She did the only thing left. She slammed the emergency stop on Atlas, sprinted to the auxiliary air dryer bypass valve, cracked it open to vent a tiny amount of stored air (counterintuitive, but it reduced backpressure), and then reset Atlas’s overload.
When the maintenance crew finally replaced Titan’s fan at 4:00 PM, Maria collapsed into a rolling chair. On the HMI, the pressure trend showed a near-perfect line at 88 PSI, with only one brief dip to 81.5 PSI.
At 2:30, Maria Chen, the shift electrician, pulled up the LogixPro simulation on her laptop—the training software she’d mastered years ago. But this wasn’t a classroom exercise. This was Exercise 2 for real. logixpro dual compressor exercise 2
Maria stared at the LogixPro window still open on her laptop. The virtual pressure gauge was steady at 95 PSI. The virtual “Dual Compressor Exercise 2” completion banner flashed green.
In LogixPro’s “Dual Compressor Exercise 2,” the goal was simple: maintain 90–100 PSI with two compressors, handle duty cycling, and prevent both from running simultaneously for too long to avoid overload. The twist? A random “fault” could disable one compressor, forcing the other to handle the load within strict time limits. She did the only thing left
Atlas groaned, then spun. The unloader, freed by the pressure relief, clicked open. The compressor started unloaded. Pressure had fallen to 82 PSI—two pounds above disaster.
She jumped to the control cabinet, fingers flying over the old Allen-Bradley pushbuttons. She disabled the automatic lead-lag and forced Atlas into continuous run. Then she saw the problem: Atlas’s unloader solenoid was sticky. The compressor was starting under full load, drawing 300% amperage. The thermal overload relay clicked once, twice—on the third click, it would trip. On the HMI, the pressure trend showed a
In the LogixPro simulation, you had ladder logic timers: T4:0 for the “minimum run time” and T4:1 for the “anti-cycle delay.” Maria had no time to program. She had to become the PLC.