The Autocalibration Sequence module controls the timing for automatically calibrating (that is, recalculating the zero offset) of the velocity pressure sensors. The sequence for calibration involves commanding the dampers to close, waiting sufficient time for the dampers to close, signalling the calibration process itself, and then returning the application to normal control. It is used in standard VAV control applications.
The calibration sequence is enabled to occur automatically if the input Days between Autocals is greater than zero. If that is the case, the first autocalibration is initiated automatically after a transfer to the controller, startup, power enable, and so on. The delay before this first autocalibration is equal to five times the FCB MAC address of the controller so that not all VAV applications on a given network trunk calibrate at the same time.
If automatic calibration is enabled, an autocalibration sequence occurs periodically based on the Days between Autocals input. The timer used to determine the next automatic calibration is restarted whenever a calibration sequence completes.
The calibration sequence can also be manually initiated on a rising edge (False to True transition) of the Autocalibration Request input (connected by default from the AUTOCAL-C network input. The module resets the PIDs to default tuning parameters if the Reset PID Tuning input is not Normal.
For information on how the FSM determines the state, see FSM (Autocalibration).