How Do Gas Furnace Thermostats Work?
Warren Johnson is an American inventor and entrepreneur who holds over 50 patents. Johnson first developed the electric tele-thermoscope when he was a professor in Wisconsin. With this invention, the thermostat was born. Does this Spark an idea?
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Electro-Mechanical
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The electro-mechanical thermostat is made from two different metals that are fused together into a strip or coil. These metals expand and contract at different rates with heat, causing the metal to curve and move as the heat changes. A vial of mercury is mounted on the strip. As the strip and vial move, the mercury flows towards two electrical contacts. When the mercury covers the contacts, a circuit is formed. This circuit controls the function of a furnace, turning it on and off.
Electronic
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The electronic thermostat does not have the moving strip of metal to detect temperature changes. It uses electronic sensors to measure temperature change, and to open and close the circuits as appropriate.
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The Anticipator
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The anticipator is a piece of wire with electrical resistance that mounts in the metal strip of a electro-mechanical thermostat. This allows the user to make finer adjustments to the way that the switch operates, and when it turns the furnace on and off.
Mercury Use
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Because of environmental concerns, manufacturers are phasing out mercury in thermostat usage. They are finding other materials to use as substitutes.
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References
- Photo Credit Heizung aufgedreht image by Tribalstar from Fotolia.com
