Temperature is a physical magnitude that expresses the degree or level
of hot or cold in our bodies or in the environment. In the international
system of units, the unit to measure temperature is the Kelvin. Below we will
speak generally about other units for the temperature measurement.
Firstly, we must distinguish between two categories of measurement units for
temperature: absolute and relative measurement units.
- Absolute are those related to absolute zero which is the lowest
theoretical temperature possible and corresponds to the point at which
molecules and atoms have the lowest level of thermal energy.
- Kelvin (international system): represented by the letter 'K' and
does not use the "º" symbol representing degrees. It was created by William
Thompson upon the basis of degrees Celsius, establishing point zero as being
absolute zero (-273.15
ºC) and keeping the same dimensions for degrees. This
was established as part of the international system of units in 1954.
- We call relative units because they compare with an established physical-chemical
process that always produces the same temperature.
- Degrees Celsius (international
system): or also referred to as degrees centigrade is represented by this
symbol: ºC. This unit of measurement defines the freezing point of water as
being 0º and the boiling point of water as being 100º, both measurements at
an atmospheric pressure and divided into a scale of 100 equal parts in which
each one corresponds to 1 degree. This scale was proposed by Anders Celsius,
a Swiss physicist and astronomer, in 1742.
- Degrees Fahrenheit (international system): this takes the division of the
points between freezing and evaporation of an
ammonium chloride solution. This was proposed by
Gabriel Fahrenheit in 1724, establishing zero and one hundred in the scale as
being the freezing and evaporation points of
ammonium chloride in water. This used a mercury
thermometer in which was introduced crushed ice and ammonium chloride in
equal parts. This concentrated saline solution gave the lowest possible
temperature in the laboratory at that time. Later, another mix of crushed ice
and pure water was used, to determine the point of 30ºF, which after was fixed
(fusion point of ice) and later the thermometer showed
water vapour occurred
(boiling point of water). The difference between these points is 180ºF, that is divided into
180 equal parts determining degrees Fahrenheit. The PCE-T395 thermometer can
measure in degrees Celsius and in Fahrenheit.
Conversion table for temperature units of measurement: