Electronic – How to create a linear current response from a passive pot circuit

currentlinearpotentiometerresistance

I am wanting to linearise the current response of a circuit which currently has the resistance change from a linear pot.

I have a current input that I want to test using a test jig/simulator.
The limits of the current inputs are 4mA and 20mA. I want to be able to drive the current above and below these limits to ensure appropriate warnings are being triggered. The voltage output is supplied from the control as well as the return reference.

The existing test jig is shown below. A linear 10K pot was used with a 470ohm resistor too.

schematic

simulate this circuit – Schematic created using CircuitLab

The current response of this circuit is in orange, while the ideal linear is in blue (point 1 is 0% twist while point 21 is 100% twisted):
enter image description here

This obviously does not have a linear current response to the twisting of the pot knob, only utilising around half/third of the pots range in the desired current range.
I have attempted a few different layouts to try and linearise the response slightly, but none were significantly better than simply choosing a 4k pot and 750ohm (E24) resistor.

Was there a resistor layout to linearise this response so it was closer to the ideal?

Best Answer

Use the pot to drive an opamp current regulator.

schematic

simulate this circuit – Schematic created using CircuitLab