'Setting' a thermostat?

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Main Question or Discussion Point

Recently, my hot water geyser wasn't heating water.. so I called up the electrical guy and he came to repair it. I don't know what he did, since I wasn't home when he repaired it.. my mom said that he 'set' the thermostat at 65 deg. C.

How exactly do you 'set' a thermostat? Since it's just a bi-metallic strip, how can u so finely graduate it to such a setting? and it's not just with the geyser.. even home heaters and ACs use similar kind of thermostats. How are they 'set' to certain temperatures?
 

Answers and Replies

mgb_phys
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Bimetal strips normally have an adjustable screw that makes the other side of the contact. You could - if you were bothered - set it by putting it in a pan of hot water at the right temperature and adusting the screw until it just closed.
I imagine commercial ones are (sort-of) calbrated
 
berkeman
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Mechanical thermostats expand with temperature, changing a mechanical position of an electrical contact. The mechanical position of the contact is pretty well definied by the temperature that is being sensed. So by rotating or moving the whole assembly, you can bias the fixture to make electrical contact at lower or higher temperatures. If you just take the cover off of any thermostatic control, its operation is pretty intuitive.

See if this wikipedia article helps some:

http://en.wikipedia.org/wiki/Thermostat
 
russ_watters
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The reason you can get fine adjustment over the thermostat is that the bimetallic strip is coiled, which magnifies the motion created by a change in temperature.

Now if all this repair guy did was set your thermostat, he didn't really repair anything.
 

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