The role of positive feedback and negative feedback - Database & Sql Blog Articles

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The core idea of ​​automation technology is feedback, which establishes the connection between input (cause) and output (result) through feedback. The controller can determine the control strategy based on the actual conditions of the input and output to achieve the predetermined system function. According to the different functions and characteristics of the feedback in the system, positive feedback and passive feedback can be divided. The following examples illustrate the role of the two feedbacks in the system.
The characteristics of negative feedback can be well understood from the word “negative”. It mainly acts on Other parts of the control system through the difference between input and output. This difference reflects the difference between the output we require and the actual output. The control strategy of the controller is to continuously reduce this difference to make the difference smaller. The system formed by negative feedback has high control precision and stable system operation. We illustrate the working process of negative feedback by introducing examples of automation principles. When a person intends to take a cup on a table, the person first needs to see the distance between his hand and the cup, and then determine the direction of his hand's movement, and the hand begins to move toward the cup. At the same time, the human eye keeps looking at the distance between the hand and the cup (the distance is the difference between the input and the output), and the role of the human brain (controller) is to constantly control the hand movement to eliminate the difference. Until the hand gets the cup, the whole process is over. As can be seen from the above example, the deviation formed by the negative feedback is the key to the person's accurate completion of the action of taking the cup. If this difference is not available, there is no way to complete the entire action. This is why people with blind eyes can't get a cup. Negative feedback is generally obtained by measuring the output value measured by the measuring component and comparing it with the input value.
Positive feedback is used primarily in the automatic control system to amplify small changes, allowing the system to operate in a stable state. And positive feedback can be used with negative feedback to make the system perform better. A familiar nuclear reaction is an example of positive feedback. Heavy nucleus such as uranium-235 and strontium-239, under neutron bombardment, usually produces two nucleus with medium proton number and emits 2-3 neutrons and 200 mega-electron volts (equivalent to 3.2×1011). joule). The neutrons that are released have losses in the non-fission nuclear reaction or miss out of the fission system, while others continue to cause heavy nuclear fission. If the number of neutrons that can cause the next nuclear fission after each nuclear fission is more than one, the fission system will form a self-sustaining chain fission reaction, and the total number of neutrons will increase exponentially with time. In this way, more and more nuclei in the reactor are fissile, releasing more energy to achieve the purpose of power generation or for other purposes. Before the reactor works, several trigger neutrons are used to get the system working. Once the reaction begins. The system itself generates a large number of neutrons to maintain the reaction. A large-scale nuclear reaction can be formed using this positive feedback mechanism. However, positive feedback is always the most useful for amplification, which will make the role in the system more and more intense, and finally the system will be damaged. Therefore, general positive feedback is used in conjunction with negative feedback, and sometimes nonlinear links (such as clipping links) are added after positive feedback. In a nuclear reactor, the intensity of the nuclear reaction is controlled by controlling the area of ​​the lead in the reactor (the lead rod can absorb neutrons) in contact with the reactants. Otherwise, we have no way to control how much power the nuclear power station generates.