Sensors & Actuators - Técnico Lisboa - Autenticação Sensors & Actuators - H.Sarmento 1 Outline • Non-electric devices. • Contact: –RTD - Resistance temperature detectors

2014-2015 Sensors & Actuators - H.Sarmento

Sensors & ActuatorsTemperature

2014-2015 Sensors & Actuators - H.Sarmento 1

Outline

• Non-electric devices.

• Contact:

– RTD - Resistance temperature detectors.

– Silicon resistive sensors

– Thermistors.

– Thermocouples.

– Semiconductor pn junction.

– Piezoelectric temperature sensors.

• Non contact

– Infrared thermometer.


Non-electric devices

• Read visually, do not produce electrical signals.

– Molecular change-of-state devices.

– Fluid expansion devices.

– Bimetallic devices.

• Disadvantages: less accurate than electrical sensors, and

temperature values not easily recorded.

• Advantages: portability and independence from a power

supply.


Molecular change-of-state devices

• Devices whose appearance changes once a certain temperature

is reached: labels, crayons, lacquers and liquid crystals.

[Source: Omega]


Fluid expansion devices

• the volume of a liquid or a gas changes as a function of

temperature.

[Source: Labon][Source: Omega]


Bimetallic devices (1)

• Two metals with dissimilar thermal expansion coefficients.

• Manufactured in different forms for cooking, refrigerators and

freezes, industrial applications.

[Source: globalspec]


Bimetallic devices (2)

• Two metals with similar moduli of elasticity and thicknesses.

• The radius of curvature r changer with temperature.

• Complex sensor: use of a displacement sensor to measure r.

thermal expansion coefficients aA,aB

BA aa

1T

t

2T

12 TT

21 TT

BAr

tTT

aa

3

212


Thermo resistive sensors (1)

• RTD (Resistance Temperature Detector), silicon resistive sensors

(KTY) and NTC (Negative Temperature Coefficients) thermistors.

RTD: Metal (Pt)KTY: doped siliconNTC: doped ceramic


Thermo resistive sensors (2)

• Power supply requirements: active (modulating).

• Stimulus perception: contact.

• Stimulus detection: absolute.

• Complexity: direct sensor.

• Type of stimulus: thermal.

• Transduction principle: resistive.

• Energy conversion: thermal electrical.


• Metallic: almost platinum (linear, predictable response, long-

term stability, and durability) used, but also nickel, copper,

tungsten (rare) and alloys.

• Resistivity increases with temperature.

Resistance temperature detectors

RTD


• Metallic: resistivity of metals increases with temperature.

• Approximate transfer function (Callendar–van Dusen):

– From -200ºC to 0ºC

– From 0ºC to 630ºC

RTD transfer function

n

nt TTTTTTRR 0

2

02010 ...1 aaa

1001 320 TCTBTATRRt

20 1 BTATRRt


• Most popular: base resistance of 100 (Pt100) , 500 (Pt500) or

1000 (Pt1000) ohms.

• The most common is Pt100 (resistance of 100 ohms specified

at 0°C).

[Source: rdt-products]

Platinum RTD

Pt100


RTD advantages

• Accurate (±0.1 ºC)

• Highly linear over limited temperature range (platinum)

• Wide temperature range

• Long term stability

• Repeatable

• Standardized.

• Resistant to contamination /corrosion

Material Temp Range

PLATINUM -260 º +650 º

NICKEL -100 º +300 º

COPPER -75 º +150 º


Standardized RTD

• Platinum RTDs are standardized:

IEC (International Electrotechnical Commission)

DIN (Deutsches Institut für Normung)IEC-751.


RTD disadvantages

Disadvantages:

• Expensive wire wound, but low cost thin film

• Low sensitivity (Pt100 0.4 ohm/ºC)

• Exist in limited values (Pt 100, Pt500, Pt1000)

• Self-heating

• Slow response time

• Sensitive to shock and vibration


RTD field of applications

Industrial applications:

• Oil & Gas industry: thermowells.

• Food & beverage, pharmaceutical and bio-technology plants:

Temperature dryers in food processes, Pasteurization, Heat

exchangers, Material storage tanks, Cheese vats, Brewhouse /

cellar, Cookers / freezers, Dehydrator, Fermentor / bio-

reactor control.

