Optris CT G5, PI 640 G7 User Manual
innovative infrared technology
Production
Quality Assurance
Research & Development
Test & Measurement
NON-CONTACT
TEMPERATURE MEASUREMENT
GLASS INDUSTRY
Glass industry
2 4 6 8 10 12 14 16
Wavelength in µm
Wavelengh [µm]
TECHNOLOGY AND PHYSICS
Inuence from the surroundings
The illustration shows that the transmissivity of air strongly
depends on the wavelength. Strong attening alternates with
areas of high transmissivity – the so-called atmospheric windows.
The transmissivity in the longwave atmospheric window (8 – 14
µm) is constantly high whereas there are measurable alleviations
by the atmosphere in the shortwave area, which may lead to false
results. Typical measuring windows are 1.1 – 1.7 µm,
2 – 2.5 µm and 3 – 5 µm.
Additional inuences can arise from heat sources in the
environment of the measuring object. To prevent wrong measuring results due to increased ambient temperatures, the infrared
thermometer compensates the inuence of ambient temperatures
beforehand (as e.g. when measuring temperatures of glass
surfaces in heating areas whereby the walls are hotter than the
glass surfaces). A second tem-perature sensing head helps to
generate accurate measuring results by automatically
compensating the ambient temperatures and a correctly adjusted
emissivity.
100
Radiation
from
ambient
n
T
Object
amb
ρ
n
T
n
T
amb
obj
= α
ε
τ
Sensor
α = Absorption ρ = Reflectance τ = Transmission ε = Emissivity
Compensating ambient influences
Emissivity and temperature measurement
For the accurate measurement of temperatures,
emissivity is a key factor. It is dependent on various
inuences and must be adjusted according to the
application.
75
Transmissivity in %
50
25
0
Spectral transmissivity of air (1 m, 32 °C (90 °F), 75 % r. F.)
Dust, smoke and suspended matter in the atmosphere can pollute
the optics and result in false measuring data. Here air purge
collars (which are installed in front of the optics with compressed
air) help to prevent deposition of suspended matter in front of the
optics. Accessories for air and water cooling support the use of
infrared thermometers even in hazardous surroundings.
Emissivity theoretically depends on the material, its surface quality, wavelength, the measuring angle and, in some cases, even
the applied measuring conguration.
Glass usually exhibits an emissivity of 0.85 in the longwave range
(8 – 14 μm). In processes with higher temperatures glass surfaces
are measured with 5.0 μm or 7.9 μm because in those spectral
ranges the emissivity is ≥0.95.
The main advantage of 7.9 µm is the lower angle dependency of
the glass surface reection in this wavelength range. This means
that the surface temperature can be measured independently of
the reection even at an inclined viewing angle.
Emissivity
2
Spectral emissivity of glass
The CoolingJacket Advanced enables an
operation within an ambient temperature
of up to 315 °C (599 °F)
Temperature measurement of glass
Hot spot detection at glass bottle production
If you measure temperatures of glass with IR thermometers or
the special IR camera optris PI G7 it implies that you take care of
reection and transmissivity. A careful selection of the wavelength
facilitates measurements of the glass surface as well as of the
deeper layers of the glass. Wavelengths of 1.0 µm, 2.2 µm or
3.9 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
reection. 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.
100
innovative infrared technology
Line scan with compact infrared camera
Optris infrared cameras are equipped with licensefree PI Connect software. The software enables the
cameras to operate as line scan cameras.
Line scanners are traditionally used in the glass
industry for various measurement procedures. In
these devices, a point detector is coupled with a
rotating mirror to consequently generate a linear
optical scan of the object. These devices are bulky
and expensive.
When using an infrared camera as a line scanner,
an arbitrary line is selected from the detector array.
In addition to the more compact construction and the
lower price, there are two signicant benets: the line
to be scanned can be positioned anywhere using the
software and the user receives a complete IR image
quasi as additional information – these are important
advantages, especially during system setup.
The cameras can accurately measure surface temperatures of moving measurement objects using minimal
apertures. This function is of particular signicance in
the glass industry, since the glass temperature has
a direct impact on the quality. During the production
process, temperatures are measured accordingly
at many points and it is possible to intervene in the
process, when necessary, if there are deviations in
setpoint temperatures.
For example, the Optris PI 450 G7, a special IR
camera for glass applications, can scan the complete
glass width using in the oat process (Up to 4 m [13 ft])
with an 80° lens using the diagonals as scan line at a
height of 2.1 m (6.9 ft).
80
Transmissivity in %
60
40
20
0
2 3 4 5
Further information in our infrared basics brochure:
www.optris.com/optris-downloads
Wavelengh [µm]
Lines have FOV of
up to 111° for detailed
process analysis.
111 °
any number of lines
800 Pixel
Up to 125 Hz data recording
of unlimited lines which in turn
produce a thermal image of
any given resolution
3
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