---
title: "Closed and open control; quality cost"
subject: "Project Engineering"
chapter: 4
key: "semester_7/project_engineering:closed-open-control-quality-cost"
source: https://www.bctengineer.com/q/semester_7/project_engineering/closed-open-control-quality-cost
site: BCT Engineering
---

# Closed and open control; quality cost

Project Engineering · Chapter 4: Project Implementation and Controlling

- Asked in: 2067 Asar (old course), 8 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/project_engineering/closed-open-control-quality-cost
- Whole chapter: https://www.bctengineer.com/md/semester_7/project_engineering/chapter-4

## Question

Explain with examples closed system and open system of control. Justify the statement "Quality costs more, but lack of quality costs even more".

## Short answer

Open system has no feedback and does not correct deviations, e.g. a timer pump; closed system measures output and corrects, e.g. thermostat. Quality costs money for prevention and appraisal, but poor quality costs more through rework, claims, and reputation loss. Total quality cost is prevention plus appraisal plus failure costs, and failure costs fall faster as prevention increases.

## Answer

#### Closed and open system of control

```text
OPEN LOOP                  CLOSED LOOP
Input -> [Process] -> Out  Input -> [Process] -> Out
                              ^                   |
                              +-- [Compare]<------+
                                  (feedback)
```

| Basis | Open system | Closed system |
|---|---|---|
| Feedback | None | Present |
| Output compared with target | No | Yes |
| Self-correction | No; changes in conditions are not corrected | Yes; deviation is corrected |
| Complexity and cost | Simple, cheap | More complex, needs measurement |
| Accuracy | Low | High |
| Examples | Pump run on a timer; releasing funds monthly without checking progress; a plan carried out blindly | Thermostat of a heater; monthly comparison of actual cost with budget and correction; irrigation gate controlled by water level sensor |

Project control should be a closed system because the environment changes and errors must be corrected.

#### "Quality costs more, but lack of quality costs even more"

Good quality needs money for prevention (planning, training, procedures) and appraisal (inspection and tests). Poor quality costs far more through failure: rework and rejection (internal failure) and repair, claims and loss of reputation (external failure). For example, testing concrete cubes costs a few hundred rupees, but a defective slab may cost lakhs to demolish and recast.

$$
\text{Total quality cost} = \text{Prevention} + \text{Appraisal} + \text{Internal failure} + \text{External failure}
$$

As spending on prevention and appraisal increases, the failure cost falls faster, so the total cost goes down to an optimum. Hence lack of quality is more costly than quality.

## Check yourself

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

1. What main difference separates closed from open systems?
   A. Open compares output
   B. Closed has feedback and compares output with target; open has none
   C. Closed has no correction
   D. Open is more accurate
   Answer: B. Closed systems self-correct through feedback. (Key point: Open vs closed)

2. Which is a closed-system example?
   A. Releasing funds monthly without checking progress
   B. Pump on a timer
   C. A plan carried out blindly
   D. Thermostat of a heater
   Answer: D. A thermostat measures temperature and corrects. (Key point: Example)

3. Why should project control be a closed system?
   A. The environment changes and errors must be corrected
   B. Because no measurement is needed
   C. Because open is more accurate
   D. Because it is cheaper
   Answer: A. Changing conditions need feedback. (Key point: Why closed for projects)

4. Why is 'lack of quality costs even more' justified?
   A. Quality has no cost
   B. Testing costs more than slab recast
   C. Failure costs like demolition and recasting exceed the cost of testing and prevention
   D. Failure never occurs
   Answer: C. Testing cubes costs a few hundred rupees, while a defective slab costs lakhs. (Key point: Quality costs)

## Related in Project Engineering

- [Quality costs more, lack costs even more](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Atotal-quality-cost-justify) — Project Engineering, chapter 4, asked 2×

## Related in other subjects

- [Traffic light system of Kathmandu: open or closed loop](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Atraffic-light-justify) — Control Systems, chapter 1