AIKON-文章详情

In the world of industrial control, the transmission of analog signals has its own unique ways, and the 4 - 20mA current signal is widely used. Have you ever wondered why it's not the more "intuitive" 0 - 20mA? Today, let's uncover the mystery behind it.
I. The "Sharp Eyes" for Fault Detection
The Confusion of Zero Signal**
In the 0 - 20mA signal range, 0mA represents the minimum measured value. However, this brings a tricky problem: when the receiving end detects a 0mA signal, it can't tell whether it means the currently measured physical quantity is at the minimum value (such as zero pressure, the lowest temperature, etc.) or there is no signal due to a line fault (such as a broken signal wire). It's like seeing complete darkness and not knowing if it's because there was no light in the first place or if the light bulb is broken.
The Ingenuity of 4mA
When using the 4 - 20mA signal, under normal working conditions, the signal current will not be lower than 4mA. Once the receiving end detects a signal less than 4mA, such as 2mA or 0mA, it can clearly determine that there is a line fault, such as a broken wire. This is like installing a pair of "sharp eyes" that can keenly detect faults in the system, allowing for timely detection of problems and maintenance, greatly improving the reliability and maintainability of industrial control systems.
II. The "Magic Shield" of Anti-interference Ability
The Inherent Advantage of Current Signals
Firstly, in the industrial environment, there are various electromagnetic interferences. For example, the startup of motors and the operation of frequency converters can all generate strong electromagnetic noise. Compared with voltage signals, current signals are less affected by interference during transmission. This is because the magnitude of a current signal mainly depends on the internal resistance of the signal source and the load resistance, and it is difficult for external electromagnetic interference to change this characteristic. So, essentially, both 4 - 20mA and 0 - 20mA, as current signals, have a certain degree of anti-interference ability.

Additional Advantage Superposition
However, the 4 - 20mA signal has another little "magic": since its minimum value is 4mA, during signal transmission, even if the current value fluctuates to some extent due to interference, as long as the fluctuation range is within a reasonable interval, the signal can still remain above 4mA, and the receiving end can still accurately identify it as a valid measurement signal rather than a fault signal. In contrast, if the 0 - 20mA signal is interfered with and the current value approaches 0mA, it may be misjudged as a fault or the minimum measured value. Therefore, the 4 - 20mA signal has an extra layer of "shield" in terms of anti-interference.
III. The "Energy-saving Way" of Signal Transmission
Consideration of Power Consumption
In industrial control, many devices need to operate for a long time, and energy consumption is a factor that cannot be ignored. For the transmission of analog signals, the power consumption of the 4 - 20mA signal at low measured values (corresponding to 4mA) is relatively higher than that of the 0 - 20mA signal (corresponding to 0mA). But in practical applications, in most cases, the measured value is not at the minimum, and at this time, the increase in power consumption of the 4 - 20mA signal has a relatively small impact on the overall energy consumption.
Overall Benefit Trade-off
More importantly, through the advantages brought by using the 4 - 20mA signal, such as the convenience of fault detection and stronger anti-interference ability, the stability and reliability of industrial control systems are greatly improved, reducing production interruptions and equipment damage caused by faults and misjudgments, and overall reducing the operating costs and energy consumption losses of industrial production. It's like in a long "energy marathon", although the 4 - 20mA signal has a slightly higher energy consumption at the "starting line" (at low measured values), with its strong "endurance" (stability and reliability), it finally achieves a better result at the "finish line" (overall operational efficiency).
In conclusion, the 4 - 20mA analog signal has firmly established itself in the field of industrial control and become a common standard for analog transmission with its significant advantages in fault detection, anti-interference ability, and overall efficiency, silently safeguarding the stable operation of industrial production.