• Etc.


Commercial RTD

wound wire (probes) thin film components

[Source: pyromation]

[Source: Omega][Source: smartsensors]


Silicon Resistive Sensors (1)

• Pure silicon (without impurities):

ni – concentration of electrons

q – electron charge

m – mobility

Eg – Band gap

K – Boltzman constant

• Resistivity decreases with temperature.

1

pniqn mm

2

3

Tm 22

3

kT

E

i

g

eTn

T 2kT

Eg

e


Doped silicon

» PTC-


[Source: Jacob Fraden, 2010]

PTC



• Silicon doped with an n-type impurities.

• Resistivity increases with temperature in a limited to arelatively small temperature range.

• Discrete silicon sensors: KTY (originally from Philips)


KTY transfer function

• Resistivity increases with temperature.

• Values usually specified at 25º C

2

000 1 TTTTRRt a


Commercial Silicon Resistive Sensors

• KTY

– Discrete

– MEMS

[Source: NXP]


Silicon Resistive Sensors advantages

• Linear

• Moderate cost.

• High sensitivity

• Low weight

• Very long operation life

• Medium long term stability


Silicon Resistive Sensors disadvantages

• Highly non-linear at temperatures below 0°C and greater than

70°C. Can ne compensated.

• Limited range of temperatures (silicon):

– Maximum: –55C to +150C.

– Typical: - 45C to +85C or 0C to +80C

• Slow response time


Silicon Resistive Sensor field of applications

• Industrial applications:

Overheating protection, Protection for power supplies,

Process temperature control, Exhaust control, Toaster

control, Temperature compensation for microprocessors

• Automotive applications:

Oil temperature, Oil level, Water temperature, Diesel

injection, Transmission, Engine coolant, Engine air, Air

conditioning


KTY linearization

• When further linearization becomes necessary a resistor (RL)

to shunt the sensor (RT) can be used.

• Linearization in a temperature range.

TLeq RRR //


RTD/KTY (1)

• Similar characteristics to RTD, but more sensitive and less

linear.


RTD/KTY (2)

• KTY with small SPAN than RTD

Material Temp Range

PLATINUM -260 º +650 º

NICKEL -100 º +300 º

COPPER -75 º +150 º

Sensor Span

KTY-81-1 -55 ºC 150 ºC

KTY-81-2 -55 ºC 150 ºC

KTY-83-1 -55 ºC 150 ºC

KTY-84-1 0 ºC 300 ºC


NTC thermistors

• Ceramic materials, normally highly resistive, made semi-conductive

by the addition of dopants.

• Small doping: Negative Temperature Coefficients (NTC).

NTC


NTC transfer function

• Transfer function highly nonlinear.

• Simpler model (lower the accuracy):

• Traditionally, thermistors are specified at temperature of 25ºC

(T0 =298.15 K).

• For a relatively narrow temperature range, β can be considered

temperature independent.

3

3

2

210ln

T

A

T

A

T

AARt

TARt

0ln

Tt eAR


NTC commercial sensors

[source: apitechnologies]


NTC advantages

• Inexpensive

• High sensitivity

• Fast response time.

• Self heating can be useful for certain applications (PTC).


NTC disadvantages

• Non linear (can be compensated).

• Fragile.

• Self heating.

• Limited range of temperatures.


NTC field of applications

• Consumer and household appliances: Burglar alarm and fire

detectors, for your oven, air conditioning, refrigerator

temperature control, or fever thermometer.

• Fibre and photographic processing, solar, meteorological,

geological, and oceanographic equipment.

• Motor winding compensation, transistor temperature

compensation, infrared sensing compensation, gain

stabilization and piezoelectric temperature compensation.


NTC linearization

• LTN –Linear Thermistor Network

vv

opBTA

V

V


Resistive temperature sensors: comparison

NTC RDT (Pt) Silicon Resistive

Temp range -55ºC +125ºC -200ºC +850ºC -50ºC +125ºC

Linearity Exponential Linear (range) Linear

Sensitivity High Low Moderate

Response time Fast Slow Slow

Long-term stability Low High Medium

Cost Low High (wire wound) Low-Medium


NTC self-heating (1)

• Voltage or current in the sensor generates self heating (Joule effect).

