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Current Loop Circuits

TEMPERATURE SENSOR WITH 4 TO 20mA CURRENT LOOP

 
I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room.  The circuit uses a very robust current loop method.  It uses a highly accurate semiconductor temperature sensor and an equally accurate voltage reference. The circuit includes a diode bridge, so it is polarity independent.  By using the component values indicated, the circuit should not require calibration.  It has a range from –40F to +120F and an accuracy of +/- one degree F.

 

Click on Drawing Below to view PDF version of Schematic

Circuit 4mA to 20MA Current Loop Temperature Sensor designed by David A. Johnson, P.E. (July 4, 2000)

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