---
title: "Case study: feasibility, drawbacks, convincing"
subject: "Instrumentation II"
chapter: 10
key: "semester_5/instrumentation_ii:cs-2072kartik-feasibility"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/cs-2072kartik-feasibility
site: BCT Engineering
---

# Case study: feasibility, drawbacks, convincing

Instrumentation II · Chapter 10: Case Study

- Asked in: 2072 Kartik, 12 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/cs-2072kartik-feasibility
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-10

## Question

Answer the following questions with respect to your case study: (i) What is techno-commercial feasibility of a system? Provide examples from your case-study experience. (ii) List the major technical drawbacks present in the existing MBI system that you witnessed at the industrial site. (iii) Give at least three feasible technical solutions to overcome the drawbacks that you witnessed. Show how your solution will offer higher reliability and incorporate fault-tolerant design practices. Include block diagrams. (iv) If you had to present your design to the company's management team, what sort of question would you anticipate? Provide a list of at least five questions that would be asked from a management point of view. How would you cope with the questions, and how would you convince the team to accept your design? (v) Repeat part (iv), but now you are trying to convince senior engineers. How will the question and answer session change compared to part (iv)? (vi) Compare and contrast your design with the existing design in terms of the following metrics: cost/performance ratio, technical specifications (hardware and software) and design complexity (provide diagrams).

## Short answer

Existing dairy pasteurizer uses manual steam valve causing ±3°C swings and no logging. Proposed system with redundant PT100, PID control, Modbus SCADA ensures ±0.5°C, reduces steam/rejects, fault tolerance via watchdog, backup sensors, fail-safe valve. Investment Rs 12 lakh, payback 10.4 months.

## Answer

**Assumed case study:** a milk pasteurisation and packaging section of a dairy plant (HTST process: raw milk tank, heat exchanger, steam-heated holding tube, cooling, filling). The existing system uses analog panel indicators, bimetal thermostats, a manual steam valve and operator logging. (If your own visit was to another plant, replace the process names; the structure of the answer stays the same.)

#### (i) Techno-commercial feasibility
It is the study of whether a proposed system is **technically possible** (suitable technology, components, skills, compatibility with the existing plant) and **commercially worthwhile** (cost, benefit, payback, risk). Example from the dairy plant: technically, a PT100 + microcontroller loop can hold 72 ± 0.5 C and all the parts are available locally; commercially, the investment of Rs 12 lakh is returned in about 10 months from savings of Rs 1.15 lakh per month (assumed), so it is feasible.

#### (ii) Technical drawbacks of the existing MBI system
Manual valve control with ±3 C swings; analog gauges with low accuracy and no logging; no alarms or interlocks; ageing sensors and drift; relay logic that is hard to modify; dependence on operators; no remote monitoring; frequent breakdowns and poor fault diagnosis; and no protection from power-quality problems.

#### (iii) Three technical solutions with fault tolerance
1. **Microcontroller PID loop with redundant sensors:** two PT100 sensors are compared; if they differ, raise an alarm and use a safe value (with three sensors, majority voting can be used).
2. **PLC-based control with HMI:** reliable industrial hardware, diagnostics and modular I/O; a hot-standby CPU is optional.
3. **Distributed nodes with SCADA:** each section has its own controller on RS-485, so the failure of one node does not stop the others.

Solution 1 (redundant sensors, watchdog, fail-safe valve):
```text
 PT100-A --+                    +--> Valve (fail-closed)
 PT100-B --+--> [MCU] + WDT ----+
 Level ----+      |  ^ brown-out  +--> Alarm
                  v
              RS-485 -> SCADA
```
Solution 2 (PLC with optional standby CPU):
```text
 Sensors --> [Input modules] --> [PLC CPU (PID)] --> [Output modules] --> Valve / pump
                                   |        |
                          [Standby CPU]   [HMI panel]
```
Solution 3 (distributed nodes):
```text
 Reception node ----+
 Pasteuriser node --+-- RS-485 bus --> SCADA PC
 Filling node ------+
```
Reliability features: watchdog timer, brown-out reset, redundant sensors, fail-safe valve, UPS, optical isolation, self-test, manual bypass and spare modules.

