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Radio Frequency Technology
City Light is in the process of evaluating communications protocols for Advanced Metering. The decision has been made to go forward with a wireless technology to transmit meter data to collectors which will be located around our service territory and then transmitted via fiber-optic cable to our offices.

The question of the best RF Network Topology technology is the next area of study and analysis for City Light. There are three competing technologies:

RF Mesh Architecture: This is a communications network made up of meters transmitting in a mesh topology. The coverage area of the meters is sometimes called a mesh cloud. This approach is reliable and offers redundancy.

RF Star Architecture: In a star topology, there is a direct connection (one RF hop) between each point on the network and the collection point. The collection point is sometimes referred to as a concentrator, collector, gateway, or WAN (wide area network) access point.

LTE/3G Cellular: This is the same technology as cellphones, but operating in a much more limited way over existing networks

There are benefits to all of these technologies, so we must consider each very carefully; evaluating proposals from AMI Vendors, before deciding which way is best suited for Seattle.

Whatever technology we decide on, City Light is committed to operating the system in a safe and reliable manner. There are many rumors and misconceptions about wireless technology for metering, and we are sensitive to the concerns expressed by some of our customers. To help better understand the RF Emissions from AMI meters as compared to other home equipment use, we have borrowed a video from our colleagues at Southern California Edison. It explains the AMI RF Field Emissions very well and succinctly.

It should be noted that the Southern California Edison's Advanced Metering system is an RF mesh network (see above), which means that signals from some meters may have to "hop" to other meters to reach the data collection point, which adds to the time it takes to communicate with the utility, especially when compared to an RF Star Network or an LTE/3G Network. Also, Southern California Edison has a read schedule that is much more frequent than what City Light is contemplating, due to their heavy reliance on time-of-use pricing to avoid peak generation. As stated on our Advanced Metering privacy page, City Light is considering a read frequency for residential and small commercial installations of a few times a day (at most) to operate the system in an efficient manner.

We included the SCE video as an introduction to RF emissions, but there is much more to the technology, with a lot of research having been done since this video was produced in 2011. Perhaps the most significant point of the video for us at City Light is the demonstration of how RF Fields drops at the square of the distance, and how the readings dropped by a factor or 10 from the one foot to three foot readings, and by another factor of 10 from the three foot to ten foot readings, with the measurements behind the meter being negligible.

Research on the effects of RF exposure continues, with a study currently being conducted in Europe that the FCC is monitoring closely. For more information on this topic, we invite you to review the following position papers and website on the topic. We will be adding to these links as we find more information on the subject, and invite your comments on these publications.

Position Papers:

California Institute of Science and Technology "Health Impacts from Smart Meters" (2011)

Electric Power Research Institute, "Radio-Frequency Exposure Levels from Smart Meters: A Case Study of One Model" (2011)

The Department of Public Service, state of Vermont "An Evaluation of Radio Frequency Fields Produced by Smart Meters Deployed in Vermont" (2013)

Electric Power Research Institute's "Characterization of Radio Emissions from Advanced Metering Infrastructure Revenue Meters (Smart Meters) in CPS Energy Residential Installations" (2014)

Web Sites:

Federal Communications Commission Radio Frequency Safety FAQ's

American Cancer Society statement on "smart meters"

European Union Smart Grid Project

University of Washington Smart Grid Project (UK guide to electric and magnetic fields and health's "Smart Meter" page:

International Commission on non-ionizing Radiation Protection