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THERMOMETER: Digital Probe | -50 Deg.C to +300 Deg.C | Durable for simple lab use

$ 27.00 excl. GST

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[Wikipedia article]

is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer or the pyrometric sensor in an infrared thermometer) in which some change occurs with a change in temperature; and (2) some means of converting this change into a numerical value (e.g. the visible scale that is marked on a mercury-in-glass thermometer or the digital readout on an infrared model). Thermometers are widely used in technology and industry to monitor processes, in meteorology, in medicine, and in scientific research.

Some of the principles of the thermometer were known to Greek philosophers of two thousand years ago. The Italian physician Santorio Santorio (Sanctorius, 1561-1636)[2] is commonly credited with the invention of the first thermometer, but its standardisation was completed through the 17th and 18th centuries.[3][4][5] In the first decades of the 18th century, Daniel Gabriel Fahrenheit made two revolutionary breakthroughs in the history of thermometry. He invented the mercury-in-glass thermometer (first widely used, accurate, practical thermometer)[1] and Fahrenheit scale (first standardized temperature scale to be widely used). These inventions helped usher in the era precision thermometry.

Physical principles of thermometry
Various thermometers from the 19th century.
Comparison of the Celsius and Fahrenheit scales

Thermometers may be described as empirical or absolute. Absolute thermometers are calibrated numerically by the thermodynamic absolute temperature scale. Empirical thermometers are not in general necessarily in exact agreement with absolute thermometers as to their numerical scale readings, but to qualify as thermometers at all they must agree with absolute thermometers and with each other in the following way: given any two bodies isolated in their separate respective thermodynamic equilibrium states, all thermometers agree as to which of the two has the higher temperature, or that the two have equal temperatures.[21]

For any two empirical thermometers, this does not require that the relation between their numerical scale readings be linear, but it does require that relation to be strictly monotonic.[22] This is a fundamental character of temperature and thermometers.[23][24][25]

As it is customarily stated in textbooks, taken alone, the so-called “zeroth law of thermodynamics” fails to deliver this information, but the statement of the zeroth law of thermodynamics by James Serrin in 1977, though rather mathematically abstract, is more informative for thermometry: “Zeroth Law – There exists a topological line M {\displaystyle M} M which serves as a coordinate manifold of material behaviour. The points L {\displaystyle L} L of the manifold M {\displaystyle M} M are called ‘hotness levels’, and M {\displaystyle M} M is called the ‘universal hotness manifold’.”[26]

To this information there needs to be added a sense of greater hotness; this sense can be had, independently of calorimetry, of thermodynamics, and of properties of particular materials, from Wien’s displacement law of thermal radiation: the temperature of a bath of thermal radiation is proportional, by a universal constant, to the frequency of the maximum of its frequency spectrum; this frequency is always positive, but can have values that tend to zero.

Another way of identifying hotter as opposed to colder conditions is supplied by Planck’s principle, that when a process of isochoric adiabatic work is the sole means of change of internal energy of a closed system, the final state of the system is never colder than the initial state; except for phase changes with latent heat, it is hotter than the initial state.[27][28][29]

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Thermometer: Digital Probe

A robust, easy to use, hand held digital thermometer with a stainless steel probe.  The stainless steel probe is resistant to most laboratory chemicals.
Temperature range from minus 50°C to plus 200°C  (2 decimal places).
Reads accurately to 1°C Fast response – about eight seconds.