That Tuesday, the thermometer on the mezzanine read 104°F. Titan’s cooling fan seized at 2:17 PM. By 2:22, its discharge temperature alarm screamed red on the control panel. The compressor didn't stop—it just kept churning, heating the air to 190°F, expanding it like a furious ghost. The pressure at the receiver tank began to drop.
“Atlas, you’re up,” she whispered, hammering the HMI start button. logixpro dual compressor exercise 2
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. That Tuesday, the thermometer on the mezzanine read 104°F
For six years, the system had run on a simple lead-lag routine: Titan ran all day, Atlas kicked in only when the pressure sagged below 95 PSI. It was dumb, but it worked. Until the heatwave. The compressor didn't stop—it just kept churning, heating
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.
Maria’s mind flashed to the exercise rubric: “When a compressor faults, the alternate must take over within 2 seconds. Pressure must not fall below 80 PSI.”
