Many of the semiconductor firms that play in the wireless space would have you believe that a single-chip Zigbee design is the answer to everyone's prayers when it comes to developing an industrial control system.
However, although chip-based solutions work well within a laboratory environment, they lack several attributes necessary to make them successful on the factory floor.
Firstly, the issue of interference needs to be seriously considered. A wireless control implementation that is truly capable of proving itself worthwhile will need to exhibit strong resistance to the various EM sources that are found in the average industrial setting, with the ability to easily move between different channels. With the Zigbee standard occupying the already over-cluttered 2,4 GHz band (which is also used by Wi-Fi and Bluetooth) it is at a disadvantage from the start.
Then there is the question of robustness. Any control solution must be able to cope with both extremes of temperature and a certain degree of mechanical stress, as life in the world of heavy industry is generally far less forgiving than most semiconductor solutions will be used to. Also, industrial locations tend to be very lossy, with a great deal of metal around that affects the strength of the signal, and reduces expected performance levels.
Reliability must be assured. For one thing the task of troubleshooting can be a long drawn out affair. Then there is the simple matter of safety too. Clearly, when working with heavy machinery there are various potential dangers involved in having a control system that might fail, and this must be taken into account at an early stage. For example, the possibility of a crane or forklift not responding correctly could have calamitous consequences. So, in order to avoid such circumstances, efforts must be made to implement a wireless control solution that is effectively 'bullet-proof'.
The roll-out of any chip-based solution will definitely require the services of an experienced RF engineer, who are normally in very short supply. Whereas with a radio module alternative, most of the complex work has already been done by the manufacturer, and as a result this will usually only call for the services of an applications engineer of average ability - far easier to get your hands on.
So herein lies the common misconception; single chip does not necessarily mean easy implementation, in fact it is usually the exact opposite. Often, the development time needed to put a semiconductor-based solution in place far outweighs the perceived cost savings, and in the end comes with a higher overall price tag, because of the man hours required to set it up correctly.
Quality versus cost
In general, the size of an industrial control system does not really justify the amount of silicon needed to make a single-chip solution truly cost-effective. Also it is worth mentioning that such implementations will often be overkill when it comes to speed. There is no great need for huge data rates in these sort of applications, it is far more a matter of reliability. This brings up another major flashpoint: the semiconductor vendors may have the specifications needed to meet the demands of high-end communications systems, but by trying to play in industrial radio they are far from their home turf. For reasons more to do with their own self interest than actual suitability, they have elected to go for a piece of the action in the industrial sphere, but in truth they do not really possess the tools to do the job.
Appearances may be deceptive
The fact is, engineers need serious solutions, not just PR stunts. What is required is a communication system that meets the actual specifications that are set, and at the same time is tough and dependable. By way of an analogy we could think of this in terms of a cross-country race. There is no point in putting a sprinter into that sort of competition, as it will not be speed that is the telling factor, it will be a mixture of stamina and ruggedness that will win the day.
With this in mind, companies like Radiometrix in the UK make sure it approaches such problems from the right angle. The firm's LMT2/LMR2 transmitter/receiver modules can provide a multichannel, low-power, high-reliability data link which can deal with interference issues, and has more than adequate range for the vast majority of industrial control systems. The LMR2 has a receive signal-strength indicator, which measures the incoming signal over a range of 60 dB. This allows the assessment of data link quality, and accurate prediction of available range margin which can be tolerated before there is a major drop in performance.
The devices conform to both EN300220-3 and EN301489-3, and can maintain a good signal over a span of at least 500 m, making them suitable for even the largest of factory sites. A data rate of 5 Kbps can be happily supported, and with up to 32 channels on offer there is ample room to manoeuvre in order to avoid interference.
Do not believe the hype
In conclusion, industrial control implementation cannot be just an afterthought. It is simply not sensible for WLAN manufacturers to assume that they can encroach on this arena using their consumer-oriented products, in an attempt to gain some additional revenue. Focused solutions are what is required. The industrial space needs devices that are optimised to those specific applications, not ones that are, in fact, targeted elsewhere, which basically have some additional functionality crudely bolted on the end.
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