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Temperature sensors
Team Members
Imtisal-e-Noor
Arooj Fatima
Taibah Jaffery
Farhan YaqoobAyaz Naveed
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temperature
Temperature
Energy level of matter
Evidenced by some physical change in matter
Temperature sensorMeasure temperature by some change in physical
characteristic.
Critical parameter for several processes andoperations
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Two basictypes oftemperature
sensors
Contact
type:
Measure their owntemperature.
Makes use ofconduction
Non-contact
type:
se convection andradiation to monitor
changes in temperature
Type of temperature sensors
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Thermocouple
!esistive temperature devices" !T#s and thermistors$
%imetallic devices
&i'uid e(pansion devices
Molecular change of state sensor
)ilicon diode temperature sensor
*nfrared temperature sensor
Contact Type Temperature )ensors
Non-contact Type Temperature )ensor
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WORKING PRINCIPLE: Converts thermal energyinto electrical energy.
%ased on the difference inthe conductivities of the two
wire metals that thethermocouple is made of+ at
a given temperature.This conductivity differenceincreases at highertemperatures andconversely+ the conductivitydifference decreases atlower temperatures.
)everal types based on thecombination of metals used
Thermocouple
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Advantage:)elf powered
)imple
*ne(pensive
,ide temperature range
isadvantages:Cold unction compensation
&east sensitive
&east stable
E(tension leads re'uired
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oltage
arying parameter
/st order 0dy1dt 2 y 3 k4"t$
5rder
-678 to /798 C
!ange
6-9 sec
!esponse time
)teel industry Thermoelectric cooling )afety
pplication
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WORKING PRINCIPLE: converts thermalenergy to resistance
,orkingChange in resistance with
change in temperatureTwo types ; !T# igher initial cost than thermocouples
&ess rugged in high vibration environments.
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.aryingparameter
!esistance
5rder !T#-linearThermistor-&inearoverashortrange?rdorderbeyondthisrange-)teinhart->artE'uation
!ange
!T#:-688to988CThermistor:-@8to6A8C
!esponsetime
!T#:6-9secThermistor:/-6sec
pplication Te(tileindustriesChemicalindustries4oodindustries
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WORKING PRINCIPLE: converts temperaturescale into motion.
,orkingMade of two pieces of
metal are put together orglued together into one.Every metal has differentcoefficient of e(pansion+ ifthe two pieces of metalthat has united thedifferent e(pansion
coefficients of the secondoint of the metal will bendwhen heated.
%imetallic devices
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Advantages:*ne(pensive
=ortable
)imple construction without leads
No power supply re'uired
isadvantages:&imited accuracy and sensitivity
alues cannot be easily recorded
Easily de-calibrated due to mechanical shock
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aryingparameter
E(pansion
pplicationMechanical clock
Thermostats
>eat engine
Circuit breaker
Electric *ron
5rder&inear
!ange
-/8 to //8 C
!esponse tim4ast
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WORKING PRINCIPLE:smiconductor diodes havetemperature-sensitive voltage vs. current characteristics
,orking*f two identical transistors areoperated at different but
constant collector currentdensities+ then the differencein their base-emitter voltagesis proportional to the absolutetemperature of the transistors.This voltage difference is thenconverted to a single endedvoltage or a current. n offsetmay be applied to convert thesignal from absolutetemperature to Celsius or4ahrenheit.
)ilicon diode temperature sensor
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Advantages:
Cryogenic temperature sensorEasy to interface with other electronics for display and
control
ccurate
*ne(pensive
ra!ba"#s:&imited temperature range "-@8 to 2/68BC typical$
)ome devices are inclined to oscillate unless
precautions are taken
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!ange
-99 to /98 C
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WORKING PRINCIPLE: li'uid e(pands as it get warmer
,orkingElements and compoundse(pand as their
temperature increases.&i'uids or solids thate(pand at a constant rateover the desiredtemperature range areused so that the amountthey have e(panded can
be measured andcompared against knowne(pansion rates todetermine the temperature
Thermometers
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dvantagesCheap
#urable
Easily calibrated
#isadvantages#isplay is harder to read
)low response
4ragile
Cant be used for thermograph
#oes not work below freeing point
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WORKING PRINCIPLE: )tate of material changes dueto change in temperature.
%asically these sensorsmeasure the change instate of a material due to avariation in temperature.These are non electric
devices and serve auni'ue purpose.Commercially availabledevices of this type are inthe form of labels+ pellets+crayons+ or lac'uers.
Change-of-state labelsindicate temperature in B4and BC.
Change of state sensors
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Advantages:,hen re'uirement is a non-reversing indication they are 'uite useful
small+ rugged+ indicator that continuously updates temperature )implest devices employed for fast measurement of temperature.
vailable in variety of shapes+ sies and forms.
Comparatively cheaper than other temperature sensors.
Measure a wide range of temperature.
ra!ba"#s: !esponse time is comparatively slow
Not as accurate as some other types
Most of these devices are meant for one time use only
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.aryingparameter)tate
change
5rderModerately
linear
!esponsetimeslow
pplicationChemical%iological
sensing
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WORKING PRINCIPLE: at specific temperature +certainintensity of infrared radiations emits
Every form of matterwith a temperatureabove absolute eroemits infrared radiation.
The cause of this is theinternal mechanicalmovement ofmolecules. The intensityof this movement
depends on thetemperature of theobect.
*nfrared sensors
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*nfraredintensity
aryingparameter
=lancks&aw
E(ponential
5rder
-98 to ?888C
!ange
4ast
!esponse time
%rewing Meteorolog
y
Climatologypplication
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Comparison 5f %asic Temperature Types
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Comparison 5f %asic Temperature Types
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Conclusion
The sensors we have discussed above all have their
own uni'ue features.
the decision of which one to use will be based upon the
re'uirement )ince most sensor choices overlap in temperature
range and accuracy+ selection of the sensor will depend
on how it will be integrated into a system.
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