---
title: "Everyday closed loop example and importance of feedback"
subject: "Control Systems"
chapter: 1
key: "semester_3/control_systems:cl-example-feedback-importance"
source: https://www.bctengineer.com/q/semester_3/control_systems/cl-example-feedback-importance
site: BCT Engineering
---

# Everyday closed loop example and importance of feedback

Control Systems · Chapter 1: Control System Background

- Asked in: 2069 Chaitra, 4 marks; 2078 Kartik, 5 marks (asked 2 times)
- Video: [Feedback Control Systems | Understanding Control Systems, Part 2](https://www.youtube.com/watch?v=5NVjIIi9fkY) — MATLAB
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/control_systems/cl-example-feedback-importance
- Whole chapter: https://www.bctengineer.com/md/semester_3/control_systems/chapter-1

## Question

Stating an example of a system that you see in everyday life, explain what you understand by closed loop system and the importance of feedback in it.

## Short answer

An automatic electric water heater (geyser) is a closed-loop system: a thermostat compares actual temperature with setpoint and switches the heater on/off to keep temperature constant. Feedback ensures accurate, stable temperature despite disturbances like cold-water inflow, reduces sensitivity to component changes, and enables automatic, safe operation.

## Answer

A **closed-loop system** is one in which the output is measured and fed back to be compared with the desired value; the difference (error) drives the system until the output equals the desired value.

#### Everyday example: automatic electric iron / water heater with thermostat
Take an electric water heater (geyser):
- **Reference:** temperature set on the thermostat knob, say 60 °C.
- **Sensor (feedback):** bimetal strip or thermostat bulb in the water.
- **Comparator and controller:** thermostat contacts compare actual and set temperature.
- **Actuator:** heating element switched ON/OFF.
- **Plant:** water in the tank; **output:** water temperature.
- **Disturbance:** cold water entering when hot water is used.

```text
 set temp +   error  +-----------+   +-------+  water temp
 -------->(Σ)------->|Thermostat |-->|Heater |---+------>
           ^ -       |  contacts |   | +tank |   |
           |         +-----------+   +-------+   |
           +-------------[Bimetal sensor]<-------+
```

When water cools below 60 °C, the error makes the contacts close and heating starts; when 60 °C is reached the heater switches off. The temperature is held near the set point whatever the usage.

#### Importance of feedback
1. **Accuracy:** output follows the set point even if the heater ages or supply voltage changes (sensitivity reduced to $1/(1+GH)$).
2. **Disturbance rejection:** cold-water inflow is automatically corrected.
3. **Faster response:** time constant reduced from $\tau$ to $\tau/(1+K)$.
4. **Safety and automation:** no person has to watch the system; overheating is prevented.
5. **Smaller steady-state error** and ability to stabilize systems that would otherwise run away.

## Check yourself

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

1. In the water heater (geyser) example, what plays the role of the feedback sensor?
   A. The heating element
   B. The bimetal strip or thermostat bulb in the water
   C. The cold water inflow
   D. The knob setting
   Answer: B. The thermostat sensor measures the water temperature and feeds it back for comparison. (Key point: Sensor in geyser)

2. Which is the disturbance in the geyser example?
   A. The set temperature
   B. Cold water entering when hot water is used
   C. The heating element
   D. The thermostat contacts
   Answer: B. Cold inflow unexpectedly lowers the temperature; feedback corrects it. (Key point: Disturbance in example)

3. By how much does feedback reduce the sensitivity of the output to heater ageing or supply changes?
   A. By 1/(1+GH) factor
   B. It increases it by (1+GH)
   C. It leaves it unchanged
   D. It makes it zero exactly
   Answer: A. Sensitivity falls to 1/(1+GH), so output follows the set point despite ageing. (Key point: Importance of feedback for accuracy)

4. When the water cools below the set 60 C, what happens in the closed-loop system?
   A. Nothing, because the setting is fixed
   B. The error makes the contacts close and heating starts
   C. The heater switches off
   D. The sensor is disconnected
   Answer: B. A non-zero error causes the controller to switch the heater on until 60 C is reached. (Key point: Closed-loop operation)

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