• At equilibrium:

• P dissipated:

• P generated:

– Current excitation

– Voltage excitation

00 TTPP

TT dissipated

dissipated

generateddissipated PP

22 IAeIRP Ttgenerated

22

Tt

generated

Ae

V

R

VP



• With current excitation:

• Final temperature (self limiting).0

2 TIeA

T Tfinal

RT

P generated

0T finalT

RT PR TP

2 IAeP Tgenerated

0TTPdissipated


P generated

0T finalT


• With voltage excitation:

• Thermistor can be destroyed.

RT PR

dissipatedPTT 0

TP

2

T

generated

Ae

VP


• Over Curie temperature, resistivity increases with temperature.

• Most PTC thermistors with Curie temperature between 60°C

and 120°C. Can be manufactured for Curie temperature as low

as 0°C or as high as 200°C.

PTC Thermistors

PTC


Voltage current characteristic

[Source: Jacob Fraden]

V RI Ohm’s law

no self-heating

resistance negative

VRTPI

limiting self


PTC commercial devices

• PTC (Positive Temperature Coefficient)

[Source: apitechnologies]


PTC Thermistors applications

• Not to measure temperature.

• Applications:

– Self-Regulating Heaters

– Over-Current Protection

– Liquid level sensing

– Constant current

– Time delay

– Arc suppression


Self-Regulating Heaters

• Initially at NTC region:

• If the voltage is high enough, the unit will self-heat until it

passes into the PTC region of resistance.

• In the PTC region, if the temperature decreases

2

IRT

RR

VP

LT

TPIR

TPIRT


Over-Current Protection

• Under normal conditions RT is low and IL depends on V.

• A short circuit or over-current condition (IL) RT causes heating.

• At Curie Point, the PTC transforms into a high resistance element,thereby limiting current to the load.

• Removing the fault condition decreases the current flow and allowsPTC to cool to its normal resistance mode.

V

TL

LRR

I


Liquid Level Sensing

• When a PTC thermistor heated in air is immersed into a liquid (orair flow condition), a larger amount of heat is dissipated than in air.

• I > Imin relay is actuated.

[Source: Epcos] IRT PTCth

thAirthLiquid


Constant current

• It is possible to obtain a nearly constant current (IS) by

connecting a PTC thermistor in parallel with a resistor.

PTCPTCPTCPTCPTC IRTPI

constantI and I sPTCRp I

PTCo IV

I RpoV


Time delay

• The relay stays energized until the PTC switches from low to

high resistance.

• The relay will only be energized after the time necessary for

the PTC to switch from low to high resistance.

[source: Spectrum Sensors]


Arc Suppression

• When the switch is opened, the PTC changes from low

resistance to high resistance, suppressing the arc.

[source: Spectrum Sensors]


Thermocouples classification

• Power supply requirements: passive (modulating).


• Stimulus detection: relative.



• Transduction principle: thermoelectric.



Thermocouples transfer function

[Source: Jacob Fraden, 2010]]

ABE

CT º00

20

2201

0

TTCTTCETTAB

Emf in tables, usually for


Commercial thermocouples

[Source: allproducts] [Source: coleparmer]


Thermocouples advantages

• Inexpensive.

• Wide temperature range (200 oC to 2600 oC).

• Most types non-linear.


• Standardized.

• Moderate cost.


Standardization

• ANSI standard (wires with different colors).

• T, J, and K are most commonly used.

[Source: University of Cambridge ]

Type Composition

J Iron/Constantan (Nickel Copper)

K Nickel chromium/Nickel Aluminum

N Nickel chromium Silicon/Nickel Silicon

T Copper/Constantan

E Nickel chromium/Constantan

R Platinum Rhodium/Platinum

S Platinum Rhodium/Platinum

B Platinum Rhodium/Platinum Rhodium


Thermocouples disadvantages

• Small sensitivity.

• Small repeatability.

• Requires two temperatures be measured (cold junction).

• Output wire in the same thermocouple material.

• Long term stability: prone to aging.

• Susceptibility to electrical noise if not shielded.


Thermocouples field of applications

• Industrial applications: gas turbine exhaust, diesel engines,

furnaces, etc.

