3 - temperature sensors 1. thermoresistive sensors 2. thermoelectric sensors 3. pn junction...

3 - Temperature Sensors3 - Temperature Sensors

1. Thermoresistive sensors2. Thermoelectric sensors3. PN junction temperature sensors4. Optical and acoustic temperature sensors5. Thermo-mechanical sensors and actuators

A bit of historyA bit of history

Temperature measurements and thermometers 1600 - thermometers (water expansion, mercury) 1650 - first attempts at temperature scales (Boyle) 1700 - “standard” temperature scales (Magelotti,

Renaldini, Newton) - did not catch 1708 - Farenheit scale (180 div.) 1742 - Celsius scale 1848 - Kelvin scale (based on Carnot’s

thermodynamic work) 1927 - IPTS - International Practical Temperature

Temperature measurements and thermometers 1600 - thermometers (water expansion, mercury) 1650 - first attempts at temperature scales (Boyle) 1700 - “standard” temperature scales (Magelotti,

Renaldini, Newton) - did not catch 1708 - Farenheit scale (180 div.) 1742 - Celsius scale 1848 - Kelvin scale (based on Carnot’s

thermodynamic work) 1927 - IPTS - International Practical Temperature

More history - sensorsMore history - sensors

Temperature sensors are the oldest 1821 - Seebeck effect (Thomas Johann Seebeck)

1826 - first sensor - a thermocouple - based on the Seebeck effect (Antoine Cesar Becquerel)

1834 - Peltier effect (Charles Athanase Peltier). First peltier cell built in 1960’sUsed for cooling and heating

1821 - discovery of temperature dependence of conductivity (Sir Humphrey Davey)1771 - William Siemens builds the first resistive sensor

made of platinum

Temperature sensors are the oldest 1821 - Seebeck effect (Thomas Johann Seebeck)

1826 - first sensor - a thermocouple - based on the Seebeck effect (Antoine Cesar Becquerel)

1834 - Peltier effect (Charles Athanase Peltier). First peltier cell built in 1960’sUsed for cooling and heating

1821 - discovery of temperature dependence of conductivity (Sir Humphrey Davey)1771 - William Siemens builds the first resistive sensor

made of platinum

Temperature sensors - general

Temperature sensors are deceptively simple Thermocouples - any two dissimilar materials,

welded together at one end and connected to a micro-voltmeter

Peltier cell - any thermocouple connected to a dc source

Resistive sensor - a length of a conductor connected to an ohmmeter

• More:Some temperature sensors can act as actuators as wellCan be used to measure other quantities

(electromagnetic radiation, air speed, flow, etc.)• Some newer sensors are semiconductor based

Temperature sensors are deceptively simple Thermocouples - any two dissimilar materials,

welded together at one end and connected to a micro-voltmeter

Peltier cell - any thermocouple connected to a dc source

Resistive sensor - a length of a conductor connected to an ohmmeter

• More:Some temperature sensors can act as actuators as wellCan be used to measure other quantities

(electromagnetic radiation, air speed, flow, etc.)• Some newer sensors are semiconductor based

Temperature sensors - typesTemperature sensors - types Thermoelectric sensors

Thermocouples and thermopiles Peltier cells (used as actuators but can be used as sensors)

Thermoresistive sensors and actuators Conductor based sensors and actuators (RTDs) Semiconductor based sensors - thermistors, diodes

Semiconductor junction sensors Others

Based on secondary effects (speed of sound, phase of light) Indirect sensing (infrared thermometers - chapter4) Expansion of metals, bimetals

Thermoelectric sensors Thermocouples and thermopiles Peltier cells (used as actuators but can be used as sensors)

Thermoresistive sensors and actuators Conductor based sensors and actuators (RTDs) Semiconductor based sensors - thermistors, diodes

Semiconductor junction sensors Others

Based on secondary effects (speed of sound, phase of light) Indirect sensing (infrared thermometers - chapter4) Expansion of metals, bimetals

Thermal actuatorsThermal actuators

A whole class of thermal actuators Bimetal actuators Expansion actuators Thermal displays Sometimes sensing and actuation is

combined in a single device

A whole class of thermal actuators Bimetal actuators Expansion actuators Thermal displays Sometimes sensing and actuation is

combined in a single device

Thermoresistive sensorsThermoresistive sensors

Two basic types: Resistive Temperature Detector (RTD)

Metal wireThin filmSilicon based

Thermistors (Thermal Resistor)NTC (Negative Temperature Coefficient)PTC (Positive Temperature Coefficient)

Two basic types: Resistive Temperature Detector (RTD)

Metal wireThin filmSilicon based

Thermistors (Thermal Resistor)NTC (Negative Temperature Coefficient)PTC (Positive Temperature Coefficient)

Thermoresistive effectThermoresistive effect

Conductivity depends on temperature

Conductors and semiconductors

Resistance is measured, all other parameters must stay constant.

Conductivity depends on temperature

Conductors and semiconductors

Resistance is measured, all other parameters must stay constant.

R = LσS

Thermoresistive effect (cont.)Thermoresistive effect (cont.)

Resistance of a length of wire

Conductivity is:Resistance as a

function of temperature:

- Temperature Coefficient of Resistance (TCR) [C]

Resistance of a length of wire

Conductivity is:Resistance as a

function of temperature:

- Temperature Coefficient of Resistance (TCR) [C]

R = LσS

σ = σ01 + α T − T0

RT = Lσ0S

1 + α T − T0

Thermoresistive effect (cont.)Thermoresistive effect (cont.)

T is the temperature [C ] 0 is the conductivity of the conductor

at the reference temperature T0. T0 is usually given at 20C but may be

given at other temperatures as necessary.

- Temperature Coefficient of Resistance (TCR) [C] given at T0

T is the temperature [C ] 0 is the conductivity of the conductor

at the reference temperature T0. T0 is usually given at 20C but may be

given at other temperatures as necessary.

- Temperature Coefficient of Resistance (TCR) [C] given at T0

Example Example

Copper: 0=5.9x107 S/m, =0.0039 C at T0=20C. Wire of cross-sectional area: 0.1 mm2, length L=1m,

Change in resistance of 6.61x10 /C and a base resistance of 0.017 at 20C

Change of 0.38% per C .

Copper: 0=5.9x107 S/m, =0.0039 C at T0=20C. Wire of cross-sectional area: 0.1 mm2, length L=1m,

Change in resistance of 6.61x10 /C and a base resistance of 0.017 at 20C

Change of 0.38% per C .

Example (cont.) Example (cont.)

