Mastering your Legacy

When considering your investment in industrial equipment, it is hard to justify throwing it all away in order to join the "Ethernet Revolution". True, the evidence of Ethernet's role in productivity enhancements, quality control, and cost reduction is overwhelming. It also appeals to our common sense as you can get data from any piece of equipment into any of the software applications that run on an office PC. But before you sign the order, a quick reality check might show that the actual cost of Ethernet-enabling your entire site is just too prohibitive.

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

One of the less obvious but most viable options is the use of device servers, 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. Not all serial-to-Ethernet products can be used on the factory floor and a true industrial device server has a completely unique set of characteristics customised for automation applications.

In the past, telltale signs of industrial device servers have been DIN rail mounting, DC power inputs, terminal block connectors and wider operating temperature specifications. However, a new breed of device 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 such as serial port emulation and protocol translation.

In layman's terms, serial port emulation (also called COM port redirection) is a software driver installed on a computer that acts as a virtual COM port, 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 needing software changes.

A popular use for COM port redirection in industrial applications is when 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.

Device servers can also be used for protocol translation, for example from Modbus serial (RTU or ASCII) to ModbusTCP or from Allen-Bradley serial (DF1) to EtherNet/IP and AB Ethernet (PCCC). Protocol translation is also used where HMI software (for example WonderWare, Intellution and RSLinx/RSView) needs to be able to monitor or collect data from a PLC. As most common industrial applications support ModbusTCP, EtherNet/IP or AB Ethernet, enabling communications from an HMI supporting one of these IP protocols to a PLC speaking the serial equivalent is now be simplified.

So, if your are considering joining the Ethernet Revolution, but cost or availability issues stand in your way, consider using industrial 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 best way of connecting your mission-critical serial devices. Many real-world problems are already being solved using the advanced industrial features of the DigiOne IA RealPort industrial device server, which incorporates multimaster device sharing and low latency communications suitable for most industrial applications.

Digi International
p104@industrialnetworking.co.uk