Hi Histonetters!

Melissa Jensen wrote about trying to melt paraffin from slides in a kitchen
microwave.  Those of you who don't care how microwaves work, delete NOW!

A magnetron in a kitchen microwave oven is either on or off.  When it's on,
it's on at full power.  When it's off, it's off (no power).  You can't rely
on the wattage on the box to tell you the true output power-  you have to
calibrate your individual microwave.  Fortunately, it's easy:

Take 1 L of distilled water at room temperature and measure the temperature
with an immersion thermometer.  Heat it in the microwave at full power for 2
minutes.  Shake the container.  Take the temperature again.  Subtract the
starting temperature from the ending temperature.  Multiply the differance
in temperature by 35 to determine the output power in watts.  Repeat twice
to determine a plus-or-minus variation.

Now that you know the output power at full power, you need to be able to
calculate the power outputs at less than full power.  For this, you also
need to know the duty cycle.  To produce 50% power, the magnetron is on at
full power for 1/2 of the duty cycle (usually 10-20 seconds) and off for 1/2
of the duty cycle.  Take a stopwatch or the second hand of a watch, set your
microwave at 50% power, and turn it on and listen.  The magnetron will come
on, go off, and come on again.  The time period from when the magnetron
comes on the first time to when it comes on again the second time is the
duty cycle.  This is set by the manufacturer and cannot be changed.

Melissa's problem is that she is trying to get an oven cycling on and off at
some output power close to 1000 watts to behave like an oven producing an
output power of less than 700 watts.  When her new oven is in the on cycles,
it is too hot.  When it is in the off cycles, the slides are cooling.

best regards,
Steven Slap

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Marketing Manager/Microwave Product Specialist
Hacker Instruments & Industries, Inc.
http://www.hackerinstruments.com
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