Conclusions from this example: Change in resistance is measurable Base resistance must be large - long and

or thin conductors or both Other materials may be used

Conclusions from this example: Change in resistance is measurable Base resistance must be large - long and

or thin conductors or both Other materials may be used

Temperature Coefficient of Resistance

Material Conductivity [S/m] Temperature Coefficint of Resistance (TCR) C

Copper (Cu) 5.7-5.9 x 107 0.0039 Carbon (C) 3.0 x105 0.0005 Constantan (60%Cu,40%Ni) 2.0 x106 0.00001 Cromium (Cr) 5.6 x 106 0.0059 Germanium (Ge) 2.2 0.05 Gold (Au) 4.1 x 107 0.0034 Iron (Fe) 1.0 x 107 0.0065 Mercury (Hg) 1.0 x 106 0.00089 Nichrome (NiCr) 1.0 x 106 0.0004 Nickel (Ni) 1.15 x 107 0.0069 Platinum (Pl) 9.4 x 106 0.01042 Silicon (Si) (pure) 4.35 x 10-6 0.07 Silver (Ag) 6.1 x 107 0.0016 Titanium (Ti) 1.8 x 106 0.042 Tungsten (W) 1.8 x 107 0.0056 Zinc (Zn) 1.76 x 107 0.0059 Aluminum (Al) 3.6 x 107 0.0043 Note: Instead of conductivity [S/m], some sources list resistivity , measured in ohm.meter = 1/ [ m). 1S/m=1/ m

Material Conductivity [S/m] Temperature Coefficint of Resistance (TCR) C

Copper (Cu) 5.7-5.9 x 107 0.0039 Carbon (C) 3.0 x105 0.0005 Constantan (60%Cu,40%Ni) 2.0 x106 0.00001 Cromium (Cr) 5.6 x 106 0.0059 Germanium (Ge) 2.2 0.05 Gold (Au) 4.1 x 107 0.0034 Iron (Fe) 1.0 x 107 0.0065 Mercury (Hg) 1.0 x 106 0.00089 Nichrome (NiCr) 1.0 x 106 0.0004 Nickel (Ni) 1.15 x 107 0.0069 Platinum (Pl) 9.4 x 106 0.01042 Silicon (Si) (pure) 4.35 x 10-6 0.07 Silver (Ag) 6.1 x 107 0.0016 Titanium (Ti) 1.8 x 106 0.042 Tungsten (W) 1.8 x 107 0.0056 Zinc (Zn) 1.76 x 107 0.0059 Aluminum (Al) 3.6 x 107 0.0043 Note: Instead of conductivity [S/m], some sources list resistivity , measured in ohm.meter = 1/ [ m). 1S/m=1/ m

Other considerationsOther considerations

Tension or strain on the wires affect resistance

Tensioning a conductor, changes its length and cross-sectional area (constant volume) has exactly the same effect on resistance as a

change in temperature. increase in strain on the conductor increases the

resistance of the conductor (strain gauge)Resistance should be relatively large (25

and up)

Tension or strain on the wires affect resistance

Tensioning a conductor, changes its length and cross-sectional area (constant volume) has exactly the same effect on resistance as a

change in temperature. increase in strain on the conductor increases the

resistance of the conductor (strain gauge)Resistance should be relatively large (25

and up)

Construction - wire RTDConstruction - wire RTD A spool of wire (length)

Similar to heating elements Uniform wire Chemically and dimensionally stable in the sensing range Made thin (<0.1mm) for high resistance

Spool is supported by a glass (pyrex) or mica support Similar to the way the heating element in a hair drier is

supported Keeps strain at a minimum and allows thermal expansion Smaller sensors may not have an internal support.

Enclosed in a glass, ceramic or metal enclosure Length is from a few cm, to about 50cm

A spool of wire (length) Similar to heating elements Uniform wire Chemically and dimensionally stable in the sensing range Made thin (<0.1mm) for high resistance

Spool is supported by a glass (pyrex) or mica support Similar to the way the heating element in a hair drier is

supported Keeps strain at a minimum and allows thermal expansion Smaller sensors may not have an internal support.

Enclosed in a glass, ceramic or metal enclosure Length is from a few cm, to about 50cm

Glass encapsulated RTDsGlass encapsulated RTDs

Construction (cont.) Construction (cont.)

Materials:Platinum - used for precision applications

Chemically stable at high temperatures Resists oxidation Can be made into thin wires of high chemical purity Resists corrosion Can withstand severe environmental conditions. Useful to about 800 C and down to below –250C. Very sensitive to strain Sensitive to chemical contaminants

Wire length needed is long (high conductivity)

Materials:Platinum - used for precision applications

Chemically stable at high temperatures Resists oxidation Can be made into thin wires of high chemical purity Resists corrosion Can withstand severe environmental conditions. Useful to about 800 C and down to below –250C. Very sensitive to strain Sensitive to chemical contaminants

Wire length needed is long (high conductivity)

Construction (cont.) Construction (cont.)

Materials:Nickel and Copper

Less expensive Reduced temperature range (copper only works up to

about 300C) Can be made into thin wires of high chemical purity Wire length needed is long (high conductivity) Copper is not suitable for corrosive environments

(unless properly protected) At higher temperatures evaporation increases

resistance

Materials:Nickel and Copper

Less expensive Reduced temperature range (copper only works up to

about 300C) Can be made into thin wires of high chemical purity Wire length needed is long (high conductivity) Copper is not suitable for corrosive environments

(unless properly protected) At higher temperatures evaporation increases

resistance

This is unrelated to the course - just a curiosity

This is unrelated to the course - just a curiosity - close-up

Thin Film RTDsThin Film RTDs

Thin film sensors: produced by depositing a thin layer of a suitable material (platinum or its alloys) on a thermally stable, electrically non-conducting, thermally conducting ceramic

Etched to form a long strip (in a meander fashion).

Eq. (3.1) applies but much higher resistance sensors are possible.

Small and relatively inexpensive Often the choice in modern sensors especially

when the very high precision of Platinum wire sensors is not needed.

Thin film sensors: produced by depositing a thin layer of a suitable material (platinum or its alloys) on a thermally stable, electrically non-conducting, thermally conducting ceramic

Etched to form a long strip (in a meander fashion).

Eq. (3.1) applies but much higher resistance sensors are possible.

Small and relatively inexpensive Often the choice in modern sensors especially

when the very high precision of Platinum wire sensors is not needed.

Tnin film RTDs - (cont.)Tnin film RTDs - (cont.)

Two types of thin film RTDs from different manufacturers

Dimensions are typical - some are much larger

Two types of thin film RTDs from different manufacturers

Dimensions are typical - some are much larger

Some parametersSome parameters

Temperature range: -250 C to 700 CResistances: typically 100 (higher available)Sizes: from a few mm to a few cmCompatibility: glass, ceramic encapsulationAvailable in ready made probesAccuracy: ±0.01 C to ±0.05 CCalibration: usually not necessary beyond

manufacturing

Temperature range: -250 C to 700 CResistances: typically 100 (higher available)Sizes: from a few mm to a few cmCompatibility: glass, ceramic encapsulationAvailable in ready made probesAccuracy: ±0.01 C to ±0.05 CCalibration: usually not necessary beyond

manufacturing

Self heat in RTDsSelf heat in RTDs

RTDs are subject to errors due to rise in their temperature produced by the heat generated in them by the current used to measure their resistance

Wire wound or thin filmPower dissipated: Pd=I2R ( I is the current

(RMS) and R the resistance of the sensor) Self heat depends on size and environmentGiven as temperature rise per unit power

(C/mW) Or: power needed to raise temperature (mW/ C)

RTDs are subject to errors due to rise in their temperature produced by the heat generated in them by the current used to measure their resistance

Wire wound or thin filmPower dissipated: Pd=I2R ( I is the current

(RMS) and R the resistance of the sensor) Self heat depends on size and environmentGiven as temperature rise per unit power

(C/mW) Or: power needed to raise temperature (mW/ C)

Self heat in RTDs (cont.)Self heat in RTDs (cont.)

