Is there a way to convert 0-10VDC to 4-20mA using resistors only? I am building a test stand that has four 0-10VDC input signals and four 4-20mA inputs. The ones I currently use have Johnson A350P's and I vary the signal with a potentiometer. When I turned in the purchase requisitions I was told that they had used resistors and resistors only to convert the 0-10 to 4-20 in the past and I didn't need to buy a converter (A350P) to do it.

I thought that changing 0-10 to 4-20 required an op-amp in addition to resistors, but I was told it had been done with resistors only on a 0-10V input with a potentiometer to vary it. I tested the old test stand that this method was used on but I couldn't get it to work. When I explained that to my boss he told me the old one worked. If it did I have no idea how so I would appreciate any help or expertise anyone that is more electronically minded could offer.

Thanks

Robert