The LED display that is in use suddenly has garbled characters due to signal problems. If it is at a major opening ceremony, the loss is irreparable. Therefore, how to improve the reliability and stability of signal transmission has become a problem that engineers have to face.
The signal is weakened as the distance increases during transmission. Therefore, the choice of transmission medium is particularly important. The following should be noted when using RS-485 as a long-distance data transmission line.
1, signal attenuation
It is not difficult to understand that the signal will be attenuated during transmission regardless of the medium transmission. We can think of the RS-485 transmission cable as an equivalent circuit composed of several resistors, inductors and capacitors, as shown in Figure 1.
The resistance of the wire has little effect on the signal and can be ignored. The distributed capacitance C of the cable is mainly produced by two parallel wires of the twisted pair. The loss of the signal is mainly due to the LC low-pass filter composed of the distributed capacitance of the cable and the distributed inductance. The higher the communication baud rate, the greater the signal attenuation. The attenuation coefficient of the conventional cable is shown in Table 1.
Therefore, in the case where the amount of data transmitted is not very large and the transmission rate requirement is not very high, we usually use a baud rate of 9 600 bps.
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