Errors are of the order of 0.01C/mW to 10C/mW (100mW/C to 0.1mW/C)

Given in air and in water In water values are lower (opposite if mW/C used)

Self heat depends on size and environment Lower in large elements, higher in small elements Important to lower the current as much as possible

Errors are of the order of 0.01C/mW to 10C/mW (100mW/C to 0.1mW/C)

Given in air and in water In water values are lower (opposite if mW/C used)

Self heat depends on size and environment Lower in large elements, higher in small elements Important to lower the current as much as possible

Response time in RTDsResponse time in RTDs

Response time Provided as part of data sheet Given in air or in water or both, moving or stagnant Given as 90%, 50% (or other) of steady state Generally slow Wire RTDs are slower Typical values

0.5 sec in water to 100 sec in moving air

Response time Provided as part of data sheet Given in air or in water or both, moving or stagnant Given as 90%, 50% (or other) of steady state Generally slow Wire RTDs are slower Typical values

0.5 sec in water to 100 sec in moving air

Silicon Resistive SensorsSilicon Resistive Sensors

Conduction in semiconductorsValence electrons

Bound to atoms in outer layers (most electrons in pure semiconductors)

Can be removed through heat (band gap energy) When removed they become conducting electrons (conduction

band) A pair is always released - electron and hole

Conductivity of semiconductors is temperature dependent Conductivity increases with temperature Limited to a relatively small temperature range

Conduction in semiconductorsValence electrons

Bound to atoms in outer layers (most electrons in pure semiconductors)

Can be removed through heat (band gap energy) When removed they become conducting electrons (conduction

band) A pair is always released - electron and hole

Conductivity of semiconductors is temperature dependent Conductivity increases with temperature Limited to a relatively small temperature range

Silicon Resistive Sensors (cont.)Silicon Resistive Sensors (cont.)

Pure silicon:NTC device - negative temperature coefficient

Resistance decreases with temperature Resistance in pure silicon is extremely high Need to add impurities to increase carrier density N type silicon - add arsenic (As) or antimony (Sb)

Behavior changes: Resistance increases up to a given temperature

(PTC) Resistance decreases after that (NTC) PTC up to about 200 C

Pure silicon:NTC device - negative temperature coefficient

Resistance decreases with temperature Resistance in pure silicon is extremely high Need to add impurities to increase carrier density N type silicon - add arsenic (As) or antimony (Sb)

Behavior changes: Resistance increases up to a given temperature

(PTC) Resistance decreases after that (NTC) PTC up to about 200 C

Resistance of silicon resistive sensor

Resistance of silicon resistive sensor - specific device

Silicon resistive sensorsSilicon resistive sensors Silicon resistive sensors are somewhat

nonlinear and offer sensitivities of the order 0.5-0.7 %/C.

Can operate in a limited range of temperatures like most semiconductors devices based on silicon

Maximum range is between –55C to +150C. Typical range: - 45C to +85C or 0C to +80C Resistance: typically 1k at 25 C. Can be calibrated in any temperature scale Made as a small chip with two electrodes and

encapsulated in epoxy, metal cans etc.

Silicon resistive sensors are somewhat nonlinear and offer sensitivities of the order 0.5-0.7 %/C.

Can operate in a limited range of temperatures like most semiconductors devices based on silicon

Maximum range is between –55C to +150C. Typical range: - 45C to +85C or 0C to +80C Resistance: typically 1k at 25 C. Can be calibrated in any temperature scale Made as a small chip with two electrodes and

encapsulated in epoxy, metal cans etc.

ThermistorsThermistors

Thermistor: Thermal resistorBecame available: early 1960’sBased on oxides of semiconductors

High temperature coefficients NTC High resistances (typically)

Thermistor: Thermal resistorBecame available: early 1960’sBased on oxides of semiconductors

High temperature coefficients NTC High resistances (typically)

Thermistors (cont.)Thermistors (cont.)

Transfer function:

[] and [K] are constants R(T): resistance of the device T: temperature in K Relation is nonlinear but:

Only mildly nonlinear ( is small) Approximate transfer function

Transfer function:

[] and [K] are constants R(T): resistance of the device T: temperature in K Relation is nonlinear but:

Only mildly nonlinear ( is small) Approximate transfer function

RT = αeβ/T

ConstructionConstruction

Beads ChipsDeposition on substrate

Epoxy encapsulated bead thermistors

Thermistors - propertiesThermistors - properties

Most are NTC devicesSome are PTC devicesPTC are made from special materials

Not as common Advantageous when runaway

temperatures are possible

Most are NTC devicesSome are PTC devicesPTC are made from special materials

Not as common Advantageous when runaway

temperatures are possible

Self heating errors as in RTDs but: Usually lower because resistance is higher Current very low (R high) Typical values: 0.01C/mW in water to 1C/mW in air

Wide range of resistances up to a few M Can be used in self heating mode

To raise its temperature to a fixed value As a reference temperature in measuring flow

Repeatability and accuracy: 0.1% or 0.25C for good thermistors

Self heating errors as in RTDs but: Usually lower because resistance is higher Current very low (R high) Typical values: 0.01C/mW in water to 1C/mW in air

Wide range of resistances up to a few M Can be used in self heating mode

To raise its temperature to a fixed value As a reference temperature in measuring flow

Repeatability and accuracy: 0.1% or 0.25C for good thermistors

Temperature range: 50 C to about 600 C Ratings and properties vary along the range

Linearity Very linear for narrow range applications Slightly nonlinear for wide temperature ranges

Available in a wide range of sizes, shapes and also as probes of various dimensions and shapes

Some inexpensive thermistors have poor repeatability - these must be calibrated before use.

Temperature range: 50 C to about 600 C Ratings and properties vary along the range

Linearity Very linear for narrow range applications Slightly nonlinear for wide temperature ranges

Available in a wide range of sizes, shapes and also as probes of various dimensions and shapes

Some inexpensive thermistors have poor repeatability - these must be calibrated before use.

Thermoelectric sensorsThermoelectric sensors

Among the oldest sensors (over 150 years)Some of the most useful and most commonPassive sensors: they generate electrical

emfs (voltages) directly Measure the voltage directly. Very small voltages - difficult to measure Often must be amplified before interfacing Can be influenced by noise

Among the oldest sensors (over 150 years)Some of the most useful and most commonPassive sensors: they generate electrical

emfs (voltages) directly Measure the voltage directly. Very small voltages - difficult to measure Often must be amplified before interfacing Can be influenced by noise

Thermoelectric sensors (cont.)Thermoelectric sensors (cont.)

Simple, rugged and inexpensiveCan operate on almost the entire range of

temperature from near absolute zero to about 2700C.

