Reducing failure probability in milk scheme

Assumed system: automated milk refilling (tank level sensing, pumps/valves, flow measurement, controller, display and billing) in a dairy depot. Failure may cause lost milk, spoilage or stoppage, so the following considerations apply.

1. Simple, proven design: use a robust industrial microcontroller/PLC and standard components; fewer parts and connectors mean fewer failures.
2. Component derating and quality: choose industrial-grade parts operating well below their ratings (voltage, current, temperature); use food-grade, corrosion-resistant sensors and valves.
3. Redundancy: duplicate critical parts (two level sensors, standby pump, backup controller or manual override); majority voting where safety matters.
4. Protection: fuses, surge/ESD protection (TVS), isolation for pump and valve drives (opto-isolators, relays with snubbers), grounding and shielding against motor noise.
5. Power reliability: UPS/battery backup, brown-out reset, filtered supply.
6. Watchdog timer and self-test: reset the controller when it hangs; check sensors at start-up; limit switches, overflow and dry-run protection with alarms.
7. Fail-safe behaviour: on a fault, the valves close and the pump stops safely, with alarm indications and a manual mode.
8. Environment: protect from moisture, washing water (IP65 enclosure), temperature and cleaning chemicals.
9. Testability and maintenance: test points, diagnostics, spare parts, preventive maintenance, operator training, documentation.
10. Software reliability: tested, simple state-machine code with error handling, and data logging.