PLCs, PMS and Alarm Systems on Board: How They Work
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Every alarm on the ECR screen, every standby pump that starts by itself and every generator that comes on line before the bow thruster is allowed to run is the work of a PLC or a power management system. When it works, nobody notices. When it does not, the ETO is called at 0300 with a blackout, a pump that will not change over or an alarm that nobody can clear. To fix it quickly you need to know what the controller is actually doing, scan by scan.
This is Part 2 of 3 in the DART Marine Automation series. You will open up the PLC (CPU, I/O, redundancy, scan cycle, IEC 61131-3 languages), follow a 4–20 mA signal from transmitter to alarm, and walk through the PMS step by step: heavy-consumer blocking, standby start, synchronising, droop and isochronous load sharing, preferential trip and blackout recovery, with the IMO and IACS limits behind each one. You get on-board checklists for auto-start, sync and alarm-loop tests and for backing up a PLC before a change, then a Python simulation of three diesel generators where you block a bow thruster, synchronise DG3 and compare how each load-sharing mode handles the step.
What you will be able to do
- Explain how a marine PLC scans, scales 4–20 mA signals, detects wire breaks and raises alarms with deadband and delay
- Follow a PMS sequence from heavy-consumer request to standby start, synchronising, breaker closing and load sharing
- Set up and test PMS auto-start, sync permissives, droop and alarm loops using checklists and the class limits behind them
- Simulate three generators in Python and compare isochronous, droop-with-PMS and droop-only load sharing
Before you start: Part 1: Ship Electrical and Automation Systems (marine-intro), or equivalent sea experience
Lessons
- The big idea: read, decide, write, repeat▶ VideoFree preview
- How it was invented and its first uses▶ VideoLocked
- Where it is used today: a tour of the ship's automation▶ VideoLocked
- The equations: scan time, 4–20 mA, synchronising and load sharing▶ VideoLocked
- Worked demo and setup: thruster request to shared load▶ VideoLocked
- Build your own, step by step▶ VideoLocked
- Python simulation labLocked
- Practice problems and quizLocked