No other sensor technology can match even a fraction of this range.

Can be produced by anyone with minimum skill

Can be made at the sensing site if necessary

Simple, rugged and inexpensiveCan operate on almost the entire range of

temperature from near absolute zero to about 2700C.

No other sensor technology can match even a fraction of this range.

Can be produced by anyone with minimum skill

Can be made at the sensing site if necessary

Thermoelectric sensors (cont.)Thermoelectric sensors (cont.)

Only one fundamental device: the thermocouple

There are variations in construction/materials Metal thermocouples Thermopiles - multiple thermocouples in series Semiconductor thermocouples and thermopiles Peltier cells - special semiconductor thermopiles

used as actuators (to heat or cool)

Only one fundamental device: the thermocouple

There are variations in construction/materials Metal thermocouples Thermopiles - multiple thermocouples in series Semiconductor thermocouples and thermopiles Peltier cells - special semiconductor thermopiles

used as actuators (to heat or cool)

Thermoelectric effectThermoelectric effect The Seebeck effect (1821) Seebeck effect is the sum of two other effects

The Peltier effect The Thomson effect

The Peltier effect: heat generated or absorbed at the junction of two dissimilar materials when an emf exists across the junction due to the current produced by this emf in the junction. By connecting an external emf across the junction By the emf generated by the junction itself. A current must flow through the junction. Applications in cooling and heating Discovered in 1834

The Seebeck effect (1821) Seebeck effect is the sum of two other effects

The Peltier effect The Thomson effect

The Peltier effect: heat generated or absorbed at the junction of two dissimilar materials when an emf exists across the junction due to the current produced by this emf in the junction. By connecting an external emf across the junction By the emf generated by the junction itself. A current must flow through the junction. Applications in cooling and heating Discovered in 1834

Thermoelectric effect (cont.)Thermoelectric effect (cont.)

The Thomson effect (1892): a current carrying wire if unevenly heated along its length will either absorb or radiate heat depending on the direction of current in the wire (from hot to cold or from cold to hot). Discovered in 1892 by William Thomson

(Lord Kelvin).

The Thomson effect (1892): a current carrying wire if unevenly heated along its length will either absorb or radiate heat depending on the direction of current in the wire (from hot to cold or from cold to hot). Discovered in 1892 by William Thomson

(Lord Kelvin).

Thermoelectric effect (cont.)Thermoelectric effect (cont.)

The Seebeck effect: an emf produced across the junction of two dissimilar conducting materials connected together.

The sum of the Peltier and the Thomson effects

The first to be discovered and used (1821)The basis of all thermoelectric sensorsPeltier effect is used in Thermoelectric

Generators (TEG) devices

The Seebeck effect: an emf produced across the junction of two dissimilar conducting materials connected together.

The sum of the Peltier and the Thomson effects

The first to be discovered and used (1821)The basis of all thermoelectric sensorsPeltier effect is used in Thermoelectric

Generators (TEG) devices

The Seebeck effectThe Seebeck effect

If both ends of the two conductors are connected and a temperature difference is maintained between the two junctions, a thermoelectric current will flow through the closed circuit (generation mode)

The Seebeck effectThe Seebeck effect

If the circuit is opened an emf will appear across the open circuit (sensing mode). It is this emf that is measured in a thermocouple sensor.

Themocouple - analysisThemocouple - analysis

Conductors a, b homogeneous

Junctions at temperatures T2 and T1

On junctions 1 and 2:

Total emf:

Conductors a, b homogeneous

Junctions at temperatures T2 and T1

On junctions 1 and 2:

Total emf:

= emfA

− emfB

Thermocouple - analysisThermocouple - analysis

A and B are the absolute Seebeck coefficients given in V/C and are properties of the materials A, B

AB=AB is the relative Seebeck coefficient of the material combination A and B, given in V/C

The relative Seebeck coefficients are normally used.

A and B are the absolute Seebeck coefficients given in V/C and are properties of the materials A, B

AB=AB is the relative Seebeck coefficient of the material combination A and B, given in V/C

The relative Seebeck coefficients are normally used.

Absolute Seebeck coefficientsAbsolute Seebeck coefficients

Table 3.3. Absolute Seebeck coefficients for selected elements (Thermoelectric series) Material [ V/°K] p-Silicon 00 - 000 Antimony ( )Sb 32 Iron (F )e 3.4 Gold (A )u 0. Copper ( )Cu 0 Silver (Ag) 0.2 Aluminum (Al) 3.2 Platinum (Pt) .9 Cobalt (Co) 20. Nickel (Ni) 20.4 Bismut h (Sb) 72.8 n-Silicon 00 to -000

Thermocouples - standard types

Table 3.4. Thermocouples (standard types and others) and some of their propertiesMaterials Sensitivity

[V/°C]a t2°C.

StandardTypedesignation

Temperaturerange [°C]

Copper/Constantan 40.9 T −270 600to Cu/60% 40Cu %NiIron/Constantan .7 J −270 to

000Fe/60% 40Cu %Ni

Chrome /l Alumel 40.6 K −270 to300

90%Ni0%Cr/% 4Cu %Ni

Chrome /l Constantan 60.9 E −200 to000

90%Ni0%Cr/60% 40Cu %Ni

Platinum(0%)/Rhodium-Platinum 6.0 S 0 40to /Pt90%Pt0%RhPlatinum(3%)/Rhodium-Platinum 6.0 R 0 600to /Pt87%Pt3%RhSilver/Paladium 0 200 600toConstantan/Tungsten 42. 0 800toSilicon/Aluminum 446 −40 0toCarbon/Sili conCarbide 70 0 2000toNote: sensitivity is the relati veSee beck coefficien .t

Table 3.4. Thermocouples (standard types and others) and some of their propertiesMaterials Sensitivity

[V/°C]a t2°C.

StandardTypedesignation

Temperaturerange [°C]

Copper/Constantan 40.9 T −270 600to Cu/60% 40Cu %NiIron/Constantan .7 J −270 to

000Fe/60% 40Cu %Ni

Chrome /l Alumel 40.6 K −270 to300

90%Ni0%Cr/% 4Cu %Ni

Chrome /l Constantan 60.9 E −200 to000

90%Ni0%Cr/60% 40Cu %Ni

Platinum(0%)/Rhodium-Platinum 6.0 S 0 40to /Pt90%Pt0%RhPlatinum(3%)/Rhodium-Platinum 6.0 R 0 600to /Pt87%Pt3%RhSilver/Paladium 0 200 600toConstantan/Tungsten 42. 0 800toSilicon/Aluminum 446 −40 0toCarbon/Sili conCarbide 70 0 2000toNote: sensitivity is the relati veSee beck coefficien .t

Seebeck coefficients - notes:Seebeck coefficients - notes:

Seebeck coefficients are rather small – From a few microvolts to a few millivolts per

degree Centigrade. Output can be measured directly Output is often amplified before interfacing to

processors Induced emfs due to external sources cause noise Thermocouples can be used as thermometers More often however the signal will be used to take

some action (turn on or off a furnace, detect pilot flame before turning on the gas, etc.)

