ABB i-bus KNX Product Manual page 42

6 G lossary
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6.1 C ontinuous and switching control
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A switching (2-point) control detects only 2 status conditions; or on off.
A continuous control works with a set value between 0% and 100% and can
therefore dose the energy supply precisely. This achieves convenient and precise
control.
6.2 H ysteresis
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The hysteresis determines the difference between switch-on and switch-off
temperature with a controller. It can be both positive and negative.
With a combination of heating and cooling control, it affects the amount of the
zone .
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Without hysteresis, the controller would switch on and off without interruption as long
as the temperature is in the range of the set value.
6.2.1 N egative hysteresis:
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Heating: The heating is carried out until the set value is reached.
The heating is only switched on again when the temperature has fallen below the
threshold set value hysteresis.
Cooling: Cooling is carried out until the set value – hysteresis threshold is reached.
The system is only switched on again if the temperature has risen above the set
value.
Cooling example:
Cooling with set value 25 °C, hysteresis = 1°C and ambient temperature 27 °C.
The cooling is switched on and only switches back off again once a temperature of
24 °C (25 °C – 1 °C) is reached.
Once the temperature rises above 25 °C, the system is switched back on again.
6.2.2 P ositive hysteresis
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Heating is carried out until the temperature reaches the set value + hysteresis
threshold.
The heating is only switched on again if the temperature has dropped below the set
value.
Heating example:
Heating with set value 20°C, hysteresis = 1°C and ambient temperature 19 °C.
The heating is switched on and only switches back off again once a temperature of
21 °C (20 °C – +1 °C) is reached.
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