Grumpy_Mike:
Look what that does to your circuit, basically it shorts things out. The current source must be isolated from the voltage reading. Having the two connected to one Arduino means it can not be isolated and so it will not work.So you need an isolated constant current supply controlled by an optically isolated PWM signal if you want to use one Arduino. However as the Arduino’s voltage resolution is only about 4mV I am not sure if it will be enough for a semiconductor wafer.
Hi Mike, thank for the reply, i think i am wrong for connecting the two part with just one arduino. But how if i use 2 arduino uno, one for the current source, and the other one for voltage measurement? Or else any suggestion for the current supply i can apply to my project? As i mentioned my system will go for analog current, not constant, as i have to follow my sv suggestion. Since this is just an university project, i would give a try and see what happens next. But i still have to ask, does the current must be constant for the measurement? 
Yes paul this is my final year project for university, not industry purpose. So is ok if the result is not as accurate as the pro instrument used in lab, just like more of concept project. Thanks for the replies above. Appreciated