• Rocket engines and amunitions.

• Homes, offices and businesses: thermostats, flame sensors

in safety devices for gas-powered appliances.


Operation principle of thermocouples

• The Seebeck emf generated in a thermoelectric circuit results

from Thomson and Peltier effects.

• Peltier effect: existence of an EMF due to the contact of two

dissimilar metals dependent on junction temperature.

• Thomson effect: Existence of an EMF due to temperature

gradients along conductors in a circuit.

• Thomson effect normally much smaller than the Peltier effect.


Seebeck effect (1)

• A current flows in a circuit with two dissimilar homogeneous

metals A and B, having the two junctions at different

temperatures.



Seebeck effect (2)

• A thermally induced potential exists across the broken

conductor, which only depends on the materials and the

temperature difference.


21 TETEE ABABAB


Law of intermediate metals (1)

• The algebraic sum of emf in a circuit composed of any number

of dissimilar materials is zero if all of the circuit is at a

uniform temperature.

• Therefore, inserting any type of wire into a thermocouple

circuit has no effect on the output as long as both ends of that

wire are at the same temperature, or isothermal.

21 TETE ABAB

21

3321

TETE

TETETETE

ABAB

CAACBAAB


Law of intermediate metals (2)

• Another consequence: the emf of the combination of two

metals is the sum of their emf against the reference material.

ABE

BCE

BCABAC EEE


Law of intermediate temperatures

• E1-2 between A and B with junctions at T1 and T2

• E2-3 between A and B with junctions at T2 and T3

• Between A and B with junctions at T1 and T3

32 TTE

21 TTE

322131 TTTTTT EEE


Reference temperature (1)

• To use a thermocouple to measure temperature, one junction

must remain at a fixed reference temperature.

• Ice Baths: reference temperature immersed into a melting ice

bath.

– Accurate and inexpensive.

– Serious limitations for many practical uses.

CABTABifino EEvvvº0

CT º00

TCTCTCETAB 1

2

21

1C

ET AB


Reference temperature (2)

• Electronically Controlled References

– Require periodic calibration and are generally not as stable

as ice baths, but are more convenient.

ambT

TABcompifino Evvvv ambTT 0

TCTCTCETAB 1

2

21

1C

ET AB

ambTABifcomp Evv


Cold junction compensation

• LT1025 - Micropower Thermocouple Cold Junction Compensator

[Source: Linear Technology]


Semiconductor PN junction classification

• Power supply requirements: active (modulating).





• Transduction principle:



• The voltage across a forward biased junction biased by a

constant current generator can provide a measure of the

junction temperature.

Semiconductor PN junction

q

kTVT

kT

E

S

g

eII 20

kT

qv

kT

EIi Dg

D 2

lnln 0

kT

qv

V

v

S

DD

T

D

eeI

i

D

g

D iIq

kT

q

Ev lnln

20


• Sensitivity

Semiconductor PN junction transfer function

D

g

D iIq

kT

q

Ev lnln

20

μA) (10 º32 1 /º2 CmV/. mA)(CmV


Commercial semiconductor PN junction

• AD590, LM335, LM35, LM3911, TMP100/101, LM75


Semiconductor PN junction advantages

• Linear

• Low cost.

• Easily integrated in ICs at low cost (temperature sensing of

microprocessors thermal-shutdown in power-supply chips).



Semiconductor PN junction disadvantages

• Junctions cannot support high temperatures (LM35 -55 ºC

- 150 ºC; LM3911- 25ºC – 85 ºC).

• Sensitivity depends on bias current.


PN junction field of applications

• Remote sensing (connected by PVC cables).

• Domestic appliances: refrigerators, freezers, water heater,

dishwasher, bread maker, radiator, drying machine, etc.

• Cellular phones.

• Hard disk drivers, personal computers.

• Process control: vehicle-mounted refrigerators, storage tanks

for cosmetics, disinfecting machine, etc.


More PN junctions

• Increase of linearity by using more PN junctions:

• Identical characteristics:

12

21

2

2

1

1

21 lnlnSD

SDT

S

D

S

D

TDDDIi

IiV

I

i

I

i

Vvvv

12

2121 ln

Ai

Ai

q

kTvv

D

DDD

mA

A

1

2

21 DD ii

Tmq

kvv DD ln21


AD590 (1)

AD590 (output current):

• Output current proportional to absolute

temperature.

