4 - 20mA, 0 - 10V and 0 - 5V are all common standard electrical signals, which are widely used in actual industrial or industrial control engineering. The differences between them are mainly reflected in the following aspects:
Anti-interference ability
4 - 20mA: The general input impedance is 250 - 300 ohms, which is not easily affected by parasitic thermocouples, voltage drop along the wire resistance, temperature drift, and magnetic field coupling induction. When the output resistance of the current source is large enough, the current caused by the interference source is very small, and the interference can usually be reduced by twisted pair. Moreover, the error caused by capacitive interference is small, and the receiver resistance is usually 250Ω, which is not small enough to produce significant errors. In addition, it can realize two-wire transmission, save wires, and also help improve anti-interference ability.
0 - 10V and 0 - 5V: Generally high impedance input, susceptible to interference. Devices such as motors, relays and "noisy" power supplies will induce voltage on the signal line, thereby attenuating the voltage sensor signal. At the same time, they are susceptible to voltage drops caused by wire resistance, especially when the cable is long.
Transmission distance
4 - 20mA: When the distance between the site and the control room is far and the resistance of the connecting wire is large, if the voltage signal is used for remote transmission, due to the voltage division between the wire resistance and the input resistance of the receiving instrument, a large error will be generated. As long as the transmission loop of the current signal does not branch, the current in the loop will not change with the length of the wire, thereby ensuring the accuracy of transmission, so it is more suitable for long-distance transmission.
0 - 10V and 0 - 5V: When the voltage signal is transmitted remotely, it is greatly affected by the resistance of the wire, and it is easy to produce signal attenuation and error. It is generally suitable for short-distance transmission, such as transmission between instruments in the control room.
Maintenance measurement
4 - 20mA: Maintenance measurement is more troublesome.
0 - 10V and 0 - 5V: Maintenance measurement calculations are very convenient.
Signal system and power supply
4 - 20mA: Two-wire transmission can be realized, DC signals can also provide power, and are not affected by load size within a certain range. The minimum current of 4mA is chosen because the circuit will not work without a static working current. 4mA is the static working current of the transmitter. At the same time, the instrument zero point is 4mA DC, which does not coincide with the zero point. This active zero point is conducive to identifying faults such as power failure and disconnection.
0-10V and 0-5V: Usually active, using a three-wire or four-wire system.
Application scenario
4-20mA: It is the most widely used analog transmission signal, suitable for occasions with severe electromagnetic interference and long transmission distances, such as signal transmission between sensors and controllers in industrial sites.
0-10V and 0-5V: It is also common in practical applications. The 0-10V signal is simple and easy to troubleshoot. Almost every industrial controller on the earth will accept 0-10V sensor signals. It is often used in short-distance and low-interference situations, such as signal transmission between instruments inside the control room.