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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
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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
Applications of
Temperature measurement technology
PRODUCTION OF GLASS
Production optimization in the
oat glass process
After the tin bath, the at glass band has a temperature of about
600 °C (1,112 °F); the rst infrared camera in line-scan mode is
applied for temperature monitoring at the transition to the cooling
zone. The glass is transported through various cooling ranges in
the cooling zone. Between the cooling ranges, infrared cameras
are also installed in the cooling ranges for temperature
monitoring, in order to guarantee optimal quality.
Software adjustments for line-scan process
Measurement areas at float glass production
Infrared cameras with line scan mode
FloatMelting process Tin bath
> 1,500 °C (2,732 °F) 600 °C (1,112 °F)
Continuous control during the production of container glass
Container glass, meaning for example bottles in all sizes
and forms, must be multiply monitored for its processrelevant temperature during the production process.
When the molten glass exits through the feeder, the glass
strand is cut. The thereby resulting molten glass drops
must have a temperature of about 1000 °C (1,832 °F) to
ensure quality. Temperature measurement was previously
only possible with point-measuring infrared thermometers
due to the high velocity. The innovative Optris PI 1M now
also enables this measurement via surface measurement
with an image rate of up to 1000 Hz.
During the forming process, which takes place at
temperatures of over 500 °C (932 °F), infrared sensors are
also used for monitoring. Since the process only takes a
few seconds, the reaction of the sensors is of critical
importance here. The thermal measurement of the
glass can be inuenced by direct measurement of the glass
surface or indirect measurement of the surface of the for-
ming tool for both the forming of the parison shape as well
as during nishing of the mould.
To complete the nishing process, another
temperature control to reduce tension takes
place in the containers. The glass is heated again
and subsequently gradually cooled in a cooling
tunnel over a period of up to 30 minutes. When
the containers exit the heating zone, the cooling
process is supported and controlled by
temperature measurement.
Cooling process
4
Single-pane safety glass production with
correct temperature measurement technology
For the production of single-pane safety glass (SPSG), the cut
and processed at glass is heated in a furnace under continuous
movement at over 600 °C (1,112 °F). During the transport of the
heated glass in the pretension zone, an infrared camera monitors the temperature distribution on the glass surface in linescan mode. During the pretension process, where the glass is
shock-cooled, inhomogeneities can be compensated. The quality
of the SPSG mainly depends on a homogeneous thermal treatment, which is ensured by the application of temperature
measurement technology.
innovative infrared technology
Infrared camera with line scan mode
Heating process Cooling process
600 °C (1,112 °F) 50 °C (122 °F)
Measurement areas at SPSG production
Ensuring the quality of laminated
safety glass
50 °C (122 °F)
Infrared
thermometer
Infrared camera
with line scan mode
Laminated safety glass (LSG) consists of at least two at panes
of glass, which are laminated in a clean room with a sheet of
PVB lm between them. The temperature of the lm can be
monitored with infrared thermometers. In the pre-lamination
furnace, the glass panes are heated in order to melt the lm and
simultaneously press the “sandwich” together, to prevent air
pockets. During the transition to the autoclaves, the temperature
distribution is monitored with an infrared camera, in order to
adjust the heating elements in the pre-lamination furnace for
subsequent panes, when necessary.
Heating with IR
radiation and rolling
Infrared thermometer /
Infrared camera
Measurement areas at LSG production
Laminating room Final control
5
Glass industry
INFRARED CAMERAS AND INFRARED THERMOMETERS
The IR thermometer’s stainless steel measuring
head is extremely small and can be employed
in ambient temperatures of up to 85 °C (185 °F)
without additional cooling. A multi-installation of
the pyrometers, e. g. in series as line scanner, is
therefore cost-efcient and can be performed
optris
Due to its special spectral range of 5.0 µm, the
pyrometer optris
measurement of glass temperatures, e.g. during
container glass production and vehicle glass
production.
