On Mon, 18 Oct 2010 11:41:03 -0500, "David"
wrote:

Drivel: US DoE can't figure out how to measure microwave oven
power
output.
http://www.federalregister.gov/articles/2010/07/22/2010-17773/energy-conservation-program-for-consumer-products-test-procedure-for-microwave-ovens-repeal-of
Sigh.

Jeff Liebermann

Your tax dollars at work, Sigh^2.
David

Yeah, it's really a tough problem. Never mind IEC-705 which has been
around since 1990.
http://www1.eere.energy.gov/buildings/appliance_standards/residential/docs/krtp1003.txt

Place about a liter of water in the oven. Measure temperature. Apply
power. Measure temperature again after a specific cooking time.

Power = (Volume_of_water) x (Temp_rise) x 4.1868 / (Cook_time)

4.1868 is joules/calorie (specific heat of water)
Power = Watts
Volume = Cubic centimeters or Milliliters
Temp rise = Celsius
Cooking time = Seconds

Every oven I've tested (6 ovens) with a liter flask and about a minute
runtime has resulted in measurements of 15% to 30% less than the rated
power. If a use more water and a longer runtime, even less (because
the magnetron decreases in RF output as it gets hot). This is not
because the manufacturers all lie, but because the IEC-705 standard
method generates inflated results for power output. This might also
offer a clue why the DoE can't seem to find a workable procedure that
produces the same results as IEC-705.

I've also measured the efficiency of these ovens. All are about 60%
(using the above test procedure).

Perhaps what's needed is a multi-million dollar research grant to
study methods of measuring microwave oven power output. However,
should such a study succeed, I'm certain the method will be ultra
complexicated and designed to sell plenty of specialized hardware and
certified testing labs. With luck, maybe even a bureaucracy to
oversee the muddle.

Hint: Don't use a big heavy Pyrex glass bowl as it becomes part of
the thermal mass and wrecks the results. Use thin chemistry glassware
or if really careful, light plastic bowls. A 10C to 20C temp rise is
sufficient. No need to boil the water. Don't leave the thermometer
inside the oven when running. Let the water temperature stabilize for
30 seconds or more at the end of a run as microwave heating is rather
uneven.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558