16 CNT-SVX17G-EN
Inputs and Outputs
5. Manual output test
6. Autocommission
7. Water valve override
Primary Airflow (Differential Pressure) Analog Input
The controller can operate with or without a valid flow value (either hardwired or
communicated). It operates under pressure-dependent control or pressure-independent
control.
Pressure-dependent Control
When a valid flow value is not present, the controller operates under pressure-dependent
control (position control). Pressure-dependent control substitutes the air valve position
for the flow measurement for all control actions.
During space-temperature control or v
entilation-flow control
During space-temperature control or ventilat
ion-flow control, pressure-dependent
control activates when the air valve position is above 75% and the airflow value is below
5% of the configured nominal airflow. Pressure-dependent control also activates when
the airflow setpoint is less than 10% of the configured nominal airflow.
During flow-tracking control
During flow-tracking control, if the airflow set
point plus the configured airflow tracking
offset is less than 10% of the configured nominal airflow and if the configured airflow
tracking offset is negative, the air valve is closed, otherwise the air valve goes to the
configured minimum airflow. These conditions do not generate an alarm message.
If the airflow sensor fails (Table 10), the controller closes the air valve if the configured
airf
low tracking offset is negative. If the configured airflow tracking offset is positive the
controller controls the air valve to the configured minimum airflow.
Pressure-independent Control
When a valid flow value is present, the controller operates under pressure- independent
control. The airflow is the calculated airflow needed to control the zone temperature +/
-2% of the configured nominal airflow. If after an airflow sensor failure, the airflow
returns to the valid range (airflow value greater than 10% of configured nominal airflow),
the controller automatically resumes pressure-independent control.
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