TIR100-2 Measurement of Thermal Emissivity · INGLAS GmbH & Co. KG 2 TIR100-2 History • 1987 First Emissiometer developed and patented by Dornier System GmbH Friedrichshafen. Application:

INGLAS GmbH & Co. KG 1

TIR100-2

Measurement of Thermal Emissivity

Dr. Thomas Meisel

INGLAS GmbH & Co. KG

Introduction

Some basic physics

Principles of measurement

prEN 15976

Working with the TIR100-2

Practical course


TIR100-2 History

• 1987 First Emissiometer developed and patented

by Dornier System GmbH Friedrichshafen.

Application: solar collector coating.

Analog Instrument, semiconductor sensor.

Range e: 0,2 .. 0,9

• 1994 Emis01 by Dornier System,

Table top, microcontroller, thermopile Sensor.

Range e: 0,10 .. 0,95

• 1996 TIR100 by INGLAS GmbH & Co.

Application: glass and solar collector coating.

Table top, thermopile Sensor.

Range e: 0,07 .. 0,95

• 2003 TIR100-2 by INGLAS GmbH & Co.

Handheld instrument, thermopile Sensor.

Range e: 0,02 .. 0,98


TIR100-2 Reference List 2/2010

4

Some Basic Physics

P = s * e * T4

P = Radiative Power [W/m2]

T = Temperature [K]

e = Emissivity

s = Planck‘s Constant [W/K4m2]

Stefan-Boltzmann‘s law

Stefan-Boltzmann‘s law

Every body with a temperature above

absolute zero radiates thermal heat.

The quantity of heat (power) is given by

Emissivity e is the degree of radiative

energy compared to that of an ideal

blackbody: e = 0 .. 1

Rule of thumb:

A body with a surface of high conductivity

(much electons) possesses a low

emissivity

(e.g. polished aluminum e ~ 0,012)

A body with low conductivity (few electrons

possesses a high emissivity

(e.g. glass e ~ 0,837)


5

Wien's displacement law

lmax = 2,9*103 /T µm

Black Body Radiation

at 100°C

0E+00

5E+06

1E+07

2E+07

2E+07

3E+07

3E+07

0 10 20 30 40 50 60

Wavelength µm

Rad

iati

on

W/m

2µ

m

100C

Wien's displacement law states that the wavelength distribution of radiated heat energy from a

black body at any temperature has essentially the same shape as the distribution at any other

temperature, except that each wavelength is displaced, or moved over, on the graph.

The wavelength of maximum radiative energy could be calculated by

6

1E+5

1E+6

1E+7

1E+8

1E+9

1E+10

0,0 5,0 10,0 15,0 20,0 25,0 30,0 35,0 40,0 45,0 50,0

Spectral distribution of thermal radiation at different temperatures

Wavelength (µm)

Rad

iati

ve

po

wer

(W/(

m2

*nm

*sr)

SpectrumT = 800 C = 1073 K

Spectrum TIR 100T = 100 C = 373 K

Spectrum DIN EN 673T = 10 C = 293 Klmax = 10,3 µm

lmax = 7,8 µm

lmax =2,7 µm

Black Body - Spectral distribution


Solar and thermal radiation in everyday life

1000 10000

0

200

400

600

800

1000

1200

1400

1600

NIR

VIS

Solare Strahlung

So

lare

Str

ah

lun

g [

W/m

2/µ

m]

Wellenlänge [nm]

Glas

IR

Thermische Strahlung 300 K

0

20

40

60

80

100

UV

Tra

nsm

issio

n [%

]

Glass transmission

Thermal radiation

at 100°C

Solar radiation

Wavelength nm

Ra

dia

tive

po

we

r


a + r + t = 1

al = el

el = 1 - rl

Spectral measurement

Principles of emissivity measurement

(1- rl)Sldl

Sldl

e =

Wavelength dependant measurement

of reflectivity with ir-spectrometer.

Mathematic evaluation of emissivity:

Integral measurement

Integral measurement with

a black body radiator. Computing

of emssivity from reflectivity

measurement:

e = 1 - r if t = 0

a = absorption

r = reflexion

t = transmission

e = emissivity

Conditions

Sl = Black body radiation

at wavelength l.

DIN EN 673

Kirchhoff's law of thermal radiation




Normal and effective Emissivity

Emissivity depends on factors such as temperature, wavelength and emission angle.

The emissivity of flat metal surfaces tends to be lower in normal direction as

hemispherical.

The TIR100-2 measures the normal emissivity. If the hemispherical (effective) emissivity

shall be calculated for a flat metal surface, correction factors have to be applied. The

EN673 lists a table of correction factors.

Rough metal surfaces, coated textiles and non conductive materials may not be adjusted

Measured normal emissivity e Relation e eff / e 0.03 1,22

0.05 1.18

0.1 1.14

0.2 1.10

0.3 1.06

0.4 1.03

0.5 1.00

0.6 0.98

0.7 0.96

0.8 0.95

0.89 0.94


Emissivity depends on surface roughness

e = 1 - r => 0,2

r = 0,8 r = 0,8 * 0,8 = 0,64

e = 1 - r => 0,36

Structures equal or larger than the dominant infrared wavelength (~10 µm at room temp.) increase

emissivity: To get low emissivity surfaces, they must be polished to a roughness of < 1/10 of

dominant infrared wavelength!

