[time-nuts] temperature sensor

jim s jwsmail at jwsss.com
Mon Jul 21 16:51:35 EDT 2014

On 7/21/2014 11:36 AM, Hal Murray wrote:
> docdailey at gmail.com  said:
>> >Ice water and boiling water coupled with altitude will give you two points.
> Has anybody used a good thermometer to measure air pressure?
> How much does the measured temperature vary between just barely boiling and a
> good roiling boil?  Or in various locations within a pot of boiling water?
When you are dealing with water phase changes, you are dealing with both 
temperature and heat.  When you get up to a point like boiling, you have 
a mass of water which is at the local boiling point and the only thing 
stopping the water from going to steam phase is the amount of heat in 
the water.  Once a pot of water is at rolling boil all of the water in 
the pan should be at and stay at the boiling point till it is all gone.

Once you remove the heat, the boiling will slow and stop, and the 
temperature will begin to fall as the water loses the heat.

As long as you maintain a balance between having the sensor too close to 
the point you are applying heat, and keeping it immersed in boiling 
water, you should be able to assume the local boiling point.  That 
boiling point has to be adjusted for pressure, which affects the temp 
the most.  Also assuming only water, and no other contaminants as 
mentioned by another poster.

The same sort of action occurs when water freezes, along with some other 
oddball issues with the crystalization.  You can arrive at the freezing 
point, and you will dwell there for some time as the water loses its 
heat and becomes solid.

The thing that is different between freezing and boiling is that as long 
as you have water and are boiling the temperature will remain at 
boiling, and no higher.

With freezing, if you are measuring water as you cool it and remove 
heat, it will go thru freezing with a pause as it goes to ice, then it 
can continue to cool as cold as you like.

so when you are measuring by using ice as a reference, you should have 
frozen the sensor or drilled it into the center of a block of ice, and 
let it come to equilibrium in the ice w/o any freezing apparatus being 
active.  It should come to the freezing point till all of the ice melts.


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