Pwm Controller - ABB i-bus KNX Product Manual

4.3.3

PWM controller

© 2009 Busch-Jaeger Elektro GmbH – A Company of the ABB Group
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Stellgröße
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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.
The PWM controller has the same continuous control as a continuous
controller. The only difference is that with a PWM controller the 1-byte
control value (0...255) is converted to a on/off ratio (0 and 1). For example,
if a control value of 70% is output, the make time will be 7 minutes and
the break time 3 minutes at a default cycle time of 10 minutes.
This transfers the advantages of continuous control (control to the desired
setpoint, no oscillations) to drives that are designed for on/off signals only,
such as electrothermal drives.
The "PWM control value cycle time" can be adjusted to optimise the control
properties of the heating or cooling system. The type of heating or cooling
and the actuator must be considered to set the cycle time appropriately.
The following recommendations can be used:
a) electrothermal actuator
It takes 2-3 minutes to open an electrothermal valve fully.
A cycle time shorter than 15 minutes is therefore not reasonable.
b) underfloor heating
The time of constant of underfloor heating is very large.
A cycle time of 20 minutes is therefore sufficient.
c) hot-water heating
Electrothermal drives are commonly used. A cycle time of
15 minutes gives very good control results.
d) electrical convector heating
Cycle times between 10 and 15 minutes, depending on
the electric heating and room conditions, are recommended.
Sollwert
Istwert
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90