Page 165 - Advanced Course

KNX ADVANCED COURSE

4.1 Constant Lighting Control: Areas of Application, Objective
This type of control system is mainly used in commercial installations where it is important
to adhere to certain regulations such as those governing the workplace but not to make
more light available than necessary. The aim is to create optimum working conditions
while at the same time saving costs. The user should also be offered an optimum level of
convenience and the internal room controller should operate independently of other
parameters which cannot be detected here.

4.2 Types of Closed-loop Control

A distinction is made between Closed-loop Control and the so-called Integral Reset. In the
first control system, the control value is directly influenced by the setpoint/actual value
differential. For example, an absolute dimming value is sent to the actuators via a
feedback function (dependent on the measured lighting level but with a variable proportion
of external light). The negative feedback of the control value on the comparison point of
the closed-loop control circuit as well as the system deviation with forward gain are
governed by one function. The greater the influence on the control value, the higher the
failure rate of the system deviation.
Integral Reset on the other hand operates according to the two-step principle. The control
value for the brightness level of the actuators is modified indirectly or gradually, namely
via relative dimming telegrams. After this type of dimming process, the lighting sensor
measures the surface again that is to be constantly illuminated, compares it with the
setpoint and then decides again in which direction further dimming should take place. The
respective level of change carried out to the control value remains constant at each new
activation. It is not dependent on the degree of system deviation
Two-step control is actually not a proper closed-loop control system as it rarely achieves
the required setpoint. This type of control only has an opening/closing point instead of
continuous dimming processes which must be provided with a sufficiently large hysteresis
to prevent the triggering of continuous opening/closing operations. This type of lighting
control is described in more detail under the section “Brightness control”.

Home and Building Management Systems KNX Association
Lighting Control Lighting Control_E0310a.doc 6/34