Seebeck coefficients are rather small – From a few microvolts to a few millivolts per

degree Centigrade. Output can be measured directly Output is often amplified before interfacing to

processors Induced emfs due to external sources cause noise Thermocouples can be used as thermometers More often however the signal will be used to take

some action (turn on or off a furnace, detect pilot flame before turning on the gas, etc.)

Thermoelectric laws:Thermoelectric laws:

Three laws govern operation of thermocouples:

Law 1. A thermoelectric current cannot be established in a homogeneous circuit by heat alone. This law establishes the need for junctions

of dissimilar materials since a single conductor is not sufficient.

Three laws govern operation of thermocouples:

Law 1. A thermoelectric current cannot be established in a homogeneous circuit by heat alone. This law establishes the need for junctions

of dissimilar materials since a single conductor is not sufficient.

Law 2. The algebraic sum of the thermoelectric forces in a circuit composed of any number and combination of dissimilar materials is zero if all junctions are at uniform temperatures. Additional materials may be connected in the

thermoelectric circuit without affecting the output of the circuit as long as any junctions added to the circuit are kept at the same temperature.

voltages are additive so that multiple junctions may be connected in series to increase the output.

Law 2. The algebraic sum of the thermoelectric forces in a circuit composed of any number and combination of dissimilar materials is zero if all junctions are at uniform temperatures. Additional materials may be connected in the

thermoelectric circuit without affecting the output of the circuit as long as any junctions added to the circuit are kept at the same temperature.

voltages are additive so that multiple junctions may be connected in series to increase the output.

Law 3. If two junctions at temperatures T1 and T2 produce Seebeck voltageV2 and temperatures T2 and T3 produce voltage V1, then temperatures T1 and T3 produce V3=V1+V2. This law establishes methods of calibration of

thermocouples.

Law 3. If two junctions at temperatures T1 and T2 produce Seebeck voltageV2 and temperatures T2 and T3 produce voltage V1, then temperatures T1 and T3 produce V3=V1+V2. This law establishes methods of calibration of

thermocouples.

Thermocouples: connectionThermocouples: connection Based on the thermoelectric laws: Usually connected in pairs

One junction for sensing One junction for reference Reference temperature can be lower or higher than sensing

temperature

Based on the thermoelectric laws: Usually connected in pairs

One junction for sensing One junction for reference Reference temperature can be lower or higher than sensing

temperature

Thermocouples (cont.)Thermocouples (cont.)

Any connection in the circuit between dissimilar materials adds an emf due to that junction.

Any pair of junctions at identical temperatures may be added without changing the output. Junctions 3 and 4 are identical (one between

material b and c and one between material c and b and their temperature is the same. No net emf due to this pair

Junctions (5) and (6) also produce zero field

Any connection in the circuit between dissimilar materials adds an emf due to that junction.

Any pair of junctions at identical temperatures may be added without changing the output. Junctions 3 and 4 are identical (one between

material b and c and one between material c and b and their temperature is the same. No net emf due to this pair

Junctions (5) and (6) also produce zero field

Thermocouples (cont.)Thermocouples (cont.)

• Each connection adds two junctions. • The strategy in sensing is:

For any junction that is not sensed or is not a reference junction:

• Either each pair of junctions between dissimilar materials are held at the same temperature (any temperature) or:

• Junctions must be between identical materials. • Also: use unbroken wires leading from the sensor to the

reference junction or to the measuring instrument. • If splicing is necessary to extend the length, identical wires

must be used to avoid additional emfs.

• Each connection adds two junctions. • The strategy in sensing is:

For any junction that is not sensed or is not a reference junction:

• Either each pair of junctions between dissimilar materials are held at the same temperature (any temperature) or:

• Junctions must be between identical materials. • Also: use unbroken wires leading from the sensor to the

reference junction or to the measuring instrument. • If splicing is necessary to extend the length, identical wires

must be used to avoid additional emfs.

Connection without referenceConnection without reference

The connection to a voltmeter creates two junctions Both are kept at temperature T1

Net emf due to these junctions is zero Net emf sensed is that due to junction (2) This is commonly the method used

The connection to a voltmeter creates two junctions Both are kept at temperature T1

Net emf due to these junctions is zero Net emf sensed is that due to junction (2) This is commonly the method used

Reference junctionsReference junctions

Reference junctions must be at constant, known temperatures. Examples:

Water-ice bath (0C)Boiling water (100C)Any other temperature if measured

A separate, non-thermocouple sensor The output compensated based on this

temperature from Seebeck coefficients

Reference junctions must be at constant, known temperatures. Examples:

Water-ice bath (0C)Boiling water (100C)Any other temperature if measured

A separate, non-thermocouple sensor The output compensated based on this

temperature from Seebeck coefficients

Thermocouples - practical considerations

Choice of materials for thermocouples. Materials affect: The output emf, Temperature range Resistance of the thermocouple.

Selection of materials is done with the aid of three tables: Thermoelectric series table Seebeck coefficients of standard types Thermoelectric reference table

Choice of materials for thermocouples. Materials affect: The output emf, Temperature range Resistance of the thermocouple.

Selection of materials is done with the aid of three tables: Thermoelectric series table Seebeck coefficients of standard types Thermoelectric reference table

Thermoelectric series tablesThermoelectric series tables

Each material in the table is thermoelectrically negative with respect to all materials above it and positive with respect to all materials below it.

The farther from each other a pair is, the larger the emf output that will be produced.

Tables are arranged by temperature ranges

Each material in the table is thermoelectrically negative with respect to all materials above it and positive with respect to all materials below it.

The farther from each other a pair is, the larger the emf output that will be produced.

Tables are arranged by temperature ranges

Thermoelectric series tableThermoelectric series table

Table 3.5 The thermoelectric series: selected elements and alloys at selected temperatures 100°C 00°C 900°C Antimony Chromel Chromel Chromel Copper Silver Iron Silver Gold Nichrome Gold Iron Copper Iron 90%Pt-0Rh Silver 90%Pt-0Rh Platinum 90%Pt-0Rh Platinum Cobalt Platinum Cobalt Alumel Cobalt Alumel Nickel Alumel Nickel Constantan Nickel Constantan Constantan

Seebeck coefficients tablesSeebeck coefficients tables

Seebeck coefficients of materials with reference to Platinum 67

Given for various thermocouple types The first material in each type (E, J, K,

R, S and T) is positive, the second negative.

Seebeck coefficients of materials with reference to Platinum 67

Given for various thermocouple types The first material in each type (E, J, K,

R, S and T) is positive, the second negative.

Seebeck coefficient tablesSeebeck coefficient tables

Table 3.6. Seebeck coefficients with respect to Platinum 67 Thermoelement type – Seebeck coefficient [ V/° ]C Tem .p [° ]C JP JN TP ,TN EN K ,P EP KN 0 7.9 32. .9 32.9 2.8 3.6 00 7.2 37.2 9.4 37.4 30. .2 200 4.6 40.9 .9 4.3 32.8 7.2 300 .7 43.7 4.3 43.8 34. 7.3 400 9.7 4.4 6.3 4. 34. 7.7 00 9.6 46.4 46.6 34.3 8.3 600 .7 46.8 46.9 33.7 8.8 700 .4 46.9 46.8 33.0 8.8 800 46.3 32.2 8.8 900 4.3 3.4 8. 000 44.2 30.8 8.2

Seebeck coefficients tablesSeebeck coefficients tables

The Seebeck emf with reference to Platinum is given for the base elements of thermocouples with respect to Platinum 67.

