Message Board Thread - "IR measurement of polyethylene solutions?"

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IR measurement of polyethylene solutions? hollybala 4/1/2004
I am trying to use a 3.0-5.3 micron IR camera with a 250 micron close-up lens to measure the axial temperature profile of an extruding polyethylene-organic molten filament. The filament is usually 30 weight percent or less linear low density polyethylene, it is elongated from about 4 mm in diameter to about 1 mm diameter through air over a distance of about 20 cm, and it cools due to air convection and solvent evaporation. I've tried a number of measurement techniques, but keep getting a much more drastic temperature drop than I should (compared to theoretical models AND holding a thermocouple under portions of the line to get the temperature). Any suggestions? Can I remove items behind the filament to leave a large space behind with only air to get the filament temperature more accurately? Please help. Thanks.
Re:IR measurement of polyethylene solutions? Doctir bob 4/1/2004
Polyethylene, like many polymer materials has a spectral transmission in the IR that can be quite high, except for absorption bands at specific wavelengths. Polyethylene has good transmission in the 3-5 micrometer waveband except for a strong absorption band centered at 3.45 micrometers due to C-H stretch. A narrow bandpass filter at this wavelength would significantly reduce the transmissive effects. It will also reduce signal, increasing the minimum temperature that can be measured.

Using your camera without a bandpass filter can be problematic due to the transmittance (t) of polyethylene. One trick is to have the foreground and background radiances equal, and enter the greybody approximation to polyethylene emissivity over the waveband of your camera. This value and the apparent temperature of the background are crucial for this to work effectively.

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