June 16, 2009 by Ian Verhappen
One of the challenges that Foundation Fieldbus has faced to date is the integration of motors and drives as end devices. This has been a significant shortcoming, since variable speed and variable frequency drives are being used more and more often in projects because, in many cases, they are more energy efficient than control valves and offer equal or better flow control. If the user chooses a variable drive, he then must choose some other protocol such as DeviceNet or Profibus DP, resulting in a system for which the user must support multiple protocols. This is not necessarily a bad thing and we are all aware that we must always use the best tool for the task at hand – within reason.
There is, however, a major initiative underway by the Fieldbus Foundation to make it easier to access high data requirement devices directly into the host system using HSE (High Speed Ethernet). HSE was developed with this objective in mind and the Foundation’s HSE RIO (Remote Input Output) team is in the process of preparing a standard to make integration of discrete in, discrete out, analogue in and analogue out (analogue I/O will also support HART information) and Foundation Fieldbus H1 available over HSE (FF H1 over HSE has been available for some time using HSE linking devices.). This will not only put all forms of conventional I/O into the native fieldbus environment easily, it will also force DCS manufacturers to provide the associated HSE port connection on their systems. Once this happens, a full range of Ethernet enabled devices will be possible (See the illustration above for a list of those devices.).
Because all these products are based on commercial off-the-shelf (COTS) Ethernet, IEEE 802.3 and IEEE 802.11, they all use the same Ethernet cabling switches, firewalls and related technology we use for any of the Industrial Ethernet protocols with industrial-grade equipment (Brave souls can use office equipment if they wish.). This is the reason we are showing a managed switch as a way to connect all these Ethernet-based products to a single port on the host/digital control system (DCS).
What will each of the devices shown in the illustration above typically be and/or do?
The first device is an HSE linking device and, as shown, it is used to connect one or more H1 segments to a single HSE connection. This will allow you to bring several H1 segments to the host system using a single port. Of course, you will still likely have to pay for the number of points you bring into the system, but at least you will need fewer I/O cards.
Next is an HSE field device, and hopefully this will be the motor control centre itself. If not, the third device shown, the gateway will be able to port another protocol, such as Profibus DP or DeviceNet, to HSE with a small box mounted in the same cabinet as the motor control so that the end user will not be aware he is using anything other than a single language (If the gateway requires you to be knowledgeable in both protocols and that you map all the points from one set of registers to another, it is not “magic” enough to be a true gateway.). It is expected that full support for this functionality as part two of the FF HSE RIO project, which depends on completion of the FDI (Field Device Interface project using OPC UA), will be released as standards and products by 2012.
The final device is the one for which a standard is presently under development by Fieldbus Foundation. This RIO device, as described above, will be modular, available in late 2009 and allow the end user to select the types of signals he wishes to have brought in to the system with a single connection – significant cable and termination savings are possible in a single configuration and operating environment of Foundation Fieldbus.
Is Foundation Fieldbus the right fieldbus for motors and drives today? No. In fact, it is not even possible. However I hope I have shown you that progress is being made towards this objective.
Ian Verhappen is an ISA Fellow, ISA certified automation professional, adjunct professor at Tri-State University and director of industrial networks at MTL Instruments, a global firm specializing in fieldbus and industrial networking technologies. E-mail him at Ian.Verhappen@ICE-Pros.com, or visit his website at www.ICE-Pros.com.