PLC ladder logic and HMI for a water booster pumping station

Station 4 lifts water from a 250 m³ underground sump to a hilltop tank 2.5 km away. It has three 22 kW pumps, and today they are controlled by float switches and relays. Last year the panel let a pump run with the sump empty and the pump burnt out. Worse, when the hilltop tank drops, all three pumps start at the same moment, the voltage dips and the main pipe bangs with water hammer.

Kestrel is moving every station to PLC control. Station 4 is the pilot. The operations engineer has written the rules: - The hilltop tank level arrives as a 4–20 mA signal (0–6 m) over a radio link. The sump level is a local 4–20 mA transmitter (0–4 m). - Start the duty pump when the hilltop tank falls below 3.0 m and stop it at 5.5 m. Start an assist pump if the level is still below 2.0 m or still falling 10 minutes after the duty pump starts. - Stop all pumps if the sump falls below 0.6 m and allow restart only above 1.2 m. - Stagger pump starts by at least 15 seconds, and allow no more than 6 starts per pump per hour. - Rotate the duty pump every 24 hours of running, and swap to the standby pump immediately if a pump trips or fails to start within 5 seconds. - If the radio link is lost for more than 60 seconds, raise an alarm and fall back to a safe mode you must propose and justify.

You do not need a PLC. You will build and test everything in a free IEC 61131-3 environment, either OpenPLC Editor or CODESYS, using its built-in simulation, and build the HMI in the same tool or in a free web HMI.

Done looks like a functional specification, a cause-and-effect matrix, the PLC program with scaling, sequencing and alarms, an HMI with overview and alarm screens, and a signed simulated factory acceptance test showing every rule works, including the failures.