Technical Instructions
RDU20U, RDU50U and RDU50.2U Room Temperature Controllers
Document Number 155-735
with LCD for Heating and Cooling Systems
November 1, 2006
Page 4
Siemens Industry, Inc.
Inversion of Output
Signal
RU50U and RDU50.2U
The output signal can be inverted with the help of DIP Switch No. 2. If set to ON, 0V
corresponds to 0% travel and 10V to 100% travel (reverse acting heating/reverse acting
cooling). In the OFF position, 0V corresponds to 100% travel and 10V to 0% travel
(direct acting heating/direct acting cooling). See Figure 7 and Figure 8 for control
characteristics.
Heating-Cooling with
Minimum Limitation
Cooling
RU50U and RDU50.2U
Figure 7. Reverse Acting Heating/
Reverse Acting Cooling Function
Diagram.
Figure 8. Direct Acting Heating/Direct
Acting Cooling Function Diagram.
T
Room temperature
Y
Out
Output percentage
W
Room temperature setpoint
XpH Proportional band heating
XpK Proportional band cooling
VR
0% to 100% minimum limitation of
cooling output
c/o
Changeover
Minimum Limitation of
Cooling Signal
Using parameter P11, the cooling signal output can be limited to a minimum value
between 0 and 100% (0 to 10 Vdc). This can be used to ensure a minimum supply air
volume. When used in connection with a VAV controller, this setting must be taken into
account. See VR in Figure 7 and Figure 8.
Return Air Temperature
The RDU Controllers provide control depending on either the measured room
temperature or the return air temperature. The return air temperature measurement
overrides the internal measurement automatically if a QAH11.1 cable temperature
sensor is connected to input 4
–3 (RDU50U and RDU50.2U) or 8–9 (RDU20U).
Parameter P12 shows which temperature sensor is currently active.
Display
(See Table 5)
•
The settings for Parameters P12, P13, and P14 cannot be changed; they are for
displaying information settings only.
•
The RDU50.2U Controller does not have a parameter setting or display for
Parameter P14.
•
Parameter P14 (RDU20U and RDU50U) displays the current heat/cool changeover
temperature 32°F to 120°F (0°C to 49°C), and
100 = Input open or no sensor connected
–Heating mode
00 = Input bridged
–Cooling mode.
•
For Parameter P12:
01 = The room temperature sensor is active.
02 = The return air temperature sensor is active.
•
Parameter P13 displays the current room temperature 32°F to 120°F (0°C to 49°C).
Operating Modes
Normal Mode
Heating or cooling mode with automatic changeover. The controller maintains the
adjusted setpoint in normal operation.