• Sensitivity: 1 μA/K

• SPAN: −55°C to +150°C

• Non linearity: ±0.3°C over full range

(AD590M)

(A) T01 -6TI


AD590 (2)

• Use of transistors:

1

221 ln -

A

A

q

kTVVV BEBER

mRq

kT

R

VVI BEBE ln

2

-2 21

4343 CC IIAA

2314 CCCC IIII

12 mAA KAI /1m

21243 2 CCCCC IIIIII

2R

VI R

C


LM35

• Output current proportional to temperature in ºF.

• Accuracy (at +25˚C): 0.5˚C.

• Sensitivity: + 10.0 mV/˚C

• SPAN: −55˚ to +150˚C

• Nonlinearity: ± 1⁄4˚C typical.

FmVV /º10

PTAT: Proportional to Absolute Temperature


Piezoelectric temperature sensors

classification

• Power supply requirements: passive (self generating).





• Transduction principle: piezoelectric



Piezoelectric temperature sensors

• The oscillating frequency is highly dependent on thecrystallographic orientation of the plate (angle of cut).

• The angle of cut depends on the temperature.

• Change in resonant frequency between 25 °C and 600 °C dependingon the cut-angle.

• GaPO4 (gallium orthophosphate): belongs to the same point groupas quartz.


Piezoelectric sensors transfer function

• Temperature dependence:

fT - crystal frequency at temperature T (in °C)

f0 - crystal frequency at reference temperature T0

202010 TTaTTaffT


Commercial piezoelectric temperature sensors

• RKTV06, RKOV206 (AXTAL)

• PTK01(AXTAL)


Piezoelectric temperature sensors advantages

• Low power consumption.

• Miniature size

• Operating temperature range ‐50°C to +180°C (standard) and

optionally up to +320°C

• High resolution down to µK range.

• Short time constant due to low thermal mass

• High shock and vibration resistance.


Infrared thermometer classification

• Power supply requirements: passive (self generating).

• Stimulus perception: non-contact.


• Complexity: complex sensor.


• Transduction principle: depending on the

detector/sensor



Infrared thermometer

• An optical system and a detector:

• Infrared radiation emitted by the object is picked up by the

optical system that focuses it on the sensor.

• The detector (sensor) converts the infrared radiation received

into electrical signals.

Optical system sensor


Infrared radiation

• Atom and molecule of an object above absolute zero temperaturevibrate emitting electromagnetic radiation, called thermal radiation.

• Blackbody spectral radiant emission

increases with temperature.

• An infrared sensor intercepts a portion of the infrared energyradiated by an object.

[Source: Hamamatsu]


Electromagnetic Radiation Spectrum

• Emitted thermal radiation is in the infrared region.

• The spectrum of this radiation ranges from 0.78 to 1000 µm

wavelength.

[Source: Raytek]


IR optical system

• For accurate temperature measurement, the target should be

larger than the instrument’s field of view or spot size.


Infrared detectors

• There are two main groups of infrared detectors:

– Thermal detectors: the temperature of the sensitive element

varies because of the absorption of electromagnetic

radiation.

– Quantum detectors: the striking photons of the infrared

radiation lead to an increase of the electrons inside the

semiconductor material.


IR detectors: advantages and disadvantages

• Thermal detectors:

– Low detection capability.

– Independent of wavelength.

– Slow response time (ms).

– Do not require cooling.

• Quantum detectors:

– High detection capability

– Dependent of wavelength.

– Fast response time (ns and ms).

– Must be cooled, except for near IR region.


Thermal detectors

• Impacting photons are absorbed by a thermally isolated

detector resulting in an increase in the temperature of the

element.

• Temperature can be sensed by:

– Thermocouple elements.

– Element with a change in charge due to the pyroelectric

effect: infrared pyrometer.

– Element with a change in resistance (metal or

semiconductor): infrared bolometers.


Quantum detectors

• Impacting photons are absorbed and generate free carriers

which are sensed by an electronic circuit:

– Photovoltaic.

– Photoresistive.


