4-20mA to 0-3V3

[bojangleelec]

Just started my analog circuits journey today.

I want to convert 4-20mA to 0-3.3V (current source is from a 24v powered transducer).

I've been trying to understand transimpedance amplifiers and ran an LTSpice simulation from a circuit I found here

Attached are the results from the simulation. I've tried playing around with the resistor values to get a better understanding of how the circuit operates but I'm having trouble wrapping my head around it.

I know for my sake that I would want 4-20mA to sit somewhere in between 0-3.3V in order to be able to detect a broken sensor wire. When I adjust the resistor values to expand the range, the signal isn't linear over the sweep.

I know that I could achieve linearity using a simple voltage divider, what is the purpose of a transimpedance amplifier if you can just do this? Less noise / greater resolution?

Looking to better understand I-V conversions so I can have a better understanding of what is best for my application

Thanks

 

[Akanimo]

Take a look at instrumentation amplifiers.

Took another look at this. Actually, due to the inherent immunity of the current loop, I'm not quite sure whether the servo noise will affect the current loop, and if it does, how much of an effect that will be.

Usually, when noise is insignificant, an opamp differential amplifier would do. Additionally, increasing the opamp Vdd (not the ADC Vref) is usually beneficial. Also, the tolerances of the resistors used play a part in CMRR.