Current Loop Transmitter For Temperature Sensor

Current loop interface has been widely used in industrial environment because it’s 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. Here is the circuit’s schematic diagram:

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. [Circuit’s schematic sources: National Semiconductor’s LM 35 Centigrade Temperature Sensor Application Note]