Positioning Of The Light Sensor - ABB i-bus KNX Product Manual

®
ABB i-bus KNX
4.7.2 Positioning of
the Light Sensor
© 2008 ABB STOTZ-KONTAKT GmbH
Planning and application
The Light Sensor measures the brightness (light density) of an area in a
room which is suitable for a reference measurement. Positioning should be
undertaken as follows:
1. The Light Sensor should be situated directly above the reference
surface, e.g. workbench. Observe the detection range of the Light
Sensor.
See: sensor polar diagram
2. The ceiling must be monitored when the room is not darkened and the
lighting is switched off. Those ceiling areas which are not directly subject
to daylight or reflections are suitable.
3. The rod should be pushed about 15 mm deep into the device right up to
the limit. The Light Sensor must be aligned with the longitudinal axis of
the rod pointing vertically downwards.
4. It must be assured that the brightness sensor only measures indirect
reflected light. Sunrays or light rays which shine directly into the rod lead
to measurement faults, just as the incidence of light mirrored directly
from surfaces.
5. The optimum installation height is between 2 and 3 m.
6. If possible measure different actual values of the Light Sensor with
different lighting relationships with daylight (cloud, sun) at the same Lux
count on the reference surfaces. The difference in the actual value
should be minimal.
Note
Rooms are lit up differently by the incidental daylight and the artificial
lighting of the lamps. Not all surfaces in the rooms, e.g. walls, floor, and
furniture reflect the light which falls on them in the same manner.
Accordingly, even though there is an exactly calibrated constant lighting
control in daily operation, deviations to the set target value may occur.
These deviations may be up to +/- 100lx should the current ambient
conditions in the room, and accordingly the reflection properties of the
surfaces (paper, persons, reorganized or new furniture), differ significantly
from the original ambient conditions at the time of calibration. Deviations
may also occur if the Light Sensor is influenced by direct or reflected light
falling on it which is not influenced or only slightly influenced by the
surfaces in the detection range of the Light Sensor.
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