When it's cold, we walk over and turn up the thermostat, and when it is hot, we walk over and turn on the air conditioner to cool us down. But, how does that little box on the wall no ifs ands or buts control the temperature of our homes or offices?
A mechanical thermostat is no ifs ands or buts a very easy device. It is basically a thermometer attached to a switch that turns on your heater, either your heat source is natural gas or electricity. If you take off the cover of your thermostat, you will see the inner workings and get a better idea of how a thermostat works.
The top layer holds a mercury switch and a thermometer coil. The mercury switch is just a small vial filled with the liquid metal, mercury. Within this vial are three wires: one at the lowest of the vial; one at the left of the vial; and one at the right of the vial. As the temperature rises or cools, the vial of mercury gets tipped to the right or the left manufacture the corresponding wire come into touch with the wire that runs along the bottom. If the mercury gets tipped to the left, a association is made that creates a current that energizes a relay, which starts the heater and circulation fan. As the room heats up, the vial levels off and once that is in balance, the association is broken causing the heater to turn off. If the mercury switch is tilted to the right, other relay causes the air conditioner to turn on.
What tips the vial in either direction is the thermometer coil that rests against the vial of mercury. The thermometer coil is constructed of a bi-metallic strip made of two dissimilar types of metal, ordinarily copper and iron, which are bonded together. Because the dissimilar metals retort to heat at dissimilar levels, this strip contracts and expands causing the coil to curl up or uncurl as the temperature changes. This curling or uncurling petition tilts the mercury vial, which then signals the heating source to kick off or on. When you adjust the temperature knob on your thermostat, you are no ifs ands or buts adjusting the tightness of the coil.
Beneath the top layer of your thermostat, you will see the circuit board, which houses the wires that no ifs ands or buts lead to the circulation fan and heat source. The circuit board is connected to the mercury switch via a metal screw and wire, which "reads" the switch and turns on the suitable heating or cooling device.
Newer on the shop are digital thermostats. These thermostats differ from the mechanical thermostats in that they use a thermistor, a resistor whose electrical resistance changes with temperature. The microcontroller in a digital thermostat measures the resistance and converts that amount to a temperature reading. Digital thermostats can save vigor because they can be programmed to turn the heat or air conditioning off or on at preset times throughout the day. For example, you can set the air conditioning to come on an hour before you come home from work, or have the heater remain off during the hours while you work and then turn on an hour before you get back so your home is warm and cozy when you open the door.
How Does a Thermostat Work?