ABB i-bus® KNX
PLANNING AND APPLICATION
2CDC072028F0219
Fig. 30: Continuous control
12.2.13.4
PI controller (PWM)
The PI controller (PWM) works like a PI controller (continuous) in principle. Unlike the procedure for a
continuous controller, the control value is converted to a 1-bit PWM switch-on/switch-off ratio prior to
output for a PI controller (PWM).
Example
With a control value of 70 % and a cycle time of 10 minutes, the switch-on time is 7 minutes and the
switch-off time is 3 minutes.
Using the PI controller (PWM) the advantages offered by continuous control (precise attainment of the
setpoint temperature) can be obtained with drives that are designed only for switch-on/switch-off sig-
nals (e.g. thermoelectric drives).
The cycle time of the PWM control value can be set to optimize the control properties of the heating/
cooling system. The type of heating/cooling and the valve drive used must be considered when setting
the cycle time. The following cycle times are recommended:
• Thermoelectric Valve Drive: 15 minutes
It takes approx. 2 … 3 minutes to open a control valve fully with a thermoelectric drive (depending on
the manufacturer). Other times must be correspondingly adapted to the heating/cooling system.
• Floor heating: 20 minutes
The time constant of a floor heater is very large (sluggish).
• Water heating: 15 minutes
A cycle time of 15 minutes produces very good control results.
• Electric convector heater: 10 … 15 minutes
The cycle time depends on the type of electric heater and the room situation.
12.2.13.5
Control value direction
If the control value is only output via a group object, the output value can be inverted. The inversion of
the output value can be necessary to actuate NC (normally closed) or NO (normally opened) valve drives
correctly.
Product manual | EN-US | VC/S 4.x.1 | 2CDC508220D0211 Rev. B
184
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