15 Minute Break

Components of a Temperature Sensor

• The Optics collect & focus the emitted energy onto a detector. Types of lenses include glass, quartz, achromat, germanium, and zinc.

• The Filters optimize the operation of the sensor to selected energy wavelengths.

• The Detector converts the infrared energy signal into an electrical signal. Common detectors include Ge, Si, InGaAs, Thermopile, PbS, PbSe, InAs.

Temperature RangeSensor Type

OpticsWavelength

Infrared Thermometers

•Brightness(a.k.a. Single-Wavelength or One-Color)

•Ratio(a.k.a. Dual-Wavelength of Two-Color)

•Multi-Variant(a.k.a. Multi-Wavelength or Other)

Three Sensor Types

Brightness Sensorε = constant

Dual-wavelength sensore-slope = ε1/ε2 – 1 = constant

Multi-wavelength Sensor (Williamson)e-slope = f(ε2)

e-slope function is material specific

Brightness Sensors

Infrared Energy vs. TemperatureCalibration Curve

PRO 42 Auto Null Sensor

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1,000

Measured Temperature (°F)

Ener

gy (W

atts

/cm

^2)

-17 8 33 58 83 108 133 158 183 208 233 258 283 308 333 358 383 408 433 458 483 508 533

Measured Temperature (°C)

2um Sensor

Temperature Application Issues

FOV TargetArea

Full FOV

Partially Filled FOV

FOV Target Areaw/ Diameter (d)

HEATED TARGETBACKGROUNDREFLECTIONS

Working Distance (D)

HEAT SOURCE

InterveningMedia

Field of View (FOV)

SENSOR

ΔT (System) = ΔT (Emissivity) + ΔT (Transmission) + ΔT (Background) + ΔT (Instrument) + ΔT (Alignment)

Brightness Sensors

• Tend to measure an average temperature value

• Are affected by changes in emissivity, optical obstruction & stray background energy

• Wavelength Matters!

• Shorter Wavelengths are less sensitive to emissivity variation and optical obstruction.

• Shorter wavelength readings are more highly weighted towards the hottest temperature viewed & longer wavelengths are less sensitive to hot reflections.

• For low-emissivity materials, the emissivity is higher at a shorter wavelength, further reducing errors.

• Wavelength selection is critical for viewing through steam, flames and products of combustion, for avoiding IR heater interference, and for measuring coated products.

Why Wavelength Matters

Atmospheric Absorption

Infrared Energy vs Wavelength

05

10152025303540455055606570

0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1,000

Measured Temperature (°F)

Tem

pera

ture

Var

ianc

e (°

F)

0246810121416182022242628303234363840

-17 8 33 58 83 108 133 158 183 208 233 258 283 308 333 358 383 408 433 458 483 508 533

Measured Temperature (°C)

Tem

pera

ture

Var

ianc

e (°

C)

2um Sensor 8-14um Sensor

Short Wavelength (2um) vs. Long Wavelength (8-14um) SensorError from 10% Emissivity Change, or 10% Optical Obstruction

Normal Spectral Emissivity of Cold Rolled Steel

0.1

0.2

0.30.4

0.5

0.6

0 1 2 3 4 5 6

Wavelength (microns)

Emis

sivi

ty

Touloukian and DeWit t

Iuchi

Gaskey Eqn.

Met allic Theory (Fe @800 C)

Emissivity vs. Wavelength

Traditional Operating Wavelength Showing Interference from Steam & Products of Combustion

Wavelength Selection to View Through Steam and Products of Combustion

Transmission Characteristics (Selective Emitters)

Wavelength μm

Wavelength μm

Wavelength μm

Wavelength μm

Glass Quartz

Polyester Polyethylene

0 5 10

0 5 10

0 5 10

0 5 10

Tran

smis

sion

%Tr

ansm

issi

on %

Tran

smis

sion

%Tr

ansm

issi

on %

Brightness Wavelength Selection

• Use the shortest practical wavelength for most applications to minimize sensitivity to emissivity variance & optical obstruction.

