[time-nuts] temperature sensor

Bill Dailey docdailey at gmail.com
Mon Jul 21 20:54:55 EDT 2014


You don't use ice as a reference.  With ice water, the same principles apply that apply to boiling water.  This is why these are convenient calibration check points.

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> On Jul 21, 2014, at 3:51 PM, jim s <jwsmail at jwsss.com> wrote:
> 
> 
>> 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.
> 
> Jim
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