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A temperature change is converted into mechanical displacement by the following temperature sensor:
  • A
    a thermo-couple.
  • B
    a Bourdon tube.
  • C
    a bi-metallic strip.
  • D
    a resistance.
Small piston engine aircraft usually use a direct reading thermometer to have an OAT indication in the cockpit. These instruments are of simple construction and do not need a power supply. The sensing element is called a bi-metallic strip and consists of two strips of dissimilar metals welded together and forming a helix. A pointer is mechanically connected to one end of the coil. As the bi-metallic helical element is heated, it will coil and uncoil as one metal expands faster than the other. This differential expansion will move the pointer over a temperature graduated dial.

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