What does the reference input element do?

Converts command v into a reference signal r of the same kind as the feedback

The manipulated variable u is

The action applied to the plant by the controller

2071 Chaitra · 4 marks

General block diagram of a control system

Short answer

A general closed-loop system has reference input, summing point for error e=r-b, controller/actuator producing manipulated variable u, plant yielding output c, and feedback sensor H. The closed-loop transfer function is C/R = G/(1+GH).

Construct a general block diagram of a control system showing the different blocks, variables and hence briefly point out their meaning.

A general (closed-loop) control system is shown below with its main blocks and signals.

                                disturbance d
                                      |
 v  +-------+ r  +    e  +-------+ u  v  +-------+  c
 -->|Ref.   |--->(Σ)---->|Contr- |--->+->| Plant |--+-->
    |input  |     ^ -    |oller +|       |       |  |
    |element|     |      |actua- |       +-------+  |
    +-------+     |  b   |tor    |                  |
                  |      +-------+                  |
                  +------[Feedback element H]<------+

Blocks

Reference input element: converts the command $v$ (e.g. a knob setting) into a reference signal $r$ of the same kind as the feedback.
Summing point (error detector): forms $e = r - b$ .
Controller (with actuator): converts the error into the manipulated variable $u$ (P, PI, PID action; motor, valve, amplifier).
Plant / process: the system to be controlled.
Feedback element (sensor): measures $c$ and gives $b = Hc$ .

Variables

Symbol	Name	Meaning
$v$	command input	desired value set by the user
$r$	reference input	command in signal form
$b$	feedback signal	measured output
$e$	actuating (error) signal	$r - b$
$u$	manipulated variable	action applied to plant
$d$	disturbance	unwanted input
$c$	controlled variable	actual output

The relation is $\dfrac{C(s)}{R(s)} = \dfrac{G(s)}{1+G(s)H(s)}$ .

✓ Answer checked by Claude Opus 5.5 (high effort)

Closed loop control system block diagram explained · Control Systems, chapter 1 · asked 4×
Control system block diagram and closed loop advantages · Control Systems, chapter 1
Define control system and closed loop block roles · Control Systems, chapter 1 · asked 5×
Derivative feedback controller: block diagram and effect · Control Systems, chapter 7 · asked 2×
Block diagram reduction: G1–G4, H1, H2, unity loop · Control Systems, chapter 3 · asked 4×
Block diagram reduction: G1–G4 with H1, H2, H3 · Control Systems, chapter 3 · asked 3×
Digital control system block diagram and advantages · Digital Control System, chapter 1 · asked 3×
PID control operation with block diagram · Embedded System, chapter 7 · asked 4×
Functional block diagram of excitation control · Power Plant Equipment, chapter 3
Digital control system and function of each block · Digital Control System, chapter 1 · asked 4×

All Control Systems chapter 1 questions →

General block diagram of a control system

Blocks

Variables

Related questions