• Use a specific wavelength to eliminate or minimize transmission or reflection issues (i.e. coatings, flames, products of combustion, water vapor, steam, water spray, plastics, glass, crystalline materials).

Compensation for Emissivity

• Single-wavelength sensors require a constant emissivity

• Select the shortest possible wavelength(1-2um) to minimize errors due to changes in emissivity

• An emissivity adjustment compensates for different emissivity values

• Many applications require repeatability, not absolute accuracy

Brightness Sensor Summary

• Short wavelengths minimize errors due to emissivity variation, optical obstruction & misalignment.

• Wavelength may be optimized to view through steam, flames & products of combustion.

• Wavelength may be optimized to view flames or gasses.

The Advantage of Auto Null• The Auto Null Sensors provide greater

accuracy & repeatability for low emissivityapplications at temperatures as low as100°F / 35°C– A Short wavelength of 2µm minimizes sensitivity

to emissivity variation.– The Patented Design provides automatic

calibration 20 times / second to eliminate noise & drift common for this type of sensor

• Used to measure low temperature metals.• Views through steam & common windows.

• Coke Conveyor Protection• CO Flame Monitor• Ladle / Refractory Preheat• Reheat Furnace Heating Zones• Dual-Phase Steel Quench• Low-Temperature Strip or Bar (Cold Mill,

Coating Lines)• Heat Treat Furnaces• Hot Metal Detector

Sample Brightness Sensor Wavelength-Critical Applications

Ratio Sensors

Compensates for Signal Dilution from Intervening Media

HEATED TARGET

FIELD OF VIEW (FOV)

SENSOR

INTERVENING MEDIA- Smoke - Spray- Dust - Dirty Windows- Steam - Partial Windows- Plasma

• Compensate for emissivity variation, and tend to measure the hottest temperature viewed.

• Are affected by changes in e-slope, wavelength-selective optical obstruction and excessively hot background reflections.

• Wavelength Matters!

Ratio Sensors

Definition of e-slope offset

For a dual-wavelength pyrometer operating at wavelengths λ1 and λ2

Error due to Emissivity Variation –Ratio Sensor

• Both measured wavelengths must be equally influenced by any optical obstruction or emissivity variation.

• Greater wavelength separation reduces sensitivity to e-slope variation and reduces sensitivity to warm interferences (scale / temperature gradients).

• Wavelength affects low temperature performance (available as low as 95 C/200 F).

Why Wavelength Matters

Dual WavelengthIncident IR Energy from Target

Two ColorIncident IR Energy from Target

OPTICAL SYSTEM

ENERGYROTATING WHEEL

W/ SELECTABLE FILTERS

ALTERNATEλA & B

SINGLE DETECTOR

RATIO TEMPCALCULATION

ALTERNATE A & B OUTPUT SIGNALS

OPTICAL SYSTEM

IR Filter

λ A: 0.7-1.08 µm

TOP DETECTOR

RATIO TEMPCALCULATION

A & B OUTPUT SIGNALS

BOTTOM DETECTORλ B: 1.0-1.08 µm

Two Ratio Designs

ENERGY

λ μm

0.6

0.5

0.4

0.3

0.2

0.1

0.00.0 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

Top Diode

Bottom DiodeAB

SOL

UT

E R

ESP

ON

SIV

ITY

Traditional “Two-Color” Wavelengths

Viewing Through Steam & Products of Combustion

100

80

60

40

20

00.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5

WAVELENGTH (MICRONS)

TR

AN

SMIS

SIO

N %

Transmission thru 0.094 in of water

Transmission thru 0.375 in of water

Infrared TransmissionThrough Water

Signal Dilution

• A measure of infrared energy compared to the amount of energy required to make a reading. 50:1 means that the sensor is collecting 50 times the energy required to make a reading.

• Typical application factors that dilute the energy signal level are– Misalignment, low emissivity, dirty optics,

water spray, dust, scale, small targets.

