For three heartbeats, nothing happened. The LEDs on the PCD3 flickered wildly. Then, one by one, the red indicators on the SAIA panel turned green. He refreshed his SCADA dashboard. Dock Door 47: Lock Engaged. Door 48: Leveler Ready. Door 49: Operational.
He opened the East_Air_Pressure comparator block. The current limit was 10.2 bar . He changed it to 11.5 bar —a safe mechanical tolerance. Then, he added a new rung of ladder logic: IF HVAC_Damper_Command = CLOSE AND Outdoor_Temp < 40F, THEN Bypass_Pressure_Check for 30 seconds.
He opened the PG5 project file and navigated to the function block controlling doors 45 through 55. The code was clean, written in SAIA’s FBD (Function Block Diagram). But one variable stood out: East_Air_Pressure .