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Temperature (and humidity) measurement: Difference between revisions
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Temperature (and humidity) measurement (view source)
Revision as of 08:43, 11 July 2014
, 11 July 2014→Diurnal Variation measurements
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This is the same cooling effect as you experience by going into a thick fog, or when you perspire a lot on exposed skin.
== James Six and Diurnal
A thermometer can be modified to hold a register of an extreme temperature (i.e. allows that extreme to be read at a time that suits the observer). It is called a Six's thermometer after the Briton, James Six, who invented the maximum and minimum registering thermometer still used today.
Colourless Alcohol on the lowest measuring side of a U-shaped glass tube expands and contracts with temperature. A liquid (which traditionally was mercury, but now is a coloured liquid that does not mix with the alcohol) pushes a slider along as the alcohol contracts for lower temperatures, but when the alcohol expands as it warms again, it passes beside the slider, therefore allowing the smallest temperature to be registered. Gravity, shaking, or a magnet are used to move the slider back against the coloured liquid to reset the Six's Thermometer.
On the highest side of the u-tube, there is a vacuum between the coloured liquid and the end of the tube and the slider in there registers the highest temperature and is reset the same way as the lowest register. Resetting once a day at a standard time stores the diurnal temperature observations. Whilst mercury was very good at pushing the sliders on its two ends, replacement liquids are unreliable, so the ban on use of mercury has effectively ended the use of the James Six design in meteorology.
An alternative way of achieving registration (preserving the value) is to have a narrow bore tube (minimum volume to be affected by expansion/contraction) with a capilary constriction separating off the bulb (that does contract but becomes isolated from the narrow bore tube permitting it to continue displaying the highest temperature). This design was used for the traditional clinical body temperature measurement, also largely abandoned following the mercury ban.▼
▲An alternative way of achieving registration (preserving the value) is to have a narrow bore tube (minimum volume to be affected by expansion/contraction) with a capilary constriction separating off the bulb (that does contract but becomes isolated from the narrow bore tube permitting it to continue displaying the highest temperature). This design was used for the traditional clinical body temperature measurement.
=Temperature Scales=
Temperature scales use a unit called degrees apparently because some early thermonmeter designs were based on circular tubes containing liquid and had 360 equally spaced markings on them as a rough way of reporting relative 'temperatures' before any formal scales based on calibrated points was introduced.
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