Example:


• Nondestructive measurement of temperature

sensitive samples at room temperature

• Black Body (semi-)sphere at 100 °C

– Homogenous, diffuse irradiation

– Allows one-click measurement of

smooth and rough surfaces

• Thermopile-sensor with Fresnel - optic

– integral ir broad band measurement

– angle of measurement 12°: comparable

to measurements under normal

incidence

– Ø10 mm spot measurement area for

small samples

Integral reflectivity measurement TIR100-2 Features


• Temperature of sample and calibration

standard must be equal

• Distance of black-body radiator to sample

surface must be identical to standard -

blackbody distance during calibration

• Use the same instrument orientation at

calibration and measurement

• Avoid strong moves of the instrument

• Keep surrounding area free of draft

• Blackbody half sphere must be completely

covered by sample (possibly use a sample

holder)

• Flexible samples should be kept plain

TIR100-2 requirements for precise measurement

The TIR100-2 is easy to use, but some

precautions should be observed to get

precise results:

As measurement of reflected power

follows T4 , small changes of surface

temperature of the blackbody, the

sample and the calibration standard

have a distinct effect on the results.

Follow the instructions in the operation

manual and the prEN 15976:


7.3 Preparation of specimens before testing

The specimens should be kept for a minimum of 2 hours at a temperature of 23 +/-2°C and

relative humidity of 50 +/-20%. Special precaution should be taken to ensure that the calibration

standards, the specimens and the apparatus are equilibrated in the same standard climatic

conditions. Air currents and draughts in the measuring area must be avoided.


8 Procedure for measurement of specimens

The apparatus should be switched on at least 2 hours before calibration and

beginning measurements. The apparatus should be installed in a fixed position and

must not be moved during measurement. The specimen is brought up to the

apparatus in a vertical orientation, pressed firmly against the spacers around the

measuring window of the apparatus and the apparatus is activated to begin

measurement. In order to avoid that the specimen temperature changes during the

measurement, the residence time of the specimen in the measuring position must be

reduced to a minimum. Between specimen positioning and start of measurement,

not more than 1 second shall pass.

If this speed of measurement is not achieved, if the measurement is otherwise

interrupted or if the measurement on a specimen is to be repeated, the specimen

should be withdrawn from the apparatus for the time it needs to cool down to

laboratory temperature. The higher the emissivity and/or the lower the specific

heat capacity ( c ) of the material, the longer the specimen will need to cool down to

laboratory temperature.

In order to reduce measurement variability to a minimum (laboratory, specimen and

apparatus related), after a time interval of maximum 1 hour, the apparatus shall be

recalibrated using the two calibration standards.


9 Expression of the results

The emissivity of the specimen is directly indicated as a three decimal number. The emissivity

mean value, all the single values per specimen and the standard deviation of the results from the

tested product shall be included on the test report. The emissivity mean-value is to be rounded to

two digits.

All single measurements resulting in an emissivity <0,02 or >0,94 (measurement range of the

apparatus) should be set to 0,02 or 0,94 respectively.



Touch screen

On/Off RS232

230V /

115 V*



Getting into operation

• Switch on instrument.

• If “Continue” is displayed and no “wait!” you

can start measuring

• It should warm up 1 hr minimum. The longer,

the better

• The instrument consumes about 24W in

operation (already heated)

• Place the instrument on a place with no

draft, eventually use a working box

• Calibration standard and samples should be

stored together at your working place to

acclimate.

• Keep samples and standard away from the

hot blackbody to avoid heating



Calibrating instrument

• Put calibration standard (black, ribbed

surface) in front of the blackbody radiator. It

should be in contact with the silicon distance

pads of the instrument

• Press CALIBRATE HIGH immediately and

wait until measurement is complete (sound)

• Remove standard immediately to avoid

heating

• Repeat procedure with low emissive

aluminum surface



Measurement

• Put sample in front of the blackbody radiator.

It should be in contact with the silicon

distance pads of the instrument

• Press MEASURE immediately and wait until

measurement is complete (sound)

• Remove sample immediately to avoid

heating


! Tip

Remeasure calibration standard every

10 min to ensure correct calibration


Measurement of glass

and massive samples

• Put the sample in tight contact to the

blackbody. Transparent samples should be

kept dark on the rear side

• Do not move instrument between calibration

and measurement. Avoid circulation around

the instrument


See also video on our Website: www.TIR100.com


Measurement of foils and textiles

• Use foil support and fix foils or textiles with

reversible adhesive tape to keep it in good

thermal contact with the support

• A magnetic fixture can be use if tape is not

suited for adhesive fixture




Measurement of the emissivity of woven textiles and

porous samples

P1 = textile

P1 = background

1-e = A * r1 + (1-A) * r2

r2 -> 0; e = 1- (A * r1)

TIR100-2 receives the reflected power of

textile and background. The instrument

computes:

If background does not reflect (r2 = 0),

textile reflects heat with r1 proportional to its

fraction of area A.

Conclusion:

Using a non ir- reflective background during

measurement, the effective emissivity of the

textile could be determined, but not the

absolute emissivity of the textiles surface!


Certificates


Certificates


TIR100-2

Measurement of Thermal Emissivity


Thank you very much for

your attention!

Documents

TIR100-2 Measurement of Thermal Emissivity · INGLAS GmbH & Co. KG 2 TIR100-2 History • 1987 First Emissiometer developed and patented by Dornier System GmbH Friedrichshafen. Application: