The differential pressure sensor is used to measure duct velocity pressure. The auto-zero solenoid is internally connected to the air velocity pressure transducer's inlet ports to enable automatic periodic re-calibration. This re-calibration ensures accurate, drift-free airflow measurement. Automatic re-calibration of the differential pressure transducers occurs upon system power-up and when airflows are stable with configurable frequency based on hours, default is every 3 hours.