Mastering your Legacy Industrial Devices Over Ethernet

When considering your investment in your installed base of Industrial equipment, it is difficult to justify throwing it all away in order to join the "Ethernet Revolution."  The evidence of Ethernet's role in productivity enhancements, quality control, and cost reduction is overwhelming.  It also appeals to our common sense.  "You mean I can get data from any piece of equipment into any of the software applications I run from my office PC?  Where do I sign!"  Then reality sets in; the actual costs of Ethernet enabling so much of your site is just too prohibitive. 

 

The fact is that a majority of the equipment in use today is not available with Ethernet connectivity without outright replacement of the hardware.  In addition, products with the "newest TCP/IP technology" are usually only available in top-of-the-line models and cost much more than the non-Ethernet equivalent.  Another reality is that many vendors do not yet offer Ethernet networking as an option, and do not offer solutions to the models of equipment you may already have installed.  However, advances in third party Ethernet retrofitting could allow you to join the revolution without having to pay the price for it. 

 

One of the less obvious, but most viable options is the use of Device Server technology.  Device Servers are hardware products that connect serial devices to Ethernet.  They make sense because serial ports are present on most industrial devices and serial communication has always been a dependable means of sharing information. Paired with the readily available, inexpensive, ever-reaching Ethernet users will be provided with a great alternative for the factory floor.

 

Experts agree that serial-over-Ethernet technology can be a very important strategy in IP enabling your site, however the differences in Device Servers are as vast as the equipment they plug into.  "Not all device servers are created equal in the Industrial world," says Mark Fondl of ICT Global, an industry leader in providing Industrial Communications solutions and services.  "There are a whole host of serial-to-Ethernet products that are virtually useless on the factory floor.  A true Industrial Device Server has a completely unique set of characteristics customized for Automation applications."

 

Telltale signs of industrially focused Device Servers have been Din Rail Mounting, DC Power Inputs, terminal block connectors, Industrial certifications, and wider operating temperature specifications.  However, a new breed of Device Server is now available with intelligence that exceeds the basic serial over TCP/IP feature set.  High-end device servers have anticipated the needs of common industrial communications problems, and addressed them with features like serial port emulation and protocol translation.

 

In laymans terms, serial port emulation (also called COM port redirection) is a software driver installed on a computer that fools the computer into thinking that it has additional COM ports attached.  These "virtual" COM ports are actually logical COM ports pointing to the IP address of the device server (where the serial device is connected). The advantage of COM redirection is that any software application that communicates via COM ports will be able to communicate with a serial device across the network as if it were plugged directly into the PC (without any changes to the software).

 

A popular use for COM port redirection in industrial applications is when a configuration or programming software needs the ability to upload or download to a remote serial device.  For this to work, the application would simply choose one of the COM ports that is mapped to a device server across the network.  The serial device plugged into the device server will be programmable just as if it were connected directly to the PC. (use picture here)

 

Another other significant capability of Device Server technology is called protocol translation, where the Device Server actually converts one protocol to another.  A few Device Servers are able to convert Modbus serial (RTU or ASCII) to ModbusTCP.  Even fewer allow the conversion of Allen-Bradley serial (DF1) to EthernetIP and AB Ethernet (PCCC). This allows a networked software application or Ethernet enabled hardware devices to communicate to a serial device using proprietary industrial TCP/IP protocols.

 

A common scenario where protocol conversion is used is in the case of an HMI software (e.g., WonderWare, Intellution, RSLinx/RSView, etc.) that needs to be able to monitor, or collect data from a PLC.  Most common industrial applications support ModbusTCP, EthernetIP or AB Ethernet.  Therefore enabling communications from an HMI supporting one of these IP protocols to a PLC speaking the serial equivalent can be simple.  In the case of the DigiOne IA RealPort, setup takes just a few short steps.  First, give the device server an IP address, launch a Web browser and enter the IP address to access the Industrial Protocol wizard, and finally choose the correct settings for the appropriate protocol.  Now the HMI software can communicate with the serial PLC as if it were a native industrial Ethernet enabled device.

 

Many real world problems can also be solved using the advanced industrial features of the Digi One IA RealPort, not found on other device servers.  Two such capabilities are MultiMaster device sharing, and low latency communications.

 

MultiMaster is truly a differentiating technology, because it breaks the rules of point-to-point serial communications by allowing multiple masters (or host devices) to simultaneously communicate to a single serial device.  For example, you could have your Intellution software communicating with a PLC at the same time a Panel HMI is talking to the same PLC.  The Digi One IA RealPort supports MultiMaster, or device sharing,  technology for a variety of popular industrial serial and IP protocols. 

 

Another specialized feature is one that is easily overlooked, but critical to certain serial protocols.  Low latency is a benefit that allows special industrial serial protocols that require a very quick response time to be able to communicate across TCP/IP networks.  Most device servers take 200 to 600 milliseconds to send a serial message across a network and receive a response.  However, some serial protocols require much tighter response times.  The DigiOne IA RealPort averages less than six milliseconds turnaround over the network; well within the requirements of virtually any serial protocol.

 

So, if your are considering joining the "Ethernet Revolution," but cost or availability issues stand in your way, consider industrially focused Device Servers to bridge your legacy devices.  And remember, not all Device Servers are created equally.  Be sure to do your homework to find the right solution for your mission critical serial-to-Ethernet needs.

 

This article was written and provided by Digi International.  Digi International is dedicated to centralizing information by providing open-connectivity of industrial devices onto Ethernet from anywhere. This can be seen in each of their product lines ranging from device servers, to terminal servers, to USB solutions, to wireless connectivity.  For more information about Digi International, please visit their website at www.digi.com.