---
title: "Control system importance and closed loop components"
subject: "Control Systems"
chapter: 1
key: "semester_3/control_systems:define-cs-importance-components"
source: https://www.bctengineer.com/q/semester_3/control_systems/define-cs-importance-components
site: BCT Engineering
---

# Control system importance and closed loop components

Control Systems · Chapter 1: Control System Background

- Asked in: 2081 Baisakh, 5 marks
- Video: [Control System-Basics, Open & Closed Loop, Feedback Control System. #bms](https://www.youtube.com/watch?v=GZDPMTBCbYA) — Engineering & Automation
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/control_systems/define-cs-importance-components
- Whole chapter: https://www.bctengineer.com/md/semester_3/control_systems/chapter-1

## Question

Define control system with its importance. What are the components of closed loop systems? Explain.

## Short answer

A control system maintains or follows a desired output by regulating plant variables. Importance: automation, accuracy, disturbance rejection, safety, energy saving. Closed-loop components: reference input, error detector, controller, actuator, plant, feedback sensor, and disturbance. Example: room thermostat controls heater.

## Answer

A **control system** is a set of components connected together so that the output of a system (temperature, speed, voltage, position) is kept at, or made to follow, a desired value.

#### Importance
- **Automation** of industries, homes and transport (lifts, washing machines, CNC).
- **Accuracy and quality** of products and processes.
- **Disturbance rejection** and steady operation under changing loads, e.g. a hydropower governor holds 50 Hz.
- **Safety** (boiler pressure control, aircraft autopilot) and **energy saving**.
- Makes **unstable systems** usable (rockets, fighter aircraft).

#### Components of a closed-loop system
```text
                       disturbance d
                            |
 r   +----+  e   +------+ u +---+---+   c
---->| Σ  |----->|Contr-|-->| Plant |----+---->
     +----+      | oller|   +-------+    |
      - ^        +------+                |
        |  b    +-----------------+      |
        +-------| Feedback/sensor |<-----+
                +-----------------+
```

1. **Reference input (set point):** desired value of output.
2. **Error detector (comparator):** forms error $e = r - b$, e.g. differential amplifier, potentiometer pair.
3. **Controller:** decides the corrective action from the error (P, PI, PID, microcontroller).
4. **Actuator:** converts controller output to power/motion, e.g. motor, valve, relay.
5. **Plant/process:** the system controlled, giving output $c$.
6. **Feedback element/sensor:** measures output, e.g. thermocouple, tachogenerator, encoder.
7. **Disturbance:** unwanted input acting on the plant.

**Example:** in a room heater, the thermostat setting is the reference, the bimetal strip is both sensor and comparator, the contacts act as controller, the heating coil is the actuator, and the room is the plant.

## Check yourself

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

1. A control system is best defined as
   A. a collection of only electrical circuits
   B. a system with no output
   C. a device that amplifies power only
   D. a set of components connected so the output is kept at or made to follow a desired value
   Answer: D. Its purpose is to regulate output to a desired value. (Key point: Definition)

2. The actuator in a closed-loop system
   A. converts the controller output to power or motion, e.g. motor, valve, relay
   B. measures the output
   C. forms the error
   D. generates the disturbance
   Answer: A. The actuator applies the control signal to the plant. (Key point: Actuator)

3. In the room heater example, the heating coil is the
   A. sensor
   B. actuator
   C. reference
   D. plant
   Answer: B. The coil provides heat power; the room is the plant and the bimetal strip is sensor and comparator. (Key point: Room heater example)

## Related in Control Systems

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- [Open and closed loop systems with block diagram](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Aol-cl-bd-role) — Control Systems, chapter 1, asked 2×

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