MODBUS Network and Daisy-Chaining
Network Wiring and Configuration • 19
7.4.7. Step 7: Set the Setpoint
Temperature Offset
The Control Link ACC seeks to maintain a
constant minimum difference between the dewpoint
of the outside air and the temperature of the door
frame. You may specify how big this difference will
be by pressing the temperature offset button on the
dewpoint sensor.
The offset button on the dewpoint sensor is located
on the lower left side of the sensor enclosure
(see
Figure 7-18
), and the offset value is indicated by
the LED in the upper left corner of the dewpoint
enclosure. The LED will normally flash once every 4
seconds.
1.
Step 1
: Push and hold the offset button for 5
seconds to enter the configuration mode. (The LED
will illuminate solid for 5 seconds prior to entering
configuration mode. After 5 seconds it will turn off
to indicate the dewpoint sensor has entered
configuration mode.)
2.
Step 2
: Release the offset button and the LED will
flash from 1 to 8 times depending on the current
offset configuration. Each LED flash represents a 1-
degree Celsius (1.8°F) incremental temperature
offset. If the button is not pushed any further, after
10 seconds the unit will exit the configuration mode
and will resume its normal operation and flash the
LED once every 4 seconds. (Repeat
Step 1
to re-
enter the configuration mode.)
3.
Step 3
: If the button is pushed within 10 seconds
after the current setting is flashed, the offset value
will increment by 1 degree Celsius (1.8°F) and the
LED will flash the new offset value as one flash per
degree Celsius of offset. For example, if the offset
is set at 8°C (14.4°F), and the button is pushed to
increment the value, the value will start over at the
1-degree Celsius offset (1.8°F).
The offset button determines the number of
degrees (in Celsius) that will be added to the value of
the dewpoint sensor to determine the target
temperature of the door frame. For example, if the
current dewpoint is 5°C (41°F) and the button is set to
a medium offset of 2°C (3.6°F), the Control Link
ACC will control the heaters to achieve a door frame
temperature of 7°C (44.6°F). As the dewpoint rises
and falls, the door frame temperature setpoint will
also rise and fall, so that the door frame temperature
will always stay slightly above the current dewpoint.
The Control Link ACC uses the offset button on
the dewpoint sensor to determine the value of the
temperature offset. The Control Link ACC prioritizes
them in the following ways:
1. If E2 is connected, the offset is configured at the E2.
2. If sharing a dewpoint sensor, the remote offset is
provided even if the Control Link ACC has its own
dewpoint sensor.
3. The local dewpoint sensor’s offset is used.
This priority structure is designed to make it easier
for temperature offsets to be changed in the field (by
simply changing it on the dewpoint sensor), and it
also allows multiple cases to use the same sensor
while using different temperature offsets.
7.4.8. Step 8 - Network
Configuration Is Complete -
Restore Power to the ACC
Restore power to the ACC and check the status of
the network by observing the LEDs on the front of
each Control Link ACC enclosure:
• If network communication is active, you should see
the
RX
LED blinking at least once every 15
seconds. If you see no activity or a regular blinking
pattern, there may be a problem with the MODBUS
Figure 7-18
-
Dewpoint Sensor Offset Button
NOTE: If the offset button is pressed for more
than 15 seconds, the LED will remain ON solid
to indicate an offset button stuck condition, but
the offset value will not be changed.
TIP: Experiment with offsets to find the
lowest possible setting that still offers good
performance. In many cases, depending on
the placement of the door frame temperature
sensor, a LOW offset will still provide good anti-
condensate performance. The lower the offset being
used, the higher the energy savings.