Signal Dilution Capability

Sensor Temperature Range

Infr

ared

Ene

rgy

Low Energy Levels

Two Color

Dual-Wavelength

SENSOR SIGNAL LOW ENERGY LIMITSIGNAL DILUTION =

Bottom Mid Top

SAMPLE SIGNAL DILUTION FACTOR VALUES

Segment of Temperature

Range

Dual Wavelength

Typical Two

Color Bottom End 5:1 1:1 or 2:1 Mid Range 500:1

1500:1 20:1

Top End 2000:1 6000:1

20:1 100:1

Sensor Signal Level

Dual-Wavelength Features• Automatic Emissivity Compensation• Compensates for scale & oxide formation• Views thru dust, dirty optics, & water Spray• Measures highly weighted average towards the

hottest temperature viewed– Accurate measurements with a partial FOV– Effective for small & moving targets like wires

& molten pours • Measures the Target Emissivity & Signal Dilution• Includes advanced ESP Filters for Signal Dilution

and Signal Strength

Ratio Sensor Summary

• Wavelength separation optimizes stability and the ability to tolerate scale & other temperature gradients.

• Ability to tolerate optical obstruction is measured by Signal Dilution.

• Selective wavelengths tolerate water, steam, flames & products of combustion.

• Difficult to measure applications in demanding industrial environments

• Applications where single wavelength sensors can not meet requirements– surfaces with low or varying emissivity– View thru obstructions or intervening media– Compensate for dirty optics, & oxide or scale

formation– Measure small or wandering targets that do

not fill the sensors field of view (FOV)

Dual Wavelength Temperature Applications

• Coke Guide• Sintered Briquette• Molten Iron Stream / Vacuum Melter• Caster Containment Zone• HSM Re-Heat Furnace Soaking Zone• Hot Mill (Scale, Water & Steam)• Weld Temperature• Heat Treat Furnaces

Sample Ratio Sensor Wavelength-Critical Applications

Multi-Variant Sensors

Multi-Variant Sensors

• Are used whenever traditional sensors are not appropriate.

• Use multiple wavelengths to characterize the emissive nature of the measurement.

• Multi-Variant algorithms are developed for each application type (usually the same from one plant to the next) to address specific emissivity or interference issues.

• Designed for difficult materials and challenging applications.

• Used where single- & dual-wavelength sensors can’t meet requirements

• Common measurements include Aluminum, Brass, Copper, Zinc, Galvanneal, Stainless Steel, Electrical Steel, High Strength Steel, Cold Rolled Steel, Magnesium, Chrome, etc… .

Multi-Wavelength Infrared Thermometers

Temperature Application Issues

FOV TargetArea

Full FOV

Partially Filled FOV

FOV Target Areaw/ Diameter (d)

HEATED TARGETBACKGROUNDREFLECTIONS

Working Distance (D)

HEAT SOURCE

InterveningMedia

Field of View (FOV)

SENSOR

ΔT (System) = ΔT (Emissivity) + ΔT (Transmission) + ΔT (Background) + ΔT (Instrument) + ΔT (Alignment)

Multi-Wavelength Design• ESP technology to accurately compensate for

complex application issues– ESPs are computer based empirical

algorithms that are application specific– The ESPs are application specific, factory

programmed, and menu selectable– Eliminate field calibration requirements

Multi-wavelength Sensor

Brightness Sensorε = constant

Dual-wavelength sensore-slope = ε1/ε2 – 1 = constant

Multi-wavelength Sensor (Williamson)e-slope = f(ε2)

e-slope function is material specific

e-slope Function Example: Oxidizing Steel

e-slope Function Example: Oxidizing Steel

Performance of Single, Dual, and Multi-Wavelength Sensorson Steel Annealing Lines

Assumes Strip Temperature of 1400°F (760°C)

-75

-50

-25

0

25

50

75

100

125

150

0.20 0.30 0.40 0.50 0.60

Surface Emissivity

Tem

p (°F

) Err

or

-44-39-33-28-22-17-11-60611172228333944505661677278

Tem

p (°

C) E

rror

Single-Wavelength Sensor: Emissivity Setting = 0.3Dual-Wavelength Sensor: E-Slope Setting = 1.0Multi-Wavelength Sensor: ESP Algorithm = Annealing

