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Closed and open control; quality cost

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.

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

Closed and open system of control

OPEN LOOP                  CLOSED LOOP
Input -> [Process] -> Out  Input -> [Process] -> Out
                              ^                   |
                              +-- [Compare]<------+
                                  (feedback)
BasisOpen systemClosed system
FeedbackNonePresent
Output compared with targetNoYes
Self-correctionNo; changes in conditions are not correctedYes; deviation is corrected
Complexity and costSimple, cheapMore complex, needs measurement
AccuracyLowHigh
ExamplesPump run on a timer; releasing funds monthly without checking progress; a plan carried out blindlyThermostat 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.

Total quality cost=Prevention+Appraisal+Internal failure+External failure\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.

✓ Answer checked by Claude Opus 5.5 (high effort)

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