
6
Module Depth
(z) mm
Aperture Width (x, mm)
Aperture height (y, mm)
Max
min
Max
Min
0
0.09
7.42
4.99
2.32
.24
7.95
6.4
2.85
2
2.40
8.49
7.30
3.39
3
3.55
9.02
8.45
3.92
4
4.7
9.56
9.6
4.46
5
5.86
0.09
0.76
4.99
6
7.02
0.63
.92
5.53
7
8.7
.7
3.07
6.07
8
9.33
.70
4.23
6.60
9
20.48
2.24
5.38
7.4
Figure D2. Aperture Height (x) vs. Module Depth (z)
Figure D3. Aperture Height (y) vs. Module Depth (z)
Therecommendedminimumaperturewidthandheight
isbasedontheassumptionthatthecenterofthewindow
andthecenterofthemodulearethesame.Itisrecom-
mended that the tolerance for assembly be considered
as well.The minimum window size which will take into
accountoftheassemblytoleranceisdefinedas:
X (min + assembly tolerance) = Xmin + 2*(assembly
tolerance)(Dimensionsareinmm)
Y (min + assembly tolerance) = Ymin + 2*(assembly
tolerance)(Dimensionsareinmm)
Window Material
Almost any plastic material will work as a window
material. Polycarbonate is recommended. The surface
finish of the plastic should be smooth, without any
texture. An IR filter dye may be used in the window to
make it look black to the eye, but the total optical loss
of the window should be 10% or less for best optical
performance.Lightlossshouldbemeasuredat885nm.
Therecommendedplasticmaterialsforuseasacosmetic
windowareavailablefromGeneralElectricPlastics.
Recommended Plastic Materials:
Material #
Haze
Refractive Index
Lexan 4
88%
%
.586
Lexan 920A
85%
%
.586
Lexan 940A
85%
%
.586
Note:920Aand940Aaremoreflameretardantthan141.
RecommendedDye:Violet#21051(IRtransmissantabove
625mm)
Shape of the Window
From an optics standpoint, the window should be flat.
This ensures that the window will not alter either the
radiationpatternoftheLED,orthereceivepatternofthe
photodiode.Ifthewindowmustbecurvedformechani-
calorindustrialdesignreasons,placethesamecurveon
thebacksideofthewindowthathasanidenticalradiusas
thefrontside.Whilethiswillnotcompletelyeliminatethe
lenseffectofthefrontcurvedsurface,itwillsignificantly
reducetheeffects.Theamountofchangeintheradiation
pattern is dependent upon the material chosen for the
window,theradiusofthefrontandbackcurves,andthe
distance from the back surface to the transceiver. Once
theseitemsareknown,alensdesigncanbemadewhich
will eliminate the effect of the front surface curve. The
followingdrawingsshowtheeffectsofacurvedwindow
ontheradiationpattern.Inallcases,thecenterthickness
ofthewindowis1.5mm,thewindowismadeofpolycar-
bonate plastic, and the distance from the transceiver to
thebacksurfaceofthewindowis3mm.
0
2
4
6
8
10
12
14
16
18
0
1
2
3
4
5
6
7
8
9
Module Depth (z) mm
Aperture
Height
(Y)
mm
Ymax
Ymin
0
5
10
15
20
25
0
1
2
3
4
5
6
7
8
9
Module Depth (z) mm
Aperture
Width
(x)
mm
Xmax
Xmin