Motorola SYMBOL MINISCAN MSXX04 - Manual (Page 37)

Installation 2 - 13
Acrylic
When fabricated by cell-casting, acrylic has very good optical quality and low initial cost. However, protect the
surface from the environment as acrylic is susceptible to attack by chemicals, mechanical stresses, and UV light.
Acrylic has reasonably good impact resistance and can be ultrasonically welded.
CR-39
CR-39 is a thermal-setting plastic produced by the cell-casting process, and is commonly used in plastic eye
glasses lenses. CR-39 has excellent chemical and environmental resistance, including good surface hardness.
Typically it does not require hard-coating, but can be hard coated for severe environments. CR-39 has reasonably
good impact resistance and cannot be ultrasonically welded.
Chemically Tempered Float Glass
Glass is a hard material which provides excellent scratch and abrasion resistance. However, unannealed glass is
brittle. Increasing flexibility strength with minimal optical distortion requires chemical tempering. Glass cannot be
ultrasonically welded and is difficult to cut into odd shapes.
CAUTION Consult an opto-mechanical engineer to recommend an appropriate window material and to
determine if coatings are appropriate for the specific application.
NOTE Do not use polycarbonate material.
Table 2-3 Suggested Window Properties
Property Description
Material Red cell-cast acrylic.
Spectral Transmission 85% minimum from 640 to 690 nanometers.
Thickness 0.059 ± 0.005
Wavefront Distortion (transmission) 0.2 wavelengths peak-to-valley maximum over any 0.08 in. diameter within
the clear aperture.
Clear Aperture To extend to within 0.04 in. of the edges all around.
Surface Quality 60-20 scratch/dig
Coating Both sides to be anti-reflection coated to provide 0.5% max reflectivity
(each side) from 640 to 690 nanometers at nominal window tilt angle.
Coatings must comply with the hardness adherence requirements of
MIL-M-13508.