che171 revised

7/24/2019 CHE171 Revised

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Temperature SensorsTemperature Sensors

Anthony O. Maputi

Kit Dominick Don U. Valle

ChE 171- Chemical Process Dynamic

and Control


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Temperature SensorTemperature Sensor

Two Kinds

Contact

Non-Contact

Main Types

Thermometers

Resistance Temperature Detector (RTD)

Thermocouples


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Contact SensorsContact Sensors

measure the temperature of the obect to !hichthe sensor is in contact by assumin" thermal

e#uilibrium

E$amples%

Thermocouples

ResistanceTemperatureDetectors(RTDs)&ull'ystemThermometers

imetallicThermometers


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Noncontact SensorsNoncontact Sensors

measures the thermal radiant po!er of the

nfrared or *ptical radiation recei+ed from a

,no!n or calculated area on its surface or

+olume !ithin it

E$ample%

Pyrometer


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esistance Temperature Detectoresistance Temperature Detector

!TD"!TD"


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esistance Temperature Detectoresistance Temperature Detector

!TD"!TD"

t is a positi+e temperature coefficient

de+ice

preferred at lo!er temperature ran"es

Two Main Types

Traditional RTDThermistor


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#latinum $ire TDs !#TDs"#latinum $ire TDs !#TDs"

.inear temperature sensors

Characteristics is established and reproducible

.inear positi+e temperature coefficient (-/00 to 002C)3ery accurate and suitable for use as a secondary

standard


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#latinum $ire TDs !#Ts"#latinum $ire TDs !#Ts"


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Schematic Dia%ramSchematic Dia%ram


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Other TDsOther TDs

10 ohms Copper TD & .''()* coe++icients

100 ohms Platinum RTD - 0045 coefficients (ne!)

100 ohms Platinum RTD - 0046/ coefficients (old)

1/0 ohms Nickel TD & .'',*) coe++icient

08 ohms Nickel&-ron TD & .''/0 coe++icients


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Mathematical ModelMathematical Model


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PrinciplePrinciple


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ThermistorThermistor


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9 !ord formed by combinin" thermal !ithresistor

s a temperature-sensiti+e resistor fabricatedfrom semiconductin" materials

The resistance decreases proportionally !ithincrease in temperature

*peratin" ran"e can be -/002C to :10002C



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Thermistors can be in the shape of a rod;

bead or disc


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9d+anta"es%

'mall si=es and fast response.o! cost

'uitability for narro! spans


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Disad+anta"es%


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Thermistor OperationThermistor Operation


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ThermocoupleThermocouple


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is the most !idely used sensor

similar to the RTD; thermocouplepro+ides an electrical measurement of

temperature


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#rinciple#rinciple

?hen / dissimilar metals are oined

to"ether to form a unction; an emf is

produced !hich is proportional to the

temperature bein" sensed


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See1eckSee1eck

2++ect2++ect

The "eneration of current in a circuit

comprisin" of t!o !ires of dissimilar

metals in the presence of temperature

difference


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Thermocouples are identified by a

single letter type and "rouped accordin" totheir temperature range


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-denti+ication-denti+ication


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Metal Com1inationsMetal Com1inations


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AdvantagesAdvantages

Durable

Inexpensive

CompactNo power required


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DisadvantageDisadvantage

Weak and Nonlinear !utput


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23pansion o+ Materials23pansion o+ Materials

Most materials expand when

their is temperature increases dueto intermolecular interaction within

the molecules is sub"ected to atemperature change#


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4illed Thermal System4illed Thermal System

&illed-system thermometers

use the phenomenon of thermal

e$pansion of matter to measure

temperature chan"e


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4illed Thermal System Classes4illed Thermal System Classes

Class 9; -.i#uid &illedClass 9;;C;D -3apour &illed

Class 9; -@as &illed

Class 3 9; -


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$hermometer$hermometer

Mercury Thermometer Alcohol Thermometer


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6imetallic Thermometer6imetallic Thermometer

Effect of une#ual e$pansion of a

bimetallic strips

Different metals ha+e different coefficient

E$ample% brass and steel strip


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Coe++icient o+ 7inear 23pansionCoe++icient o+ 7inear 23pansion


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#yrometers#yrometers9 pyrometer is a type of remote-sensin" thermometer

used to measure the temperature of a surface !ithout

physical contact

measures the amount of heat radiated; rather than the

amount of heat conducted and con+ected to the sensor

it is a de+ice that from a distance determines the

temperature of a surface from the spectrum of

the thermal radiation it emits


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Optical #yrometerOptical #yrometer


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-n+rared Thermometers and Di%ital

#yrometers


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Applications

Smelter -ndustryO8er&the&1ath #yrometer

Tuy9re #yrometer

Steam 1oilers

:ot Air 6alloons

;as tur1ine en%ines


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%ummar&%ummar&


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Thank youfor your

kind

attention

che171 revised

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