Operating Instructions

Applications
Siemens Building Technologies, Inc. 25
Airflow Control
There are two parts to the flow control; they operate in succession and never at the same
time. If a change occurs in the face area, feed forward control is used; during steady state
conditions the PID control loop is used.
Feed Forward Control - When a change in the face area is detected, Feed forward control
is used. This control uses a table created during the calibration sequence to adjust the
actuator signal to the proper voltage, determined by the required airflow, flow setpoint.
PID Control Loop – When the face area remains constant, the PID control loop is used. The
PID loop controls the air valve based on the values of the exhaust flow and the flow setpoint.
The loop output increases or decreases the output voltage and ranges from –100% to 100%.
 -100% is the maximum extend which closes the valve at full speed.
 0% holds the valve at is current position.
 100% is the maximum retract which opens the valve at full speed.
Calibration
Autozero Module (AZM) – Used when the damper cannot be closed and constant airflow is
needed.
 For a controller used with an AZM, calibration occurs without closing the air valve.
 For a controller used without an AZM, the damper is briefly commanded closed to get
a zero airflow reading and an accurate air valve position during calibration.
Venturi Air Valve Operation
The controller uses an embedded table statement and a feedback loop working together to
operate the supply or general exhaust Venturi Air Valve. The table contains 15 pairs of
“active” voltage/flow values, and 15 pairs of “inactive” voltage/flow values. The active values
are used to operate the Venturi Air Valve at various desired airflows.
Venturi Calibration
Calibrate the air valve at least once during start-up; the application determines the
relationship between the exhaust airflow and the voltage curve on the Venturi valve actuator.
Prerequisites for calibrating the exhaust air valve:
 Fully operational exhaust airflow systems.
 Calibration and normal operation of the Differential Pressure Transmitter.