Concept of Temperature and Thermometers by acrc213

VIEWS: 91 PAGES: 33

									                                  INTRODUCTION


I. TEMPERATURE AND THERMOMETERS

     The words temperature and heat are used together so often that they may appear
to mean the same thing. Although temperature and heat are closely related, they are
definitely not the same thing. Temperature is a property of an object related to the
average kinetic energy and not a property of an object. One of the effects heat can have
when it enters an object is to increase its temperature.
     We measure temperature because good health is associated with a range of
normal temperature. First and foremost, we check it to look for fever. Physicians have
recognized fever as a sign of illness since ancient times several thousand years before
Christ, although they have not known exactly what causes it until the 20th century
(Atkins, 1991). In the late nineteenth century, bacteria and other microorganisms were
identified as able to induce fever, but how they did it was not known. Then, in the latter
part of this century, scientists identified a substance they called “endogenous pyrogen”
which later became a generic term for more specifically identified substances found at
the cellular level and identified with the help of DNA cloning. We also measure body
temperature to track the thermal effect of environmental exposure - hypothermia and
hyperthermia - and to monitor and control deliberate warming or cooling of the body for
therapeutic purposes. Finally, we check temperature to monitor for possible thermal
side effects of certain drugs.
     A thermometer is used in health care to measure and monitor body temperature. In
an office, hospital or other health care facility, it allows a caregiver to record a baseline
temperature when a patient is admitted. Repeated measurements of temperature are
useful to detect deviations from normal levels. Repeated measurements are also useful
in monitoring the effectiveness of current medications or other treatments.
     Many of the thermometers we see and use are made of a thin glass tube
containing a liquid. The temperature is measured by observing how far up the tube the
liquid rises. However, we have already seen that α is not a constant so that liquid




                                                                                            1
expansion is not uniform and the rise in the liquid is not linear with temperature. Worse,
different liquids have different nonlinear expansions.
     We could pick a standard substance and all agree to measure temperature by the
expansion of this substance, but it is unsatisfactory to have our measuring devices tied
to particular substances. It would be best if we had a temperature measuring device
which was independent of any particular material.


II. THERMAL EXPANSION
     Most materials expand when their temperature is increased and contract when it is
decreased. This property is in part due to the increase in average kinetic energy of
molecules with increasing temperature. The increased average speed of the molecules
causes an increase in the average separation of the molecules. The amount that an
object expands depends on its size, the material of which it is made, and the size of the
temperature change. The quantitative expression for the amount of linear thermal
expansion in an object is ∆L=Lα∆T where ∆L is the change in the length L of the object,
∆T is the change in temperature of the object and α is its coefficient of linear expansion.
     If the length of the side of some object increases with temperature, then so does its
surface area and volume. The effects of thermal expansion are visible in many places
other than thermometers. Bridges are designed with sliding joints at both ends so that
they may expand and contract without buckling. Standard railroads are constructed with
gaps where rails are joined together to allow for expansion and contraction. The
creaking and pinging sounds made by a stove when it heats up are due to its catching
and slipping as it expands.
     Water is an important exception to the general rule that substances expand with
increasing temperature and contract with decreasing temperature. Water behaves
“normally” at most temperatures, but if it is cooled at about 4ºC, it will expand with
further cooling until it reaches 0ºC. At 0º water freezes to ice, in the process expanding
even further. When ice is cooled below 0ºC, however, it contracts as most substances
do. The effects of the expansion of water with decreasing temperature, especially the
expansion of water when it freezes, are far ranging. Water freezing in pipes or engine
cooling systems can damage them irreparably. Damage done to foods when they are



                                                                                              2
 frozen is due primarily to cells burst by the expansion of water turned to ice. Some
 foods tolerate being frozen better than others, but none tolerate repeated freezing and
 thawing.


III.   BRIEF HISTORY

        1596. Galileo Galilei is often claimed to be the inventor of the thermometer.
 However, the thermoscope could not strictly be called a thermometer: since a
 thermometer is an instrument that must measure temperature differences; Galileo's
 thermoscope did not do this, but merely indicated temperature differences. The
 predecessor to the thermometer, the thermoscope is a thermometer without a scale; it
 indicates differences in temperature only i.e. it can show if the temperature is higher,
 lower or the same, but unlike a thermometer it cannot measure the difference nor can
 the result be recorded for future reference.
        1612. The Italian, Sanctorio Sanctorius (1561-1636) is generally credited with
 having applied a scale to an air thermoscope at least as early as 1612 and thus is
 thought to be the inventor of the thermometer as a temperature measuring device.
 Santorio's instrument was an air thermometer. Its accuracy was poor as the effects of
 varying air pressure on the thermometer were not understood at that time.
        1654. The sealed liquid-in-glass thermometer, more familiar to us today, was
 invented by the Grand Duke of Tuscany, Ferdinand II (1610-1670). His thermometer
 had an alcohol filling. Although this was significant, his thermometer was inaccurate and
 there was no standardized scale in use.
        1714. Gabriel Fahrenheit (1686-1736) was the first person to make a
 thermometer using mercury. Combined more predictable expansion of mercury with
 improved glass-working techniques led to a much more accurate thermometer.
 He used the discovered fixed points to devise the first standard temperature scale for
 his thermometer. He divided the freezing and boiling points of water into 180 degrees.
 The value 32 was chosen as the figure for the lower fixed point as this produced a scale
 that would not fall below zero.
        1868. Carl Wunderlich published research findings of body temperature from
 over 1 million readings in over 25,000 patients made with a foot-long thermometer used


                                                                                         3
in the axilla. Wunderlich's principal contribution was the establishment of a range of
normal temperature from 36.3 to 37.5°C. This was popularized in the U. S. by Edouard
Seguin, who translated it from German. Seguin also is believed to be the first clinician
in the U. S. to use the term "vital signs".

