Page 214 - Robot Builders Source Book - Gordon McComb
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5.4 Temperature Sensors 201
FIGURE 5.40 Thermocouple-based
temperature sensor.
2. The phenomenon of thermal expansion of solids and liquids can be utilized in
temperature sensors. For example, a bimetallic strip, as shown schematically in Figure
5.41, is an effective on-off temperature sensor. The bimetallic strip 4 consists of two
different metallic strips 1 and 2 welded together. When heated or cooled this strip
bends because the thermal expansion coefficients of each layer are different. (The strip
is flat only at one specific temperature value.) As a result, contact 4 touches immov-
able contact 3, thus closing gap A.
In Figure 5.42 an expansion thermosensor based on a liquid is schematically shown.
The liquid is contained in capsule 1, which is located on or attached to the measured
element. When heated or cooled the liquid changes its pressure because of its change
FIGURE 5.41 Bimetallic "on-off"
temperature sensor.
FIGURE 5.42 Temperature sensor based on
TEAM LRN
thermal expansion of liquid.
