Why the standard signal is 4-20mA?
In the industrial production control process, especially in the continuous production process, it is often necessary to control some physical quantities, such as temperature, pressure, and flow. These physical quantities are constantly changing over time. In the field of control, these physical quantities that change continuously over time are called analog quantities.
4-20mA is a common analog current signal and a standard signal. The minimum current is 4mA and the maximum current is 20mA. When transmitting signals, due to the resistance on the wires, if voltage transmission is used, there will be a certain voltage drop in the wires, and the signal at the receiving end will have a certain error. Therefore, current signals are generally used as the standard transmission of the sensor.
So why is the starting point of 4-20mA not 0mA? When the sensor is connected, poor contact or disconnection may occur due to some reasons. After the line is disconnected, the receiving device cannot collect the current signal, causing the true 0mA to be confused with the line disconnection, making it impossible to judge. If the starting point is set to 4mA, it is easy to determine the disconnection. At the same time, setting it to 4mA has many advantages for two-wire signal transmission.
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