Temperature

Temperature - the amount of heat energy in a body (degrees Celcius oC or Kelvin K ), can be measured in a number of ways: Volume changes As fluids and gases heat up they expand. Mercury and alcohol bulb thermometers use this principle to indic...

Temperature - the amount of heat energy in a body (degrees Celcius ^oC or Kelvin K ), can be measured in a number of ways:

Volume changes
As fluids and gases heat up they expand. Mercury and alcohol bulb thermometers use this principle to indicate temperature. SUch instruments cannot be considered sensors as they cannot provide data for automatic logging.

Bimetal strips expand at different rates. This expansion is amplified mechanically for use mainly in chart recorders and applications requiring low accuracy.

Non-contact sensors use beams of light in the infra-red wavelengths, to infer the surface temperature of a target. (Hot surfaces absorb less of the beam).

Thermistor based thermometers offer a high degree of accuracy with a fairly limited temperature range (typically from -50 to +180C).

Thermocouples are made of two types of metal wire, which generate a small current when the junctions are at different temperatures.
T-type thermcouples (Copper and Constantan) provide high accuracy over a smaller range than do K-type thermocouple based thermometers. These which offer a much wider measuring range as is required in a blast furnace for example or pottery kiln.