Suppression of Internal Interference in Electrical Equipment

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Suppression of Internal Interference in Electrical Equipment

1 Generation and transmission of interference

1?1Generation of interference

In the process of working, electrical equipment is subject to various interferences from the inside as well as external interferences. Therefore, for the anti-interference of electrical equipment, it is necessary to suppress external interference and minimize the adverse effects of internal interference on the equipment. Internal interference can be divided into two categories, one is internal noise, and the other is internal electromagnetic and electrostatic interference.

1?2 Internal noise

The internal noise of electrical equipment is the "thermal noise", "shot noise" and "contact noise" generated by various internal components.

(1) Thermal noise Thermal noise is also called electronic noise. It is caused by the temperature fluctuations caused by the heat generated by the electronic components inside the device when they are working, as well as the changes in component parameters caused by changes in ambient temperature. Because this noise is generated by the thermal motion of electrons, it is called thermal noise. This noise increases with the increase of temperature. The suppression of this type of noise mainly starts from reducing the temperature inside the device.

(2) Shot noise Shot noise is caused by the random emission of electrons (or holes) and mainly exists in semiconductor devices such as electron tubes, transistors, field effect transistors, and thyristors. Since the carriers in semiconductors are independent, they are discontinuous and irregular at each brief moment. The changes in electrical properties caused by this irregularity become noise with a wide spectrum range.

(3) Contact noise Contact noise is caused by the fluctuation of conductivity due to incomplete contact between two materials. They include noise caused by poor contact of contacts of switch components, connectors, relays, contactors, etc., dynamic noise inside transistors, noise caused by poor quality or characteristics of components, and electrochemical noise formed by different metal contact surfaces, contact noise or noise caused by looseness, etc. Since contact noise mostly occurs in the low frequency band, it is the main noise source in low-frequency circuits.
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