Infrared field of applications

• Manufacturing processes for metals, glass, cement, ceramics,semiconductors, plastics, paper, textiles, coatings.

• Fire-fighting, rescues and detection of criminal activities(intrusion).

• Measurement of human body temperatures (1 second timeresponse).

• Building heating.

• Electrical power generation and distribution (hot spotdetection).


IR temperature sensors advantages

• No contact.

• Fast response times.

• High repeatability.

• Good stability over time.


IR temperature sensors disadvantages

• Cost.

• Complexity.

• Emissivity variations affect temperature measurementaccuracy.

• Accuracy affected by dust, smoke, background radiation, etc.


Commercial IR temperature sensors (5)

[Source: Omega]

[Source: Raytek]

[Source: Texas instrument, Dec.2012]

[Source: Ge-sensors and measurement]


Bibliography

• Jacob Fraden, “Handbook of modern sensors: physics, designs, and applications”, Springer, 4th edition,

2010.

• Ramon Pallaá, Sensors and Signal Conditioning, John Wiley and Sons, 2001

• Pavel Ripka and Alois Tipek, Modern sensors Handbook, Instrumentation and measurement series, ISTE

Ltd, 2007

• Temperature Sensors: advantages & disadvantages, TD034 appliication note, Maesuement specialities,

2003. Available at: http://www.meas-spec.com/downloads/Temperature_Sensor_Advantages.pdf

• Klaus-Dieter Gruner, Principles of Non-Contact Temperature Measurement, Raytech. Available at:

http://support.fluke.com/raytek-sales/Download/Asset/IR_THEORY_55514_ENG_REVB_LR.PDF

• Spectrum Sensors & Controls, PTC Thermistors Applications. Available at

http://www.digikey.com/Web%20Export/Supplier%20Content/api-technologies-1171/pdf/api-ptc-

applications.pdf?redirected=1

• J. Shieh et al., The selection of sensors, Progress in Materials Science, Volume 46, Issues 3–4, 2001, Pages

461–504

• Low Cost Non-Electronic Temperature Gages, Application Notes,

http://www.omega.com/temperature/Z/pdf/z197.pdf

• Edmund J. Winder and Arthur B. Ellis, Thermoelectric Devices: Solid-State Refrigerators and Electrical

Generators in the Classroom, Journal of Chemical Education, Vol. 73 No. 10 October 1996.

• Shujun Zhang† and Fapeng Yu, Piezoelectric Materials for High Temperature Sensors, Journal of the

American Ceramic Society, Vol. 94, No. 10, 2011

http://www.meas-spec.com/downloads/Temperature_Sensor_Advantages.pdf


http://www.digikey.com/Web Export/Supplier Content/api-technologies-1171/pdf/api-ptc-applications.pdf?redirected=1

http://www.omega.com/temperature/Z/pdf/z197.pdf


Bibliography

• Measurements specialities, Temperature sensors advantages & disadvantages, Application note TD034,

October 2003. Available at: http://meas-spec.com.cn/downloads/Temperature_Sensor_Advantages.pdf

• Klaus-Dieter Gruner, Raytek, Principles of Non-Contact Temperature Measurement. Available at:

http://support.fluke.com/raytek-sales/Download/Asset/IR_THEORY_55514_ENG_REVB_LR.PDF.

• Optris, Infrared thermometers, Basic Principles Of Non-Contact Temperature Measurement.Available at:

http://www.optris.com/applications?file=tl_files/pdf/Downloads/Zubehoer/IR-Basics.pdf.

• Characteristics abd use of infrared detectors, Thechnical information SD-12, Hamamatsu Available at:

https://www.hamamatsu.com/resources/pdf/ssd/infrared_techinfo_e.pdf.

•

http://meas-spec.com.cn/downloads/Temperature_Sensor_Advantages.pdf


http://www.optris.com/applications?file=tl_files/pdf/Downloads/Zubehoer/IR-Basics.pdf

https://www.hamamatsu.com/resources/pdf/ssd/infrared_techinfo_e.pdf

Documents

Sensors & Actuators - Técnico Lisboa - Autenticação Sensors & Actuators - H.Sarmento 1 Outline • Non-electric devices. • Contact: –RTD - Resistance temperature detectors