¤Do you think you could use a normal thermometer to measure the surface of the sun? ¤Special thermometers have been developed to measure extreme conditions or special situations ¤Each of these special thermometers contain a sensor – material which is affected by changes in temperature ¤The sensor produces a signal – information about temperature, such as an electrical current ¤The signal affects the responder – a pointer, light or other mechanism that used the signal in some way
The Thermocouple
¤In a thermocouple, wires made of two different metals are twisted together ¤When the wire tips are heated, a small electrical current is generated ¤The amount of current depends on the temperature of the wires ¤The current from the thermocouple can be used to turn on a switch or valve ¤They are used to measure extremely high temperatures where normal devices would fail as the liquid in them would boil
The Bimetallic Strip
¤The bimetallic strip is made of two different metals joined firmly together ¤As the strip is heated one metal expands more than the other ¤The strip is then forced to coil more tightly and the opposite occurs when cooled ¤Movement of the strip can operate a type of electrical switch ¤Usually used in furnaces, air conditioners, refrigerators, etc
The Recording Thermogram
¤The recording thermometer uses a bimetallic strip that coils and uncoils as the temperature changes ¤One end of the strip is attached to a light metal lever that holds a special pen ¤The pen writes on a large drum lined with paper that rotates once every seven days and keeps track of temperature over a week
The Infrared Thermogram
¤Objects don’t have to be glowing red hot to give off radiation ¤Anything warmer than absolute zero gives off IR (infrared radiation) – similar to light but undetectable to your eyes ¤Infrared radiation can be photographed with special films or detected by sensors that display images on screens