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UNT-SVX07A-EN 59
Operation
sequence of
operation
Zone Sensor
The Tracer
ZN520 controller accepts the
following zone sensor module inputs:
• Space temperature measurement
(10kΩ thermistor)
• Local setpoint (either internal or
external on the zone sensor module)
• Fan switch
• Timed override (On) and Cancel timed
override
• Communication jack
Space Temperature Measurement
Trane zone sensors use a 10kW
thermistor to measure the space
temperature. Typically, zone sensors are
wall-mounted in the room and include a
space temperature thermistor. As an
option, the zone sensor can be unit-
mounted with a separate space
temperature thermistor located in the
unit’s return air stream. If both a
hardwired and communicated space
temperature value exist, the controller
ignores the hardwired space
temperature input and uses the
communicated value.
External Setpoint Adjustment
Zone sensors with an external setpoint
adjustment (1kΩ) provide the Tracer
ZN520 controller with a local setpoint (50
to 85°F or 10 to 29.4°C). The external
setpoint is exposed on the zone sensor’s
front cover.
When the hardwired setpoint adjustment
is used to determine the setpoints, all unit
setpoints are calculated based on the
hardwired setpoint value, the configured
setpoints, and the active mode of the
controller. The hardwired setpoint is used
with the controller’s occupancy mode
(occupied, occupied standby, or unoccu-
pied), the heating or cooling mode, the
temperature deadband values, and the
heating and cooling setpoints (high and
low limits) to determine the controller’s
active setpoint.
When a building automation system or
other controller communicates a setpoint
to the controller, the controller ignores
the hardwired setpoint input and uses
the communicated value. The exception
is the unoccupied mode, when the
controller always uses the stored default
unoccupied setpoints. After the controller
completes all setpoint calculations, based
on the requested setpoint, the occupancy
mode, the heating and cooling mode, and
other factors, the calculated setpoint is
validated against the following setpoint
limits:
• Heating setpoint high limit
• Heating setpoint low limit
• Cooling setpoint high limit
• Cooling setpoint low limit
These setpoint limits only apply to the
occupied and occupied standby heating
and cooling setpoints. These setpoint
limits do not apply to the unoccupied
heating and cooling setpoints stored in
the controller’s configuration.
When the controller is in unoccupied
mode, it always uses the stored unoccu-
pied heating and cooling setpoints.The
unit can also be configured to enable or
disable the local (hardwired) setpoint.
This parameter provides additional
flexibility to allow you to apply communi-
cated, hardwired, or default setpoints
without making physical changes to the
unit.
Similar to hardwired setpoints, the
effective setpoint value for a communi-
cated setpoint is determined based on
the stored default setpoints (which
determines the occupied and occupied
standby temperature deadbands) and
the controller’s occupancy mode.
Fan Switch
The zone sensor fan switch provides the
controller with an occupied (and occupied
standby) fan request signal (Off, Low,
Medium, High, Auto). If the fan control
request is communicated to the
controller, the controller ignores the
hardwired fan switch input and uses the
communicated value. The zone sensor
fan switch input can be enabled or
disabled through configuration using the
Rover service tool. If the zone sensor
switch is disabled, the controller resorts
to its stored configuration default fan
speeds for heating and cooling, unless the
controller receives a communicated fan
input.
When the fan switch is in the off position,
the controller does not control any unit
capacity. The unit remains powered and
all outputs drive to the closed position.
Upon a loss of signal on the fan speed
input, the controller reports a diagnostic
and reverts to using the default fan
speed.
On/Cancel Buttons
Momentarily pressing the on button
during unoccupied mode places the
controller in occupied bypass mode for
120 minutes. You can adjust the number
of minutes in the unit controller
configuration using Rover service tool.
The controller remains in occupied
bypass mode until the override time
expires or until you press the Cancel
button.
Communication jack
Use the RJ-11 communication as the
connection point from Rover™ service
tool to the communication link — when
the communication jack is wired to the
communication link at the controller. By
accessing the communication jack via
Rover™, you can access any controller
on the link.
Communications
Tracer
ZN520 controller communicates
via Trane’s LonTalk protocol. Typically, a
communication link is applied between
unit controllers and a building automation
system. Communication also is possible
via Rover, Trane’s service tool. Peer-to-
peer communication across controllers is
possible even when a building
automation system is not present. You do
not need to observe polarity for LonTalk
communication links.
The controller provides six 0.25-inch
quick-connect terminals for the LonTalk
communication link connections, as
follows:
• Two terminals for communication to the
board
• Two terminals for communication from
the board to the next unit (daisy chain)
• Two terminals for a connection from the
zone sensor back to the controller
Table O-SO-16. Zone sensor wiring
connections
TB1 description
1 space temperature
2 common
3 setpoint
4 fan mode
5 communications
6 communications