1. What are the advantages and disadvantages of voltage and current signals?

　　Answer: The advantage of voltage input (0-5V/0-10V) is that the signal is easy to handle (it can also be tested for "disconnection"), but the disadvantage is that the long-distance transmission signal is attenuated.

　　The advantage of the current signal input (4-20mA) is that the voltage at the input terminal can be transmitted over a long distance without attenuation. The disadvantage is that the signal needs to be converted (current to voltage), which is slightly troublesome. As for interference, both types of input have this problem, and both require careful handling of the noise problem.

　　In summary, if the signal transmission distance is longer (10 meters or more than 100 meters), use current input, if the signal transmission distance is relatively short (within 5 meters), use voltage input. The transmission distance between 5-10 meters is available in two forms, depending on your habits and needs of the site, and it is completely up to you to control it flexibly.

　　Generally, the input impedance of the A/D input port is very large, reaching more than several megabytes. The input current is very small. The resistance voltage drop in the wire can be ignored. Because the input impedance is very high, it is susceptible to interference. Especially when the signal is small. The anti-interference of the current signal is much stronger.