The degree Celsius (°C) is a unit of temperature named after the Swedish astronomer
Anders Celsius (1701–1744), who first proposed a similar system in 1742. The Celsius
scale sets 0.01 °C to be at the triple point of water and a degree Celsius to be 1/273.16
of the difference in temperature between the triple point of water and absolute zero.
Until 1954 the scale was defined with the freezing point of water at 0 °C and the boiling
point at 100 °C at standard atmospheric pressure, this definition is still a close
approximation to the actual definition and is for that reason commonly (but wrongly)
used to refer to the scale.

Since there are one hundred graduations between these two reference points, the
original term for this system was centigrade (100 parts) or centesimal. In 1948 the
system's name was officially changed to Celsius (a third name which had also been in
use before then) by the 9th General Conference on Weights and Measures (CR 64),
both in recognition of Celsius himself and to eliminate confusion caused by conflict with
the use of the SI centi- prefix. While the values for freezing and boiling of water remain
approximately correct, they are no longer suitable as reference points for a formal
standard. The current official definition of the Celsius scale sets 0.01 °C to be at the
triple point of water and a degree to be 1/273.16 of the difference in temperature
between the triple point of water and absolute zero. This definition was adopted in 1954
at the 10th General Conference on Weights and Measures, the very same definition
given for the kelvin. For the practical calibration of thermometers, the International
Temperature Scale of 1990 defines many additional reference points.

http://en.wikipedia.org/wiki/Celsius

Fahrenheit is a temperature scale named after the German physicist Gabriel
Fahrenheit (1686–1736), who proposed it in 1724.



                                                                                         4
In this scale, the freezing point of water (1 E2 K) is 32 degrees Fahrenheit (written "32
°F"), and the boiling point is 212 degrees, placing the boiling and melting points of water
180 degrees apart. Thus the unit of this scale, a degree Fahrenheit, is 5/9ths of a kelvin
(which is a degree Celsius), and minus 40 degrees Fahrenheit is equal to minus 40
degrees Celsius.

There are several competing versions of the story of how Fahrenheit came to devise his
temperature scale. One states that Fahrenheit established the zero (0 °F) and 100 °F
points on his scale by recording the lowest outdoor temperatures he could measure,
and his own body temperature. He took as his zero point the lowest temperature he
measured in the harsh winter of 1708 through 1709 in his home town of Gdańsk
(Danzig) (-17.8 °C). (He was later able to reach this temperature under laboratory
conditions using a mixture of ice, ammonium chloride and water.) Fahrenheit wanted to
avoid the negative temperatures which Ole Rømer's scale had produced in everyday
use. Fahrenheit fixed his own body temperature as 100 °F (normal body temperature is
closer to 98.6 °F, suggesting that Fahrenheit was suffering a fever when he conducted
his experiments or that his thermometer was not very accurate), and divided his original
scale into twelve divisions; later dividing each of these into 8 equal subdivisions
produced a scale of 96 degrees. Fahrenheit noted that his scale placed the freezing
point of water at 32 °F and the boiling point at 212 °F, a neat 180 degrees apart.

The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base
units. It is defined as the fraction 1/273.16 of the thermodynamic (absolute) temperature
of the triple point of water.

A temperature given in kelvins, without further qualification, is measured with respect to
absolute zero, where molecular motion stops (except for the residual quantum
mechanical zero-point energy). It is also common to give a temperature relative to the
Celsius temperature scale, with a reference temperature of 0° C = 273.15 K,
approximately the melting point of water under ordinary conditions.




                                                                                          5
The kelvin is named after the Scottish physicist and engineer William Thomson, 1st
Baron Kelvin; his barony was in turn named after the River Kelvin, which runs through
the grounds of the University of Glasgow.

Thermodynamics (from the Greek thermos meaning heat and dynamis meaning
power) is a branch of physics that studies the effects of changes in temperature,
pressure, and volume on physical systems at the macroscopic scale by analyzing the
collective motion of their particles using statistics. Roughly, heat means "energy in
transit" and dynamics relates to "movement"; thus, in essence thermodynamics studies
the movement of energy and how energy instills movement

Units of temperature

The basic unit of temperature (symbol: T) in the International System of Units (SI) is the
kelvin (K). One kelvin is formally defined as exactly 1/273.16 of the temperature of the
triple point of water (the point at which water, ice and water vapor exist in equilibrium).
This puts the freezing point of water (which cannot be measured with high precision)
and the zero point of the Celsius scale at 273.15, not 273.16. The (unattainable)
temperature 0 K is called absolute zero and corresponds to the point at which the
molecules and atoms have the least possible thermal energy. An important unit of
temperature in theoretical physics is the Planck temperature (1.4 × 1032 K).

In the field of plasma physics, because of the high temperatures encountered and the
electromagnetic nature of the phenomena involved, it is customary to express
temperature in electronvolts (eV) or kiloelectronvolts (keV), where 1 eV = 11,605 K.

For everyday applications, it is often convenient to use the Celsius scale, in which 0 °C
corresponds to the temperature at which water freezes and 100 °C corresponds to the
boiling point of water at sea level. In this scale a temperature difference of 1 degree is
the same as a 1 K temperature difference, so the scale is essentially the same as the
Kelvin scale, but offset by the temperature at which water freezes (273.15 K). Thus the
following equation can be used to convert from degrees Celsius to kelvins.




