reversing 4-20ma logic 1

thanks for the help on an analyzer in previous post. i now find i have another difficulty coupling the sensors i'm considering and the equipment i want to control. the equipment expects a directly propotional 4-20 man signal but the sensor will yield an inversely proportion signal.

this is a pressure application 0-28" water column.

so 4ma on the sensor represents 0 pressure and 20ma represents 28". I need to reverse that logic so that 20ma represents 0 pressure and 4 ma represents 28". Is there a "reverser" that i can put in the current loop or that sets up its own current loop and then can output the inverse of the result onto the operating loop.

thanks