Page 176 - Advanced Course

KNX ADVANCED COURSE

interfaced via a control function e.g. offset adjustment is a so-called master/slave circuit
(see the explanations in section 5).

Light strip 1 Light strip 2 Light strip 3

~ 26 % ~ 48 % ~ 70 %
Receiver
Slave 2 Slave 1 Master

500 lx required illuminance

Necessary
artificial light
Existing
daylight

Figure 11: Brightness control of a light strip, combined with offset control for the other light
strips

4.7.3 Fundamental Mismatch

A mismatch always occurs in this system. This is based on the one hand on the different
lighting spectrum of natural light and artificial light and on the other hand, on the different
angle of illumination. The more external light comes in, the greater the measuring error,
because the natural light also is picked up by the sensor rod directly instead of only from
the controlled surface by reflection. A curve of the controlled variable is produced
dependent on the external brightness which reaches its minimum in a ratio of 50:50
between the proportion of external and internal light. The system must always be
balanced under these lighting conditions.

Ф internal Optimum adjustment value
[lx]

Actual
value

500 Setpoint

250

Ф external
Actual Proportion of Proportion of [lx]
internal value artificial light external light

Figure 12: Behaviour of the actual value dependent on the level of external light

Home and Building Management Systems KNX Association
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