ABB i-bus KNX Product Manual

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ABB i-bus KNX Product Manual Manual pdf 114 page image

ABB i-bus® KNX Planning and application© 2008 ABB STOTZ-KONTAKT GmbH 1124.6 Characteristic adjustmentSometimes it is necessary to adjust the dimming characteristic of lighting tothe sensitivity of the human eye. This can be undertaken with acharacteristic adjustment. Normally the object value 0…255 is assigned withthe proportional brightness value 0 %…100 % (see normal characteristic inthe illustration). This curve can be converted by four value pairs to anadjusted curve. A liner interpolation of the characteristic is undertakenbetween the value pairs.If the lights should be brighter in the lower range, the brightness value ofobject value 1 can be increased or reduced. In the upper example (seefigure) in the first value pair the brightness for value 1 has therefore beendefined at 30 %. The other value pairs in the example have been defined sothat 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 brightnessvalue of 0.3 % and the minimum control value 1 sets the maximumbrightness value of 100 %.The feedback brightness values received via object Status brightness valueor Brightness value/Status also take the curve into consideration, i.e. acontrol variable of 76 (30 %) is transformed to a brightness value of 65 % tocontrol the lighting. The lighting feeds back 65 %. This value is transformedonce again to 76 (30 %) and provided as a brightness value in the KNX. Inthis way, a constant lighting control of a Lighting Controller is possible tooperate without difficulties, as the control value and the feedback directlycorrespond and a correct control factor can be calculated.NoteThe value, dimming and brightness values are used before thetransformation. Through the transformation a setting signal may result forthe lamps which is less than or greater than the maximum or minimumbrightness values.KNX control value 76 = 30%Lamp brightness 65%KNX feedback 76 = 30 %7665%Adjustment curveObject Brightness valueBrightnesscontrol outputNormal curve