Hysteresis - Theben KNX Series Handbook

6.7 Hysteresis

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Hysteresis determines the difference between a controller's switching on and off
temperature.
It can be both positive and negative.
With a combination of heating and cooling control, it influences the amount of the dead zone.
Without hysteresis, the controller would activate and deactivate continuously, as long as the
temperature lies within the range of the set point.
6.7.1 Negative hysteresis:
Heating: Is provided until the set point has been reached.
Afterwards, the heating is only switched on again when the temperature falls below the
"Hysteresis set point value" threshold.
Cooling: Lasts until the "Hysteresis set point" threshold has been achieved.
Afterwards, it is only switched on again when the temperature rises above the set point.
Example of additional heating stage:
Additional stage with a set point of 20 °C, hysteresis 0.5 K and starting temperature 19 °C.
The additional stage is switched on and does not switch off again until the set point (20°) is
reached.
The temperature decreases, and the additional stage only is switches on at 20 °C-0.5K= 19.5 °C.
Cooling example:
Cooling with set point of 25 °C, hysteresis = 1 °C and ambient temperature 27 °C.
The cooling is switched on and switches off again only when a temperature
of 24 °C (25 °C – 1 °C) is achieved.
It switches on again when the temperature rises above 25 °C.
6.7.2 Positive hysteresis
Heating lasts until the temperature reaches the "set point + hysteresis " threshold.
The heating is only switched on again when the temperature falls below the set point value.
Heating example:
Heating with set point 20 °C, hysteresis = 1 °C and ambient temperature 19 °C.
The heating is switched on and only switches off again when a temperature of 21 °C
(= 20 °C + 1 °C) is achieved.
It switches on again when the temperature falls below 20 °C.
RAMSES 718 P / RAMSES 718 S
Appendix
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