Application

Sequence of Operation
Room Temperature and CTL TEMP
8
Siemens Industry, Inc. Application Note, App 2033 140-1023
2015-08-07
CTL STPT Using Standard/Absolute Mode (Digital Room
Unit, Revision 26 and later)
Digital Room Unit (2200/2300 Series Firmware Revision 26 and later)
When STPT SPAN is set to 0, the room setpoint adjustment on the digital room unit
functions in a standard mode. The range of the adjustment is based on RM STPT MIN
and RM STPT MAX.
CTL STPT is set equal to RM STPT DIAL. The values for RM STPT MIN and RM
STPT MAX are applied to limit RM STPT DIAL before it is copied into CTL STPT.
Room Temperature and CTL TEMP
ROOM TEMP is the temperature that is being sensed by the room temperature sensor
(RTS).
CTL TEMP is the room temperature that is used for control purposes. In other words,
what the application is trying to do is to maintain CTL TEMP at the control setpoint.
If CTL TEMP is overridden then,
 CTL TEMP equals its overridden value and ROOM TEMP has no effect on the
value of CTL TEMP.
Occupied and Unoccupied Modes
The occupied/unoccupied status of the space is determined by the status of
OCC.UNOCC. The control of this point differs depending on whether the controller is
monitoring the status of a wall switch or if the controller is connected to a field panel.
When a wall switch is physically connected to the termination strip on the controller at
DI 2 and WALL SWITCH = YES, the controller monitors the status of DI 2. When the
status of DI 2 is ON (the switch is closed), OCC.UNOCC is set to OCC indicating that
the controller is in occupied mode. When the status of DI 2 is OFF (the switch is open),
OCC.UNOCC is set to UNOCC indicating that the controller is in unoccupied mode.
When WALL SWITCH = NO, the controller does not monitor the status of the wall
switch, even if one is connected to it. In this case, if the controller is operating stand-
alone, the controller stays in occupied mode all the time. If the controller is operating
with centralized control (connected to a field panel), the field panel can send an
operator or PPCL command to override the status of OCC.UNOCC.
Unoccupied Mode Override Switch
If an override switch is present on the room temperature sensor and a value (in hours)
other than zero has been entered into OVRD TIME, then by pressing the override
switch, a room occupant can reset the controller to occupied mode for the length of
time set in OVRD TIME. The status of UNOCC OVRD changes to OCC and remains
there until OVRD TIME elapses, at which point UNOCC OVRD changes back to
UNOCC and the controller returns to unoccupied mode.
NOTE:
Only during unoccupied mode (MODE = Unoccupied) can a room sensor’s override
switch set the controller to occupied mode; if MODE equals anything other than
Unoccupied, UNOCC OVRD will equal UNOCC.