1. How to prevent faults?
The following recommendations are made to reduce communication failures.
1. It is recommended that you use and purchase the RS485 converter provided by the manufacturer or the RS485 converter of the recommended brand.
2. Manufacturers will perform a lot of tests on the RS485 converters and require them to perform production and quality tests based on their fixed performance parameters. Therefore, the RS485 converters are compatible with access control devices. Do not covet cheaply buy the 485 converters of the miscellaneous manufacturers.
3. Strictly follow the RS485 bus construction specifications to avoid any chance.
4. Adopt a scientific and reserved solution for the RS485 bus project with long lines and heavy loads.
5. If the communication distance is too long, for example, more than 500 m, a repeater or 485 hub is recommended.
6. If there are too many loads, for example, more than 30 devices are connected to a bus, you are advised to use a 485 hub to solve the problem.
7. Perform onsite commissioning with all devices. During onsite commissioning, you must carry several long-distance and multi-load converters, a common laptop, a multimeter for testing circuit disconnection, and several 120-ohm terminal resistors.
2. Which of the following are common communication faults when the RS485 bus is used?
1. No communication, no response.
2. Data can be uploaded but cannot be downloaded.
3. The system prompts interference during communication, or the communication indicator blinks continuously when communication is not performed.
4. Sometimes the communication is successful, sometimes the communication fails, some commands can be executed, and some commands cannot be executed.
3. What are the debugging methods when a fault occurs?
Before commissioning, ensure that the cables are correctly connected and the construction
complies with the specifications. You can use the following debugging methods based on the problems that occur.
1. The law of common land:
Connect the GND cables of all RS485 devices using one cable or shielded cable to avoid potential differences that affect communication between all devices.
2. Terminal resistance method:
Connect 120-ohm terminal resistors in parallel to the 485+ and 485- ports of the last RS485 device to improve communication quality.
3. Intermediate segmentation method:
Check whether the device is overloaded, whether the communication distance is too long, or whether a device affects the entire communication line.
4. Separate stay wire method:
Pull a cable to the device separately to check whether the cable is causing the communication failure.
5. Replace the converter.
Carry a few converters with you to rule out if the quality of the converter is affecting the communication quality.
6. Notebook debugging method:
Ensure that the laptop is a normal device and replace the computer with the laptop. If the laptop is normal, the serial port of the computer may be damaged or injured.
In weak-current intelligent projects, RS485 is widely used, most commonly used in the access control system, BA system, intelligent lighting system, and parking lot management system. With the popularization of digital networks, RS485 is rarely used in weak-current projects.
