Temperature transducers: Embarrassment of riches

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Temperature transducersEmbarrassment of riches

• Most material properties change as a function
  of temperaturelength, density, resistivity,
  Youngs modulus What about specific heat Hs?
• Nitinol demo shape memory alloy
• What we most passionately want a sensor
  providing voltage output
• Diode current
• Platinum strip
• Thermistors
• Thermocouples

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http//www.nitinol.com/
Shape setting refers to the process used to form
Nitinol. Whether the Nitinol is superelastic or
shape memory, in the cold work or straightened
condition, it is often necessary to form the
material into a new memory shape. This is done
by firmly constraining the material into its new
shape in a fixture or on a mandrel and then
performing a heat treatment. The heating method
can be an air or vacuum furnace, salt bath, sand
bath, heated die, or other heating method. The
temperature should be in the range of 500-550C
with higher temperatures resulting in lower
tensile strengths. Cooling should be rapid to
avoid aging effects, a water quench is
recommended. The heat treatment time should be
such that the material reaches the desired
temperature throughout its cross-section.
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Fever strips color change in cholesteric liquid
crystals Measure change in reflected light
eformsnews.blogspot.com/2007/10/how-e-paper-works.
html
rose chafer beetle www2.cnrs.fr
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Specs accuracy / range speed of response
spatial localization
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• What we really want is not temperature-sensitive
  shape, or temperature-sensitive color, but
  temperature-sensitive voltage, for direct input
  into electronic instrumentation
• We will see that desire for voltage in pure
  form, with thermocouples, but for now
• How does increasing temperature affect
  resistivity? of metals? of semiconductors?
• The case of the diode

but
What man most passionately wants is his living
wholeness and his living unison, not his own
isolate salvation of his soul. Man wants his
physical fulfillment first and foremost, since
now, once and once only, he is in the flesh and
potent. For man, the vast marvel is to be alive.
For man, as for flower and beast and bird, the
supreme triumph is to be most vividly, most
perfectly alive. Whatever the unborn and the dead
may know, they cannot know the beauty, the marvel
of being alive in the flesh. DH Lawrence
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Interlude sensing heat by capturing photons E
hn Demo IR sensing (camera)
http//www.flir.com/US/
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Interlude 2 Bimetallic strip
howstuffworks.com
www.diracdelta.co.uk/science/source/b/i/bimetallic
strip/source.html
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Bimetallic strip thermal expansion coefficients
a from S.E. Derenzo, Interfacing, Prentice-Hall
(1990)
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Platinum temperature standard From Derenzo,
page 157 "Platinum is a noble metal that can
withstand high temperature and harsh chemicals
with good stability."
The problem measuring resistance normally
involves passing current through the resistor,
thereby heating up the componentJoule heat
I2R
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Thermistors (Lab 5) sintered semiconductor
material
TE is a property of the semiconductor material
used to make the thermistor. Boctor and Ryff
suggest a nominal value of 4000 deg K
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Power-in will equal power-out at asymptotic
temperature equilibrium
?T Ttherm - Tamb
While the self-heat temperature is increasing,
mass is storing energy
The Leaky Integrator again!
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Comes then our humble servant the Lab 5 FTQ
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Thermoelectric effects and thermocouples

• Seebeck effect (passive diffusion)
• Thomson effect (heat differential EMF)
• Joule effect (I2R heating)
• Peltier effect (cooling by pumping electrons)

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Electrons speed up or slow down under the
influence of contact potential difference. In the
first case the kinetic energy of the electrons
increases, and turns into heat. In the second
case the kinetic energy decreases and the joint
temperature falls down. ixbtlabs.com/articles/pel
tiercoolers/
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Attaching N and P doped elements in series
If electrons are forced from the low mobility to
the high mobility side, the effect is like an
expanding gas in a refrigerator, and the junction
will be cooled.
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More elements in series
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Mammals sensing temperature

• Peripheral vs central locations of sensing
• In the skin, two types sensors for
  warmer sensors for cooler
• Warm range 30-45C
• Cold range 10-35C
• Once skin is taken below 10C, cold receptors
  stop firing and cold becomes a good local
  anesthesia
• Temperature-sensitive proteins in sensor cell
  membranes open channels for Na or K

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Mammalian temperature sensors

• Firing rates of skin sensors obey power laws as
  a function of ? temperature
• When the body becomes too warm, blood vessels in
  the skin dilate, allowing heat to escape through
  the surface of the skin. Special glands called
  sweat glands produce a salty secretion called
  perspiration that evaporates off the surface of
  the skin, taking heat with it. When the body
  becomes too cold, the opposite processes occur.
  Sweat glands are shut down, and blood vessels in
  the skin constrict, keeping the blood away from
  the surface of the body, where heat could be
  lost. In addition, the muscles begin to contract
  rapidly and shiver, which generates significant
  heat.www.sparknotes.com/testprep/books/sat2/biol
  ogy/chapter9section1.rhtml
• If hypothalamic neurons sense temperature less
  than normal, then metabolism, and muscle activity
  (including shivering) will be increased.
• If hypothalamic neurons sense core temperature
  greater than normal, they trigger responses like
  cooling by evaporation of sweat.

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Fever

• Increased core temperature may be due to athletic
  activity, or fever, or high ambient temperature.
• Fever is due to toxins released by infecting
  bacteria or virus.
• The toxins affect membrane proteins in membranes
  of temperature-sensitive neurons. An abnormally
  higher response threshold is set.

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A mammals reaction to high or low ambient
temperature

• How can a mammal cool itself when the ambient
  temperature is 110?
• How can a mammal warm itself when the ambient
  temperature is 20?