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Connect PLCs and Bar-Code Scanners in Factory

A bottle manufacturer for the liquor industry wanted to find a way to simplify its pallet wrapping process. In the current setup, each carton of bottles has a bar-code label that identifies the bottle size. A bar-code scanner sends this data to a computer with two serial ports – one connected to the bar-code scanner, the other connected to a Programmable Logic Controller (PLC). Allen-Bradley/
Rockwell Automation software running on the PC converts the ASCII bar-code data to a DF1 message that the PLC can understand. The PLC uses this data to instruct a shrink-wrap machine how to wrap a pallet of cartons (i.e., how tall the pallet is, how many revolutions, etc.).

This setup is problematic for two primary reasons. First, multiple PCs are stationed across the plant floor in a hot, dirty and unstable environment, so they are prone to damage and require frequent maintenance. Second, the conversion and programming software packages carry licensing fees for each PC. Both of these factors increase the total cost of ownership of the pallet wrapping system.

The manufacturer decided to rethink its application design. They first considered moving the computers to the back office and running long serial cables to the bar-code scanners and PLCs. However, this did not address the software licensing issue and also created the risk of cabling problems. They also considered replacing the PLCs with Ethernet-enabled versions, but new PLCs still might not be able to handle the ASCII data from the scanners without expensive third-party modules. The company also considered purchasing Ethernet bridges from the existing PLC manufacturer, but without an extra serial port they could not connect a bar-code scanner.

The company’s material handling integrator recommended the Digi One® IAP, a small DIN rail mounted device server. It offers one Ethernet port and two serial ports – one of which can act as a pass-through port to connect the bar-code scanner, the other to connect the PLC. Its ability to not only bridge serial DF1 to Allen-Bradley EtherNet/IP, but also to perform ASCII-to-DF1 protocol translation was a key selling feature. It also offers multi-master technology, which enables multiple masters, like the programming and the data collection software packages, to access the PLC simultaneously. With the Digi One IAP, one workstation in the office can access every PLC on the plant floor, thus drastically reducing license fees.

The bottle manufacturer saw immediate benefits from choosing the Digi One IAP. It is easy to install via a built-in web server with browser-based setup wizard, eliminating software training; it offers true interoperability between industrial devices and industrial protocols with ASCII protocol translation and protocol bridging; and it promotes cost savings by eliminating the need to buy, install and maintain multiple PCs and software licenses. The only real challenge after choosing the Digi One IAP was deciding what to do with the old PCs.

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