One of the greatest benefits of using TCP/IP networks for automation, monitoring and control functions is the fact that they allow us to join various sites together no matter the physical distance between them. This allows province or countrywide systems to be controlled from a single control room, which not only reduces operational costs and staff requirements, but also greatly increases monitoring and analysis of the system by conglomerating all monitoring data transmission to a single, central location. This means controllers not only have the information about components of the system they are directly working with, but also other components that could indirectly affect their operations. For instance a controller operating a generator plant could be made aware of breakdowns in the coal supply line well before they are directly affected. Reponses to changes or issues on the system can be quickly reacted to, and often can be resolved before they become a serious problem.
Wired vs. wireless technologies
A big reason why TCP/IP networks are so easy to use for these types of applications is the fact that they can be run over a variety of different media. The most commonly used in industrial and utility systems are fibre optic (for longer cable runs as well as inter building runs) and copper or Ethernet cables (for shorter, inner building runs or within cabinets). However, both of these are wired technologies, which have different pros and cons when compared to the wireless options available.
The most obvious pro of using wireless communication links is the fact that cables do not have to be laid. This means that installing a wireless link requires less physical preparation. Also in some areas laying of cable may not be feasible at all (cable paths are inaccessible, crossing of main traffic thoroughfares or bodies of water, solid rock making burying of cables hard/impossible etc.), in which case wireless is generally a better and cheaper option.
However, while installation is generally much easier with wireless signals, the performance of wireless generally cannot match that of a wired link. Wireless mostly offers slower speeds than wired links (56 Mbps for standard 802.11). Generally, in the industrial and utility worlds high bandwidth is not as much of a concern as low latency, and so the low bandwidth of wireless when compared to wired links is mostly not a concern. However, this is still a point that must be taken into consideration when considering wireless backup links on the network.
Another differentiator between wireless and wired signals is their susceptibility to outside interference. Physical cables have the advantage of stability and higher resistance to external interference. A physical cable will generally either establish a connection (cable is ok) or will not (cable is broken), and so is mostly a black or white option. If the connection does not establish, 95% of the time it simply means the cable is broken somewhere and must either be repaired or replaced. Note that this is not always the case, as copper (Ethernet) cables can be affected by outside EMI (Electro Magnetic Interference) which can detrimentally affect the connection stability. However, as long as the cable installers stick to some basic principles (not running parallel to power lines for long distances or avoiding machinery or appliance that can create interference (fridges, air conditioners, microwaves etc. for instance)), and using fibre optic rather than copper cabling where possible, this should not be too much of an issue.
Wireless signals, on the other hand, are greatly affected not only by EMI, but also inclement weather. In fact some wireless links will end up working better during a certain time of the year, as temperatures, humidity and other external factors change. This could end up being a simple loss of the occasional packet, or could manifest as something more serious, such as losing sections of the network as they lose their wireless communications link. This shows us that wireless planning does not only involve standard questions such as what budget and locations are available, but also is very reliant on what the link is meant to be used for, and the average traffic amounts that may be on the link. So installing a wireless link to replace a gigabit backbone link on the network which experiences an average of 50 Mbps is not really feasible, however using a wireless link to connect a remote, out-of-the-way substation to the rest of the network for basic monitoring functions, where the device only requires 100 Kbps is definitely an option for wireless.
It is also important to note that standard WiFi (802.11) is not the only wireless technology available. Two other commonly used wireless Ethernet connections are WiMAX and 2G/3G/4G (GSM). WiMAX is similar to WiFi, with two major functional differences, namely that the links can be much longer distances (Up to 45-50 km in some cases), and secondly the fact that WiMAX works over a closed spectrum rather than an open one. A closed spectrum means that a user must apply with a service provider for a specific ‘slice’ of the spectrum available (also based on the geographic area) before that spectrum can be used. However, once registered, that spectrum (in the geographic area it was associated with) can only be used by the customer, and thus interference with other, existing WiMAX setups in the area will not be a concern. Cellular connections connect either to the public Internet via an ISP, or to a private WAN (wide area network). Once connected to the internet or a privately owned WAN our communication distance is only limited by infrastructure. For instance using a public ISP and 3G, one can effectively communicate to any other point in the world that has Internet connection. 3G and WiMAX both require monthly rental payments however, unlike standard WiFi where the only cost is the initial capital. However, they do offer much greater distances when compared to WiFi. With 3G connections, one is reliant upon a third-party’s infrastructure (the ISP). This means that there is no guarantee on the quality of the throughput, and in the event there is a problem with the connection (tower down for instance), there is no guarantee of when the connection will be fixed. For this reason 3G connections are not recommended for mission-critical applications.
Conclusion
In conclusion, wireless links definitely have their place in the industrial and utility worlds, however proper planning and consideration for the site must be taken into account, as well as the use of the wireless link. Using wireless in the correct places can save huge amounts of capital and time, however using it in an inappropriate location can lead to huge losses of capital, time and productivity, if the link is not stable enough for the requirements.
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