Armored communication double shielded cable ASTP-120 Ω

Armored communication double shielded cable ASTP-120 ΩAnother issue is the signal ground. The above connection method can work normally in many situations, but it has hidden great risks. There are two reasons for this: (1) Common mode interference problem: RS-485 interface uses differential transmission to transmit signals, and there is no need to detect signals relative to a reference point. The system only needs to detect the potential difference between the two lines. But people often overlook that transceivers have a certain common mode voltage range. The common mode voltage range of RS-485 transceivers is -7 to+12V. Only when the above conditions are met can the entire network work normally. When the common mode voltage in the network line exceeds this range, it will affect the stability and reliability of communication, and even damage the interface. (2) EMI (electromagnetic compatibility) issue: The common mode part of the output signal from the driver requires a return path. If there is no low impedance return channel (signal ground), the common mode part of the signal will return to the source end in the form of radiation, and the entire bus will radiate electromagnetic waves outward like a huge antenna.
Due to the default RS232 interface of the PC, there are two methods to obtain the RS485 circuit of the PC upper computer: (1) converting the RS232 signal of the PC serial port into an RS485 signal through an RS232/RS485 conversion circuit. For complex industrial environments, products with surge protection and isolation barriers are selected. (2) Through PCI multi serial port cards, expansion cards with RS485 output signals can be directly selected.Armored communication double shielded cable ASTP-120 Ω