2-Point Controller - ABB i-bus KNX Product Manual

4.3.1

2-point controller

© 2009 Busch-Jaeger Elektro GmbH – A Company of the ABB Group
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22 °C
21 °C
20 °C
Stellgröße
1
0
Note: after switching the control value on or off the room continues to heat or
cool because the heating elements are still hot or cool.
A 2-point controller has two output states, which switch depending on
the current value. If the current value is above the parameterised setpoint
(22 °C at 21 °C setpoint), the control value "0" is sent to the bus.
If the current value is below the parameterised setpoint (20 °C at 21 °C),
the control value "1" is sent.
A 2-point controller is recommended if the control value is only required to
switch between the two states ON and OFF, such as an electrothermal valve
connected to a switching actuator. A 2-point controller can deal with control
deviations with large changes of the command variables, but never comes
to rest.
2-point controllers always have an integrated hysteresis, which varies
around the setpoint, to prevent fast oscillations of the output states.
The hysteresis can be parameterised in different magnitudes. For example,
if the setpoint in heating mode is 21 °C and the hysteresis is 1.0 K,
the controller switches on if the temperature falls below 20.5 °C and off
if it exceeds 21.5 °C. The "hysteresis" parameter depends on how fast the
heating can heat up the room and how fast the cooling can cool the room
and also on the sensitivity to temperature of the people in the room.
The hysteresis should not be set too small, because a switching actuator
will be continuously opening and closing. The hysteresis must also not be
too great, because the temperature variations in the room will be too large.
Hysterese
Sollwert
Istwert
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