Remote temperature sensing and thermal imaging can be invaluable tools for process control and optimization. Their
utilization is limited within the metal processing industries, however, as bright metal surfaces are highly reflective, with
low emissivity that can vary critically with oxide thickness and alloy composition. Any infrared temperature
measurement is vulnerable to background reflection and limited to the uncertainty in the emissivity.
An enclosure or cavity made of any material offers an approximation to blackbody radiation, as both emitted and
reflected radiation are collected within the cavity, and background radiation is excluded by the geometry. By exploiting
natural cavities formed during processing, emissivity-independent measurements can be made.
This paper presents thermal imaging data from an aluminum rolling application. Data was gathered using Land's FTI-E
imaging system. Based on an uncooled amorphous silicon array, the system provides measurement in the range 200°C to
600°C to an accuracy of ±1°C. The 320 x 240 pixels each have field of view 570:1, providing a total viewing angle of
32° by 24°. Data was processed by Land's LIPS ASPS software, which features a patented algorithm for identifying the
area of true temperature measurement within the cavity. The software automatically locates the wedge as the strip is
coiled, and tracks its position as the coil increases in size. Successive profile graphs are collated to form a '2D map' of
the whole strip.
The results demonstrate that accurate, emissivity-independent temperature measurements can be obtained from the
wedge-shaped cavity formed where the sheet aluminum joins the roll.
As thermal imaging becomes a more accepted technology in industrial environments it can provide
exciting new solutions to applications that have been previously dominated by single point pyrometers.
The new development of an uncooled focal plane array thermal imager with a narrow band 3.9μm
filter and background compensation processing enables measurements in industrial furnaces to provide
temperature profiling of the product.
This paper will show why the use of a 3.9μm camera with a borescope optic is the most accurate noncontact
method for in-furnace temperature measurement. This will be done using the example of a
reheat furnace where in a controlled trial using an instrumented billet the measurement from the IR
device was shown to accurately track the thermocouple temperature during a variety of furnace
operating conditions.
KEYWORDS: Cameras, Infrared cameras, Imaging systems, Sensors, Temperature metrology, Infrared sensors, Electronics, Head, Signal processing, Control systems
New uniform camera electronics were developed for different stationary line and 2D infrared cameras for non-contact temperature measurement. The 16bit analog/digital converter used enables a maximum pixel rate of 10 MHz. The electronics are based on a System Of Programmable Chip (SOPC) solution using a PLD with an embedded processor. The ability to reprogram the PLD allows an inexpensive adaptation to different sensor types and various industrial applications. The embedded processor executes the signal processing, including the necessary signal corrections. In addition, the embedded processor controls and monitors the camera head, monitors the operation of the chopper/shutter motor and internal temperature sensors, and can be used to control a number of functions such as triggering or frame rate. The PC communicates with the micro-controller via an asynchronous interface. The other essential components of the digital signal-processing unit include a serializer, a flash memory and an SRAM. The new 16bit camera electronics have been incorporated into the following 2D infrared cameras PYROVIEW 256 with a pyroelectric array (256 x 128 pixel)
PYROVIEW 320 with a microbolometer array (320 x 240 pixel)
The paper will describe technical properties and typical applications in industrial applications for both devices as well as the advantages and disadvantages of pyroelectric vs. microbolometer arrays. In addition, since the newly developed 16bit camera electronics also provide the basis for faster line cameras (PYROLINE with pyroelectric arrays of 128 x 1 and 256 x 1 and an InGaAs line array with 256 x 1), selected applications of these cameras will also be discussed.
The PYROLINE/ MikroLine cameras provide continuous, non-contact measurement of linear temperature distributions. Operation in conjunction with the IR_LINE software provides data recording, real-time graphical analysis, process integration and camera-control capabilities. One system is based on pyroelectric line sensors with either 128 or 256 elements, operating at frame rates of 128 and 544 Hz respectively. Temperatures between 0 and 1300DGRC are measurable in four distinct spectral ranges; 8-14micrometers for low temperatures, 3-5micrometers for medium temperatures, 4.8-5.2micrometers for glass-temperature applications and 1.4-1.8micrometers for high temperatures. A newly developed IR-line camera (HRP 250) based upon a thermoelectrically cooled, 160-element, PbSe detector array operating in the 3 - 5 micrometers spectral range permits the thermal gradients of fast moving targets to be measured in the range 50 - 180 degree(s)C at a maximum frequency of 18kHz. This special system was used to measure temperature distributions on rotating tires at velocities of more than 300 km/h (190 mph). A modified version of this device was used for real-time measurement of disk-brake rotors under load. Another line camera consisting a 256 element InGaAs array was developed for the spectral range of 1.4 - 1.8 micrometers to detect impurities of polypropylene and polyethylene in raw cotton at frequencies of 2.5 - 5 kHz.
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