Example, J type thermocouples use Iron and Constantan. Column JP lists the Seebeck emf for Iron with respect to

Platinum Column JN lists the emfs for Constantan. Adding the two together gives the corresponding value for

the J type thermocouple in Table 3.5. JP and JN values at 0C in table 3.3 : 17.9+32.5=50.4 V/C gives the entry in the J column at 0 C in Table 3.5.

The Seebeck emf with reference to Platinum is given for the base elements of thermocouples with respect to Platinum 67.

Example, J type thermocouples use Iron and Constantan. Column JP lists the Seebeck emf for Iron with respect to

Platinum Column JN lists the emfs for Constantan. Adding the two together gives the corresponding value for

the J type thermocouple in Table 3.5. JP and JN values at 0C in table 3.3 : 17.9+32.5=50.4 V/C gives the entry in the J column at 0 C in Table 3.5.

Seebeck coefficients by typeSeebeck coefficients by type

Table 3.7. Seebeck coefficients for various types of thermocouples Thermocouple type – Seebeck coefficient [ V/° ]C Tem .p [° ]C E J K R S T -200 2. 2.9 .3 .7 -00 4.2 4. 30. 28.4 0 8.7 0.4 39. .3 .4 38.7 00 67. 4.3 4.4 7. 7.3 46.8 200 74.0 . 40.0 8.8 8. 3. 300 77.9 .4 4.4 9.7 9. 8. 400 80.0 . 42.2 0.4 9.6 6.8 00 80.9 6.0 42.6 0.9 9.9 600 80.7 8. 42. .3 0.2 700 79.8 62.2 4.9 .8 0. 800 78.4 4.0 2.3 0.9 900 76.7 40.0 2.8 .2 000 74.9 38.9 3.2 .

Thermoelectric reference tableThermoelectric reference table

List the transfer function of each type of thermocouple as an nth order polynomial, in a range of temperatures.

Ensure accurate representation of the thermocouple’s output and can be used by the controller to accurately represent the temperature sensed by the thermocouple.

An example of how these tables represent the transfer function is shown next

List the transfer function of each type of thermocouple as an nth order polynomial, in a range of temperatures.

Ensure accurate representation of the thermocouple’s output and can be used by the controller to accurately represent the temperature sensed by the thermocouple.

An example of how these tables represent the transfer function is shown next

Thermoelectric reference table (cont.)

Table 3.8. Transfer function for type E thermocouples Temperature range [° ]C Exact reference emf (volt ) age

[E m ]v Reference temperature T [° ]C

0 to 400 400 to 000

(+.86987799 0 x x T +4.3094462 x 0-2 x T2 +.722038202 x 0- x T3 -.402066808 0x -7 x T4 +.42922x 0-9 x T -2.48008936 0x -2 x T6 +2.33897249 x 0- xT7 -.9462968 0x -8 x T8 +2.627497 x 0-22 xT9) x0

Within ± 0.°C .70222 0 x x E -2.2097240 0x - x E2 +.480934 x 0-3 x E3 -.7669892 0x - x E4 2.9347907 0x +.33834 x 0 x E -2.6669928 0x -2 x E2 +2.3388779 x 0-4 x E3

Table 3.8. Transfer function for type E thermocouples Temperature range [° ]C Exact reference emf (volt ) age

[E m ]v Reference temperature T [° ]C

0 to 400 400 to 000

(+.86987799 0 x x T +4.3094462 x 0-2 x T2 +.722038202 x 0- x T3 -.402066808 0x -7 x T4 +.42922x 0-9 x T -2.48008936 0x -2 x T6 +2.33897249 x 0- xT7 -.9462968 0x -8 x T8 +2.627497 x 0-22 xT9) x0

Within ± 0.°C .70222 0 x x E -2.2097240 0x - x E2 +.480934 x 0-3 x E3 -.7669892 0x - x E4 2.9347907 0x +.33834 x 0 x E -2.6669928 0x -2 x E2 +2.3388779 x 0-4 x E3

Thermoelectric reference tableThermoelectric reference table

Table entry for type E thermocouples. Second column is the exact representation of the

output emf (voltage) in V as a 9th order polynomial. The third column shows the inverse relation and

gives the temperature based on the emf of the thermocouple within a specified error – in this case ±0.1C.

The latter can be used by the controller to display temperature or take action

Table entry for type E thermocouples. Second column is the exact representation of the

output emf (voltage) in V as a 9th order polynomial. The third column shows the inverse relation and

gives the temperature based on the emf of the thermocouple within a specified error – in this case ±0.1C.

The latter can be used by the controller to display temperature or take action

Standard thermocouples - propertiesStandard thermocouples - properties

Table 3.9. Common thermocouple types and some of their properties. Materials Sensitivity

[ V/° ] C a t2° .C

Standard Type designation

Recommended temperat urerange [° ]C

Co /pper Constantan 40.9 T 0 to 400 ( 270 - 400)

/60% 40%Cu Cu Ni

Iron/Constantan ,7 J 0 to 760 ( 20 - 200)

F /60% 40%e Cu Ni

Chromel/Alumel 40.6 K 200 to 300 ( 270 - 372)

90%Ni0% /% 4%Cr Cu Ni

Chromel/Constantan 60.9 E 200 to 900 ( 270 - 000)

90%Ni0% /60% 40%Cr Cu Ni

Platinum(0%)/Rhodium-Platinum

6.0 S 0 to 40 ( 0 - 760)

Pt/90%Pt0%Rh

6.0 R 0 to 600 ( 0 - 760)

Pt/87%Pt3%Rh

Silv /er Paladium 0 200 to 600 Constantan/Tungsten 42. 0 to 800 Silicon/Aluminum 446 40 to 0 Carbon/Silico nCarbide 70 0 to 2000 Platinum(30%)/Rhodium-Platinum

6.0 B 0 to 820 Pt/70%Pt30%Rh

Nickel/Cromium-silico nalloy N ( 270 - 260) Not :e the temperature ranges shown are recomm .ended Nominal ranges are lower and higher and shown in bracket .s

Table 3.9. Common thermocouple types and some of their properties. Materials Sensitivity

[ V/° ] C a t2° .C

Standard Type designation

Recommended temperat urerange [° ]C

Co /pper Constantan 40.9 T 0 to 400 ( 270 - 400)

/60% 40%Cu Cu Ni

Iron/Constantan ,7 J 0 to 760 ( 20 - 200)

F /60% 40%e Cu Ni

Chromel/Alumel 40.6 K 200 to 300 ( 270 - 372)

90%Ni0% /% 4%Cr Cu Ni

Chromel/Constantan 60.9 E 200 to 900 ( 270 - 000)

