Motorola 6700 Especificaciones descargar pdf (Pagina 18)

2 - 4 Symbol SE6700 Integration Guide

Window Material

Many window materials that look clear can contain stresses and distortions that reduce performance. For this

reason, only cell-cast plastics or optical glass is recommended (with or without an anti reflection coating,

depending on the application). Following are descriptions of three popular window materials: PMMA, ADC

(CR-39

), and chemically tempered float glass. Table 2-1 outlines the suggested window properties.

Cell Cast Acrylic (ASTM: PMMA)

Cell Cast Acrylic, or Poly-methyl Methacrylic (PMMA) is fabricated by casting acrylic between two precision sheets

of glass. This material has very good optical quality, reasonably good impact resistance and low initial cost, but is

relatively soft and susceptible to attack by chemicals, mechanical stresses, and UV light. Therefore polysiloxane

coating is strongly recommended. Acrylic can be laser cut into odd shapes and ultrasonically welded.

Cell Cast ADC (ASTM: ADC)

Also known as CR-39

, Allyl Diglycol Carbonate (ADC) is a thermal-setting plastic produced by cell-casting. Most

plastic eyeglasses sold today are uncoated, cell-cast

CR-39. This material has excellent chemical and environmental resistance, and reasonably good impact

resistance. It also has quite good surface hardness, and therefore does not have to be hard-coated, but may be

coated for severe environments. This material cannot be ultrasonically welded.

Chemically Tempered Float Glass

Glass is a hard material that 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.

Commercially Available Coatings

Anti-Reflection Coatings

Anti-reflection coatings can be used for stray light control or to achieve maximum working range, and can be

applied to the inside and/or outside of the window to reduce the amount of light reflected off the window back into

the engine. However, they are expensive and have very poor abrasion and scratch resistance.

Table 2-1

Suggested Window Properties

Property Description

Material Clear cell-cast acrylic

Thickness 0.06 in. (1.5 mm)

Wavefront Distortion (transmission) 0.2 wavelengths peak-to-valley maximum and

0.04

maximum rms 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

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