Gira KNX 2139 00 Product Documentation page 126

Room temperature controller | Room temperature controller - General
An additional heating or cooling level as PI control works in the same way as the PI
control of the basic level, with the exception that the setpoint will shift, taking account
of the configured level width.
Switching PI control
With this type of feedback control, the room temperature will also be kept constant by
the PI control algorithm. Taking the mean value for a given time, the same behaviour
of the control system will result as you would obtain with a continuous controller. The
difference compared with continuous feedback control is only the way how the com-
mand value is output. The command value calculated by the algorithm in cycles of
every 30 seconds is internally converted into a pulse-width-modulated (PWM) com-
mand value signal and sent to the bus via a 1-bit switching object. Taking into ac-
count the cycle time settable using the parameter "PWM cycle time" in the parameter
branch "Room temperature controller x -> RTCx - General -> Command value out-
put", the mean value of the command signal resulting from this modulation is a meas-
ure for the centred valve position of the control valve and thus a reference for the set
room temperature.
A shift of the mean value, and thus a change in the heating capacity, can be obtained
by changing the duty factor of the switch-on and switch-off pulses of the command
value signal.
If the command value is changed, the current PWM cycle is adapted as required so
that the duty factor corresponds as directly as possible to the new command value.
This adaptation is carried out in the same way as during activation of the valve out-
puts (see figure 8).
For a command value of 0% (permanently off) or of 100% (permanently on), a com-
mand value telegram corresponding to the command value ("0" or "1") will always be
sent after a cycle time has elapsed.
For switching PI control, the controller will always use continuous command values
for internal calculation. Such continuous values can additionally be sent to the bus
via a separate 1-byte value object, for example, as status information for visualisation
purposes (if necessary, also separately for the additional levels). The status value
objects will be updated at the same time as the command value is output. The para-
meters "On change by (0 = inactive)" and "Cyclical (0 = inactive)" have no function
here. An additional heating or cooling level as switching PI control works in the same
Heating actuator 6-gang with controller | Order no. 2139 00 | 21393100
Image 27: Continuous PI control
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