90%Ni0% /60% 40%Cr Cu Ni

6.0 S 0 to 40 ( 0 - 760)

Pt/90%Pt0%Rh

6.0 R 0 to 600 ( 0 - 760)

Pt/87%Pt3%Rh

Silv /er Paladium 0 200 to 600 Constantan/Tungsten 42. 0 to 800 Silicon/Aluminum 446 40 to 0 Carbon/Silico nCarbide 70 0 to 2000 Platinum(30%)/Rhodium-Platinum

6.0 B 0 to 820 Pt/70%Pt30%Rh

Nickel/Cromium-silico nalloy N ( 270 - 260) Not :e the temperature ranges shown are recomm .ended Nominal ranges are lower and higher and shown in bracket .s

Thermocouple (exposed junction)

Thermocouple (flexible, to be cemented to surface)

Thermocouple (protected junction)

Semiconductor thermocouplesSemiconductor thermocouples

Semiconductors have highest Seebeck coefficients

Typical values are about 1mV/C Junctions between n or p type

semiconductors with a metal (aluminum) are most common

Smaller temperature ranges (usually –55 C to about 150C.

Some materials - up to 225CNewer devices - up to about 800C

Semiconductors have highest Seebeck coefficients

Typical values are about 1mV/C Junctions between n or p type

semiconductors with a metal (aluminum) are most common

Smaller temperature ranges (usually –55 C to about 150C.

Some materials - up to 225CNewer devices - up to about 800C

Semiconductor thermocouples: operation

Pure semiconductor: electrons in valence/covalence bonds Few electrons are available for conduction Adding heat moves them across the energy gap into the

conduction band To increase number of electrons - need to dope the

material

Pure semiconductor: electrons in valence/covalence bonds Few electrons are available for conduction Adding heat moves them across the energy gap into the

conduction band To increase number of electrons - need to dope the

material

Doping Add impurities - various materials Increases availability of electrons (n-type)

or holes (p-type) Increases the Seebeck coefficient Silicon has 4 valent electrons Add impurity with 5 electrons to create n

type silicon Add impurity with 3 electrons to create p

type silicon

Doping Add impurities - various materials Increases availability of electrons (n-type)

or holes (p-type) Increases the Seebeck coefficient Silicon has 4 valent electrons Add impurity with 5 electrons to create n

type silicon Add impurity with 3 electrons to create p

type silicon

P type silicon junction (on aluminum) Aluminum is deposited on an intrinsic layer of

silicon The silicon is doped with materials from the IIIrd

group in the periodic table materials such as Boron (B), Aluminum (Al),

Galium (Ga), Indium (In) and Thalium (Tl) N type silicon junction (on aluminum)

The silicon is doped with materials from the Vth group in the periodic table

materials such as Phosphorus (P), Arsenic (As), Antimony (Sb) and Bismuth (Bi)

P type silicon junction (on aluminum) Aluminum is deposited on an intrinsic layer of

silicon The silicon is doped with materials from the IIIrd

group in the periodic table materials such as Boron (B), Aluminum (Al),

Galium (Ga), Indium (In) and Thalium (Tl) N type silicon junction (on aluminum)

The silicon is doped with materials from the Vth group in the periodic table

materials such as Phosphorus (P), Arsenic (As), Antimony (Sb) and Bismuth (Bi)

Periodic table - semiconductorsPeriodic table -

semiconductors

ThermopileThermopile

n thermocouples in series electrically

In parallel thermallyOutput is n times the

output of a single thermocouple

n thermocouples in series electrically

In parallel thermallyOutput is n times the

output of a single thermocouple

Thermopiles (cont.)Thermopiles (cont.)

Used to increase outputSometimes done with metal

thermocouplesExample: pilot flame detector: 750 mV

at temperature difference of about 120C. about 100 metal thermocouples.

Used to increase outputSometimes done with metal

thermocouplesExample: pilot flame detector: 750 mV

at temperature difference of about 120C. about 100 metal thermocouples.

Semiconductor thermopilesSemiconductor thermopiles

Each thermocouple has higher output than metal based devices

A few thermocouples in series can produce relatively high voltage

Used to produce thermoelectric generators.

Outputs upwards of 15V are availableKnown as Peltier cells

Each thermocouple has higher output than metal based devices

A few thermocouples in series can produce relatively high voltage

Used to produce thermoelectric generators.

Outputs upwards of 15V are availableKnown as Peltier cells

Peltier cellsPeltier cells

Made of crystalline semiconductor materials such as bismuth telluride (Bi2Te3) (n-p junctions)

Peltier Cells are often used for cooling and heating in dual purpose refrigerators,

Can also be used as sensors and can have output voltages of a few volts (any voltage can be achieved)

Also used as power generators for small remote installations

Made of crystalline semiconductor materials such as bismuth telluride (Bi2Te3) (n-p junctions)

Peltier Cells are often used for cooling and heating in dual purpose refrigerators,

Can also be used as sensors and can have output voltages of a few volts (any voltage can be achieved)

Also used as power generators for small remote installations

Peltier cells (cont.)Peltier cells (cont.)

Junctions are sandwiched between two ceramic plates

Standard sizes are 15, 31, 63, 127 and 255 junctions

May be connected in series or parallel, electrically and/or thermally.

Maximum temperature difference of about 100C Maximum operating temperatures of about

225C Also used as power generators for small remote

installations

Junctions are sandwiched between two ceramic plates

Standard sizes are 15, 31, 63, 127 and 255 junctions

May be connected in series or parallel, electrically and/or thermally.

Maximum temperature difference of about 100C Maximum operating temperatures of about

225C Also used as power generators for small remote

installations

Some thermopiles (Peltier TEGs)

Details of the TEG construction

P-N Junction temperature sensors

A junction between a p and an n-doped semiconductor

Usually silicon (also germanium, galium-arsenide, etc.)

This is a simple diodeForward biased

A junction between a p and an n-doped semiconductor

Usually silicon (also germanium, galium-arsenide, etc.)

This is a simple diodeForward biased

P-N junction sensor (cont.)P-N junction sensor (cont.)

