The STP50N06 is the best choice because of the higher power rating.
You won't be able to get .001 ma accuracy. Lets say the pot turns 180 degrees. 0 will be 0 ma and 50k will be 5 amps. So each degree is about 28 ma. You could add a "fine" adjustment with a smaller pot in series with the 50k. But the resistance of the sense resistor will probably make it vary by more than .001ma. as it heats up.

 

The STP50N06 is the best choice because of the higher power rating.
You won't be able to get .001 ma accuracy. Lets say the pot turns 180 degrees. 0 will be 0 ma and 50k will be 5 amps. So each degree is about 28 ma. You could add a "fine" adjustment with a smaller pot in series with the 50k. But the resistance of the sense resistor will probably make it vary by more than .001ma. as it heats up.

I am not looking for perfect .001ma accuracy but close would be nice ... I know Dave Jones came pretty close to .001ma with his setup and a buffer opamp to help get the finer adjustments.. I plan on bread boarding it and see what happens cause nothing is set in stone ...Also have the idea to use the last opamp after the buffer connected to the amp meter threw a relay in order to preset the current ??? Is this possible or is there a better way???



Thanks
Jay Sr

 

Ahh, I see I found his video . The buffer amp doesn't do anything. It is the 10 turn pot that gives it the better adjustment. But they can be pretty expensive.
It is probably easiest just to measure the voltage across the 1 ohm resistor to get the current. The reading will then be .001 amp with 3 didgets after the decimal. But don't forget the resistor will have a few % tolerance so the true accuracy is not really that good.
PS. Have you calculated the power in the sense resistor for 5 amps?