© 2009 Merten by Schneider Electric
39
Push-button, 4-gang plus with room temperature control unit and IR receiver
Multifunction with RTCU and FanCoil 1817/1.0
Getting to know and parameterising the room temperature control unit
The temperature overshoot above or below the hyster-
esis apparent in the diagram is caused when the heat-
ing/cooling system continues to emit heat or cold into
the room after it has been switched off.
Setting rules for the 2-step control
"Hysteresis of the 2-step control" parameter:
• Small hysteresis:
Leads to small fluctuations, but frequent switching.
• Large hysteresis:
Leads to large fluctuations, but infrequent switching.
|
In general, due to the influences of the heating sys-
tem and the room, the temperature fluctuations in
the room are significantly higher than the hystere-
sis.
Continuous and switching PI control
For the PI control, the correcting variable is calculated
from a proportional and an integral share. The calcula-
tion is governed by parameters such as:
• Temperature difference between actual value and set-
point
• Proportional range
• Reset time
In this way, the controller can correct the room temper-
ature quickly and accurately. The corresponding cor-
recting variable is transferred via a 1 bit/1 byte value to
the bus.
The standard control parameters for the most common
system types are already installed in the controller:
• Warm water heating
• Underfloor heating
• Electric heating
• Fan convector
• Split unit
• Cooling ceiling
You can also set the control parameters for the propor-
tional range and the reset time manually, but you should
know exactly which actuators are connected and the
control conditions in the room.
Continuous PI control
For the continuous PI control, the corresponding 1 byte
correcting variable is transmitted 0-100% directly via
the bus to the heating actuator or an EMO valve drive,
which convert the correcting variable directly to a de-
gree of opening. However, this is only transmitted when
the newly calculated correcting variable has changed
by a specified percentage.
Switching PI control (PWM)
With the switching PI control, also known as the PWM
control, the correcting variables calculated by the con-
troller (0-100%) are converted into a pulse-width mod-
ulation (PWM). Within a constant, defined cycle time,
the control actuator is opened ("1") and then closed
again ("0") for the calculated percentage period. For ex-
ample, when a correcting variable of 25% is calculated
for a cycle time of 12 minutes, a "1" is transmitted at the
beginning of the cycle time, and a "0" is transmitted af-
ter three minutes (= 25% of 12 minutes)
.
When the setpoint temperature changes, the controller
recalculates the required correcting variable and trans-
mits it still within the current cycle (broken line).
Correcting variable
Calculated correcting
variable
t
t
100 %
50 %
0 %
100 %
50 %
0 %
1
0
Correcting variable
Calculated
correcting variable
t (min)
t (min)
0
15
30
45
60
100 %
80%
60%
40%
20%
0 %
