At present, there are two common schemes for passive two-wire 4-20mA display modules. The comparisons are as follows:
Option One:
The current signal is converted into a voltage signal by an operational amplifier, and then the voltage signal is converted into a digital signal using a single-chip A/D unit or a dedicated A/D conversion IC. Finally, the microcontroller reads the digital signal in A/D and displays it. On the LCD.
This scheme uses operational amplifiers and a large number of peripheral resistors in the signal conversion stage, which affects the reliability of the whole machine and is easily affected by the temperature drift and zero drift of the device. In the A/D conversion process, common microcontrollers and common A/D converter ICs have the disadvantage of having a lower bit-count conversion accuracy, affecting the accuracy of the measurement.
Option II:
The current signal is processed by a dedicated 2-wire 4-20mA signal acquisition MCU. The current signal is converted into a voltage signal through a precision resistor outside the signal acquisition I/O port, and then enters into a PGA unit with 10 kinds of magnification selection to amplify, and finally enters an 18-bit full differential input ΣΔ ADC type analog-to-digital conversion unit to convert the voltage signal into Digital signals are displayed on the LCD.
This scheme has no peripheral operation to amplify the analog circuit in the signal conversion section, so it has high reliability and is not affected by temperature drift and zero drift. The 18-bit fully differential input ΣΔADC type A/D conversion unit in the A/D conversion section can guarantee the accuracy of data conversion. At the same time, the general-purpose I/O port of this special-purpose single-chip microcomputer has the I/O function of the ordinary one-chip computer, it is relatively easy to realize the functions such as communication, display, control.
From the comparison of the above two schemes, it can be seen that processing a current signal through a dedicated two-wire 4-20mA signal acquisition single-chip microcomputer has the advantages of high reliability, high precision, and freedom from signal drift, zero drift, and the like. This program is more and more used in magnetic field level gauges, float level gauges and other field display monitoring and control instruments.
The above is related to the introduction of "comparison of several common solutions for two-wire 4-20mA display modules". For more information on level measurement such as level switch and magnetic flap level gauge, please pay attention to WeChat public number. :Jiweimeter. (The article is taken from:, please indicate the source.)
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