---
title: "Reducing failure probability in milk scheme"
subject: "Instrumentation II"
chapter: 7
key: "semester_5/instrumentation_ii:milk-scheme-failure"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/milk-scheme-failure
site: BCT Engineering
---

# Reducing failure probability in milk scheme

Instrumentation II · Chapter 7: Circuit Design

- Asked in: 2073 Chaitra, 5 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/milk-scheme-failure
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-7

## Question

Kathmandu Milk Supply Scheme has planned to automate the milk refilling process. As an engineer, what would be your design considerations to reduce the probability of failure of the system?

## Short answer

Reduce failure probability by using a simple, proven controller with industrial-grade derated components, redundant sensors and standby pump, protective isolation, UPS, watchdog timer, fail-safe stop, IP65 enclosure against moisture, diagnostics, and tested software with error handling.

## Answer

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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which is a redundancy measure for the milk system?
   A. Single sensor only
   B. Two level sensors, standby pump and manual override
   C. Remove manual mode
   D. One pump with no backup
   Answer: B. Duplicating critical parts avoids single points of failure. (Key point: Redundancy)

2. What should happen on a fault?
   A. Valves close, pump stops and alarm is given
   B. Pump runs faster
   C. Valves open fully
   D. System ignores the fault
   Answer: A. A safe state prevents overflow and spoilage. (Key point: Fail-safe)

3. What enclosure protection suits the washed dairy environment?
   A. Open frame
   B. Paper housing
   C. No protection
   D. IP65 enclosure against moisture and washing water
   Answer: D. Moisture and cleaning chemicals are the main hazards. (Key point: Environment)

## Related in Instrumentation II

- [Case study: proposed system design](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-proposed-system-design) — Instrumentation II, chapter 10
- [Communication via satellite as unguided scheme](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asatellite-unguided) — Instrumentation II, chapter 5
- [Reducing conductive noise coupling](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aconductive-noise-reduce) — Instrumentation II, chapter 6
- [ATM in hotel card reader failure](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aatm-hotel-problem) — Instrumentation II, chapter 6
- [Technical dilemmas in circuit design](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adesign-dilemmas) — Instrumentation II, chapter 7
- [Case study: revamping MBI system for CEO](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-ceo-revamp) — Instrumentation II, chapter 10

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