Page 168 - Advanced Course

KNX ADVANCED COURSE

Figure 2: Example of a closed-loop controller with an integrated sensor
In the objects of figure 1, it is possible to detect that further possibilities can be
implemented apart from the actual dimming function (= control value). These options
enable a very convenient use of the control system:
Setpoint adjustment via absolute (direct) value control
Master /slave function for additional lighting circuits
Toggling between manual and automatic mode via all operator functions which the
dimming actuator is aware of (i.e. switching, dimming and value setting)
The previous statements about the procedure used by DPT 3.007 2 do not however mean
that an integral reset can only be carried out with DPT 3.007 only. This procedure can
also be implemented with DPT 5.001 telegrams. The controller thus starts with an initial
value, mainly 0 or 255, and sends further telegrams as with DPT 3..07, which now contain
8 bit values that are reduced or increased by a constant value compared to the previous
value. Some devices also manage to retrieve the present dimming value of the actuator to
be controlled and start from this one instead 0 or 100%. The benefit of this procedure
compared to DPT 3.007 appears to be that the resolution increases until it reaches steps
of 0.4%. This means it is possible to make even finer adjustments in the dimming process.
The bus load should however be taken into account since it rises when smaller changes in
the value are carried out.
The device shown in figure 2 is an example for 8-bit closed loop control.

4.4.3 Actuators
No particular requirements are placed on the dimming actuators initially as only the 4 bit
or 8 bit object is required for integral reset. It is however important to be able to select
whether this type of actuator should switch off or not when dimming down continually. It is
likewise the case with the opposite process. If the closed-loop control is switched on, it
should be possible to switch on using 4 bit dimming commands. The timing/dimming curve
must be active for both 8 bit value dimming and the 4 bit dimming process as the actuator
otherwise dims brighter or darker step by step. The KNX dimmers and dimming actuators
that are currently available on the market fulfil almost all these conditions which is not
always the case with older devices. To optimise the dimming process, the dimming speed

Home and Building Management Systems KNX Association
Lighting Control Lighting Control_E0310a.doc 9/34