1 August 2006
Ethernet strategies in practice
Adding network connectivity has devices and equipment worldwide and accessible
By Shaye Shayegani and Nicholas Sheble
Connecting equipment to the network has provided a number of benefits to companies in the industrial automation market. As more realize these benefits, there is an increased desire to take advantage and expand them into new management practices for improved operational efficiencies and possible revenue streams. However, on the factory floor, there is a large mix of non-networked legacy devices and newer networked equipment that all communicate differently.
A systems integrator would encounter several questions in order to develop a system that can communicate with new networked and non-networked legacy equipment:
How does the backend system access both types of devices?
How do we integrate this equipment and maintain the same user experience or interface?
What network media is the way to go—Ethernet, Wi-Fi, proprietary wireless, or maybe Fiber Optic?
Will this require a combination of wired and wireless?
To answer these questions, one must first examine the options of connecting legacy non-networked legacy equipment to the network.
An understanding of the benefits of network-enablement, including the ability to remotely monitor, manage, and control attached equipment, is required in order to improve processes and efficiencies, provide proactive maintenance, streamline operations, or enable a service revenue model.
Powerful networking keys
For facilities that run automated assembly and manufacturing equipment, time is money. Every minute a machine is idle, productivity drops and the cost of ownership soars.
Therefore, many automated factory floor machines have dedicated PCs to control them. In some cases, handheld PCs work to reprogram equipment for different functions.
These previously isolated pieces of industrial equipment could be networked to allow them to be controlled and reprogrammed over the network, saving time and increasing factory efficiency.
Adding network connectivity allows devices and equipment to be accessed and monitored from a central location or from anywhere in the world.
However, exactly how can this be accomplished?
Since many industrial and factory automation devices such as PLCs, motor drives, motion controllers, conveyers, and packaging systems have different interfaces or use proprietary communication protocols, the first challenges are determining how to provide connectivity and how to interact with any number of different data protocols.
For most applications, device servers provide a solution for establishing network connectivity and enabling communications by supporting the necessary protocols.
These powerful networking solutions provide the ability to utilize the serial interface on the equipment to establish network access and allow for virtually any kind of data transaction.
Device servers defined
A device server is a specialized appliance designed to network-enable virtually any type of device independent of any operating system.
A common misconception with a device server is it is merely a piece of hardware providing serial to Ethernet conversion. In reality, it is a combination of flexible hardware, highly adaptive and configurable firmware, and often-sophisticated software for the host computer.
Device servers are a solution for providing network connectivity facilitating remote equipment access through a specified network media (Ethernet, Wi-Fi, Cellular, etc), providing data transportation as opposed to conversion. In many cases, they provide protocol translation and high security.
To be successful, a device server must provide a simple solution for networking a device while maintaining access and user interaction to that device as if it were locally available through its serial port. This is particularly important since the original software likely only communicates with the local serial port on the host computer.
To facilitate such interaction, sophisticated software must be included on the host system to play traffic cop and redirect application data destined for the local serial port out the network interface and through the device server where the serial device now resides. Additionally, the device server should provide for the multitude of connection possibilities that a device may require on both the serial and network sides of a connection.
For instance, should the device stay connected all the time to a specific host or PC?
Are there multiple hosts or network devices that want or need to connect to the newly networked equipment?
Are there specific requirements for an application, which requires the serial device to reject a connection from the network under certain circumstances?
The bottom line is a device server must have both the flexibility to service a multitude of diverse requirements and be able to do this in a manner transparent to the end user.
Moving from serial to Ethernet
For some devices, the only access available to a network manager or programmer is via a serial port. The reason for this is partly historical and partly evolutionary.
Historically, there was no network interface; equipment costs were high, the life cycle of the equipment quite lengthy, and there was no confidence that a network could provide a realized benefit. Additionally, adding an Ethernet interfacing has usually been a lengthy development process involving technology and expertise the equipment vendors did not have in house.
Some companies did not believe Ethernet was necessary for their products, which were destined for a centralized computer center. Others felt the development time and expense required to have an Ethernet interface on the product was not justified.
Justifying their position, the networking infrastructure of many sites has only recently been developed to the point that consistent and perceived stability has been obtained. As users and management have become comfortable with the performance of the network, they now focus on how they can maximize corporate productivity in non-IS (information system) capacities.
Device server technology solves this problem by providing an easy and economical way to connect the equipment to the network.
