Application

Sequence of Operation
Calibration
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Siemens Industry, Inc. Application Note, App 2520 140-1217
2015-05-06
Example
If CTL FLOW MIN = 250 cfm, and CTL FLOW MAX = 1000 cfm,
the low limit of FLOW STPT = (250 cfm/1000 cfm) × 100% flow
= 0.25 × 100% flow
= 25% flow.
Since 25% of 1000 cfm = 250 cfm, the minimum airflow out of the terminal box will be 250 cfm.
Calibration
Calibration of the controller’s internal air velocity sensor(s) is periodically required to
maintain accurate air velocity readings. CAL SETUP is set with the desired calibration
option during controller startup.
Depending on the value of CAL SETUP, calibration may be set to take place
automatically or manually. If CAL AIR = YES, calibration is in progress.
At the end of a calibration sequence, CAL AIR automatically returns to NO. A status of
NO indicates that the controller is not in a calibration sequence.
Floating Control Actuation Auto-correct
In addition to the existing options for floating control actuator full stroke actions, all
floating control actuators are provided with additional logic to fully drive open or closed
when commanded to 100% or 0%.
Fail Mode 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, the controller operates using the last known
temperature value.
Performing the Automated Fault Detection and
Diagnostics
VAV ATEC controllers have a built-in checkout procedure that performs a basic fault
detection and diagnostic routine. It can be manually initiated at any time after the
controller has been installed. This procedure tests all of the necessary I/O and ensures
the controller can operate within the set airflow range, between CLG FLOW MIN and
CLG FLOW MAX.
To perform the checkout procedure, set CHK OUT to YES. When the procedure has
completed, CHK OUT returns to NO and the results display in CHK STATUS, Table
Possible Failure Value and Description .