Reality Check – Wireless Lessons from the Real-World
Environmental Effects on Wireless: Seasonal Effects on Signal Propagation and Equipment Reliability
By John Welch – Apprion Wireless Advisor
In our February 2010 eNewsletter, we started our Wireless Lessons series on "The Environmental Effects on Wireless" with a look at weather related precipitation in the form of rain, snow, ice and fog. This month, we'll take a look at the seasonal effects on signal propagation and equipment reliability. The environmental effects of seasonal factors on industrial sites and equipment are often overlooked. Important seasonal factors to consider include the impact of:
- Temperature variances on the life and proper functionality of equipment
- Ability to service equipment and maintenance
- Wind changes that cause equipment losses and damages
- The effects of scheduled plant shutdowns and restarts
Temperature variances on the life and proper functionality of equipment
As we pointed out last month, temperature variances are similar to weather related occurrences but are seasonal phenomena happening primarily in the late spring or fall. Temperature variances should not be confused with the temperature extremes within which the equipment can operate, called temperature rating. Instead, temperature variances are quick, extreme changes in temperature which cause the equipment to breathe in moisture. As it cools, the moisture condenses on the surface housing and circuit boards causing problems. Cables, especially RF cables, suffer as they cool. The core material (dielectric) "breathes", drawing in moisture and gradually diminishing the performance of the system.
To combat this effect, careful selection of equipment is necessary. Also weather-proofing materials should be regularly inspected and maintained.
Ability to service equipment and maintenance
In a well designed industrial system, the radio and infrastructure equipment is constantly monitored and most problems can be and are solved remotely. But occasionally a visit to the equipment is needed and, at specific times of the year, roads may be impassable. The presence of ice formations on ladders and handrails may place a servicer at physical risk and the need of a man-lift on a patch of ground which may at times be muddy is a poor choice of location.
In these and other similar situations the designer should choose an alternate location or a redundant system during his engineering visit in order to minimize the impact on overall system functionality, should there be seasonal risk factors.
Wind changes that cause equipment losses and damages
Wind loading effects on structure may cause the complete loss of equipment. Wind loading is a complex subject involving both the necessary knowledge of the calculations involved in wind shear analysis and an understanding of how topography and structure may channel a breeze into a destructive force. A visit to the location by a qualified and experienced designer is necessary to identify this and many other variances.
The effects of scheduled plant shutdowns and restarts
In essence, industrial facilities are dynamic: constantly changing in needs and availability. Temporary area or plant shutdowns are necessary for the maintenance and upgrading of industrial facilities and should be accounted for in the overall design. It is often necessary during seasonal effect times to cut electrical power to, or in, the area's shutdown. This, along with the movement of heavy machinery and new construction, can severely impact wireless services to adjacent working areas where process monitoring, video, VoIP or any number of wireless services are in use.
The designer of the system should not only have a good understanding of the processes within a facility, but a good understanding of the facility's long range plans. Only with this understanding can he develop a system which is robust against the "seasonal" changes of the area.
Conclusion:
In conclusion of this section, seasonal effects are more than just the growth of trees but a key factor which cannot be overlooked in the selection of technologies and equipment, as well as equipment location. Seasonal effects also include the scheduled maintenance of the coverage areas and are a leading influence in the survivability and maintenance of a successful wireless infrastructure.
 John Welch is a Senior Wireless Systems Engineer at Apprion. John has over thirty years experience in technology and engineering with RF, digital and analog devices and various wireless communication and video systems. He brings over 12 years of specialized wireless implementation and design experience with industrial, metropolitan and military wireless infrastructures and systems. Implementations to date include a last mile point to point wireless system under the 802.11 and 802.16 standards, a metropolitan wireless 802.11 deployment in the Auckland, New Zealand central business district and numerous industrial wireless network implementations at oil/gas, chemical and power facilities. In addition, John has developed patents and new inventions for wireless networking systems, antenna design and deployment methodologies.
|