The key to network-enabling equipment is in a device server’s ability to handle two separate areas:
The connection and communication between the equipment and the device server
The connection and communication between the device server and the host computer or other network devices
Traditional terminal, print, and serial servers were developed specifically for connecting terminals, printers, and modems to the network and making those devices available as networked devices.
Now, more modern demands require other devices be network-enabled, and therefore device servers have become more adaptable in their handling of attached equipment. Additionally, they have become even more powerful and flexible in the manner in which they provide network connectivity.
Anything goes – wired, wireless
Device servers provide the ability to securely and remotely control, monitor, diagnose, and troubleshoot all kinds of equipment over a network or the Internet, enabling a company to preserve and extend its investment in present equipment.
Now that Ethernet has proven to be reliable, robust, and deterministic enough for the industrial automation environments, it is logical that solution providers would also want to leverage the benefits of wireless network technology.
Obviously, one of the biggest advantages of wireless is mobility. Without a physical connection, wireless networks allow the application or device to move. It can save on the cost of Ethernet cabling and is ideal in situations where a physical wired connection can be difficult or even impossible.
The term wireless can relate to many technologies such as Cellular, 802.11, Bluetooth, ZigBee, WiMax, and a number of other proprietary high- and low-power solutions.
All wireless technologies provide common initial benefits such as untethered connectivity and mobility. Some offer added benefits of low power consumption, long range, and better immunity to interference or high bandwidth. Some provide easy integration with traditional IT networks.
802.11, also called Wi-Fi, has emerged as standard for wireless local area networks, mainly because of its IT heritage and easy integration with traditional network systems. The IEEE 802.11 standard provides many variations with 802.11b/g being the most common variation at this point.
When striving to network-enable a variety of devices, the three most important considerations are connection viability, work environment, and cost.
Primarily, a network must be viable for long-term use. Bandwidth and infrastructure requirements will depend on the size of the network and its intended usage. The network must provide flexibility and scalability to serve the needed number of connections, and assure data security and integrity at all times. The type of environment the network must operate in is also a consideration.
Global System for Mobile Com-munications (GSM) and General Packet Radio Service (GPRS) technologies are beginning to work for even more remote networking applications.
GSM is the world’s most widely used mobile system, and it is on the 1900 MHz frequency in America and on the 900 MHz and 1800 MHz frequencies in Europe, Asia, and Australia.
GPRS is a packet-linked technology that enables high-speed (up to 115 kilobit per second) access to wireless Internet in a GSM network. GPRS is IP-based and allows users to be online continuously.
Cost is often the most crucial con- sideration when it comes to any technology implementation, and establishing network connectivity is no exception. A misconception is that establishing a viable network is quite expensive and requires extra cabling in order to establish a proper connection.
Some view wireless technology as rather expensive when in actuality it can offer a much more cost-effective means for establishing a connection compared to wired technology that sometimes requires massive amounts of cabling to implement.
ABOUT THE AUTHORS
Shaye Shayegani (shaye@lantronix. com) has degrees in computer science and computer hardware. He is a senior application engineer at Lantronix. Nicholas Sheble (firstname.lastname@example.org) is the senior technical editor for InTech.
Water System Unplugs: Ethernet boosts efficiency at growing Canadian burgh and halts expensive quick fixes www.isa.org/link/WaterUnplugs
Industrial Ethernet takes the test: There are questions about reliability and performance in manufacturing plants. www.isa.org/link/IndusEthernettest
Ethernet in Motion Control www.isa.org/link/EthernetMotion
Wireless Ethernet in Factory and Industrial Applications www.isa.org/link/WEFIA
Firmware is software embedded in a hardware device. Often it comes via flash ROMs, and an end user can update it (http://en.wikipedia. org/wiki/Firmware).
ROM (read only memory) holds programs and data that must survive when the computer turns off. Because ROM is nonvolatile, data in ROM will remain unchanged the next time the computer turns back on.
Flash ROM: To change the contents of a conventional EPROM, the chip has to be removed and erased using ultra-violet radiation. It can then be electrically repro-grammed. A flash ROM, by contrast, can be reprogrammed electrically in situ, i.e. it can be reprogrammed through software (http://www. archivemag.co.uk/gloss/F.html).
Serial port, or interface for serial communication, is an interface in which only one bit transmits at a time. Most serial ports on personal computers conform to the RS-232C or RS-422 standards. A serial port is a general-purpose interface that can be used for almost any type of device, including modems, mice, and printers although most printers connect to a parallel port.