MICRO-EPSILON TIM 400 Manual de usuario descargar pdf (Pagina 74)

Temperature measurement of glass

If you measure temperatures of glass it

implies that you take care of reflection

and transmissivity. A careful selection

of the wavelength facilitates measure-

ments of the glass surface as well as

of the deeper layers of the glass. Wave-

lengths of 1.0 µm, 1.6 µm or 2.3 µm are

appropriate for measuring deeper layers

whereas 5 µm are recommended for

surface measurements. If temperatures

are low, you should use wavelengths

between 8 and 14 µm in combination

with an emissivity of 0.85 in order to

compensate reflection. For this purpose

a thermometer with short response time

should be used as glass is a bad heat

conductor and can change its surface

temperature quickly.

Spectral transmissivity of glass

2 3 4 5

Wavelength in µm

Transmissivity in %

100

Temperature measurement of plastics

Transmissivities of plastics vary with the

wavelength. They react inversely pro-

portional to the thickness, whereas thin

materials are more transmissive than

thick plastics. Optimal measurements

can be carried out with wavelengths,

where transmissivity is almost zero and

independent from the thickness. Poly-

ethylene, polypropylen, nylon and po-

lystyrene are non-transmissive at 3.43

µm, polyester, polyurethane, teflon, FEP

and polyamide are non-transmissive at

7.9 µm. For thicker and pigmented films

wavelengths between 8 and 14 µm will

do. The manufacturer of infrared ther-

mometers can determine the optimal

spectral range for the temperature mea-

surement by testing the plastics materi-

al. The reflection is between 5 and 10 %

for almost all plastics.

Spectral permeability of plastics made from polethylene.

2 3 4 5 6 7 8 9 10 11 12 13 14

100

Transmissivity in %

Wavelength in µm

0.03mm thickness

Spectral transmissivity of plastic layers made of polyester

2 3 4 5 6 7 8 9 10 11 12 13 14

100

0.03mm thickness

Wavelength in µm

Transmissivity in %

Physical Basics

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