Background:
In a distributed project in a factory in South China, each box-type transformer has three to five combiner boxes. The data of the combiner boxes is connected to the SmartLogger through 485 cables in series, and the baud rate is 9600. When the SmartLogger communicates with the combiner box, the communication between the three combiner boxes connected to the SmartLogger 7 is disconnected.
Troubleshooting procedure:
Capture packets for RS485 communication of the combiner box and find that the packets of the combiner box are incorrect, as shown in the following figure.
Contact the combiner box manufacturer to check the onsite situation and data. The manufacturer recommends that the baud rate of the device be changed to 4800 for testing.
After the baud rates of the RS485 port and combiner box on the SmartLogger are changed onsite, the combiner box communication is restored.
Summary:
The baud rate is defined as bai, which is the number of bits transmitted per dusecond. The unit is bit per second (bit/s). For example, the baud rate is usually set to dao9600 bit/s. That is, 9600 bits are transmitted per second, that is, 9600/8 = 1200 bytes are transmitted per second. One byte is equal to 8 bits.
A higher baud rate indicates a higher transmission speed, which means faster data changes (higher level switching) and higher frequency. In the communication process, the inductance of the conductor is a constant: L0=μ0 ×L× (In2L/R-0.75) /2π.
L0: inductance of the straight conductor (H)
L: wire length (m)
R: wire radius (m);
μ0: Vacuum permeability, μ0 = 4π10-7 [H/m]
The inductive reactance of the wire is equal to:
XL = 2πfL, where XL is the inductive reactance, f is the frequency, and L is the coil inductance (the preceding formula indicates that the inductance in the wire is not changed). That is, a larger frequency f indicates a larger inductive reactance XL and a stronger signal blocking capability, the larger the signal consumption, the shorter the transmission distance.
Therefore, for some long-distance RS485 communication, the longer the distance, the more likely the signal interference is. Therefore, when the long-distance transmission is faulty, you can try to reduce the baud rate.
