The ordinary glass thermometer is also a complete system. Again the bulb is the sensor but the column of liquid and the scale on the glass is the processor and indicator. Mercury is used for hot temperatures and coloured alcohol for cold temperatures.
Figure
The problems with glass thermometers are that they are
· Brittle
· Mercury solidifies at -40oC.
· Alcohol boils at around 120 oC.
· Accurate manufacture is needed and this makes accurate ones expensive.
· It is easy for people to make mistakes reading them.
Glass thermometers are not used much now in industry but if they are, they are usually protected by a shield from accidental breakage. In order to measure the temperature of something inside a pipe they are placed in thermometer pockets.
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