Siemens BACnet ATEC 125-5050 - Manual (Page 15)

Chapter 2 – Applications
15
Siemens Industry, Inc. BACnet ATEC Owner's Manaul
125-5050, Rev. AA 4/20/2010
Calibration
Air Velocity Sensor
Calibration of the controller's internal air velocity sensor is periodically required to
maintain accurate air velocity readings. Calibration may be set to take place
automatically or manually.
Autozero Module (AZM)
Used when damper cannot be closed and constant airflow is needed.

For a controller used with an AZM, calibration occurs without closing the damper.
Application 6520, 6521, 6522, 6523.

For a controller used without an AZM, the damper is briefly commanded closed to
get a zero airflow reading and an accurate damper position during calibration.
Application 6520, 6521, 6522, 6523.
Hot Water Valve
Calibration of a hot water valve (if used) is done by briefly commanding the valve
closed. Application 2863, 2865, 2867.
Damper Status Operation
It is possible, after a period of operation, for the calculated damper position to differ
from the actual (physical) damper position.
If this occurs, the controller will
automatically compensate for any difference by
readjusting the calculated damper position. This calculated position may not match the
actual position.
Fail-safe Operation
If the air velocity sensor fails, the controller uses pressure dependent control. The
temperature loop controls the operation of the damper.
If the room temperature sensor fails, then the controller operates using the last known
temperature value.
Heating and Cooling Switchover
The heating/cooling switchover determines whether the controller is in heating or
cooling mode by monitoring the room temperature and the demand for heating and
cooling (as determined by the temperature control loops).