Gira KNX 2139 00 Product Documentation page 127

Room temperature controller | Room temperature controller - General
way as the PI control of the basic stage, with the exception that the setpoint will shift,
taking account of the configured level width. All PWM control options will use the
same cycle time.
Cycle time:
The pulse-width-modulated command values are mainly used for activating electro-
thermal drives (ETD). In this regard, the room temperature controller transmits the
switching command value telegrams to an actuator equipped with semiconductor
switching elements to which the drives are connected (e.g. heating actuator). By set-
ting the cycle time of the PWM signal on the controller, you can adapt the feedback
control to the drives used. The cycle time sets the switching frequency of the PWM
signal and allows adaptation to the adjusting cycle times of the valve drives used (the
adjusting time it takes the drive to bring the valve from its completely closed to its
completely opened position). In addition to the adjusting cycle time, take account of
the dead time (the time in which the valve drives do not show any response when be-
ing switched on or off). If different actuators with different adjusting cycle times are
used, take account of the longest of the times. Always note the information given by
the manufacturers of the actuators.
During cycle time configuration, a distinction can always be made between two
cases...
Case 1: Cycle time > 2 x adjusting cycle time of the electrothermal drives used (ETA)
In this case, the switch-on or switch-off times of the PWM signal are long enough for
the actuators to have sufficient time to fully open or fully close within a given time
period.
Advantages:
The desired mean value for the command value and thus for the required room tem-
perature will be set relatively precisely, even for several actuators triggered at the
same time.
Disadvantages:
It should be noted, that, due to the full valve lift to be continuously 'swept', the life ex-
pectancy of the actuators can diminish. For very long cycle times (> 15 minutes) with
less sluggishness in the system, the heat emission into the room, for example, in the
vicinity of the radiators, can possibly be non-uniform and be found disturbing.
This setting is recommended for sluggish heating systems (such as underfloor
heating).
Even for a bigger number of triggered actuators, maybe of different types, this
setting can be recommended to be able to obtain a better mean value of the
adjusting travels of the valves.
Case 2: Cycle time < adjusting cycle time of the electrothermal drives used (ETA)
In this case, the switch-on or switch-off times of the PWM signal are too short for the
actuators to have enough time to fully open or fully close within a given period.
Heating actuator 6-gang with controller | Order no. 2139 00 | 21393100 Page 127 of 257