                                                                                          6
In the United States, the Fahrenheit scale is widely used. On this scale the freezing
point of water corresponds to 32 °F and the boiling point to 212 °F. The following
formula can be used to convert from Fahrenheit to Celsius:




                                                                                    7
                          TYPES OF CLINICAL THERMOMETERS


I. DIRECT:
    1. LIQUID EXPANSION
               Liquid-in-glass thermometers are simple devices consisting of a bulb
      attached to glass chamber filled with liquid, column marked with a measurement
      scale.
                                                                 Clear
                                                                 glass




                                                                          Lens
                                                                          front




                 White
                backing
                                                                           Capillary


                           <<cross section of a liquid-in-glass thermometer>>



             a) PARTS
                   This type of thermometer is a small tubular instrument of rather thick
             glass. It consists essentially of a small vacuum tube of uniform bore closed
             at one end and connected at the other with a chamber (either a bulb or a
             short tube of larger bore). A Celsius or a Fahrenheit scale (or both) is
             etched on the front of the thermometer; opposite this the glass is milky or
             semiopaque, to facilitate reading the temperature.


             b) PRINCIPLE OF USE
                   Liquid-in-glass thermometers rely on the simple principle that a liquid
             changes its volume relative to its temperature. Liquids take up less space


                                                                                         8
when they are cold and more space when they are warm. As the liquid in
the bulb heats up, it expands and begins to rise into the column. When it
reaches equilibrium, the liquid stops rising. The level of the liquid is read
against the scale on the column and the result is called a temperature.
      The liquid is sometimes colored alcohol but can also be a metallic
liquid, mercury to be specific. Both mercury and alcohol grow bigger when
heated and smaller when cooled. Inside the glass tube of a thermometer,
the liquid has no place to go but up when the temperature is hot and down
when the temperature is cold. Numbers are placed alongside the glass tube
that mark the temperature when the line is at that point.


c) PRECAUTIONS ON USAGE
      MERCURY-IN-GLASS




                 <<RECTAL>>                         <<AXILLARY>>



              A mercury-in-glass thermometer is a thermometer consisting
       of mercury in a glass tube. Calibrated marks on the tube allow the
       temperature to be read by the length of the mercury within the tube,
       which varies according to the temperature.

          • ADVANTAGES
                 Mercury's unique characteristics are perfect for measuring
          temperatures for the following reasons: It has large and uniform
          expansion abilities, its silvery appearance allows for easy reading,
          & its ability to remain a liquid over a wide range of temperatures.



                                                                                9
   • DISADVANTAGES
           When liquid mercury (also known as elemental or metallic
   mercury) is spilled, it forms droplets that can accumulate in the
   tiniest of spaces and then emit vapors into the air. Mercury vapor
   in the air is odorless, colorless, and very toxic. Most mercury
   exposures occur by breathing vapors, by direct skin contact or by
   eating food or drinking water contaminated with mercury.
           Health problems caused by mercury depend on how much
   has entered your body, how it entered your body, how long you
   have been exposed to it, and how your body responds to the
   mercury. All mercury spills, regardless of quantity, should be
   treated seriously.
           Since   then,   mercury   thermometers    have     become
   increasingly rare, as mercury is highly and permanently toxic to
   the nervous system. Many countries have banned them outright
   from medical use.

ALCOHOL-IN-GLASS




     Similar to mercury-in-glass thermometer but contains colored
alcohol.



                                                                    10
               • ADVANTAGES
                      It is less toxic than a mercurial thermometer

               • DISADVANTAGES
                    Alcohol has a density smaller density of 0.79 g/cm 3
               [compared to the density of mercury = 13.6 g/cm 3] The density of
               an object depends on its temperature because the size of an
               object changes with temperature. If the size of an object increase
               when its temperature is increased, then the same amount of
               mass occupies a larger volume. With alcohol, there is greater
               increase in volume, requiring either a longer stem or a wider
               capillary tube.


2. CHEMICAL - DOT MATRIX OR PHASE CHANGE
        Plastic strips or adhesive patches that indicate a temperature in
  response to the thermal change in chemical dots are referred to as dot matrix
  or phase change thermometers.

        a) PARTS




             The chemical dot thermometer has 50 dots (temperature sensors)
        on the distal end of a flexible polystyrene plastic strip; each dot
        represents a temperature increment of 0.1[degrees]C over a range of
        35.5[degrees]C to 40.4[degrees]C.
             Single-Use Clinical Thermometer is an individually wrapped,
        disposable instrument for accurately measuring body temperature. A




                                                                               11
sensor matrix at the tip of the thermometer consists of temperature-
indicating dots.


b) PRINCIPLE OF USE
     These devices vary in usefulness depending on their resolution. If
the smallest unit they can display is a full degree, they are probably of
limited value. But if they can give readings in tenths or 2 tenths of a
degree, they are as useful as other types of thermometers.


       b.1) DOT MATRIX. Each dot contains a different combination of a
chemical mixture that will melt and change colour from beige to bright
blue at a specific temperature. Temperature readings are indicated by
the number on the thermometer that corresponds with the last blue dot.
       The device registers a temperature within 60 seconds and can be
read after waiting an additional 10 seconds for a stable measurement;
the last dot to turn blue constitutes the body temperature.


       b.2) LIQUID CRYSTAL DISPLAY. A chemical thermometer may
be made by impregnating spots of liquid crystal material onto a spatula.
If mixed with suitable dyes the transition from solid to liquid phase is
demonstrated by the color of the spot. The spots can be arranged to
change color in increments of 0.2F over the clinical temperature range
such that the number of spots changing color indicates the temperature.
Liquid crystal paints are also available which can be used to




                                                                         12
                demonstrate temperature distribution by color over parts of the body.




