ABB 129740-002 interference sources affecting the PLC control system and the general impact of industrial control equipment, the same sources of interference, mostly generated in the current or voltage drastic changes in the parts of these charge drastic movement is the source of noise, that is, the source of interference. Types of interference are usually divided according to the cause of the interference, noise interference pattern and the different waveform properties of the noise.

ABB 129740-002 according to the different reasons for noise generation, divided into discharge noise, surge noise, high-frequency oscillation noise, etc.; according to the different waveforms and properties of the noise, divided into continuous noise, episodic noise, etc.; according to the different modes of noise interference, divided into common-mode interference and differential-mode interference. Common mode interference and differential mode interference is a more commonly used classification method. Common mode interference is the signal to ground potential difference, mainly by the grid string into, ground potential difference and space electromagnetic radiation in the signal line induced by the common state (same direction) voltage iteration of the formation.

ABB 129740-002 common-mode voltage is sometimes larger, especially with poor isolation performance of the distributor power supply room, the transmitter output signal common-mode voltage is generally higher, some can be as high as 130V or more. Common mode voltage through the asymmetrical circuit can be converted to differential mode voltage, directly affecting the measurement and control signals, resulting in component damage (this is the main reason for the high damage rate of some system I / O module), this common mode interference can be DC, can also be AC. Differential mode interference refers to the role of the signal between the poles of the interference voltage, mainly by the electromagnetic field in the space between the signal coupling inductance and unbalanced circuitry to convert the common mode interference in the formation of the voltage, which allows the direct superposition of the signal, which directly affects the measurement and control accuracy.