CONTROL SYSTEM – OPEN AND CLOSED LOOP

 

What is a control system?
A control system is a group of electronic, mechanical, pneumatic, hydraulic, etc. components. They are used together to achieve a desired goal.

So that it can be considered a control system at least must have three essential elements are: A Variable control an actuator and reference point (set-point).

Control loop

For example , to fill a 500-liter tank with water, we need a hydraulic pump, a water intake and the electronic elements for turning the system on and off. In this case, the reference point is how full you want a tank.

Control system

What is an open loop system?
An open loop control system is characterized in that it does not receive any information or feedback on the state of the variable, usually these are used when the variable is predictable and has a wide margin of error, since the time can be calculated or the times the cycle must be repeated to complete the process.

Example open loop

Parts of an open loop
There are basic elements that make up an open loop control system:

Control element
It is responsible for processing the input signals and making a decision to send it to the correction element.

Correction element
This element is the one that produces a change in the process, usually this block refers to the actuator, since it has the ability to make physical changes in the process.

Process
It is also known as a plant and they are all the characteristics of the process, for example how long it takes to perform or how many times the same procedure needs to be done, etc.

Open tie

What is a closed loop system?
This system is more complete since it receives information on the states that the variable is taking. This feedback is achieved by placing sensors that send information from key points in the process so that it can act autonomously.

Closed loop example

Parts of a closed loop
This system has the main elements of open loop (Control, correction and process) and includes two more.

Comparison item
This comparator receives feedback information on the changes that the process is undergoing, and generates an error signal of the current state of the variable with respect to the reference point, to send it back to the controller to make a decision again

With an error signal, it means that it sends a signal, whether it has already reached the point of regency or has not arrived or also in more complex systems we can know how much time is left to reach the goal.

Measuring element
These elements are usually sensors that measure system information and feed it back to the comparator.

Closed loop

Examples
Open loop control system
We will use the same example of filling a 500lts tank of water.

To solve this system with an open loop we need to know how many liters of water we fill per second, in this case we fill 1 liter every 5 seconds.

Open loop example

So based on the calculations we need a control circuit that keeps a hydraulic pump active for 416.66 minutes and deactivates after time, but as we can see this system is not so complete since we cannot know if it was actually full, since If the system undergoes a variation such as a lower flow, it cannot be detected and the tank will not fill.

Example open loop

closed loop control system
Using the same example, in this system it does not matter how much time passes since level sensors are installed to have a feedback and thus power for the system when it is full or start it when it is detected that it is below the minimum level.

Example closed loop

 

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