Stainless Steel Measurements

1400

1450

1500

1550

1600

1650

1700

1750

1800

1850

1900

1950

2000

Elapsed Time

Mea

sure

d Te

mpe

ratu

re (°

F)

Reference T/CSingle-Wavelength SensorDual-Wavelength SensorMulti-Wavelength Sensor

TemperatureSensor

AverageVariance

StandardDeviation

Single Wavelength -23°F 32°FDual Wavelength 29°F 53°FMulti Wavelength 1°F 5°F

ESP can compensate for Changes in Emissivity from 0.4 to 0.9

700710720730740750760770780790800810820830840850860870880890900

Tem

pera

ture

(°F)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Emis

sivi

ty

Reference T/C (°F)

Emissivity

Dual Wavelength (°F)

Single Wavelength (°F)

Multi Wavelength (°F)

TEST PROFILE TEST RESULTS

Sample Material:Sensor Model:Temperature Range:Change inEmissivity:

GalvannealSteel110-10700 to 2100°F0.1 to 0.7

SensorSingle WavelengthDual WavelengthMulti Wavelength

Avg.Var.

-50°F 21°F -1°F

Std.Dev.36°F 6°F 2°F

Performance of Single, Dual, and Multi-Wavelength Sensorson Galvanneal Measurements

Annealing FurnaceMild, Stainless, High Strength and High

Temperature AlloysHot-Dip LinesGalvanize, Galvalume and GalvannealTube MillsCold Rolled Alloys

Sample Multi-Variant Sensor Applications

• Steel Annealing Lines• Cold Rolled Steel Strip• Nonferrous and High Alloy Metals

– preheating, forming, heat treating• Nonferrous coating lines• Glass Mold Measurements• Many applications where single- and dual-

wavelength sensors won’t work

Sample Multi-Wavelength Applications

Alignment Issues

Defining the Sensor FOVSpot Size (d) @ Working Distance (D)

d = D/F• d = Focal Diameter• D = Focal Distance• F = Optical Resolution Factor

(Formula applies to English and metric units of measurement)

Typical Sensor FOV Diagram

00.51.01.52.02.53.0

0 1 2 3 4 5 6

Working Distance From Front End Plate (feet)

Targ

et D

iam

eter

(Inc

hes)

FOV36in/100 : 0.36in at 36inches

Alignment Guidelines

Measured Target

Reflected EnergyFrom Surroundings

Transmitted Background Energy

45�

Energy Emittedby Target

Sight Tube orFurnace Wall

Window

Sensor FOV

Alignment Guidelines • FOV must clear sight tubes & obstacles

• Windows must be transparent at the sensor operating wavelength

• Position & align to eliminate interference from background & reflected energy

• Rule of thumb for angle of incidence from normal : generally up to 60°, rough surfaces up to 85 °

• Provide access to tight spaces• Some operate in strong magnetic fields.• Survive hostile environments.

• Glass / Quartz• Small diameter, non-conductive mono-filament• Standard mono-coil multi-strand• Stainless Steel Braid• ArmorGuard• Rigid Light Guides

Fiber Optic Systems

PRO 90 With ArmorGuard

Advanced Signal Conditioning:ESP Filtering

• Brightness Technology– Auto Null Technology for Low-Temperature, Short-Wavelength,

Single-Wavelength Measurements. – Low or Varying Emissivity at Low Temperatures (below 400-600 F /

200-300 C)– Low Temperature Measurement through Windows. – Narrow band wavelengths to avoid common interference sources or

to measure selective emitters.• Dual-Wavelength Technology

– Compensates for varying emissivity, optical obstructions, temperature gradients, and misalignment.

– Unique wavelength selection to view through water and steam and for low-temperature measurement.

– Advanced Signal Conditioning with Unique ESP Technology• Multi-Wavelength Technology

– Used for Non-Greybody Measurements.– Advanced Signal Conditioning with Unique ESP Technology

Williamson’s Advanced Infrared Technologies

• Line Scanners• Thermal Imaging Cameras• Flame Detectors• Hot Metal Detectors• Two-Component Background

Compensation System• Laser Reflection Multi-Variant Type

Other Infrared Technologies