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Read a 4 - 20 mA transducer


#1

I would like to use a Panda II or a Cerbuino to read the output from a transducer. The transducer I would like to read is a pressure transducer whose output is currrent which varies from 4 to 20 mA in proportion to the pressure input. I can put a 150 ohm resistor into the current loop to produce a voltage drop. At 20 mA the voltage drop would be 3 volts. How can i read voltage drop using the analog inputs? Should i place resistors in the lines measureing the voltage drop to limit current?


#2

o@ Bill_Wyo - you can measure the voltage across the 150 ohm resistor. connect ground to one side, and an A input to the other.


#3

Thanks. I did not know if the ground on the board would accurately reflect the level of ground on the power supply driving the current loop. i thought i might have to have an analog input on both sides of the resistor. I am a bit worried about drawing too much current into my board when I read the analog inputs. I can set this up and check my reads with a multi meter.


#4

@ Bill_Wyo - You are interested in the potential across the resistor. You will have to make sure the ground goes on the lower voltage side, since the ADC does not handle negative values. You do not have to worry about the ADC drawing too much current. The ADC impedance is high enough not to affect the circuit being measured.