Design of PIC microcontroller and AD5410 chip control system output 4-20mA current signal

The current signal output by instruments and sensors is mostly 4-20mA. Why is it 4-20mA? Because 4-20mA sensors are mostly two-wire systems, that is, the signal line and the power line share two wires. If the starting point is 0mA, it will be impossible to distinguish whether the signal is 0mA or the sensor is not working; in addition, the starting point is 4mA, which is also helpful for the system to judge whether the sensor is powered off or short-circuited.

So how do we generate a 4-20mA current signal? With the rapid development of digital circuits today, systems with single-chip microcomputers as the core are everywhere. However, single-chip microcomputers are digital signals, while current is an analog signal. This requires DA conversion, that is, converting digital signals into analog signals.

At present, the common scheme for the microcontroller to control the system to output a 4-20mA current signal is:

Today I want to recommend a chip: AD5410, which is produced by ANGLOG DEVICE. It is a single-channel 12-bit serial input DAC chip. The communication method with the microcontroller is SPI bus. The microcontroller only needs to write the value to AD5410 through SPI to output the corresponding current value. Its power supply range is: 10.8-40V.

The above picture shows a 4-20mA current output product designed with PIC microcontroller as the core. AD5410 has a rich error diagnosis mechanism, which can greatly improve the anti-interference ability of the design. The current output formula is as follows:

N: The resolution of DA conversion, this chip is 12 bits;

D: is the decimal equivalent value of the loaded DAC code;