Current Loop Transmitter for Temperature Sensor

This is a design for current loop transmitter circuit. Current loop interface has been widely used in industrial environment because it is robustness. Noise resistance and fail detection capability made it suitable for long distant transmission in harsh environment. This circuit provide current loop transmitter for temperature sensor. This is the schematic figure.


In the temperature measurement is done by LM35 temperature sensor chip. You can use general silicone diode such as 1N4001. The current controller function is done by LM317 current/voltage regulator. This circuit will draw a consistent current proportional to the temperature being measured, regardless the supply voltage variation caused by noise or long wire’s temperature-dependent resistance variation.