I have a unit that measures temp with a thermistor. I want to use it to measure voltage. I am trying to build a circuit to emulate a thermistor. Here are the parameters. 24v control = 37.8K. 1v control change = -1k so there is an inverse relation ship. Control voltage range = ideal is 6 to 42 volts but can be as tight as 12 to 28 volts. The 3.5 volts is applied to the thermistor buy the unit. The unit and control voltage cannot and should not share a common ground. I have a basic knowledge of electronic but need some help getting started. I was thinking of using some sort of VCR or solid state pot. Any help is greatly appreciated.