Technical Guide/Reference and FAQs

Temperature Measurement

The most commonly known method of measuring temperature is with the liquid filled glass thermometers that are attached to buildings to measure air temperature or inserted in your mouth to measure internal body temperature.  These are based on the principle that the liquid will expand or contract inside the glass tube depending on the external temperature.  It is understood that physical temperature effects all matter by increasing its volume when heated and decreasing volume when cooled.  This is not the only way that temperature effects the physical world.  Temperature has an effect on many different material properties that can be recorded and measured.

Besides physical volume, temperature effects electrical properties as well.  A change in temperature effects the conductivity or resistance of any material.  In the case of conductors, a change in temperature will actually create an electrical voltage.  In the case of insulators, a change in temperature will effect the level of resistance of the material.

Temperature measurement devices or sensors can be separated into two categories: Contact and Non-Contact.  Contact sensors are the most popular and inexpensive.  There is a broad variety of contact sensors.  Non-contact sensors are newer technology that are more expensive, but usually more accurate.

Below is a list of the different types of temperature sensors that are currently available.

Contact Sensors
	Thermocouples
	RTD's
	Thermistors
	Liquid-In-Glass Thermometers
	Gas and Vapor Thermometers
	Filled System Thermometers
	Bimetal Thermometers
	Semiconductor Thermometer Devices
	Phase Change Thermometers
Non-Contact Sensors
	Radiation Thermometers