Characteristic Adjustment - ABB i-bus KNX Product Manual

®
ABB i-bus KNX
4.6

Characteristic adjustment

© 2008 ABB STOTZ-KONTAKT GmbH
Planning and application
Sometimes it is necessary to adjust the dimming characteristic of lighting to
the sensitivity of the human eye. This can be undertaken with a
characteristic adjustment. Normally the object value 0...255 is assigned with
the proportional brightness value 0 %...100 % (see normal characteristic in
the illustration). This curve can be converted by four value pairs to an
adjusted curve. A liner interpolation of the characteristic is undertaken
between the value pairs.
65%
Brightness
control output
If the lights should be brighter in the lower range, the brightness value of
object value 1 can be increased or reduced. In the upper example (see
figure) in the first value pair the brightness for value 1 has therefore been
defined at 30 %. The other value pairs in the example have been defined so
that they result in a curve that has a flatter progression in the upper range.
With relative dimming a flatter dimming ramp is thus achieved.
In extreme cases the brightness characteristic can even be inverted.
X = 1 -> Y = 255 (100 %) and X = 255 -> Y = 1 (0.3 %)
In this case, the maximum control value 255 sets the minimum brightness
value of 0.3 % and the minimum control value 1 sets the maximum
brightness value of 100 %.
The feedback brightness values received via object Status brightness value
or Brightness value/Status also take the curve into consideration, i.e. a
control variable of 76 (30 %) is transformed to a brightness value of 65 % to
control the lighting. The lighting feeds back 65 %. This value is transformed
once again to 76 (30 %) and provided as a brightness value in the KNX. In
this way, a constant lighting control of a Lighting Controller is possible to
operate without difficulties, as the control value and the feedback directly
correspond and a correct control factor can be calculated.
Note
The value, dimming and brightness values are used before the
transformation. Through the transformation a setting signal may result for
the lamps which is less than or greater than the maximum or minimum
brightness values.
Adjustment curve
76
KNX control value 76 = 30%
Lamp brightness 65%
KNX feedback 76 = 30 %
Normal curve
Object Brightness value
112