ABB i-bus KNX Product Manual page 222

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ABB i-bus KNX
Planning and application
This produces the following DALI characteristic:
A
A´
B
C
D
KNX value (A) = DALI value, lamp power (B)
The table assumes ideal DALI equipment (DALI dimming range 0.1...100%) and in the DG/S a KNX
dimming range of 0.4...100%.
Rows A and A´ are the brightness value that the gateway receives via the KNX as a digital numeric value
(0...255) or in % (0...100). The gateway converts this value to the DALI value, lamp power (row B). Finally,
the luminous flux (row C) emitted by the lamp is the result of the logarithmic DALI characteristic. The
gateway then returns the brightness value status (row D) on the KNX.
The dimmable range printed on the ballast relates to the luminous flux. Typical specifications are 3% or
0.2%, which equate to KNX values of 49% (126) or 10% (26) due to the logarithmic nature of the DALI
curve.
The maximum possible dimming range can only be set with DALI equipment, which has a dimming range
up to 0.1% (KNX value 1 or 100/255% = 0.4%). Other DALI equipment has a limited dimming range. This
value is a physical property of the ballast and cannot be changed. This dimming limit has nothing to do
with the minimal dimming value parametrized in the application.
For example, take a ballast with a minimum physical luminous flux of 3% as shown below. This means that
a dimming range of 126...254 is available in the KNX. This in turn means that the lowest brightness value
that can be set and fed back on the KNX is 126 or 50%. The ballast sets KNX values of less than 126 or
50% to this threshold value and the gateway feeds them back on the KNX.
A
A´
B
C
D
The characteristic curve and linearization described in the following section allows the brightness values
on the KNX to be mapped to the usable range of the ballast. This enables a higher resolution for the
brightness values on the KNX. However, nothing changes in the physical threshold values of the ballast
and the light yield.
220 2CDC507164D0201 | DG/S x.64.1.1
KNX value
KNX
KNX value [%]
DALI value (lamp power)
Luminous flux [%]
Logi
cal
KNX status brightness
KNX
value
KNX value 0 1
KNX
KNX value [%] 0 0.4
DALI value (lamp
0 1
power)
Luminous flux [%] Logi 0 3
cal
KNX status
KNX
0 126
brightness value
0 1 60 85 126 144 170 195 210 220 229 235 241 246 250 255
0 0.4 24 33 49 57
0 1 60 85 126 144 170 195 210 220 229 235 241 246 250 254
0 0.1 0.5 1 3 5
0 1 60 85 126 144 170 195 210 220 229 235 241 246 250 255
–log. Calculation->
8 26 60 85
3 10 24 33
8 26 60 85
3 3 3 3
126 126 126 126
67 77 82 86 90 92
10 20 30 40 50 60
Luminous flux (C)
126 144 229 235 241
49 57 90 92 95
126 144 229 235 241
3 5 50 60 70
126 144 229 235 241
95 97 98 100
70 80 90 100
246 250 255
97 98 100
246 250 254
80 90 100
246 250 255