at a significant cost in cabling and cable support infrastructure. Fortunately, this is no longer the case since modern hardware allows these devices to be daisy-chained and even supports setting up redundant ring structures.
4. Field updates. Ethernet-based RFID systems are part of the network and, therefore, downloads are performed from one location via the network itself. The most common update mechanism uses FTP (File Transfer Protocol) and, therefore, can be carried out with readily available tools. Using FTP, I recently updated an entire automotive plant (116 read locations) in one day.
5. PLC logic debug tools. In the world of automation, it is common practice to reuse PLC logic. Programmers routinely copy large blocks of ladder logic code from an old program into a new one without worrying too much about the details. This is good practice and, in most cases, saves time and limits logic errors. But what if things do not work out as intended? Again, Ethernet-based RFID is at an advantage. Controllers can keep logs of hundreds of interactions with the PLC and the connected R/W heads, making them available via web browser. As soon as things go wrong, the programmer can look at the record, identify the command that was sent and the response the involved hardware issued, and determine what needs to be changed. And by saving this information in a file, the device manufacturer can quickly assist in solving the problem. There can never be too much diagnostics, and making it easy to access this information over the network increases its usefulness significantly.
RFID systems are not the only automation products that benefit from using an industrial Ethernet solution. Vision sensors and 2D code readers benefit from Ethernet, too, since images can be transmitted for evaluation, gateways to low-level sensor network solutions are easily configured, and functional safety controllers are conveniently programmed and monitored. Machine builders frequently using RFID systems should take a look at an Ethernet-based solution. The advantages speak for themselves.
Helge Hornis is the manager of Intelligent Systems at Pepperl+Fuchs.