Water Boil Detector

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haklesup
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Post by haklesup » Fri Nov 02, 2007 12:55 pm

Sharp makes it

http://www.sharpusa.com/products/Functi ... 49,00.html

This link just shows the microwave drawer oven but they also have the same thing integrated into a range with a conventional oven and electric cooktop. I think it is mostly a style choice but would be useful in a small kitchen of a single or couple. Wouldn't need to take up counter space but you give up some oven space.

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MrAl
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Post by MrAl » Fri Nov 02, 2007 6:29 pm

Hi again,

Oh ok i see what they are doing now. It is basically to save space
in the kitchen.

Oh yeah i almost forgot to mention...
If the line voltage is relatively constant in your area then you
can also use a variac to control the cooking power level.
Turn the variac down a little to get less cooking power.
Min voltage is about 85 volts i think, as that will produce little
or no cooking at all. I guess you would have to calibrate the dial
somehow too...possibly based on how long it takes to boil a cup of
water from say 60 deg F and repeat at different levels and do the
math. A styrofoam cup works pretty well.
LEDs vs Bulbs, LEDs are winning.

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MrAl
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Post by MrAl » Sat Nov 03, 2007 10:50 am

Hello again,


I did a few actual tests last night. Here's what happened.

The thermo probe is inserted into one of the slots in the back where
the hot air comes out. The humidity meter is about 6 inches away
from the slots but in the direct path of the hot air as it gets blown out.


First, the temperature goes up pretty fast. It reached 122 deg F
just as the foam started to appear. Problem is, turning the oven off
and let it rest for a few minutes and the temperature comes
back down to 106 deg F and then starting up again on power high
it starts to foam at 110 deg F. This means the temperature isnt
*directly* related to the foaming, but then maybe if i do it the
same way each time it will be.

Also, and most interesting, is that the humidity goes *DOWN* as
the oven heats up. Big shocker there. I could only imagine that
the heated inside of the oven is not getting the air from the inside.
This means the humidity sensor would have to be put inside the oven
for this measurement to work.
BTW my humidity meter only goes down to 20 percent and anything
lower than that shows up as the text "LO" which indicates it's too low
to be measured by that meter.


Here is how it went...

[Spaghetti]

Put in water, ambient T=88degF, H=24%
Set count down timer for 11:00, Power high
at timer=5:00 T=102 deg F
at timer=0:00 T=114 deg F, H=20%
Put in salt, stir, put in spaghetti
Set timer =10:00 T=105 deg F, H=21%
at timer=6:00 T=116.4 deg F, H="LO"
at timer=5:00 T=118.0 deg F, H="LO"
at timer=0:00 T=121.8 deg F, H="LO" (foam appears)

Set timer for 8:00 on power 3 to cook spaghetti.
at timer=0:00 stopped

Set timer for 6:00 on power high (106 deg F)
at timer 5:00 had to stop because of foaming ( 110deg F)

Set timer for 5:00 on power 3 to finish cooking.


As a side note, i also realized that my pot has a glass top that sort of
slants down at the sides so perhaps a laser beam could be directed
to point in one side and out the other. When the foam appears it is
quite cloudy so it would prevent the beam from getting to a sensor
mounted on the other side of the oven.
I wonder now if the usual laser pointers are good enough to be used
for this as the thing would have to be running for around 10 minutes
constantly (continuous duty) unless i pulsed it but then i would need
to build a circuit just for pulsing.
The only drawback to this is that if i ever broke the pot top and had
to get another one i might not be able to find one with that kind of
top so i would not be able to use the laser method like that again.
LEDs vs Bulbs, LEDs are winning.

rshayes
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Post by rshayes » Sat Nov 03, 2007 11:02 am

Some of the hot air exhausted from a microwave oven may be the cooling air for the magnetron, and may not be related to the cooking at all.

Temperature measurement might not be a good way to detect boiling. When the water reaches the boiling point, the temperature will stay constant at the boiling point until the water has boiled away. The heat of vaporization of water is quite high, and additional heat goes into vaporizing the water rather than raising its temperature above the boiling point.

The humidity sensor has a better chance of working, since I would expect the humidity to increase abruptly as the water boils.

arealperson
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humidity sensor

Post by arealperson » Sun Nov 04, 2007 11:40 pm

Hi: For a low cost humidity sensor have you tried running a lead pencil over a piece of paper?

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haklesup
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Post by haklesup » Mon Nov 05, 2007 11:26 am

Hi: For a low cost humidity sensor have you tried running a lead pencil over a piece of paper?
How would that work? Are you making a resistor that changes as the paper absorbs water?

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MrAl
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Post by MrAl » Mon Nov 05, 2007 12:52 pm

Hi again,

I havent tried any humidity sensors yet, just my meter which happens
to have humidity too but it only goes down to 20 percent.
Also, as i wrote before i would have to put it in the oven with the
pot because the air coming out goes down in humidity as
the pot cooks.
LEDs vs Bulbs, LEDs are winning.

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Joseph
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Post by Joseph » Tue Nov 06, 2007 12:44 pm

I wonder about the possibility of visually detecting steam condensation on the door window.

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MrAl
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Post by MrAl » Tue Nov 06, 2007 2:14 pm

Hi Joe,


Well, i dont usually see any steam on the front door when it starts to
foam up.

I also did a second test, and this time it didnt start to foam until the
temperature rose to 140 degrees F. Im not sure though if this
difference is because the sensor might have been moved a little
from where it was the first time. The third test will tell me this.
LEDs vs Bulbs, LEDs are winning.

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Joseph
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Post by Joseph » Tue Nov 06, 2007 4:30 pm

Hi Al,
I like how you've reported on your measurements. I was not the greatest at lab reports for science classes. I would have felt good having you in my lab group.

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MrAl
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Post by MrAl » Tue Nov 06, 2007 6:14 pm

Hi again,

Well thanks Joe :smile:
I hope this works one way or an other.
LEDs vs Bulbs, LEDs are winning.

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