Page 184 - Advanced Course

KNX ADVANCED COURSE

5.6 Installation Notes

The installation instructions for the open-loop lighting control system are reduced to notes
about the installation of the sensor head:
It must be directed outside or be installed outside the building.
Its recording of the lighting level may not be influenced by seasonal variations such as
leaves on the trees which stand between it and the sky or snow on the receiving lens.
Its measurement may (for interior installation) also not be invalidated by the shutter.
An installation behind the shutter or roller blind should be avoided where possible.
The presence of shutters require a particular type of control: if proportionally-controlled
shutters are present, the louvres of the shutters can be adjusted in parallel to the
external brightness instead of the light.
For an optimum adaptation of rooms that face different directions, it is advisable to use
at least 2 differently positioned sensors: one in a south-east direction and another in a
north-west direction. Large buildings may require even more sensors which should
then be placed as perpendicular as possible to the respective façade and point
upwards.

6 Brightness Control, combined with Master/Slave Control

6.1 Objective

With combined open-loop/closed-loop lighting control, you are in general pursuing the aim
of saving costs without having to relinquish the benefits of a partially true closed-loop
control system. These can be:

a simple setting procedure
optimum lighting conditions in at least one position in the room
always the correct lighting level in the rooms even when combined with light direction
and sun protection systems.

6.2 Principle

An internal sensor measures the lighting level of a surface that should be regulated – as in
closed-loop control which was described in detail above. The measured values of the
sensor are further processed in a control program resulting in a control value which is
used to trigger the actuator that is responsible for the direct light strip. To eliminate the
requirement for further sensors (and also their deviation), it transfers a full control curve
via offset adjustment to all other curves. The required offset adjustment can be
determined by 2-3 simple measurements: at an artificial lighting level of 25%, 50% and
75%, the necessary offset of the controlled light strips is determined in comparison to the
regulated strip to arrive at the required setpoint in lux. The largest recorded differential
(upwards) per strip is then taken as this guarantees that the minimum lighting level never
falls below the setpoint.

Home and Building Management Systems KNX Association
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