       To understand liquid crystals, we must return again to the microscopic structures
of solids and liquids. Crystalline solids are highly ordered materials. The spacing
between particles in a crystal is so regular that, once you know exactly where a few of
the particles are located, you also know exactly where millions of other nearby particles
are located. This regularity is called positional order. The particles in a crystal are also
highly oriented, so that if you know the orientations of a few particles, you also know
exactly how millions of other nearby particles is oriented. This second regularity is called
orientational order. In contrast, normal liquids don‟t have positional or orientational
order. Knowing the positions and orientations of a few particles in a liquid tells you little
about the positions and orientations of nearby particles.


       Liquid crystals lie in between solids and liquids. Like normal liquids, liquid
crystals have little positional order. Knowing where some of the particles in the liquid
crystal are won‟t help you locate other nearby particles. But liquid crystals do have
substantial orientational order. Liquid crystals are composed of rod-like or disk-like
molecules that align themselves with one another, even though their positions are free
to change. These molecules move about like those in a normal liquid but they remain
highly oriented, like those in a crystalline solid. Hence the name “liquid crystal.”




                                                                                           13
http://images.google.com/imgres?imgurl=http://www.barrettresearch.ca/teaching/liquid_
crystal/mesogen-
nematic.jpg&imgrefurl=http://www.barrettresearch.ca/teaching/liquid_crystal/LC02.htm&
h=232&w=80&sz=6&tbnid=1vp2o7Kek82CCM:&tbnh=103&tbnw=35&hl=en&start=2&pr
ev=/images%3Fq%3D%2522liquid%2Bcrystal%2522%2Bpositional%2Border%26svnu
m%3D10%26hl%3Den%26lr%3D

       The molecules in the liquid crystal thermometer are made of cholesterol, and are
called cholesteric liquid crystals. The molecules are rod-shaped. The rods form layers in
the liquid crystal, the rods in adjacent layers running in a slightly different direction from
those in the layer above or below. From one layer to the next the rods form a structure
like the stairs of a spiral staircase. The spiral staircase rises through some distance
before the molecules twist around parallel to their original direction.

       Liquid crystals are actually quite common in biological systems. For example, cell
membranes in animals are liquid crystals. Among the most familiar liquid crystals are
the pearly, iridescent liquid hand soaps and shampoos. Their striking optical properties
come about because of their remarkable orientational order. Liquid crystals interact
strangely with light, a feature that makes them useful in electronic watch displays and
computer screens. It‟s just such a strange interaction between a liquid crystal and light
that makes a plastic film thermometer work.


       The liquid crystal used in a thermometer is not quite as simple as that. The liquid
crystal used in a thermometer is a chiral nematic liquid crystal, which has a natural twist



                                                                                            14
to it so that the preferred molecular orientation spirals around like a corkscrew, as you
look across the liquid in one particular direction. A chiral nematic liquid crystal still has
only orientation order, but that orientational order is a complicated spiral one.
       The spiral orientation of its molecules gives the chiral nematic liquid crystal a
twisting, wave-like appearance. It even has “crests,” where the molecules all tend to
point up and down, rather than to the side. The spacing between adjacent crests is
called the pitch, the same word used to describe the distance between adjacent threads
on a screw. The pitch of a chiral nematic liquid crystal is responsible for its remarkable
optical properties.




http://chirality.swarthmore.edu/RecentTalks/GenIV_files/slide0009_image012.gif


       This pitch may be only a few tens of nanometers or many microns, depending on
the liquid crystal‟s chemical composition and on its temperature. Increasing the
temperature shortens the pitch. This dependence of pitch on temperature is what makes
liquid crystal thermometers possible. In a particular chiral nematic liquid crystal, there
may be a narrow range of temperatures over which the pitch of the spiral is equal to the
wavelengths of visible light in that liquid. When the liquid crystal‟s temperature is in this
range, it suddenly begins to reflect colored light!
       For example, if at 28 °C the pitch of a particular liquid crystal is equal to the
wavelength of blue light, then that liquid will appear brilliantly blue when illuminated by
white light because it will reflect blue light back toward your eyes. If at 26 °C, the pitch is
longer and is equal to the wavelength of red light, then the liquid will appear red. If at 24
°C, the pitch is longer than the wavelength of any visible light, then the liquid will reflect
only infrared light and will appear transparent. This phenomenon is called selective
reflection and is caused by constructive interference, a wave behavior.


                                                                                             15
       Why should cold crystals with closely spaced layers reflect red light and warmer
more spread out layers reflect blue light? The resolution of this problem came when I
found out that the temperature affects not only the spacing of the layers but the twist
angle from one layer to the next. When the liquid crystal warms up the layers spread
apart slightly, but, in addition, each layer of rods rotates a little more relative to the later
below it. This means it takes fewer layers and therefore a shorter distance between
layers of parallel rods. So when the temperature increases the spacing between layers
in which the rods are parallel decreases. The color goes from red when cold to blue
when hot.

       The liquid crystals are usually encapsulated, packaged in microscopic plastic
spheres. This allows the material to be cut. They are also thermally rugged which allows
them to be laminated to protect them from hard handling in a high temperature
laminating machine.

