In this article, we shall discuss the important differences between open-loop and closed-loop control systems (open-loop control system vs closed-loop control system).
Open-Loop Control System
A type of control system that does not use feedback from
output to input is referred to as an open-loop
control system. In other words, a control system without a feedback loop is
called an open-loop control system.
The open-loop control system is also called a non-feedback control system. An open-loop control system consists of four major components namely, input, controller, plant, and output. In the case of the open-loop control system, the desired output is produced by the processing of input signals by the controller according to the predetermined commands. Therefore, the open-loop control system does not measure and compare the actual output and the desired output. Consequently, open-loop control systems are less efficient and reliable.
Open-loop control systems are mostly used in applications
where extremely precise output is not desired, such as traffic lights,
washing machines, irrigation systems, etc.
Closed-Loop Control System
A type of control system that has a feedback path from
output to input to produce the desired output is referred to as a closed-loop control system.
The feedback path allows the system to measure the actual output and compare it with the desired output to produce the most precise output.
A closed-loop control system typically consists of an
open-loop control system with a feedback path. Therefore, closed-loop control
systems are used in applications where highly accurate and precise output is
required, such as in air conditioners, manufacturing systems, medical
processing systems, defence systems, aerospace, etc.
Now, let us discuss the key differences between open-loop
and closed-loop control systems.
Differences between Open-Loop and Closed-Loop Control Systems
All the important differences between the open-loop control
system and the closed-loop control system are listed in the following table:
Basis of Comparison |
Open-Loop
Control System |
Closed-Loop
Control System |
Definition |
A control system which has no relation between input and output, i.e.
no feedback path from output to input, is called an open-loop control system. |
A control system that has a feedback path from output to input, and
forms a closed path is called a closed-loop control system. |
Feedback element |
Open-loop control systems do not use the feedback element. |
Closed-loop control systems always use a feedback element. |
Accuracy |
Open-loop control systems are considered inaccurate. |
Closed-loop control systems are considered accurate. |
System complexity |
Open-loop control systems are simple. |
Closed-loop control systems are complex. |
Price |
Open-loop control systems are economical. |
Closed-loop control systems are expensive. |
Automatic output correction |
Open-loop control systems do not correct variations in output due to
external disturbances. |
Closed-loop control systems can correct variations in output due to
external disturbances automatically. |
Control action |
In open-loop control systems, the control action is independent of
the system output. |
In closed-loop control systems, the control action depends on the
system output. |
Number of components |
Open-loop control systems require fewer components to implement. |
Closed-control systems require more components to implement. |
Reliability |
Open-loop control systems are less reliable. |
Closed-loop control systems are more reliable. |
Maintenance |
Open-loop control systems demand less maintenance. |
Closed-loop control systems demand higher maintenance. |
Bandwidth |
Open-loop control systems have smaller bandwidths. |
The closed-loop control system has larger bandwidth. |
Optimization |
In open-loop control systems, optimization is not possible. |
In closed-loop control systems, optimization can be achieved. |
Stability (in terms of operation) |
Open-loop control systems are considered unstable, and they may
oscillate. |
Closed-loop control systems are considered stable due to the presence of a feedback system. |
Energy efficiency |
Open-loop control systems are less energy efficient. |
Closed-loop control systems are comparatively more energy efficient. |
Applications |
Open-loop control systems are used in applications where less precision
in output is acceptable, such as washing machines, hand drier, coffee makers,
etc. |
Closed-loop control systems are used in applications where high
precision in output is desired, such as traffic signals, medical instruments,
manufacturing systems, air conditioners, etc. |
Hence, this is all about the important differences between the open-loop control system and the closed-loop control system.