What is the analog 4-20mA current output?

4-20mA analog output is a common analog control method, usually used by the controller to remotely transmit sensor signals. Its principle is to convert the sensor signal into a 4-20mA analog signal, and then transmit it to the control system. 4-20mA analog output has good stability, reliability and high accuracy, so it has been widely used in the field of industrial control.

The 4-20mA .DC signal system is the analog signal transmission standard used by the international electrotechnical commission (IEC) process control system. Our country also adopts this international standard signal system. The instrument transmits signals using 4-20mA.DC and receives signals using 1-5V.DC, that is, it adopts a signal system of current transmission and voltage reception. The signal current of general instruments is 4-20mA, which means the minimum current is 4mA and the maximum current is 20mA.

When transmitting signals, you must consider that there is resistance on the wire. If voltage is used for transmission, a certain voltage drop will occur on the wire, and the signal at the receiving end will produce a certain error. So the current signal is used as the standard transmission of the transmitter. So why choose 4-20mA? The upper limit of 20mA is due to explosion-proof requirements. Based on safety, practically, power consumption and cost considerations, the spark energy caused by the current switching of 20mA is not enough to ignite gas. The reason why the lower limit is not set to 0mA is to detect disconnection. The current will not be lower than 4mA during normal operation. When the transmission line is disconnected due to a fault, the loop current drops to 0, and 2mA is often used as the disconnection alarm value.

Why use current output instead of voltage output?

In industrial sites, using an instrument amplifier to complete signal conditioning and long-term transmission will cause the following problems: First, because the transmitted signal is a voltage signal, the transmission line will be interfered by noise; second, the distributed resistance of the transmission line will cause voltage drop; third, how to provide the operation voltage of the instrumentation amplifier on site is also a problem. So in order to solve the above problems and avoid the influence of nosie, we use current to transmit signals, because current is not sensitive to noise. The 4-20mA current loop uses 4mA to represent the zero signal and 20mA to represent the full scale of the signal. Siganls lower than 4mA and higher than 20mA are used for alarms of various faults.

What types of 4-20mA current loops are there?

Two-wire and three-wire systems. The current-type transmitter converts the physical quantity into 4-20mA current output, and it must be powered by an external power supply. The most typical one is that the transmitter requires two power lines, plus two current output lines, for a total 4 wires, which is called a four-wire transmitter. Of course, the current output can share a wire with the power supply, which can save one wire, so now the four-wire transmitter is basically called a three-wire transmitter. However, it is worth nothing that the 4-20mA current itself can power the transmitter. The transmitter is equivalent to a special load in the circuit. This kind of transmitter only needs to be connected to 2 external wires, so it is called a two-wire transmitter.

What are the functions of 4-20mA?

4-20mA analog output is widely used in the transmission and reception of transmitter signals in the field of industrial control. The transmitter can convert the signal generated by the sensor into a 4-20mA current signal for transmission, such as temperature, pressure, physical parameters such as flow rate, and chemical parameters of analytical instruments.

The pH/ORP controlelr, conductivity controlelr, Dissolved Oxygen Controller, Turbidity Controller, Cod Controller, etc. developed and produced by Daruifuno all have 2 channels of 4-20mA current output, so that users can use 4-20mA analog signal to output the data. In addition to the 4-20mA analog signal, our online water analyzers also provide RS485 digital signal. If you want to know more about our products, please contact us.