2-Point Controller - ABB 2CSYK1201C Product Manual

MYLOS Building Automation
®
7.3.1

2-point controller

A 2-point controller has two output states, which switch depending on the current value. If the current value is above
the parametrised setpoint (22 °C at 21 °C setpoint), the control value "0" is sent to the bus.
If the current value is below the parametrised 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 an output terminal. 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 parametrised 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.
Planning and use
T
22 ûC
21 ûC
20 ûC
1
0
Continuous room heating or cooling in spite of the ON/OFF value of the
control value depends on the thermal inertia of the heating or cooling element.
Hysterese
Sollwert
Istwert
t
t
MYLOS Building Automation | Planning and use 67
®