#### (iv) Questions from management and how to answer
1. What is the total cost and payback? Show the figures: Rs 12 lakh, 10.4 months.
2. What if it fails? Manual bypass, watchdog, spares and vendor support.
3. How many staff are required or affected? A training plan, and redeploying workers.
4. How long will the shutdown be? Install in phases during the off-peak time.
5. What is the effect on quality and sales? Records for food-safety audits.
6. Who maintains it? Training and an AMC contract.

Convince them with a pilot, numbers (savings, risk reduction), reference installations and a clear timeline.

#### (v) Senior engineers
The questions are more technical: accuracy and calibration, ADC resolution and noise, control algorithm and stability, EMC and grounding, protocol and timing, firmware testing, MTBF, scalability, and standards. Answer with calculations (0.037 C per count), test results, circuit and timing diagrams, and a test plan. The management discussion, by contrast, is about money and risk.

#### (vi) Comparison with existing design
| Metric | Existing | Proposed |
|---|---|---|
| Cost / performance | Low cost, low performance | Higher cost, much better accuracy and savings |
| Hardware | Gauges, thermostat, relays | Sensors, ADC, MCU, SSR, RS-485 |
| Software | None | Control, alarm, logging firmware |
| Accuracy | ±3 C | ±0.5 C |
| Complexity | Simple | Moderate (needs skills) |
```text
 Existing: sensor -> operator -> valve
 Proposed: sensor -> ADC -> MCU -> valve  (+ PC log)
```

## Check yourself

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

1. What does techno-commercial feasibility examine?
   A. Only whether the components can be bought
   B. Only the payback period
   C. Whether the system is technically possible and commercially worthwhile (cost, benefit, payback, risk)
   D. Whether operators like the system
   Answer: C. It combines technical possibility with commercial worth. (Key point: Techno-commercial feasibility)

2. How do two PT100 sensors improve fault tolerance?
   A. They double the ADC resolution
   B. Readings are compared; if they differ an alarm is raised and a safe value is used
   C. They remove the need for a watchdog
   D. They make the valve open faster
   Answer: B. Comparing redundant sensors detects a faulty one and allows a safe fallback. (Key point: Redundant sensors for fault tolerance)

3. How does the question session with senior engineers differ from that with management?
   A. Engineers ask about money and risk, management about ADC noise
   B. There is no difference
   C. Both ask only about payback
   D. Engineers ask technical questions (accuracy, noise, stability, EMC, MTBF) while management asks about cost, risk and payback
   Answer: D. Management focuses on money and risk; engineers want calculations, test results and diagrams. (Key point: Management vs engineer questions)

4. What temperature accuracy is claimed for the proposed design versus the existing one?
   A. +/-0.5 C versus +/-3 C
   B. +/-3 C versus +/-0.5 C
   C. +/-0.037 C versus +/-3 C
   D. Both are +/-0.5 C
   Answer: A. The proposed loop holds +/-0.5 C, an improvement over the existing +/-3 C. (Key point: Accuracy comparison)

## Related in Instrumentation II

- [Case study: existing vs proposed system](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-2074asoj) — Instrumentation II, chapter 10
- [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
- [Case study: new system vs existing (cost, manpower)](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-cost-manpower-automation) — Instrumentation II, chapter 10, asked 4×
- [Case study: recommended changes and convincing](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-recommend-changes) — Instrumentation II, chapter 10, asked 2×
- [Case study: plan, feasibility and ROI](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-2075chaitra) — Instrumentation II, chapter 10
- [Case study: workflow, factors, proposed design, benefits](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-2076chaitra) — Instrumentation II, chapter 10

## Related in other subjects

- [Experience of case study performed](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Acase-study-experience) — Energy Environment and Society, chapter 6, asked 2×
- [Proposal; feasibility study of a road project](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Aproposal-questions-feasibility-road) — Project Engineering, chapter 2
- [Case study: Nepal Electricity Authority / Telecom](https://www.bctengineer.com/question.md?key=semester_7%2Forganization_and_management%3Acase-study-nea-nt) — Organization and Management, chapter 9
- [Pre-feasibility site-specific investigations](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aprefeasibility-site-investigations) — Hydropower Engineering, chapter 2