       A plastic strip thermometer contains a series of different chiral nematic liquid
crystals that are viewed through clear number-shaped openings in the otherwise
opaque strip. Behind each temperature number is a liquid crystal that reflects visible
light only at the temperature represented by that number. Because the liquid crystals
have black plastic behind them, they appear black unless they are selectively reflecting
light. For any given temperature, only one patch of liquid crystal is selectively reflecting
light and it illuminates the number corresponding to the strip‟s temperature.




                c) PRECAUTIONS ON USAGE

                      The plastic strips can be placed in the oral cavity, in the axilla, and
                in the rectum with a special covering. They are not for use in the ear.
                When using them, the clinician needs to bear in mind the same issues
                pertaining to the site being measured as has been discussed elsewhere.

                      Good tissue contact is essential. Some dot matrix thermometers
                are very sensitive to storage temperatures and must be reset if they are



                                                                                              16
exposed to extremes. Others adapt readily. Some retain the reading
while others reset after a short time, so immediate recording is advised.



d) ADVANTAGES & DISADVANTAGES
      A valuable benefit of these devices is that they are disposable
and therefore eliminate the risk of cross contamination between
patients. Of course, this assumes they are disposed of properly.
Reusable versions are available for home use.
     The use of the single-patient use chemical dot thermometers is a
viable alternative due to low cost, and ease of use. Chemical Dot
Thermometers provide a viable option for accurate temperature
measurement when compared with the electronic thermometer in the
orally intubated patient population. Chemical dot thermometers can not
be used in patients at the extremes of temperature: <35.5ºCor > 40.4ºC
Placement of the chemical dot thermometers at times required use of a
tongue blade to move the tongue to ensure accurate placement in the
sublingual pocket.




                                                                            17
II. INDIRECT
     1. THERMOCOUPLE




                                                              Thermocouple




                                                   http://www.answers.com/main/science.jsp



               A thermocouple consists of two junctions at two different metals. If the two
      junctions are at different temperatures, a voltage is produced that depends on
      the temperature difference. Usually one of the junctions is kept at a reference
      temperature such as in an ice-water bath. The copper-constantan thermocouple
      can be used to measure temperatures from -190 to 300ºC. For a 100ºC
      temperature difference, the voltage produced is only about 0.004V (4mV).
      Thermocouples can be made small enough to measure the temperature of
      individual cells.


     2. DIGITAL
               Electronic digital thermometers are well-known and widely used, including
      use for the measurement of body temperature. Such thermometers have several
      advantages including fast response time, ease of reading and the lack of mercury
      or other potentially harmful liquids. Digital thermometers typically utilize a sensing
      element mounted inside a metallic shield, the latter being affixed to a rigid probe


                                                                                             18
(This type of assembly is not readily adaptable to a pacifier thermometer.) The
most common sensor is a thermoresistor (or thermistor). This device changes its
resistance with changes in temperature. A computer or other circuit measures
the resistance and converts it to a temperature, either to display it or to make
decisions about turning something on or off.
       Digital thermometers are one of the electronic devices which is self-
explanatory and which is usually simple to operate with the user‟s manual. It
usually beeps when it finished taking the temperature. There are three major
types of digital: ear digital thermometers, pacifier digital thermometers & oral
rectal, axillary thermometers.


 INFRARED


   A. TYPANIC


       It turns out that the eardrum is an extremely accurate point to measure
body temperature from because the part of the brain that controls our body
temperature which is called the hypothalamus,



                                                      Tympanic




                                                http://www.digitalthermometers.net



                                                                                     19
it shares the same blood supply as the tympanic membrane in the ear. If the core
body temperature alters this can be seen sooner at the tympanic membrane than
at other areas of the body. The problem with the eardrum is that it is so fragile.
You don't want to be touching the eardrum with a thermometer.
     This makes the detection of the eardrum's temperature a remote sensing
problem. It turns out that the remote sensing of an object's temperature can be
done using its infrared radiation. The vibration & movement of molecules in all
matter generate infrared energy. As temperature increases so does the
corresponding molecular activity resulting in increased infrared energy. Infrared
technique is a very good way to detect the temperature of a person's eardrum.

     a) PARTS
      • Tympanic Probe: Provides accurate, reliable temperature readings in
          about one second.
      • Retractable IR Sensor: Innovative design retracts the IR probe when
          not in use and protects the probe if the 9020 is dropped to prevent
          damage.
      • Probe Cover Dispenser: Stores 100 disposable probe covers and
          keeps them clean until use.
      • Integrated     Probe    Cover    Loading       System:   One-step   system
          automatically applies a cover onto the probe before each temperature
          measurement and removes it when finished.
      • One-Piece Construction: Solid ABS plastic design is extremely durable
          and easy to carry from patient to patient.
      • Large LCD Screen: Provides easy to read results from a distance.
      • Farenheit/Celsius Conversion: Temperature readings can be taken and
          displayed in either Farenheit or Celsius.
      • Pulse Timer: Audible tones can be heard at 0, 15, and 30 seconds.
      • Optional Wall-Mounted Thermometer Holder: Allows thermometer to
          be secured to a wall or cabinet to prevent misplacement or theft.




