June 16, 2009 by Ian Verhappen
There is lots of talk and coverage of industrial wireless technology in the trade press. Once again there are multiple camps at work; WirelessHART, OneWireless, the two industry standards camps and, of course, the ISA100 standard that is also under development, which both camps say they will fully support once it gets adopted.
One good thing about the ISA100 standard is that the group developing it is planning to support the ability for it to effectively “tunnel” other standard protocols through or over the ISA100 protocol. This tunneling means that once ISA100 is available, each of the other fieldbus protocols should be able to operate with little or no change to the user layer of the protocol itself. That means when you implement Fieldbus, for example, over ISA100, all the functions and capabilities will remain the same as if you were running over wire.So other than these “standards,” what are the other considerations associated with installing a wireless system?
Those would be power and security.
One of the benefits of wireless installations is that they can be installed anywhere. But because they do not need to have a power or signal cable installed, they obviously will require some alternate energy source to operate. Fortunately, with the improvements in battery technology and the continuing trend of microprocessors getting more done with less energy, it is now possible under certain conditions to get in excess of five years – and in some cases up to 10 years – operating life from battery supplies with transmitters. The key words here are “certain conditions” because the battery life equation is a balance of distance to transmit (signal power) and awake time (frequency of updating) or how often and long the device must actually be sending the signal. Keep in mind that if the device is being used in a mesh network, it must not only transmit when it has an update to send to the network, but also when it needs to relay (receive and forward) a message from another node in the network
The good news is that there are a number of technologies available and being developed that are able to provide the low levels of power needed to operate a wireless transmitter. Among the options are the well-known solar panel and thermal sources (thermopile, which is really a bunch of thermocouples connected together) and some innovative new ideas based on scavenging energy from the natural vibrations that occur in a process pipe
The last, and probably most important, item on the power front is to be sure that you have selected the right level of power for your system; enough to get the signal through the “concrete and steel jungle” of your facility, but not too much because then you are “wasting precious energy” and potentially causing interference with other systems that may not even be in your facility. It is unlikely that you will actually “swamp” or override a signal in your neighbor’s plant, but you could consume an available frequency band or make it easier for someone else to capture your signal and use it in some unintended way. This raises the other big concern folks have with wireless – security.
The good news on the security front is that the technology itself incorporates many features that provide a level of security. All the wireless standards mentioned above use FHSS (Frequency Hopping Spread Spectrum) technology, which means that the signal uses a very narrow bandwidth for a very short duration and the “randomly” hopping (obviously not totally random or the transmitter and receiver would be looking for each other in different places during the next transmission cycle) change of the frequency used within the available bandwidth. This random change makes it very difficult for a device outside of the network to capture the signal without knowing the pattern it has to follow.
The other security feature is the inclusion of standard encryption technology in the messages themselves, often 128 bit as a minimum. Thus if a message should be captured, it is difficult to “break open” the message, which is quite small, without having a large enough sampling of messages to be able to decrypt the security code/pattern of the message. One does not hear of too many digital phones being “tapped” these days, because they use encryption as well, so we know the technology works.
Wireless is still in its infancy, but does have a niche and hence all the press it is currently receiving. However, as I’ve said numerous times in past columns, the secret to success of a good project is a good design up front, hence the continuing need to stay current with technology or find the people who are able to help you.
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
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