Fume hood startup behavior

Fume hood DXR startup
When power is applied to the fume hood DXR, runtime operations proceed in a defined sequence: Input devices that influence the airflow setpoint are read immediately (sash sensors, face velocity sensor, sash position switches). The DXR calculates a flow setpoint using the new sensor data and applies the airflow control loop, bringing the airflow under control (the amount of time is dependent on the speed of the damper motor and associated loop tuning).

The fume hood DXR can be configured to always start in "Auto" mode by setting "Fume hood exhaust air setpoint selection" parameter (in the FhSpEh AF) to Auto. This allows the system to determine the fume hood exhaust air setpoint. Or, in installations where the user can select a setpoint from the ODP (e.g., face velocity or airflow setpoint), the fume hood DXR can be configured to initialize the setpoint value that was selected and stored during the previous session.
The DXR stores certain dynamic data, like the fume hood user’s selected setpoint, on a fixed, 30-minute interval. If the Fume hood exhaust air setpoint selection value has been selected from the ODP as "Setpoint 1" (or ..2, or ..3) instead of "Auto", then the DXR starts with the setpoint that was in effect the last time the controller stored data on a 30-minute cycle.)

Operator display panel startup
(for P87 ODP)
When power is applied to the ODP, it starts according to its own defined sequence of events. The ODP and the DXR are typically powered up together, but the ODP start-up sequence takes longer than the DXR start-up sequence. This means that the DXR will take control of the fume hood exhaust flow before the ODP is ready for use. When this happens, the ODP screen will display "FAILED - DO NOT USE" and the red alarm LED will illuminate (no audible alarm). This process normally takes less than one minute before the ODP takes over.