The infrared thermometer optris
®
CT G5
®
CT G5 is perfectly suited for the
®
CTlaser G5
allows for temperature measurement of smallest
objects of 1 mm (0.04 in) from a distance of
70 mm (2.76 in). Due to its very short response
time of 10 ms it is often used for fast processes.
even in limited spaces. The temperature range is
from 100 °C to 1,650 °C (212 °F to 3,002 °F).
optris
With a spectral range of 5.0 µm, the two-part infrared
thermometer optris
precise measurement of glass surfaces. The devices
are employed for temperature measurement in e.g. manufacturing processes of vehicle glass and and at glass.
®
CTlaser G5
®
CTlaser G5 is especially designed in
The infrared thermometer optris® CSlaser G5HF
has been specically designed for temperature
measurement of glass. Its standardized two-wire
interface provides a reliable measuring data
transmission and allows for an easy integration
of the temperature sensors into a PLC.
optris
The optris® CSlaser G5 is perfectly suited for temperature control of production processes of at glass and
vehicle glass. Also, the measurement during cooling
and heating processes of single-pane safety glass
and laminated sheets safety glass is important.
®
CSlaser G5HF
Also in the manufacturing of
laboratory glass equipment or the
production of glass bottles, the pyrometer
delivers excellent results and is thus employed
for quality assurance and process coordination.
The IR thermometer is additionally equipped with
an innovative double laser visor for a precise
marking of the measuring spot. A variety of optics
ensures high adaptability with diverse applications.
6
®
The infrared cameras optris
G7 are industry specic models within the PI series.
They are especially developed for the glass in-
dustry, working with a spectral range of 7.9 μm.
PI 450 G7 and PI 640
innovative infrared technology
The temperature range of 200 °C to 1,500 °C
(392 °F to 2,732 °F) allows the implementation in
diverse applications in production, dressing and
further processing of glass.
optris
These infrared cameras should be used when temperature values within a eld are to be detected. In due
to the low price an infrared camera could be the better
solution in comparison to rows of infrared thermometers.
The infrared thermometer optris
an extremely short response time of 6 ms. The
unchoppered sensor allows a continuous temperature surveillance of fast processes in a spec-
trum of –50 °C up to 975 °C (–58 °F up to 1,787 °F).
The thermal imager optris® PI 160 allows for exact
For fast processes
optris
optris
Both products are preferably used in the packaging
industry and in bottling plants. In mass production,
it is essential that high-output processes are monitored
®
PI 450 G7 / PI 640 G7
®
CTfast LT has
®
PI 160 and
®
CTfast LT
Line
scan
camera
measurements from an object size of 1.5 mm
(0.06 in) on and is, due to its measurement speed
of 120 Hz, perfectly suited for employment in
research and development, test stations, and
process automation as well as for portable
measurement tasks.
continuously and without friction.
Deciding which of the two products should
be used, depends on the measuring area. From
a measurement of more than 7 measuring points,
it is less expensive to use an infrared camera.
The pyrometer optris® CThot LT has been
developed for the most extreme conditions in
high-temperature areas and is acclaimed for
its especially high temperature resistance.
Employment of the infrared thermometer in
ambient temperatures of up to 250 °C (482 °F)
optris
The optris® CThot LT is used in production
processes and rening processes of glass.
Due to its extremely high temperature
resistance, it is also suitable for ovens
and closed chambers.
®
CThot LT
without additional cooling poses absolutely no
problems. Due to the mentioned features, the
IR pyrometer is especially suited for applications in
glass industries. On request, the IR thermometers
are available as models for applications in
explosion-threatened areas.
7
Subject to change · Temperature measurement glass industry-BR-US2017-11-B
Optris Infrared Sensing, LLC
200 International Drive
Suite 170
Portsmouth, NH 03801 USA
Phone: (603) 766-6062
E-mail: sales@optris-ir.com
www.optris.com
innovative infrared technology
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