Instruments for measuring temperature

What is a thermometer?

The thermometers are instruments to measure temperature . This is a scalar physical quantity that records the thermal level (heat or cold) of bodies. According to the unit systems , the temperature can be expressed in: Kelvin (K), Celsius (° C), Fahrenheit (° F), Rankine (° R, ° Ra) or Réaumur (° Ré, ° Re).

History of thermometers

Galileo Galilei was the inventor of the thermoscope, what we know today as a thermometer . It was a container made of glass, with a glass tube that was shaped like a sphere at the tip. A mixture of water and alcohol was placed in the container , the hotter it was, the more it went up the tube.

Francesco Sagredo and Santorio Santorio would be the true forerunners of the thermometer as we know them today, since they were the ones who added a numerical scale between the years 1611 and 1613.

How thermometers work

One of the ends of the thermometer is sensitive, it is that part that will have contact with the body or substance that is expected to measure the temperature. The alcohol or mercury will rise through the cylinder, when it no longer rises, the value it reached is recorded on the scale: that will be the temperature of the body or substance .

In the case of digital thermometers, the sensor will take the thermal value of the body or substance and will increase or decrease a numerical value that will reflect the temperature.

Examples of instruments for measuring temperature

These instruments work differently, but all must be calibrated so that they can give a very small margin of error in the measurement.

  • Mercury thermometer: Fahrenheit created this thermometer in 1714, which is still used in some countries. Mercury, the only liquid metal, expands as it experiences changes in temperature.
  • Thermohydrograph : used to record temperature and relative humidity in the area of ​​meteorology.
  • Pyrometer : used to measure too high temperatures typical of factories and others. Returns a somewhat more accurate value than other types of thermometers. They work by taking infrared radiation, with the distribution of thermal radiation or with photoelectricity.
  • Maximum Thermometer and Minimum Thermometer: also known as Six’s thermometer, it is an instrument used in meteorology and horticulture to control the high and low temperatures of the day. .
  • Liquid thermometers: they work with thermochromic liquid crystals. These crystals are encapsulated and embedded in a long piece of flexible, adhesive plastic.
  • Bimetallic foil thermometers: consist of two metal foils with different sensitivity to heat. The sheet with the greatest expansion capacity is folded on the inside.
  • Digital thermometers: uses circuits and sensors that serve to show very small values ​​of temperature.
  • Thermocouple or Thermocouple: it is a transducer created by the union of two metals with a very low potential difference, joined at one end. When this extreme changes its temperature, a voltage is produced whose value represents the registered temperature.
  • Resistance thermometer: they relate the electrical resistance of a body with the temperature. They work by transforming a variation in electrical resistance into a variation in temperature.
  • Gas thermometer: different gases are used that can expand with heat. They work with constant pressure and volume.
  • Thermistors: it is a type of resistance that is more capable of registering variations in temperature than a common resistance.

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