With respect to transmitter signal transmission in industrial automation applications, 4~20mA is one of the most common choice. In the case there will be a linear relationship between the process variable( pressure, level, temperature, etc.) and the current output. 4mA represents lower limit, 20mA represents upper limit, and range span is 16mA. What kinds of advantage distinguish 4~20mA from other current and voltage outputs and become so popular?
Current and voltage are both used for electrical signal transmission. However current signal is more preferred than voltage in instrumental applications. One of the core reason is that constant current output is less likely to cause voltage drop over long range transmission as it’s able to raise driving voltage to compensate transmission attrition. Meanwhile, compared with voltage signal, current exhibits a more linear relationship with process variables that contribute to more convenient calibration and compensation.
Lightning Protection Immersion Level Transmitter, 4~20mA 2-wire
In contrast to other regular current signal scale(0~10mA, 0~20mA etc.) the main feature of 4~20mA is it doesn’t choose 0mA as the corresponding lower limit of measuring range. The rationale to rise the zero scale to a live one is to tackle with dead zero problem which means the inability to detect system malfunction cause a failure leads to 0mA output indistinguishable if the lower current scale is also 0mA. As for 4~20mA signal, break down could be clearly identified by current abnormally dropping under 4mA since it would not be considered as a measured value.
4~20mA Differential Pressure Transmitter, live zero 4mA
In addition, the 4mA lower limit ensures the minimum necessary power consumption to operative the instrument while 20mA upper limit restricts fatal injury to human body for safety reasons. 1:5 range ratio consistent with traditional pneumatic control system contributes to easy calculation and better design. Current loop-powered 2-wire has strong noise immunity is convenient for installation.
These advantages in all aspects naturally make 4-20mA one of the most versatile instrumentation output in process control automation. Shanghai WangYuan is a over 20 years instrumentation manufacturer. We provides outstanding instruments with 4-20mA or other customized output options for pressure, level, temperature and flow control.
Post time: Apr-26-2024