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.
If the doors didn’t work, the dock became a parking lot. If the dock became a parking lot, the turkeys spoiled. And if the turkeys spoiled… Marco didn’t want to finish that thought. saia ddc
His finger hovered over the Download Changes button. He opened the East_Air_Pressure comparator block
He grabbed his laptop and a fieldbus cable, then jogged across the yard, dodging a reversing yard dog. At the east wing’s main DDC panel, Marco plugged in. The SAIA PCD3 controller’s LEDs were blinking an irregular pattern—two fast, one slow. He’d seen that before. Not a hardware failure. A logic trap. Then, he added a new rung of ladder
He ignored it for thirty seconds. Sensors glitched. But then:
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 .