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]