AD5421 is a complete loop powered 4mA-20mA digital to analog converter designed to meet the needs of intelligent transmitter manufacturers in the industrial control field. It provides a high-precision, fully integrated, and low-cost solution. In conventional applications, it fully meets user needs, but in the field of industrial transmitter use, taking pressure transmitters as an example, the mainstream pressure transmitters on the market have an accuracy level of 0.05% FS and 0.075% FS. At this accuracy level, the temperature drift of the current loop will have a significant impact on the accuracy of the transmitter. This article presents a temperature drift correction method for the current loop.

The above figure shows the record of the output current of AD5421 affected by ambient temperature without linear correction. Here, 20 ℃ is used as a reference. When the ambient temperature is higher than 20 ℃, the actual output current at both 4mA and 20mA points monotonically increases; When the ambient temperature is below 20 ℃, the actual output current at both 4mA and 20mA points decreases monotonically.

Number 1: Output current at low point 4mA and high point 20mA

Temperature affected curve graph

Y4mA = 0.00000001 * X3 - 0.00000193 * X2 + 0.00029822 * X + 3.99497932

Y20mA = 0.00000000 * X3 - 0.00000655 * X2 + 0.00134627 * X + 19.97566210

The theoretical output current at 4mA and 20mA points at any temperature can be calculated using the above formula, and the driving value of AD5421 can be increased or decreased based on this current to ultimately output the standard 4mA or 20mA.