[Histonet] microwave reproducibility

[Robert Chiovetti]

Gloria,

I agree with Rene, heating a known volume of water in the microwave for about 60 seconds and measuring the change in temperature of the water is probably the best way to document the reproducibility of the microwave.  Just measure the temperature of the water before you heat it, then gently stir the water and measure the temperature again after you've heated it.  Subtract the two and record the increase in temperature.

You'll probably have to experiment with the volume of water you heat, since you'll want to heat the water to a point somewhere below its boiling point.  It would probably be a good idea to make about 3 tests for each power level of the oven, then calculate an average of the 3 readings.  Begin each test with water that's near room temperature.  A good starting point would probably be to heat about 500 ml or 1 L of water for 60 seconds and see what you get.  You can expect some variation in the results, probably a degree or two in temperature, but microwave ovens are remarkably reproducible in this respect.

Heating a volume of water for a set time is the first step in calculating the output (in Watts) of your microwave, and there are formulas to take the results to the next step and actually calculate the wattage of the oven.  The full calculations probably aren't necessary for day-to-day operation, though.  

With age, the magnetron in the oven (the part that emits the microwaves) can gradually become less efficient.  In that case you would notice less of an increase in temperature of the water.  You'll also have records to show whether the magnetron is working properly during normal operation.  Factors like total available power, the condition of the high voltage transformer, the control circuits for the magnetron and lots of other things could affect the microwave's output, so it's a good idea to do this test on a "regular" basis.  That probably means weekly or monthly, I don't know for sure.  Maybe there are others on Histonet who have some suggestions here.

Just be sure to always heat the same volume of water for the same length of time, and you'll have the records you need.

Hope this helps.

Cheers,

Bob

 
Robert (Bob) Chiovetti, Ph.D.
Southwest Precision Instruments
www.swpinet.com 
The Desert Southwest's Microscopy Resource
132 North Elster Drive
Tucson, AZ 85710-3212
Tel./Fax 520-546-4986
Member, Arizona Small Business Association
(www.asba.com)

----- Original Message ----
From: GLORIA MUNOZ <gmmunoz <@t> prodigy.net>
To: histonet <@t> lists.utsouthwestern.edu
Sent: Friday, August 17, 2007 8:36:50 AM
Subject: [Histonet] microwave reproducibility

Hi HistoNetters:
     Just wondering if any of you have a procedure to share on microwave reproducibility for a store-bought, non-medical microwave.  We had our CAP inspection recently and were asked to come up with a method to test the microwave.  The inspector recommended heating distilled water for one minute at each of the three different power levels and documenting the results.  Does anyone know of another, maybe better, way?
     Thanks a lot, enjoy reading your entries, and hope you all have a restful weekend...........gloria
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