                                                                                20
b) PRINCIPLE OF USE
        Infrared thermometers measure temperature using electromagnetic
 radiation such as infrared emitted from object. By knowing the amount of
 infrared energy emitted by the object and its emissivity.( It is a measure of
 a material's ability to absorb and radiate energy, ratio of the energy
 radiated by an object at a given temperature to the energy emitted by a
 perfect radiator, or blackbody, at the same temperature.) , the objects
 temperature can be determined. The most basic design consists of a lens
 to focus the infrared energy on to a detector, which converts the energy to
 an electrical signal that can be displayed in units of temperature after
 being compensated for ambient temperature variation. This configuration
 facilitates temperature measurement from a distance without contact with
 the object to be measured. As such, the infrared thermometer is useful for
 measuring temperature under circumstances where thermocouples or
 other probe type sensors cannot be used or do not produce accurate data
 for a variety of reasons. Some typical circumstances are where the object
 to be measured is moving; or in applications where a fast response is
 required
        All of the objects around you are radiating infrared energy right
 now. Human beings don't have any sensors that can detect subtle
 differences in infrared, but our skin can detect objects radiating lots of
 infrared energy. . Heat is lost from the body by heat radiation &
 evaporation. The rate at which we produce heat and lose it determines the
 body temperature.       Temperature causes vibration & movement of
 molecules which generate infrared energy. As temperature increases so
 does the corresponding molecular activity resulting in increased infrared
 energy.
           The idea behind the temperature sensor in the ear thermometer is
 to create a device that is sensitive to very subtle changes in infrared
 emission. One common sensor is the thermopile, which can be accurate




                                                                            21
 to a tenth of a degree. The thermopile sees the eardrum and measures its
 infrared emissions


c) ADVANTAGES & DISADVANTAGES
        A valuable benefit of these devices is that they are disposable and
 therefore eliminate the risk of cross contamination between patients.
 However, it requires a stock of fresh probe covers, and, since it measures
 the temperature in the tympanic membrane or ear drum, it can provide a
 much higher temperature reading due to infection in the middle ear (otitis
 media) than is actually true for core body temperature. There is little risk of
 spreading illness to others when fresh probe covers are used each time.


d) PRECAUTION
          To ensure reliable readings it is important to ensure that the
 thermometer points correctly towards the tympanic membrane in the ear.
 For this to occur the nurse needs to slightly pull the ear lobe up and
 backwards to straighten the ear canal. This allows the thermometer to
 obtain a better “view” of the tympanic membrane and therefore operate
 more efficiently.
        Between patients, a clean cover is attached to the probe to prevent
 any cross contamination and the device has a „prompt‟ symbol shown on
 the display to ensure this practice is adhered to.




                                                                              22
   B. TEMPORAL




       For centuries parents have used a hand on the forehead to check for
fever. The temporal artery thermometer takes this same idea and makes it
official, using infrared light to measure temperature from the temporal artery,
which runs across the forehead and down the neck. Simply place the
thermometer's quarter-size probe in the middle of your child's forehead and wipe
it slowly across to the hairline. You'll get a reading in a few seconds. This gentle
thermometer's technology is highly accurate, making it a comparable alternative
to taking a temperature by mouth, ear, or rectum. It's especially useful if your
child is sleeping or has an ear infection.

     a) PRINCIPLE OF USE

              Arterial temperature is the same temperature as the blood flowing
       from the heart. It is the best determinate of body temperature. Under
       normal circumstances, arterial temperature is close to rectal temperature,
       but almost a degree Fahrenheit (or 0.5 degrees Celsius) higher than an
       oral temperature, and 2 degrees Fahrenheit (1 degree Celsius) higher
       than an underarm temperature. The temporal artery thermometer scans
       the forehead area for the temporal artery and it is almost impossible to


                                                                                  23
 miss the artery during a scan unlike of the ear thermometer which is said
 to give inconsistent readings because of inconsistent positioning of the
 probe to the ear.

b) DISADVANTAGE

        A major reason ear thermometers are considered inaccurate by
 medical professionals is because the positioning of the probe in the ear
 canal is inconsistent, thus creating inconsistent readings and frequently
 missing fevers. The temporal artery thermometer scans the forehead area
 for the temporal artery and it is almost impossible to miss the artery during
 a scan. Also, the person whose temperature is being taken does not like
 something inserted in their ear, making good positioning even more
 difficult. The gentle scan across the forehead is comfortable and not
 objectionable. The TemporalScanner has been proven more accurate
 than ear thermometers by a Harvard Medical School study.
        Under normal circumstances, arterial temperature is close to rectal
 temperature, but almost a degree Fahrenheit (or 0.5 degrees Celsius)
 higher than an oral temperature, and 2 degrees Fahrenheit (1 degree
 Celsius) higher than an underarm temperature.
 At times, you can expect larger differences from temperatures taken at
 other body sites. This is because of two main reasons:
    Temporal artery temperature changes faster than temperature taken
     rectally
    Temporal artery temperature is not affected by the things that cause
     oral and underarm temperatures to be misleading. For example,
     drinking, coughing, talking, or mouth breathing can easily affect oral
     temperature, and skin blood flow changes with a fever can easily affect
     axillary temperature.




                                                                            24
 ELECTRONIC


   A. PACIFIER
      Recording a baby's body temperature is an essential part of the
upbringing, care and preventative needs vital to a child's healthy development.
The traditional areas for temperature measurement are rectal, axillary and oral.
The oral method is the most precise for the lay person as the other methods
require adjustments to the actual readings for an accurate temperature. An oral
device is also less intrusive and upsetting to a feverish baby. A pacifier
thermometer would act to soothe and calm a child making the procedure easier
and resulting in more exact readings.

      a) PRINCIPLE OF USE

              A pacifier thermometer have one or more electrical sensors within
      the pacifier nipple. Digital measurement and display units external to the
      nipple is provided. An insulating nipple core can be utilized to improve the
      speed and accuracy of sensor response. Two or more sensors along with
      digital logic selection of the highest constant reading can be used to avoid
      false low readings. Additional conventional features can be provided as
      well.

