ABB i-bus
®
KNX
Commissioning
136 2CDC508134D0202 | FCA/S 1.x.x.1
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.
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 OFF <-> speed 1 = 10 %
Threshold value speed 1 <-> speed 2 = 20 %
Threshold value speed 2 <-> speed 3 = 30 %
Hysteresis 15 %
Behavior when ascending from speed 0:
Speed 0 transition at 25 % (≥ 10 % + hysteresis).
The new speed is 2 (25 % is between 20 % and 30 %).
Accordingly, speed 1 is omitted.
Behavior when descending from speed 3:
Speed 3 transition at 14 % (< 30 % – hysteresis).
The new speed is 1 (15 % is between 10 % and 20 %).
Accordingly, speed 2 is omitted.
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