[PLUG-TALK] Smart power meters
keithl at gate.kl-ic.com
Sun Oct 13 00:49:59 PDT 2013
On Fri, Oct 11, 2013 at 10:09:11AM -0700, Denis Heidtmann wrote:
> Yikes, this is getting complicated! There are reports (
> which are at opposite ends of the controversy. Issues such as
> unpredictable duty cycles of the transmissions, effects of unpredictable
> reflections on exposure, and finally debates about non-thermal biological
> effects of non-ionizing radiation make coming to any reasonable conclusion
> difficult if not impossible.
> One of the reports mentions the future use of rf transmitters in electrical
> appliances to send power use information to the smart meters. This is news
> to me. Do modern appliances have such things? I guess I am a Luddite.
> Normally I would want to err on the side of caution. I rarely use a cell
> phone, I removed our wireless home phone, but still use a wireless router
> (convenience v.s. caution conflict). There is a smart meter on my house.
> What to do? And what to tell my relative?
Cell phones blast up to a watt of power right next to your head.
The average (assuming a close tower) might be 100 milliwatts (WAG).
Zigbee packets (one of the protocols used for smart power appliances)
uses less than 500 microjoules. If a hypothetical smart appliance
is sending status to a base station with every state change, say a
water heater turning on or off, it might make a few dozen such
signals a day, at many meters distance. Inverse square law applies.
So ... exposure from 10 minutes daily of cell phone / smart phone
exposure? 100mW * 600s / (0.1m)² -> 6000 J/m² per day. We can
assume that the effects, if not zero, are small enough that cell
users live long enough to pay their bills. I imagine we would
all notice if these devices killed every user in less than fifty
years, so the minimum lethal long term exposure is greater than
100 MJ/m² lifetime dose. Probably far, far larger.
Exposure from 24 state change packets per hour, 576 packets per
day, from all your smart appliances, an average of 5 meters away?
576 * 500μJ / (5m)² -> 12 mJ/m² per day, 2ppm of the cell phone
dose. A 50 year dose of that is 200 J/m² (not MJ) lifetime dose.
2ppm of the lifetime cell phone dose, 1/500K, which kills far
less than 100% of cell phone users.
Meanwhile, the death rate from an additional hour of television
watching is about 1/200K, extrapolating from a 104/100K annual
death rate from watching 2 additional hours of television per week.
(see http://tinyurl.com/DeathbyTV ). So, your concerned relative
can watch half an hour less of television, one time, to more than
compensate for a lifetime radio energy dose from a house full of
If you want more accurate numbers for all these things ...
measure them! Assuming you can find a home with smart appliances
in it (Intel may have a demo in the area), ask a well-equipped
ham radio operator to help you measure the actual packet energies.
Keep in mind, though, that many of these are 80 year olds who've
been around kilowatt transmitters all their lives. They will
probably say all the concern about consumer RF exposure is
Nonsense or not, those of us with the ability to read, think,
measure, and calculate have a responsibility to do so, not
parrot third-hand claims that may have been pulled out of
Keith Lofstrom keithl at keithl.com
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