INSTALLATION INSTRUCTION FOR PIR-150
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2824-00002
Required Properties of a Terminating Screen
The material of the screen has to block the thermal infrared radiation in the first place. Additionally it should
be non-reflecting and thermally insulating to avoid unwanted signals from reflected heat sources and
secondary radiation from strong sources heating up the screen from behind.
Since smooth surfaces – although dull for visible light – reflect the longer wave-length radiation of the
thermal infrared much better, a rough or structured surface has to be used.
Wood has all the required properties if the surface is treated according to the recommendation but almost
any plastic material would be suitable. If in doubt about thermal transmission verify the performance with
tests or consult the manufacturer.
Reflections from Screen and Ground Surface
Special attention has to be taken to possible reflections from the rising or setting sun which may generate
strong signals together with fast moving clouds. In cases where the screen is facing sunrise or sunset at any
time of the year the top of the screen has to be tilted towards the detector to reflect the sun into the
ground.
The ground has to be as non-reflecting as possible even when wet, use proper drainage to avoid forming of
puddles. Reflections from snow can not be avoided technically and an increased occurrence of nuisance
alarms while the ground is covered with snow has to be accounted for.
Recommended Screen Dimensions
The following table indicates recommended values for the dimensions of a terminating screen in function of
the distance.
Depending on the nature of possible nuisance alarm sources behind the screen, larger dimensions have to
be chosen (e.g. sources with strong thermal contrasts like heavy vehicles, trains or aeroplanes) to avoid
unwanted alarms.
Distance X
Recommended screen width
Recommended screen height above axis
25 m
1.00 m
0.75 m
50 m
2.00 m
1.50 m
75 m
3.00 m
2.25 m
100 m
4.00 m
3.00 m
125 m
5.00 m
3.75 m
150 m
6.00 m
4.50 m
