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4mA to 20mA distance sensor

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gustavolsilvano2

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Hello everyone!

I'm implementing a circuit in which I transduce a current value that comes from a inductive sensor 4 to 20mA into voltage (1 to 5V) and insert in my PIC ADC port. For that I used a 270 Ohms resistor and an opamp that isolate my circuit and saturate the voltage, which will impossibilitate my ADC port to colect voltage signal above 5V. I want you to see if the circuit is ok, or if there's anything that I can change to improve it.

Thanks

Gustavo
 

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Hello Gustavo,

Maybe the 270 Ohm is too high, because it would create 5.4V at 20mA. The opamp has also a maximum input voltage. Thus it might be useful to put a Z-diode to protect the input against overvoltage. In some cases a reverse protection is also useful (to avoid negative input voltage or ground loops).

Enjoy your design work!
 

I would put a 10K resistor in place of the short from -ve input to output. Then put a pot (1K?) across your supply and feed the -ve input from the slider via another 10K resistor. You should then be able to get rid off the 4mA X 270 ~ 1V of static output from your op amp by adjusting the pot. Likewise you can trim the output to -ve input resistor to give you some convenient scaling factor.
Frank
 

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