The following circuit is presented here. Basically it is a circuit that keeps constant current through the OUT terminals even if the resistance of the 'Device Under Test' changes. The current value can be varied (4 - 20mA) using the VR1 potentiometer. The author makes a good job explaining the functionality but I have one question.
What is the purpose of R3?
As I understand it, the voltage at the positive input of the op-amp (pin 3) has to vary from 160mV up to 800mV and this is achieved with the R1, R2, VR1 and R4 resistors. So why is R3 there?
Thank you.
What is the purpose of R3?
As I understand it, the voltage at the positive input of the op-amp (pin 3) has to vary from 160mV up to 800mV and this is achieved with the R1, R2, VR1 and R4 resistors. So why is R3 there?
Thank you.