ABB i-bus KNX Product Manual page 138

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ABB i-bus KNX
Commissioning
Example: Three-speed fan, fan control with hysteresis
Using hysteresis avoids continual switching between the fan speeds caused by fluctuating input signals
around the threshold value.
Important
How does the fan react if the switch thresholds overlap as a result of using hysteresis?
1) Hysteresis defines the speed at which the speed change occurs.
2) If the speed transition occurs, the new speed is determined using the control value and the set
switch thresholds. The hysteresis is not taken into account.
Control values are rounded to whole percentages by the device.
3) A control variable with the value 0 always results in speed 0.
An example:
Parameterized:
Threshold value speed 1 <-> speed 2 = 20 %
Threshold value speed 2 <-> speed 3 = 30 %
Hysteresis 15 %
Behavior when ascending from speed 0:
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Behavior when descending from speed 3:
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136 2CDC508134D0202 | FCA/S 1.x.x.1
Threshold value OFF <-> speed 1 = 10 %
Speed 0 transition at 25 % (≥ 10 % + hysteresis).
The new speed is 2 (25 % is between 20 % and 30 %).
Accordingly, speed 1 is omitted.
Speed 3 transition at 14 % (< 30 % – hysteresis).
The new speed is 1 (15 % is between 10 % and 20 %).
Accordingly, speed 2 is omitted.