Construction of the sensorConstruction of the sensor

Forward current is temperature dependent Any semiconductor diode will work Usually the voltage across the diode is sensed

Forward current through diode

Voltage across diode I0 - saturation current Eg - band gap energy q - charge of electron k - Boltzman’s constant C - a temp. independent

constant T - temperature (K)

Forward current through diode

Voltage across diode I0 - saturation current Eg - band gap energy q - charge of electron k - Boltzman’s constant C - a temp. independent

constant T - temperature (K)

I = I0eqV/2kT

Vf = Egq − 2kT

q lnCI

If C and I are constant, Vf is linear with temperature

Diode is an NTC deviceSensitivity: 1-10mV/C (current dependent)

If C and I are constant, Vf is linear with temperature

Diode is an NTC deviceSensitivity: 1-10mV/C (current dependent)

P-N junction - operation parameters

Forward biased with a current source10-100A typically (low currents -

higher sensitivity)Maximum range (silicon) –55 to 150CAccuracy: ±0.1 C typicalSelf heating error: 0.5 mW/CPackaging: as a diode or as a transistor

(with additional circuitry)

Forward biased with a current source10-100A typically (low currents -

higher sensitivity)Maximum range (silicon) –55 to 150CAccuracy: ±0.1 C typicalSelf heating error: 0.5 mW/CPackaging: as a diode or as a transistor

(with additional circuitry)

The LM35 sensorThe LM35 sensor

Other temperature sensorsOther temperature sensors

OpticalAcousticalThermomechanical sensorsThermomecahnical actuators

Optical temperature sensorsOptical temperature sensors

Noncontact Conversion of optical radiation into heat Most useful in infrared temperature sensing Relies on quantum effects - discussed in the following

chapter Other sensors rely on phase difference in

propagation Light propagates through a silicon optical fiber Index of refraction is temperature sensitive Phase of detected light is a measure of temperature

Noncontact Conversion of optical radiation into heat Most useful in infrared temperature sensing Relies on quantum effects - discussed in the following

chapter Other sensors rely on phase difference in

propagation Light propagates through a silicon optical fiber Index of refraction is temperature sensitive Phase of detected light is a measure of temperature

Acoustical temperature sensorAcoustical temperature sensor

Speed of sound is temperature dependent

Measure the time it takes to travel through the heated medium

Most sensors use ultrasonic sensors for this purpose.

Speed of sound is temperature dependent

Measure the time it takes to travel through the heated medium

Most sensors use ultrasonic sensors for this purpose.

= 331.5

273.15

= 331.5

273.15

Acoustical temperature sensorAcoustical temperature sensor

Thermo-mechanical sensorsThermo-mechanical sensors

Changes of physical properties due to temperature Length Volume Pressure, etc.

Expansion of gasses and fluids (thermometers) Expansion of conductors (thermometers,

thermostats) Many have a direct reading (graduation, dials) Some activate switches directly (thermostats) Examples:

Changes of physical properties due to temperature Length Volume Pressure, etc.

Expansion of gasses and fluids (thermometers) Expansion of conductors (thermometers,

thermostats) Many have a direct reading (graduation, dials) Some activate switches directly (thermostats) Examples:

Gas expansion temperature sensor

Rise in temperature expands the gasDiaphragm pushes on a “sensor” (strain

gauge, potentiometer) or even a switchThe sensor’s output is graduated in

temperature

Rise in temperature expands the gasDiaphragm pushes on a “sensor” (strain

gauge, potentiometer) or even a switchThe sensor’s output is graduated in

temperature

Thermo-pneumatic sensorThermo-pneumatic sensor

Called a Golay cellGas expands in a flexible cellMotion moves a mirror and deflects lightExtremely sensitive device

Thermal expansion of metalsThermal expansion of metals

All metals expand with temperature

Volume stays constant - length changes

Each metal has a coefficient of linear expansion .

is usually given at T1, temperatures in C.

All metals expand with temperature

Volume stays constant - length changes

Each metal has a coefficient of linear expansion .

is usually given at T1, temperatures in C.

l2 = l11 + α T2 − T1 m

Coefficients of linear expansion

Table 3.10. Coefficients of linear expansion for some. Coefficients are given per ° .C Material Coefficien t of expansio na, x0 Aluminum 2.0 Chromium 30.0 Copper 6.6 Gold 4.2 Iron 2.0 Nickel .8 Platinum 9.0 Phosphor-bronze 9.3 Silver 9.0 Titanium 6. Tungsten 4. Zink 3

Thermal expansion of metalsThermal expansion of metals

Coefficients of linear expansion are small

They are however measurableCan be used to directly operate a lever

to indicate temperatureCan be used to rotate a shaftIn most cases the bimetal configuration

is usedServe as sensors and as actuators

Coefficients of linear expansion are small

They are however measurableCan be used to directly operate a lever

to indicate temperatureCan be used to rotate a shaftIn most cases the bimetal configuration

is usedServe as sensors and as actuators

Example: direct dial indicationExample: direct dial indication

Metal bar expands as temperature increases Dial arrow moves to the left as temperature rises Very small motion The dial can be replaced to a pressure sensor or a

strain gauge

Metal bar expands as temperature increases Dial arrow moves to the left as temperature rises Very small motion The dial can be replaced to a pressure sensor or a

strain gauge

Bimetal sensorsBimetal sensors

Two metal strips welded togetherEach metal strip has different coefficient of

expansionAs they expand, the two strips bend. This

motion can then be used to: move a dial actuate a sensor (pressure sensor for example) rotate a potentiometer close a switch

Two metal strips welded togetherEach metal strip has different coefficient of

expansionAs they expand, the two strips bend. This

motion can then be used to: move a dial actuate a sensor (pressure sensor for example) rotate a potentiometer close a switch

Bimetal sensors (cont.)Bimetal sensors (cont.)

To extend motion, the bimetal strip is bent into a coil. The dial rotates as the coil expands/contracts

Bimetal sensors (cont.)Bimetal sensors (cont.)

Displacement for the bar bimetal: r - radius of

curvature T2 - sensed

temperature T1 - reference

temperature (horizontal position)

t - thickness of bimetal bar

Displacement for the bar bimetal: r - radius of

curvature T2 - sensed

temperature T1 - reference

temperature (horizontal position)

t - thickness of bimetal bar

d = r 1 − cos80 L

md = r 1 − cos80 L

Bimetal switch (example)Bimetal switch (example)

Typical uses: flashers in cars, thermostats)Operation

Left side is fixed Right side moves down when heated Cooling reverses the operation

Typical uses: flashers in cars, thermostats)Operation

Left side is fixed Right side moves down when heated Cooling reverses the operation

Bimetal coil thermometerBimetal coil thermometer

Bimetal switch (car flasher)Bimetal switch (car flasher)

3 - temperature sensors 1. thermoresistive sensors 2. thermoelectric sensors 3. pn junction...

platinum temperature

acoustic temperature

newer sensors

thermoresistive sensors

sensors thermoresi

temperature scales boyle

thermomechanical sensors

kelvin scale

Documents

nanostructured high temperature bulk thermoelectric energy

ceramic high temperature thermoelectric heat exchanger and

tewa temperature sensors - media.digikey.com...

sks sensors temperature sensors catalogue

data sheet temperature sensors sensytemp tsp311, tsp321...

nanostructured high temperature bulk thermoelectric … ·...

enhanced high temperature thermoelectric characteristics of

nanostructured high-temperature bulk thermoelectric energy...

fabrication of high temperature thermoelectric energy

high-entropy alloys as high-temperature thermoelectric...

a thermoelectric cooler temperature controller for fiber...

rtd temperature sensors high accuracy sensors for a...

lfi-3751 with autotune pid thermoelectric temperature...

testequity tec1 thermoelectric temperature chamber operation...

tsp411 sensytemp temperature sensors temperature sensors for

understanding vacuum furnace temperature measurement...

development of a 100-watt high temperature thermoelectric

compact rtd temperature sensors - pinnacle...

ceramic high temperature thermoelectric heat...

for and ,please con˜gure online. temperature sensor...