Thermometer
A thermometer is a device used to measure and display the temperatures. This field of study of thermometry.
General principles
Most thermometers measure their own temperature (that of his party used to measure). This temperature is that of the environment if there is thermal equilibrium between the thermometer and the environment.
This means, for example, if a thermometer is exposed to sunlight, it will be warmer than the air, and that this temperature difference depends entirely on its color and its breakdown, and therefore a temperature measured in these conditions is totally fantastic compared to the air temperature. (That's why meteorologists measure temperature in ventilated shelter.)
Temperature measurement can be based on the expansion and the pressure body (solid, liquid or gaseous), or any other physical property (electrical changes in the case of the thermocouple, the color of light emission for high temperatures, etc.. ) which varies with temperature. This general principle is implemented in many different ways as needed (temperature ranges measured, type of materials to study, etc..). The usual liquid thermometers are thermometers and mercury thermometers alcohol, but it is also possible to find thermometers rapeseed oil.
The applications are many thermometers, meteorology, medicine, cooking, for regulation in industrial processes, etc..
Invention of the thermometer
The first thermometer was invented in 1654 by the Duke of Tuscany in Florence.
He was 50 graduations. In winter it down to 7 degrees and climbing in summer to 40 degrees. As the ice melts, it showed 13 degrees.
Progress in the eighteenth century
Rene-Antoine Reaumur Ferchault in 1730 built the first thermometer 'spirit of wine', the former name of ethanol. Towards the middle of the eighteenth century, two types of mercury thermometers received centesimal a division between the melting point of ice and boiling water.
In 1702, the Danish astronomer Ole Roemer makes an alcohol thermometer marking the boiling water at 60 ° and crushed ice to 7.5 °. In 1717, the German scientist Gabriel Daniel Fahrenheit replaces alcohol with mercury and the thermometer gives its final form. It also offers the first temperature scale to be adopted widely enough, setting to 32 ° F temperature of melting ice and 96 ° F the normal blood temperature: 32 ° F is the melting point of ice and 212 ° F is the boiling point of water under normal atmospheric pressure.
In 1730, Reaumur, French naturalist and physicist, built the alcohol thermometer for which he was using the 0-80 scale, where zero is the freezing point of water, and where 80 is the boiling point of alcohol (spirit of wine), as Reaumur tended to be confused with the boiling water.
The Swedish physicist Anders Celsius in 1741 built a mercury thermometer calibrated so that 0 corresponded to the point of boiling water, and 100 to the freezing point of water, which was used from 1742 to 1750 at observatory of Uppsala.
The Celsius scale was then calibrated in the opposite direction of the centigrade scale we know today. Only after the death of Celsius, which occurred in 1744, his colleagues, we think that the initiative came mainly the famous Swedish naturalist Carl von Linne-reversed directions of the Celsius scale to give it its present form, namely 0 for the freezing temperature of water, and 100 to its boiling point. Indeed, in 1745, Linnaeus presented to the Swedish Academy and a mercury thermometer marking 0 ° for the melting ice and 100 ° for the boiling water.
At the same time, the permanent secretary of the Academy of Fine Arts in Lyon, Jean-Pierre Christin (1683-1755), built by the architect Peter Lyons Casati a mercury thermometer scale centesimal bottom, it presented March 19, 1743 at the public meeting of the academy.
The Swedish Celsius thermometer and the thermometer of Casati Lyons would have had a limited use if the French Revolution had given the world the modern metric system, and if the Commission on Weights and Measures, established by the Convention, n 'decided in 1794 that "the degree thermometer [would] be the hundredth part of the distance between the end of the ice and the boiling water.
Thermometer for professional use
Thermometers for professional use are highly accurate. They have a very large measuring range and high speed acquisition. They can display two temperatures with a calculation of Delta T. Thermometers for professional use can be used with a protective cover against shock, dust and moisture. They are used with different probes according to use:
* Air probe
* Clamp probe for measurement on a pipe, plates, etc..
* Sensor for air / gas / liquid
* Contact probe
* Thermocouple Probe
* Probes immersion / penetration
* Sensors to measure surface temperature
* Etc..
Depending on the needs probes are equipped with different sensors. The type of measure will set the probe type. The choice of suitable probe depends on several criteria:
* The measurement range
* Accuracy
* Response time
* Robustness
* Form
The types of sensors
* Thermocouple
* Platinum resistance sensor (Pt100)
* Thermistor (NTC)
Thermometers for professional use are also infrared measurements without contact or distance
They are used for measuring temperature:
* Air Conditioning
* Liquid
* Pipe
* Air
* Warm room
* Oven
* Oven
* Powders
* Etc..
Thermometers for food
There are different types of thermometers. The thermometers used in the minutes in the health checks, must comply with the decree of July 1997. These thermometers have probes with sensors variable resistance (NTC = resisatnce temperature coefficient negative), or Pt100 resistance of 100 ohms at 0 ° C. This ensures through standards, uncertainties closer and a better measurement accuracy.
The ranges of this type of material (usually between -200 and 600 ° C for Pt100 and -50 to +150 ° C for NTC) can cover all traditional applications in food processing.
The exact measurements are essential to heart, they are intrusive and destructive.
There are also means of control such as thermometers operating by receiving infrared radiation, to control very quickly uniformity of temperature. The accuracy of this thermometer has limited its use therefore requires training and awareness of the interpretation of results. Infrared temperature measurement of the film or packaging and not the heart of the product.
Read also
wikipedia
