Detailed explanation of the voltage used in RS485

1, Voltage range of RS485
The RS485 standard specifies the voltage range for interface use, typically between -7V and+12V. This voltage range allows RS485 signals to maintain sufficient signal strength during long-distance transmission, while also resisting certain electrical noise interference. The RS485 interface adopts a differential signal transmission method, where the voltage difference between two signal lines represents the logical state, rather than the absolute voltage value of a single signal line. Therefore, even if there is a deviation in the voltage value in practical applications, as long as the voltage difference between the two signal lines remains unchanged, the logical state can still be correctly identified.
2, The reason for choosing this voltage range
The selection of RS485 voltage range from -7V to+12V is mainly based on the following considerations:
Anti interference capability: The higher voltage range enables RS485 signals to better resist electrical noise and interference during transmission. This is particularly important for using the RS485 interface in industrial environments or areas with high levels of electromagnetic interference.
Long distance transmission: A higher voltage range means that the signal has less attenuation in the cable, supporting longer transmission distances. This makes the RS485 interface suitable for application scenarios that require long-distance communication.
Compatibility and stability: The voltage range of the RS485 interface is compatible with some other communication standards, such as RS232 and RS422. This makes it possible to use multiple communication standards simultaneously in the same system. Meanwhile, a stable voltage range also helps to ensure the stability and reliability of communication.
3, Comparison with other communication standards
Compared to other common communication standards, the voltage range of RS485 has certain advantages. For example, the voltage range used by the RS232 interface is usually between -15V and+15V. Although it can also provide strong anti-interference ability, its transmission distance is relatively short. The TTL interface uses a lower voltage range (usually between 0V and 5V) and is susceptible to noise interference during long-distance transmission. In contrast, the voltage range of RS485 maintains strong anti-interference ability while also supporting longer transmission distances.
4, Factors to consider in practical applications
In practical applications, the following factors need to be considered when selecting and using the RS485 interface:
Cable selection: Select appropriate cable types and specifications based on transmission distance and signal quality requirements. Impedance matching and signal amplification measures may be required for long-distance transmission to maintain signal quality.
Terminal device matching: Ensure that the RS485 interface of terminal devices (such as computers, PLCs, etc.) matches the electrical characteristics of cables to avoid communication failures.
Power stability: In order to ensure the stable operation of the RS485 interface, a stable power supply needs to be provided. In environments with significant power fluctuations, additional power stabilization measures may be necessary.
Electromagnetic interference protection: When using the RS485 interface in environments with high electromagnetic interference, appropriate electromagnetic interference protection measures need to be taken, such as using shielded cables, increasing grounding, etc.
In summary, the voltage range of -7V to+12V used by the RS485 interface is selected based on its excellent anti-interference ability and long-distance transmission characteristics. In practical applications, we need to configure and use the RS485 interface reasonably based on specific requirements and environmental conditions to ensure communication stability and reliability.