              A temperature sensing membranes is disposed within a pacifier
      which is provided at a first end with a first portion suitable for insertion into
      the mouth. The second portion at a second end of pacifier opposite the
      first end are where the         plurality of electronic temperature sensing
      membranes, which are mounted in a periphery of first portion, are
      connected. These temperature sensing membranes are thermistors.
      Thermistors are connected to an electronic circuit which is capable of
      processing input temperature information received from the temperature
      sensing members and transmitting said processed input temperature
      information to a display means connected to the circuit.




                                                                                     25
        First portion of said pacifier is provided with an outer sheath and an
 insulating core. The core is made from a resilient foam material. The
 sheath and the core are made from materials selected for high and low
 thermal conductivity, respectively, and high and low heat capacitance
 characteristics, respectively. Circuit display, on-off power switch, and
 electrical battery are housed within said second portion of said pacifier.

        Electronic circuit comprises a number of electronic signal amplifiers
 at a first end corresponding to the number of said temperature sensing
 members. Connected to the circuit is an analog/digital signal converter.
 The converter, connected in series to each said amplifiers, is connected to
 computer microcontroller. The display driving means at a second end of
 the circuit is connected to the microcontroller. Microcontroller inputs
 temperature information received from temperature sensing members and
 compares the received temperature information such that the highest
 temperature information received that remains constant over an arbitrary
 period of time is recognized as a highest temperature reading which will
 be supplied to the display driving means and the display means.


b) DISADVANTAGE

        Pacifier thermometers and skin strips other than Temp-a-Dot brand
 are not considered reliable.




                                                                              26
   B. ORAL, RECTAL AND AXILLARY




                                                http://www.digitalthermometers.net




       DigitaL thermometers can be used orally, rectally and under the arm.
These are precise and durable medical device. Like other digital thermometer, it
either beeps or signals when it finished reading temperature. Some even have
fever alarm feature. These digital thermometers contains detachable probe with
probe cover. These thermometers can operate °F and °C . Some even offer
different languages.

       Almost all brands have a memory feature. It remembers the last
temperature it took. After the function check and display of temperature, it will
start flashing meaning that it is ready to take a temperature. The temperature can
be taken by oral, axillary or rectal method.

       Oral method: Place the thermometer probe under tongue, it must rest in
the correct area with your mouth closed.

       Axillary method: This is an alternative method for babies or very young
children. Although simpler, the axillary method is less accurate and takes longer.



                                                                                     27
The underarm must be dry. Point the thermometer upward and place the tip well
into the patient‟s underarm. The underarm must be kept away from air. When
using this method, the thermometer must be hold securely in place for 2-4
minutes (depending on the manufacturer) ignoring beeps.

       Rectal method: This method is recommended for babies or very young
children who breathe through their mouth. Like the other rectal thermometers,
lubricate the tip with a water soluble jelly such as KY jelly. The patient should lie
on his side, knees slightly bend. If the patient is a baby, place the infant lying on
its stomach with legs hanging down, either across your knee or at the edge of a
bed or changing table. This positions the baby‟s rectum properly for safe and
easy insertion of the thermometer. With one hand, gently slide the tip of the
thermometer no more than ½ inch into the rectum. If you detect resistance of any
kind, stop. Hold thermometer in place during temperature measurement. Once
used rectally, the thermometer should not be used orally, for sanitary reasons.

       There will be beeps which confirm the completion of temperature
measurement. After hearing these beeps, remove the thermometer and read
temperature on display.




     a) DISADVANTAGES
              A rectal temperature is the "gold standard" for establishing the core
       body temperature and can be used at any age. However, people really
       dislike having the thermometer placed in their rectum and protest it
       volubly. Parents should carefully clean the thermometer after each use.
       Otherwise viruses and bacteria can be easily spread among family
       members handling the contaminated thermometer or touching surfaces
       where the thermometer has been placed.
              Axillary temperatures are less upsetting and are actually good
       measures of temperature in newborns, children birth to 30 days of age.
       However, care needs to be taken to place the tip of the thermometer in the
       center of the armpit and to restrain the arm against the side to assure that


                                                                                   28
an accurate temperature is obtained. It might take a few seconds longer to
obtain than a rectal temperature.
      Oral temperatures rely on being old enough to cooperate with
holding the thermometer under the tongue with the lips closed around it.
This is often a challenge for the child with a stuffy nose who cannot easily
breathe well through his or her nose. Again, care should be taken to clean
there thermometer between uses since viruses and bacteria abound in the
mouth and can be shared among family members easily through handling
the thermometer as well as touching surfaces with which the thermometer
has been in contact.




                                                                          29
                APPLICATION: MEASURING BODY TEMPERATURE


I. PHYSIOLOGY

       The body temperature is the difference between the amount of heat produced by
body processes and the amount of heat lost to the external environment.


