How to Make a Dial Thermometer
A thermometer may be any device that measures temperature. The bulb thermometer is the most familiar type of thermometer, but dial thermometers are also very common. A dial thermometer is most useful for controlling temperature and relies on a bimetallic strip. These types of thermometers are especially common in ovens and refrigerators.
Instructions
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1
Make a bimetallic strip. Metals expand at a relatively constant rate and different metal expand at different rates. By attaching two strips of metal to each other, you have a strip of metal that curls at a constant rate in response to changes in temperature.
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2
Roll a long bimetallic strip into a spiral so that the metal that expands the fastest when it's heated is on the outside of the spiral. A longer strip will be more sensitive to changes in temperature, but the spiral provides a more compact shape.
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3
Place the bimetallic spiral into a container. Attach the end of the spiral that's in the center to the center of the container. When the temperature increases, the end of the spiral will move around the container at a fixed rate.
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4
Attach a dial to the outer end of the bimetallic spiral. Create a temperature scale on the cardboard by calibrating the thermometer against known temperatures. This configuration will allow you to measure the temperature according to the position of the dial.
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Install the dial thermometer in an oven to control its temperature. In this application, the oven begins to heat when it's turned on, which causes the bimetallic spiral to expand. When the outer end of the spiral reaches a point specified by the temperature setting, it closes a circuit which causes the oven to maintain its present temperature.
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