Pi Controller (Pwm) - ABB i-bus KNX Product Manual

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ABB i-bus KNX
Appendix
12.4.3

PI controller (PWM)

The PI controller (PWM) basically operates exactly like the PI controller (continuous). The only difference
is that the control value of a PI controller (PWM) is converted to a 1 bit PWM switch-on/switch-off ratio
before it is output.
If a control value of 70 % is output and the preset cycle time is 10 minutes, the switch-on time will be
7 minutes and the switch-off time will be 3 minutes.
Using the PI controller (PWM) transfers the advantages offered by continuous control (precise attainment
of the setpoint temperature) to drives that are designed only for switch-on/switch-off signals (e.g.
electrothermal drives).
The "PWM control value cycle time" is adjustable to optimize the control characteristics of the heating or
cooling system. The type of heating or cooling and the valve drive used must be taken into account.
•
Electrothermal Valve Drive:
Depending on the manufacturer, it takes around 2 to 3 minutes to open a control valve with
electrothermal drive. A cycle time of 15 minutes has proven useful in practice. Other times must be
correspondingly adapted to the heating/cooling system.
•
Floor heating:
The time constant of a floor heater is very large (sluggish). A cycle time of 20 minutes suffices.
•
Water heating:
A cycle time of 15 minutes produces excellent control results.
•
Electric convector heating:
Depending on the electric heating and the room situation, cycle times between 10 and 15 minutes are
recommended.
240 2CDC508220D0211 Rev. A | VC/S 4.x.1