Art. No. SC 1000 KNX
The command values calculated by the control algorithm are output via the "Heating command
value" or "Cooling command value" communication objects. Depending on the control algorithm
selected for the heating and/or cooling mode, the format of the command value objects is,
among other things, also specified. 1-bit or 1-byte actuating objects can be created in this way
(see page 206). The control algorithm is specified by the parameters "Type of heating control"
or "Type of cooling control" in the "Room temperature control -> Controller general" parameter
branch and, if necessary, also with a distinction of the basic and additional stages.
Continuous PI control
PI control is an algorithm which consists of a proportional part and an integral part. Through the
combination of these control properties, you can obtain room temperature control as quickly and
precisely as possible without or only with low deviations.
When you use this algorithm, the room temperature controller will calculate a new continuous
command value in cycles of 30 seconds and send it to the bus via a 1-byte value object if the
calculated command value has changed by a specified percentage. You can use the "Automatic
transmission on change by…" parameter in the "Room temperature control -> Command value
and status output" parameter branch to set the change interval in percent.
Figure 87: Continuous PI control
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 command 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) command value signal and sent to the bus via a
1-bit switching object after the cycle time has elapsed. The mean value of the command value
signal resulting from this modulation is a measure for the averaged position of the control valve,
thus being a reference to the room temperature set, taking account of the cycle time which you
can set through the "Cycle time of the switching command value…" parameter in the "Room
temperature control -> Command value and status output" parameter branch.
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.
The duty factor will be adapted by the controller only at the end of a time period, depending on
the command value calculated. This applies to any change of the command value, regardless of
what the ratio is by which the command value changes (the "Automatic transmission on change
by…" and "Cycle time for automatic transmission..." parameters will have no function in this
Page 171 of 347
Software "Smart Control 501511"
Functional description
