TRICONEX 3009 Invensys card series multifunctional processing spare parts

TRICONEX 3009

TRICONEX 3009

TRICONEX 3009

Electromagnetic interference sources and their interference with the system

1. Interference sources and general classification of interference

The interference sources that affect the PLC control system, like those that affect industrial control equipment in general, are mostly generated in areas where the current or voltage changes sharply. These areas where the charges move violently are noise sources, i.e. interference sources.

The types of interference are usually divided according to the reasons for the interference, the noise interference mode, and the different waveform properties of the noise. Among them, according to the different causes of noise generation, it can be divided into discharge noise, surge noise, high-frequency oscillation noise, etc; According to the waveform and nature of noise, it can be divided into continuous noise, occasional noise, etc; According to different noise interference modes, it can be divided into Common-mode interference and differential mode interference. Common-mode interference and differential mode interference is a common classification method. Common-mode interference is the potential difference between signal and ground, which is mainly formed by the superposition of common state (same direction) voltage induced on the signal line by power grid series, ground potential difference and space electromagnetic radiation. The common mode voltage is sometimes relatively high, especially when using power distribution rooms with poor isolation performance. The common mode voltage of the transmitter output signal is generally high, and some can reach over 130V. Common mode voltage can be converted into differential mode voltage through asymmetric circuit, which directly affects measurement and control signal and causes damage to components (this is the main reason for high damage rate of I/O modules in some systems). This Common-mode interference can be DC or AC. Differential mode interference refers to the interference voltage acting on the two poles of the signal, which is mainly caused by the coupling induction of the space electromagnetic field between the signals and the voltage formed by the Common-mode interference converted by the unbalanced circuit. This kind of direct superposition on the signal directly affects the measurement and control accuracy.