       Heat produced – Heat lost = Body temperature


       Regulation.   The   balance    between    heat   lost   and   heat   produced,   or
thermoregulation, is precisely regulated by physiological and behavioral mechanisms.
For the body temperature to stay constant and within an acceptable range, the
relationship between heat production and heat loss must be maintained. This
relationship is regulated by neurological and cardiovascular mechanisms. The nurse
applies knowledge of temperature-control mechanisms to promote temperature
regulation.
       Neural and Vascular Control. The hypothalamus located between the cerebral
hemispheres, controls body temperature the same way a thermostat works in the home.
A comfortable temperature is the “set point” at which a heating system operates. In the
home a fall in environmental temperature activates the furnace, whereas a rise in
temperature shuts the system down.
       The hypothalamus senses minor changes in body temperature. The anterior
hypothalamus controls heat production. When nerve cells in the anterior hypothalamus
become heated beyond the set point, impulses are sent out to reduce body
temperature. Mechanisms of heat loss include sweating, vasodilation (widening) of
blood vessels, and inhibition of heat production. Blood is redistributed to surface vessels
to promote heat loss. If the posterior hypothalamus senses the body‟s temperature is
lower than the set point, heat conservation mechanisms are instituted. Compensatory
heat production is stimulated through voluntary muscle contraction and muscle
shivering. When vasoconstriction is ineffective in preventing additional heat loss,
shivering begins. Disease or trauma to the hypothalamus or to the spinal cord, which
carries hypothalamic messages, can cause serious alterations in temperature control.


                                                                                         30
       Heat Production. Thermoregulation depends on the normal function of heat
production processes. Heat is produced in the body as a by-product of metabolism,
which is the chemical reaction in all body cells. Food is the primary fuel source for
metabolism Activities requiring additional chemical reactions increase the metabolic
rate. As metabolism increases, additional heat is produced. When metabolism
decreases, less heat is produced. Heat production occurs during rest, voluntary
movements, involuntary shivering, and nonshivering thermogenesis.
       Heat loss and heat production occur simultaneously. The skin‟s structure and
exposure to the environment result in constant, normal heat loss through radiation,
conduction, convection, and evaporation.
       Basic Mechanisms of Heat Transfer

              radiation........................through space without contact

           Up to 55%-85% of the human body‟s surface area radiates heat to the
           environment. Peripheral vasodilation increases blood flow from the internal
           organs to the skin to increase radiant heat loss. Peripheral vasoconstriction
           minimizes radiant heat loss. Radiation increases as the temperatures
           difference between the objects increases. However if the environment is
           warmer than the skin, the body absorbs heat through radiation.

conduction....................through objects by direct contact

Conduction
In heat flow by conduction, thermal energy represented by the vibration of molecules
moves from one place to another place. The vibrating molecules collide with their
neighbors setting them into motion. A high temperature pulse will naturally propagate
into a low temperature region as the vibrational energy spreads. If a high temperature
pulse which is propagating into a cold metal bar is followed by a low temperature pulse
the high temperature pulse will spread both ways. Into the cold temperatures in front of
it and behind it. This is why heat flow is different from wave motion. Once a wave (of
water, on a string, of sound or light) starts moving in a material it will keep moving
regardless of what happens behind it.



                                                                                      31
           Heat conducts through contact with solid, liquids, and gases. When the warm
           skin touches a cooler object, heat is lost. Conduction normally accounts for a
           small amount of heat loss. The nurse increases conductive heat loss when
           applying an ice pack or bathing a client with a cool cloth. Applying several
           layers of clothing reduces conductive loss. The body gains heat by
           conduction when contact is made with materials warmer than skin
           temperature. Water is an especially good medium for heat transference as it
           conducts heat away from the body 25 times faster than air. That's because it
           is 25 times more dense than air. In the same manner, steel, aluminum and
           copper conduct heat away faster than water. As a rule of thumb, heat loss by
           conduction is about 2% of overall loss. However, wet clothing increases the
           loss to 15%.

convection.....................through air or liquid as contact medium

Convection                                                                            Air is
warmed by conduction, the warmer air rises transporting thermal energy to the
thermometer. Air expands when it is warmed becoming less dense than the surrounding
air and therefore buoyant. Similarly, air falls when it is cooled. Convection occurs when
thermal energy is transported from one place to another by the motion of a liquid or a
gas. We can break convection into two types: natural convection in which the motion is
driven by differences in density of fluids, and forced convection in which the fluid is
moved by pumps or fans.

           Convection is heat transfer by mass motion of a fluid such as air or water
           when the heated fluid is caused to move away from the source of heat,
           carrying energy with it. Convection above a hot surface occurs because hot
           air expands, becomes less dense, and rises. Hot water is likewise less dense
           than cold water and rises, causing convection currents which transport
           energy. Convection can also lead to circulation in a liquid, as in the heating of
           a pot of water over a flame. Heated water expands and becomes more
           buoyant. Cooler, more dense water near the surface descends and patterns



                                                                                          32
          of circulation can be formed, though they will not be as regular as suggested
          in the drawing.

          A fan promotes heat loss through convection. Convective heat loss increases
          when moistened skin comes into contact with slightly moving air. Convection is
          also made more effective by an increase in the velocity of the medium as it flows over
          the warm object.

                                         SOURCES

http://www.brannan.co.uk/thermometers/invention.html
http://www.energyquest.ca.gov/how_it_works/thermometer.html
http://en.wikipedia.org/wiki/Thermometer
http://www.perfusion.com.au/CCP/Physics&Chem/Clinical%20Thermometer%20Types.htm
http://www.graduateresearch.com/thermometry/theory.htm
http://www.graduateresearch.com/thermometry/tips.htm
http://www.epa.gov/epaoswer/hazwaste/mercury/spills.htm
http://www.digitalthermometers.net/placeear.htm
http://www.temperatures.com/sarssensors.html
http://www.temperatures.com/stds-cl.html




   Medical Physics by John R. Cameron; James Skofronick, 1978




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