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ABB i-bus KNX
© 2010 ABB STOTZ-KONTAKT GmbH
Commissioning
Example: Three speed fan, hysteresis with fan control
Using hysteresis a continuous switching between the fan speeds around the
threshold value with deviating input signals can be avoided.
Important
How does the fan react if the switch thresholds overlap by the use of
hysteresis?
1) The hysteresis defines from which point the set speed transition 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
considered.
3) A control variable with the value 0 always results in speed 0.
An example:
Parameterised:
Threshold value OFF <-> speed 1 = 10 %
Threshold value 1 <-> speed 2 = 20 %
Threshold value 2 <-> speed 3 = 30 %
Hysteresis 15 %
Behaviour 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.
Behaviour 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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