RE: drying slides in a microwave

From:Abizar Lakdawalla

RE: drying slides in a microwave

Steven, the completely on and completely off is not strictly true, there are a range of domestic microwave ovens which use pulse width modulation, I think Panasonic calls its "inverter" technology, which modulate the average power and are not completely on or completely off.


> -----Original Message-----
> From: Steven Slap []
> Sent: Thursday, March 28, 2002 6:51 AM
> To: HistoNet Server; Melissa Jensen
> Subject: drying slides in a microwave
> 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
> **********************************************
> Marketing Manager/Microwave Product Specialist
> Hacker Instruments & Industries, Inc.
> **********************************************
> --

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